From 2003 to 2017, highly pathogenic avian influenza (HPAI) epidemics, particularly H5N1, H5N8, and H5N6 infections in poultry farms, increased in South Korea. More recently, these subtypes of HPAI virus resurged and spread nationwide, heavily impacting the entire poultry production and supply system. Most outbreaks in poultry holdings were concentrated in the southwestern part of the country, accounting for 58.3% of the total occurrences. This geographically persistent occurrence demanded the investigation of spatial risk factors related to the HPAI outbreak and the prediction of the risk of emerging HPAI outbreaks. Therefore, we investigated 12 spatial variables for the three subtypes of HPAI virus-infected premises . Then, two prediction models using statistical and machine learning algorithm approaches were built from a case-control study on HPAI H5N8 epidemic, the most prolonged outbreak, in 339 IPs and 626 non-IPs. Finally, we predicted the risk of HPAI H5N1 and H5N6 occurrence at poultry farms using a Bayesian logistic regression and machine learning algorithm model [extreme gradient boosting (XGBoost) model] built on the case-control study. Several spatial variables showed similar distribution between two subtypes of IPs, although there were distinct heterogeneous distributions of spatial variables among the three IP subtypes. The case-control study indicated that the density of domestic duck farms and the minimum distance to live bird markets were leading risk factors for HPAI outbreaks. The two prediction models showed high predictive performance for H5N1 and H5N6 occurrences [an area under the curve (AUC) of receiver operating characteristic of Bayesian model > 0.82 and XGBoost model > 0.97]. This finding emphasizes that spatial characteristics of the poultry farm play a vital role in the occurrence and forecast of HPAI outbreaks. Therefore, this finding is expected to contributing to developing prevention and control strategies. The avian influenza virus, a member of the Orthomyxoviridae family, is primarily classified as highly pathogenic avian influenza virus (HPAIv) and low pathogenic avian influenza virus (LPAIv) based on the degree of pathogenicity in chickens according to the World Animal Health Organization (OIE). Chickens or turkeys exposed to HPAI develop acute systemic symptoms that lead to death . The virThe main route of transmission of HPAIv to humans is direct or indirect contact with live or dead poultry infected with the virus in live bird markets (LBMs), backyard poultry flocks, or direct contact with fluids that contain the virus , 3, 4. ASince the first case was reported at a domestic chicken farm on December 10, 2003, South Korea has experienced multiple HPAI epidemics that resulted in more than 1,100 cases with the three different subtypes of HPAIv: H5N1, H5N8, and H5N6. From 2008 to 2011, a single subtype (H5N1) of < 100 cases were confirmed in poultry holdings across the nation within 140 days of each epidemic . In partInterestingly, the spatial distribution of HPAI outbreaks in Korea appears to be concentrated in the small southwestern region, Naju, and its central region, Eumseong, where the majority of domestic ducks in Korea are produced irrespective of the subtype of the virus , 9, 10. The poultry production environment in Korea has similar and distinctive characteristics to those of Asian countries, where identical or different spatial factors contribute to the risk of HPAI. For example, a large proportion of land is covered by rice fields  around poultry farms, and a relatively large proportion of domestic duck farms . On the other hand, domestic ducks are commonly raised indoor, thus they hardly have direct contact with wild birds. Furthermore, most poultry farms have large and medium-scale production capacities. For example, 97.6% of domestic duck farms and 92.3% of chicken farms produced more than 5,000 and 10,000 birds, respectively for the first quarter of the year 2020, according to livestock survey of the Korea Institute for Animal products quality Evaluation .Additionally, the different subtypes of HPAIv presented heterogeneous pathogenicity to poultry and shedding levels, which is assumed to differently influence the time to report the detection of infection period and, consequently, the magnitude of the epidemic. For example, the H5N8 subtype occurring in 2014–2016 caused relatively mild clinical symptoms in duck species, compared with the H5N6 subtype in the 2016–2017 epidemic . In contHence, at the expected emergence of the new HPAI , it is cAs illustrated in In this study, three different subtypes  of the HPAI epidemic in South Korea were included to examine the spatial characteristics of the IPs and predict the risk of occurrence, as summarized in The spatial variables associated with HPAI occurrence on a poultry farm were selected from previous research on risk factors , 23–27 awww.worldpop.org) for 2011, 2014, 2016 at a resolution of 1 km. The densities of chicken farms and domestic duck farms of each study farm were extracted from a raster map constructed with the geographical coordinates of chicken and domestic duck farms provided by the Animal and Plant Quarantine Agency, Ministry of Agriculture, Food and Rural Affairs in South Korea in 2016 using the ArcGIS version 10.8.1 . An LBM is a place to sell live chickens or ducks and is known to play a major role in distributing viruses  data obtained from the Shuttle Radar Topography Mission of the United States Geological Survey in 2014. From the DEM data, the topological wetness index (TWI) across the nation was estimated, and the value of individual poultry holdings was extracted based on its geographical coordinates. The TWI index is an indicator of water accumulation and local drainage, defined as a function of the total catchment area, flow width and slope gradient . It is often used as a proxy for soil moisture because it integrates the water supply from upslope and downslope water drainage. The proportion of the forest, rice paddy fields, water bodies, and wetlands within a 3km-radius from each study farm were calculated using the national land cover map at the 5 m spatial resolution provided by the Environmental Spatial Information Service, Ministry of Environment, South Korea, in 2009 and 2017. The determination of the radius range (3 km) for the proportion of each type of land cover was made according to the standard operative procedure for HPAI, South Korea, where the area within a 3-km radius from an HPAI-infected premise or localities of HPAI-positive surveillance area in wild birds was classified as a biosecurity zone mainly due to the high risk of local spread. Additionally, data on driveways were retrieved from the Korea National Transport Information Center in 2010, 2014, and 2016. Human density data were obtained from an open-source database for spatial demography  was used for comparison tests.Explanatory data analysis for 12 spatial variables was conducted on H5N1, H5N8, and H5N6 subtypes of HPAIv-infected chicken and duck holdings  to understand the spatial characteristics. An analysis of variance test or Kruskal–Wallis test, dependent on the normality of the variable to be tested, was performed to compare the mean of the spatial variables among the three subtypes of HPAIv-IPs , followed by a To identify spatial risk factors associated with HPAI incidence in poultry holdings, especially chicken and domestic duck farms, a case-control study was designed for the 2014–2016 HPAI H5N8 epidemic because it was the most prolonged nationwide outbreak  . A case P < 0.2 in univariate analysis  were estimated to check the degree of multicollinearity. Consequently, the variables were excluded from the logistic analysis if the value of VIF value exceeded 3 . Subsequanalysis . Furtheranalysis , 36.Finally, the prediction model using the Bayesian multiple logistic regression analysis was built from the case-control study on the H5N8 epidemic with significant variables and non-significant associations because of the generalization of the model to predict other epidemics where other variables could be contributable to HPAI infection at poultry holdings. In addition to statistical approaches to predict other subtypes of HPAI outbreaks, the extreme gradient boosting (XGBoost) model was constructed using the same case and control farms of H5N8 epidemic used in the Bayesian multiple logistic regression analysis. Then, the XGBoost model predicted the probability of H5N1 and H5N6 subtypes of HPAI occurrence. XGBoost is a tree-based method used to model nonlinear relationships using the boosting technique to adaptively combine a large number of relatively simple tree models with improving predictive performance. Boosting refers to an ensemble method in which sets of models are trained sequentially, with each model learning from the errors of its predecessor, transforming a weak classifier into a strong classifier using weights. In addition, the XGBoost algorithm uses a regularized loss function to minimize overfitting. This diminishes the effect of a single tree on the final score by scaling down the weight of each new tree. Furthermore, it uses a variable selection approach to build a tree . In the We predicted the probability of incidence for other subtypes of HPAI in chicken and domestic duck holdings across the nation. We used 88 H5N1 IPs, 335 H5N6 IPs, 270 non-IPs, and 335 non-IPs randomly selected during each corresponding epidemic see  using twpost-hoc analysis revealed similar characteristics in the combination of pairs , at lower elevations with a spacious rice field, very low human density, and higher domestic duck farm density than other subtypes of HPAI virus IPs. In contrast, H5N6 IPs with a higher proportion of chicken farms  were placed at higher elevations with higher forest area, higher human, and chicken farm density, and closer to driveways. Additionally, H5N1 IPs, similar proportion in farm species, located in the medium range of elevations between H5N8 and H5N6 IPs, had the lowest chicken and duck farm density with the lowest minimum distance to the wintering site for wild birds and the LBM.2, whereas the minimum distance to LBM had a negative correlation, which decreased to zero at a point of 1.3 km. For more details on the dependence between a set of spatial variables and the HPAI outbreak, refer to More specifically, for the adjusted odds ratio of spatial variables in both chicken and duck farms, a higher domestic duck farm density and lower minimum distance to the LBM contributed to H5N8 occurrence in farms of these species. When comparing case and control farms producing only chicken, a higher chicken farm density and lower minimum distance to LBM significantly increased the risk for HPAI occurrence see . The marGeographically, both models consistently predicted a higher probability of HPAI occurrence in Naju, Yeongam, and Suncheon, which are the southwestern parts, and Anseong, Cheonan, and Eumseong, which are the central parts of the nation, irrespective of the subtype see . HoweverWith the expectance of the emergence of novel HPAIv, it is imperative to precisely predict the risk of HPAI occurrence among poultry farms to implement proper biosecurity measures. South Korea is one of the countries under the area at high risk of HPAI occurrence, in the particular winter season, with massive damages recently even worsening due to the geographical location adjacent to endemic countries, part of East Asian–Australasian Flyway, the intensification of poultry production. Unfortunately, animal health and production authorities in South Korea have limited knowledge about the common risk factors related to various subtypes of HPAI epidemics in poultry farms from a spatial perspective. Therefore, this study aimed to identify spatial risk factors associated with HPAI infection in poultry farms, as discussed in previous studies in many other countries, and subsequently predict the probability of infection in poultry farms at high risk in order to prevent HPAIV occurrence in the near future.In this study, the three subtypes of HPAIv-IPs exhibited geographically heterogeneous characteristics, although similarities between the pairs of different subtypes of the outbreaks were often observed. In particular, land use surrounding IPs varied across the subtypes of the HPAI epidemic. This can be partly explained by the difference in composition of species in infected farms, which is closely related to the demographic and economic conditions in South Korea. The domestic duck farms in South Korea are concentrated in relatively small areas, especially in the southwestern region, which produced 48% of total ducks in 12,247 square kilometers according to the Korean National Agriculture Statistics, but chicken farms are evenly distributed throughout the country.Unlike domestic duck farms, most HPAI cases in chicken farms are reported in layer farms, which appear to require far more labor force than domestic duck farms because of a variety of specialized work, including cage cleaning, egg collection, and delivery, which is attributed to its location close to human populated areas where people are easily recruited . Also, tAdditionally, governmental intervention strategies driven by the transmision pathway during an epidemic could affect the disparity in spatial characheristics. For example, during the 2010–2011 H5N1 epidemic, the trade through the LBM, was not prohibited and became the major source of infection with pathogens. After numerous HPAI infection cases were found to be epidemiologically linked to the LBM, the government rapidly imposed heavy restriction on live bird sales, such as the temporary closure of LBM during the H5N8 and H5N6 epidemic. Consequently, at higher value for the minimum distance to the LBM from IPs during theses epidemics was observed compared with H5N1 IPs.In a case-control study of the HPAI H5N8 epidemics, duck farm density and minimum distance to the LBM were found to be major predisposing factors for HPAI infection in poultry farms. The density of domestic duck, as the previous study reported that there was a strong association between the density of ducks and HPAI outbreak farms, was also identified as an important risk factor of HPAI in Korea in this study , 41. GenMoreover, all-in-all-out production practices are not usually adapted to domestic duck farms, where day-old ducklings were introduced into the farms continuously without the least downtime  because Additionally, meat ducks that account for more than 90% of ducks in South Korea have a rearing period of 45 to 48 days, longer than the breeding period of meat chickens (21 to 27 days), which led to longer HPAIv periods . This loThe Bayesian logistic regression and XGBoost model built based on the H5N8 case-control study demonstrated a relatively high predictive performance  for retrospective (H5N1) and prospective epidemics (H5N6), although they outperformed the risk prediction for H5N8 outbreak. This suggests that although the overall spatial characteristics of IPs among the three subtypes of epidemics showed disparity to some extent, the distributions of spatial variables of IPs and non-IPs during the H5N1 and H5N6 epidemics were distinguishable to clarify either HPAI infection or non-infection. Moreover, significant key variables of those IPs, such as the minimum distance to the LBM, had enough values to give weights to the model for a higher probability of HPAI infection. For instance, the mean of the minimum distance to the LBM for H5N1 IPs and H5N6 IPs was 1.04 and 2.41, respectively. This value is lower than H5N8 IPs, leading to higher odds of HPAI infection in the logistic model and probability in the XGBoost model. Additionally, the machine learning algorithm model demonstrated higher predictive performance than the statistical model, especially for H5N1 and H5N6. The XGBoost is a tree-based approach that uses the regularized method, where the number of splits and depth in the decision tree is restricted by defining the minimum entropy gain necessary to create further splits . Indeed,In addition, from a geographical perspective on the distribution of poultry holdings at high risk, two regions, the central and southwest part of the country, were constantly predicted by the two models to have a higher probability of infection, which was consistent with the observed data. South Korea geographically has spacious land with plenty number of lakes, streams, and rivers in the western part and mountainous areas in the eastern part. The HPAI H5N8 outbreak in 2014 occurred in the southwestern part of South Korea in the early stages of the epidemic, with a large number of infections and continued in the eastern and central parts of the country. Similarly, the HPAI H5N1 and H5N6 outbreaks began in the central part of the country, spread to the eastern part of South Korea, but mostly occurred in the southwestern part, especially Yeongam, and Naju. This suggests that the occurrence of HPAI is largely affected by the biological characteristic of HPAIv subtype and the spatial characteristics associated with the production system and market chain structure. This is also supported because H5N1 and H5N6 occur in similar areas and farms where HPAI recurrences appear even though ownership and trading affiliates change.It is important to consider addressing this issue in future work. First, we used poultry density data from 2016; however, according to the national livestock statistics, from 2011 to 2017, the number of duck and chicken farms slightly decreased, and new poultry farms rarely opened. However, depopulated farms started their production 6 months later, and density was presumed to remain similar across the study periods. Additionally, we chose the spatial variables based on the previous studies with a lack of elucidation of complex interactions among those variables. Thus, it is needed to build the prediction model based on the selection of variables from an understanding of the causal relationship of the variables with HPAI infection, such as a directed acyclic graph. Moreover, we used spatial data from diverse sources inherently with different spatial resolutions due to a diversity of spatial variables. Basically, the higher the spatial resolution of data for the corresponding spatial variables is, the closer the extracted value of the observation is to the true one. Therefore, we derived the value of corresponding spatial variables from the local data source, which provided a higher spatial resolution to minimize the deviation between the extracted and true value of spatial variables for study farms. Some variables extracted from a lower resolution, such as human density, where local data sources were not available, are likely to deviate from the true value. And the study farm within the cell of the spatial resolution had an identical value to the given variables. However, the 1 km spatial resolution (30 arc-second) was still considered to be high spatial resolution . Thus, gNonetheless, this study was the first to investigate the spatial risk factors of all subtypes of the HPAIv in South Korea from 2010 to 2017 and predict the risk of occurrence at the farm level. The results of this study emphasize that the viral and spatial characteristics of the poultry farm play an essential role in the development of HPAI. Therefore, to prevent and prepare for future HPAI occurrence, it is important to study the spatial characteristics of existing virus-type farms to prepare for the introduction of new viruses and to establish livestock prevention and prevention strategies based on this. Therefore, it is necessary to formulate HPAI prevention and response strategies through risk-based surveillance.The original contributions presented in the study are included in the article/D-sY and BC conceived and designed the study. D-sY acquired the data, performed data analyses, and wrote the original draft. KH and JK supported data collection. BC, KH, and JK edited the subsequent drafts. All authors read and approved the final manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


The mean values of the concentrations of BOD, NH4, and NO3 met the requirements, but the concentration of NO2 exceeded the requirements (1.0 mg/L vs. 0.08 mg/L). These results were achieved under a hydraulic retention time in the activated sludge reactor of 8 h, and the MLSS for the free-floating and immobilized activated sludge was 0.2 and 0.9 g/L, respectively.This research estimates the efficiency of domestic wastewater treatment in the removal of organic pollutants and nitrogen compounds with a two-stage treatment sequence , and with the application of floating carriers in the activated sludge reactor. The materials “Polyvom”, “Polystyrene” and “Bioballs” were adopted as floating carriers with previously determined filling ratios in the reactor volume of 10%, 20% and 20%, respectively. After the first stage of the study, it was found that the most effective treatment was achieved using the “Polyvom” material. Therefore, only this floating carrier was considered in the second and third stages of the study. Within the stages of the research, lab-scale benches operated under different operation modes of the treatment sequence. At the end of the study, it was possible to achieve the following levels of purification: BOD The reduction in access to fresh water globally has already acquired serious proportions. This concerns even countries with a large available volume of fresh water sources, since if it is not so noticeable yet, consumption is growing, and the sources are not being replenished . TherefoAs mentioned above, optimization of wastewater treatment processes is required because wastewater after purification is discharged back into the aquifer, which, in turn, results in a significant influence of wastewater on the composition and quality of water in the aquifer. A serious problem for water bodies is eutrophication, which is caused by the presence of nitrogen (N) and phosphorus (P) compounds in the water. These two elements , which appear in aquifers mostly with treated wastewater discharge, stimulate the growth of the flora of the reservoir, but these processes are destructive to the fauna ,5.4), as well as dissolved and suspended organic nitrogen fractions. The suspended fraction of organic nitrogen can be hydrolyzed into a dissolved fraction and then converted into the form of ammonium nitrogen by heterotrophic bacteria that use it as a biogenic source, and autotrophic nitrifying bacteria that use ammonium nitrogen as an energy source [Due to the peculiarities of water consumption , a significant proportion of treatment facilities (more than one third) receive low-concentrated wastewater, especially with regard to the content of organic pollutants . As a rey source .2) and nitrates (N–NO3) and subsequent denitrification of N-NOx compounds to nitrogen gas (N2) [At most municipal wastewater treatment plants, a two-stage biological nitrogen removal process is traditionally used, including aerobic nitrification of ammonium nitrogen to nitrites (N–NOgas (N2) .Denitrification is carried out under anoxic conditions by heterotrophic denitrifying microorganisms, whose vital activity requires a source of biodegradable carbon (as an electron donor). Therefore, the efficiency and speed of denitrification in such schemes is strictly limited by the amount of available organic matter in the wastewater entering the treatment facilities .Available experience reveals several possible directions for further research: the investigation of hydraulic retention time (HRT) ,12, the To date, various treatment sequences have been developed using the principles of nitrification and denitrification ,15, whicSecondary treatment reactors can be designed as an ASR  with triAlthough activated sludge treatment is undoubtedly more efficient than TF, trickling filters may be efficient enough to remove residual contamination with less demand for area and energy consumption in a multi-stage treatment ,19. In aAnother option for the operation of the WWTP can be a two-stage scheme using TF at the first stage and ASR at the second stage . In receIn various literary sources ,28, it iThe use of immobilized microflora, which may improve the elimination of both organic and nitrogen compounds from wastewater, is one potential strategies to intensify the process of advanced secondary treatment of wastewater . The surBased on the above, this research was performed on three types of floating carriers (FC) applied in ASR, and the treatment sequence was enhanced with the addition of a TF. The research was carried out at Moscow State University of Civil Engineering on a lab-scale bench operating in flow-through mode.The study presented in this paper has continued the previous research of the author on the application of floating carriers (FC) for biological wastewater treatment, which described the investigation of three types a–c of FCFor this study, a research procedure was initially proposed in accordance with The principle of the research used earlier  was most-peptone enzymatic—110 g;-sodium chloride—68.8 g;-potassium nitric acid—1.2 g;-soda ash—16.2 g;1. Synthetic wastewater made on the basis of the following components was used for the study:2. The synthetic wastewater solution was prepared in such a way as to ensure that its composition and the composition of real wastewater that is supplied for treatment to facilities in the Russian Federation are consistent.3. Based on the above, the concentrations of BOD during the study were in the range of 100 to 250 mg/L, and the concentrations of ammonium nitrogen impurities ranged from 15 to 35 mg/L.4. Sampling of wastewater throughout the study was carried out manually for the purpose of subsequent analysis based on standard methods used in Russia.-5);Biological oxygen demand ;-4);Ammonium nitrogen (NH-2);Nitrites (NO-3);Nitrates (NO-Dissolved oxygen (DO).5. Wastewater samples were examined according to the following indicators: Within the research, a two-step sequence of treatment was implemented . The stuThe ASR model was made in the form of a cylinder with a height of 1 m, an internal diameter of 100 mm, and a volume of 8 L. The model of the TF had the same dimensions as the ASR , with the filtering layer of the loading material of a height of 0.9 m.The loading material consisted of plastic cylindrical elements with a polyethylene mesh coating . The labAfter treatment, the effluent was discharged to the secondary clarifier (SC), where the mixed liquid was divided by sedimentation into purified wastewater, which was discharged, and the biofilm, which was settled into the sedimentary cone and returned to ASR by means of an airlift. Synthetic wastewater was prepared in a plastic tank (volume 60 L) and supplied to the following treatment set-up. The ASR, TF, and SC were connected to each other with rubber hoses (diameter of 10 mm), which allowed the collection of samples. The ASR was supplied with air by a compressor. Air distribution was achieved by means of a ceramic aeration system, which provided fine-bubble aeration. The recirculation of the activated sludge was air-driven. 3 day−1; the flow rate of RAS was 0.1 m3 day−1 (recirculation rate—250%); and the HRT in the ASR was reduced from 8 to 5 h due to the addition of the second step of the treatment. The HRT in the SC was 2.5 h. A key aim of the research was to maintain similar conditions on the three treatment benches. The wastewater flow rate was 0.04 mIn total, three benches were under simultaneous operation conditions, on which FC samples were examined in parallel. On bench 1, the ASR was equipped with the PS floating carrier with a filling ratio (FR) of 10%; the second bench was equipped with the PV floating material with an FR of 20%, and the BB floating carrier was installed on bench 3 with an FR of 20%. 5) on a similar level of 80–90% with approximately the same average concentration of BOD5 in the influent. As can be seen in 4 mean concentrations in the effluent were 2.7 mg/L, 6.7 mg/L, and 14 mg/L for PV, PS, and BB, respectively. The overall ammonium oxidation was not sufficient to produce the required quality. Despite the similar (and positive) results of the experiment regarding the removal of organic pollutants , the lev5 and NH4. In this current research, NO2 and NO3 were also analyzed to estimate the completeness of nitrification and denitrification processes. However, 2 (4 (for the PV floating carrier) were not matched by any sustainable results for other forms of nitrogen.In a previous study , attentiwever, 2 . Relativ4, as well as the treatment efficiency in the activated sludge reactor. The combination of the two steps of treatment enabled a very high efficiency of BOD5 removal: 91%, 96%, and 95% for PS, PV, and BB, respectively. The two-step efficiencies for NH4 were 81%, 94%, and 61%, respectively. The best results at this stage, both from the viewpoint of treatment efficiency and in absolute values, were achieved in the unit equipped with PV. It is important to note that the results were obtained under a very low value of MLSS of free-floating sludge. At the same time, this FC provided the highest rate of attachment of microorganisms on its surface. In contrast, the BB floating carrier showed three times lower levels of attachment of sludge (0.3 g/L vs. 0.9 g/L), which probably led to poor treatment efficiency. However, as can be seen in In stage 2 of the research, the treatment sequence of the laboratory unit was changed. The flow of the RAS from the SC was redirected to the TF . The modified technological scheme is shown in 5 and NH4 in comparison to the other two units; therefore, further studies were carried out only with a PV floating carrier. The results of the analyses carried out at stage 2 are presented in As indicated earlier, the lab bench equipped with a PV floating carrier showed generally better purification rates for BOD4 removal, confirmed the assumption that the operation of ASR without a flow of RAS can make the process of treatment more stable, even taking into account that the average influent concentrations of BOD5 and NH4 in Stage 2 had increased significantly. The maximum values of BOD5 and NH4 in the influent were recorded at 240 mg/L and 31 mg/L, respectively . At the same time, the level of pollution removal in this stage increased, and the absolute values of the concentration in the effluent were lower than those in the previous stage. Taking into account the effect in the TF, the BOD5 and NH4 indicators met the requirements of the standards . Thus, it can be concluded that the changes made to the operating mode of the installation had a positive impact on its efficiency.4, NO2, and NO3), in stage 3, it was decided to return to the more common HRT value equal to 8 h in ASR. At the same time, the RAS flow was reduced from the previous value of 250% to 100%. The scheme of operation of the installation remained similar to that used in stage 2  in the stage 3 indicates better nitrification/denitrification conditions and intensity in the system, which resulted from both the redirected RAS flow and the higher value of HRT. This also speaks in favor of improved stability in the treatment process compared with the results in stages 1 and 2.2 see  and a ri5 and NH4 remained at a consistently high level, and the absolute values of these indicators in the effluent met the required standards. Attention is drawn to the fact that the MLSS value for free-floating sludge in the system was significantly lower compared with stage 2, but this did not affect the quality of treatment. To summarize the efficiency in all three stages of the research, the removal of organic pollutants (BOD) and NH4 in the systems with floating carriers is well investigated under various conditions [As can be seen from nditions ,40. RediHowever, despite earlier assumptions, the increase in HRT did not lead to a complete decrease in the concentration of nitrites to the standard values , whereasAfter the completion of the research, three samples of the FC were collected to evaluate their stability by analysis of the COD value. The COD indicates the destruction of the sample which may cause emission of unstable particles of the FC into wastewater. The sample of FC, which was not used for treatment, has a COD value of 2.4 mg/L . After b4, respectively). The other two FCs, Polystyrene and Bioballs, had comparable carbon removal efficiencies (81% and 88%) but significantly lower ammonium removal efficiencies (74% and 40%). Based on these results, the studies were continued. However, only the Polyvom FC was used in the later stages of the study.A comparative analysis of the operation in and ASR of three types of floating carriers showed that the highest efficiency was achieved when using the Polyvom material (91% and 89% for BOD and NH4) and improved the purification process stability (particularly nitrification and denitrification). According to the indicators of BOD, NH4, and NO3, the required values of pollution concentrations in discharged wastewater were achieved.In stages 2 and 3 of the study, the treatment sequence was modified first by redirecting the RAS flow (to a TF instead of an ASR), and then by changing the hydraulic retention time in the ASR (from 5 to 8 h). The corrections enabled higher efficiency . In the conditions of a real WWTP, such a mode of operation will reduce the costs  for the treatment of excessive activated sludge.It is noted that despite the applied changes, it was not possible to achieve the required removal of nitrites from wastewater (1.0 vs. 0.08 mg/L), which is one of the promising areas for further research. In addition, it is of interest to study the work of floating carriers in membrane bioreactors. This combination may, on the one hand, increase the efficiency of cleaning processes; on the other hand, the floating carrier can be considered as a method to mitigate membrane fouling; the removal of the cake layer on the membrane surface occurs due to the friction of the floating carrier on the membrane surface ,43.The following conclusions can be drawn based on the performed study:


Aiming at the phenomenon that the emulsification degreeof thecomposite oil displacement agents affects the recovery factor, compositeoil displacement agents of the P/S binary system and the A/S/P ternarysystem were taken as research objects. Emulsion particle size andstability were tested and evaluated, and the effects of the surfactantand alkali content on the emulsification degree of emulsion were investigated.The concept of the emulsification stability index and its measuringmethod were put forward, and a method was used to test and evaluatethe emulsification stability of the emulsion. The results showed thatthe emulsion formed by the ternary system had the smallest averageparticle size, the best stability, and the best emulsification stability.The binary composite system was second, and the polymer solution didnot form an emulsion. The emulsification stability index method couldeffectively quantify the emulsification degree of the emulsion. Withina certain range, the increase of the surfactant and alkali contentin the composite oil displacement agent was beneficial to the improvementof the emulsification degree of the emulsion. The most notable feature of the polymeris that it can reduce the mobility of the displacement fluid, expandthe swept volume, and reduce the remaining oil saturation.5 The most significant feature of the surfactant is that it can reducethe interfacial tension between oil and water so that crude oil canbe easily peeled off from the rock surface and the residual oil saturationcan be reduced.7 The most notable feature of thealkali is that it can react with oleic acid to form surfactants, whichcan react with other components in the oil displacement agent to improveoil displacement efficiency.9As an enhanced oil recoverytechnology, chemical flooding has beengradually extended to the development of various oil and gas fields,especially in China, where chemical flooding has become an importantmethod for oil and gas field development to increase production andefficiency.13 During chemical flooding, surfactants are easily adsorbed on thesurface of oil droplets to form stable emulsions. The emulsificationbetween chemical flooding agents and crude oil and the propertiesof the formed emulsions have become research hotspots for oilfielddevelopment practitioners. In 1995, Aderangi and Wasam14 studied the coalescence of a single dropletat the liquid–liquid interface in a binary system oil–wateremulsion composed of surfactants and polymers and found that interfacialtension is not strongly correlated with coalescence time or speed.In 2009, Angle15 studied the rheology ofheavy crude oil emulsion and found that heavy crude oil emulsion canreduce the flow resistance of heavy crude oil. In 2013, Pei16 conducted an alkali flooding test for heavyoil reservoirs that were not suitable for thermal recovery. The resultsshowed that the alkali solution penetrated into the crude oil andformed a W/O emulsion with the crude oil, which reduced the flow capacityof the water phase and increased the sweep efficiency. In 2015, Xuan17 studied the effect of polymers on emulsion stabilityin poly-surface binary composite flooding. The polymer was found tobe beneficial to the stability of the emulsion. With the increasein shear rate, the stability became better and the droplet size becamesmaller. In 2017, Mandal and Chakraborty18 found in the experiments that the rheological trends of emulsionsin a shear rheometer and porous media were consistent, and the rheologicalcharacteristics of emulsions were very different when the compositionwas different. In 2018, when Lu19 studiedthe rheological laws of emulsions in porous media, he found that thetype, composition, dispersed phase concentration, and dispersed phasedroplet size of the emulsions all affect it. The research on the emulsionsformed by chemical oil displacement agents and crude oil mostly focuseson the rheological properties of emulsions and the effects of theviscosity of composite oil displacement agents and oil–waterinterfacial tension on the properties of emulsions. There are fewsystematic studies on the effect of the surfactant and alkali contentin composite oil displacement agents on the emulsification degreeof emulsion. Additionally, the evaluation method for the emulsificationdegree of emulsion needs to be improved.In recent years,it has been found that under certain conditions,the emulsification between oil and water enhances oil recovery morethan the effect of low interfacial tension. The effect of profilecontrol and oil displacement produced by chemical oil displacementagents in contact, and emulsification with crude oil in reservoirshas attracted more and more scholars’ attention.This work systematicallytested and evaluated the effects of alkalisand surfactants on the emulsification degree of emulsions. A new testingmethod for emulsification degree was proposed, and related conceptswere introduced. The rationality of the method was demonstrated bycomparing the test results of this method with the results of theclassical emulsion particle size and Turbiscan Stability Index (TSI)test methods. These studies are important for emulsion control andflooding technology in oil and gas fields, as well as for determiningthe emulsification degree of emulsions.22.1–3, reaching the ultra-low interfacial tensionstandard. Changing the content of the surfactant and alkali couldchange the ability of the system to reduce the interfacial tension.The interfacial tensions of the binary system were 4.6 × 10–2 and 9.5 × 10–3 mN/m, respectively,both of which reached ultra-low interfacial tension but were higherthan those of the ternary system, indicating that the interfacialtension between oil and the system could be reduced to a certain extentby only increasing the surfactant content when the components of thebinary system remained unchanged.The interfacialtension of each scheme is shown in 2.2The interfacial tension between the oil displacementsystem and the crude oil is an important factor affecting the degreeof emulsification. The emulsion droplets prepared by the above schemesystems and simulated oil were, respectively, placed under a microscopeto observe the particle size distribution. The results are shown in 21 After the surfactant is addedto the system, the surfactant molecules are spontaneously adsorbedon the oil-system interface, which reduces the interfacial tensionbetween the oil and the system, thereby reducing the interfacial energy,and the system gradually tends to a thermodynamically stable state.At the same time, surfactant molecules form an interfacial film withcertain strength on the surface of oil droplets, making the structureof oil droplets more stable, which slows down the mutual attractionand coalescence of oil droplets.23 Therefore,the simulated oil temporarily exists in the form of small oil droplets,and the morphology of the emulsion observed under the microscope isshown in 25 Therefore, the average particlesize of the emulsion droplets observed under the microscope becomessmaller, as shown in 27 Therefore, the oil droplets appearedsmaller under the microscope, as shown in It can be seen from 2.329 For the binary system, the wholesample container was all-emulsion at the beginning, the light transmittancewas poor, and the backscattered light intensity was high. With theprogress of the destabilization process, the intensity of the backscatteredlight in the lower part of the sample decreased greatly, and the lighttransmittance became better, indicating that the water content ofthe emulsion here increased, the emulsion droplets began to float,and the lower part gradually transformed into the water phase. After2 h, the curves were divided into two obvious parts. The samples inthe height range of 0–20 mm basically changed to the waterphase, the samples in the height range of 20–21 mm were emulsionsthat were not completely broken, and the samples above a 21 mm heightbasically turned into the oil phase, as shown in The destabilization process of the emulsion within 2 h of eachsystem was further studied. 31 The relationship between the TSI of the emulsion and the time isshown in The TSI can quantitatively characterize the stabilityof the emulsion.The larger the TSI, the greater the fluctuation of the average backscatteredlight intensity in each scan, and thus the more unstable the system.2.42.4.1t is the step size, and the area under the water retention rate curvewithin a single time span is used as the step-length emulsificationstability index (z), which reflects the step-lengthemulsification stability of the emulsion during this period of time(the comprehensive performance of the emulsification strength andstability of the emulsion within this time range). The ideal step-lengthemulsification stability index value is 100% × Δt. (3) The cumulative emulsification stability index: asshown in Z), which reflects the emulsion’s cumulative emulsificationstability over that time period, and the value is equal to the sumof all the step-length emulsification stability indexes over thattime period. The slope of the ideal cumulative emulsification stabilityindex curve is 1.In order to describe the emulsification strength andstability characteristics of the emulsion in the process of watershedding, three concepts, which are the emulsion water retention rate,step-length emulsification stability index, and cumulative emulsificationstability index, were defined. (1) The water retention rate (fw):as shown in The water retention rate can indicate the emulsificationstrengthof the emulsion at any time, and the higher the water retention rateat any time, the stronger the emulsification strength at that time.During the water separation process of the emulsion, the change inthe water retention rate within a period of time represents the changein the emulsification strength of the emulsion within this period,and the change in the emulsification strength during this period reflectsthe stability of the emulsion within this period of time, and thegreater the variation range of the emulsification strength, the worsethe stability of the emulsion during this period. The step-lengthemulsion stability index reflects the comprehensive performance ofthe emulsification strength and stability of the emulsion in the longtime range of any step. The smaller the step size, the more prominentthe emulsification strength of the emulsion in the step size. Whenthe step size is close to 0, it means that the emulsification strengthof the emulsion at this moment is the water retention rate. The cumulativeemulsification stability index reflects the comprehensive performanceof the emulsification strength and stability of the emulsion duringany period of time during the water separation process of the emulsion.When this time period is the time period of the whole emulsion waterseparation process, the cumulative emulsification stability indexcharacterizes the comprehensive performance of the emulsificationstrength and stability of the emulsion during the whole time period.2.4.2fv, water retention rate fw, step-length emulsification stability index z, and cumulative emulsification stability index Z were calculated. The area under the water retention curve was calculatedby the trapezoidal rule as the step-length emulsification stabilityindex, and the cumulative summation of multiple step-length emulsificationstability indexes was used as the cumulative emulsification stabilityindex. They were calculated as follows.fv is thewater separation rate, V1 is the volumeof the separated aqueous solution, mL, V2 is the volume of the oil-displacing agent solution used when preparingthe emulsion, mL, fw is the water retentionrate, z is the step-length emulsification stabilityindex, i is any time in the process of water separationof the emulsion, Δt is the time step, h, H is the unit time, H = 1 h, Z is the cumulative emulsification stability index, and zx is the emulsion stability index ofany step length in the process of water separation of the emulsion,0 ≤ a < b.The newly prepared emulsion was placed ata constant temperature, the volume of the water layer at differenttimes was tracked and recorded, and the water separation rate 2.4.3t = 1 h was set.The ideal step-length emulsification stability index was 100% ×1. The step-length emulsification stability index and the cumulativeemulsification stability index curves of different emulsion systemsare shown in The water separation process of the emulsion lastedfor 6 h, and the step size ΔAs shown in As shown in The relationships between the eigenvaluesof the step-length emulsificationstability indexes and the cumulative emulsification stability indexesof the five composite oil displacement agent emulsions were N2 >N3> N1 > L2 > L1. Therefore, their emulsification stabilityfrom highto low was N2 > N3 > N1 > L2 > L1. 2.4.4The smaller the particle size of the dispersedphase of the emulsion, the stronger the emulsification degree. Thesmaller the TSI value of the emulsion, the stronger the emulsificationdegree. The larger the emulsification stability index, the strongerthe emulsification degree. The characterization values of the emulsificationdegree of the emulsions formed by the five kinds of composite oildisplacement agents in the three abovementioned methods were compared,as shown in As can be seen from 3(1)The lower the interfacial tensionbetween the oil and the system, the better the thermodynamic stabilityof the emulsion and the smaller the average particle size of the dispersedphase. The relationship between the emulsification degrees of thecomposite system emulsion is ternary system > binary system, andthepolymer solution did not form an emulsion.(2)The instability rate of the binarysystem emulsions was fast, and the stability of the emulsions waspoor. The active substances generated by alkali and oleic acid hada synergistic effect with the surfactant in the ternary system, whichgreatly increased the stability of the emulsions.(3)The concept and algorithm of the emulsificationstability index were proposed, and the method of the emulsificationstability index could effectively quantify the emulsification stabilityof the emulsions.(4)Withina certain range, the increaseof the surfactant and alkali content in the composite oil displacementagent was beneficial to the improvement of the emulsification degreeof the emulsions.44.16 and solid content 90.6% (w)] were purchasedfrom the PetroChina Daqing Refining and Chemical Company. Sodium carbonate,analytically pure, was obtained from the Tianjin Kaitong ChemicalReagent Co., Ltd. CNPC Daqing Oilfield B oil production plant combinedstation exports sewage, which was used as experimental water. Thewater quality analysis is shown in Petroleum sulfonate [effective content of 40% (w)] and partiallyhydrolyzed polyacrylamide (HPAM) [relative molecular weight 12 to16 × 10The IKA T25 high-speed disperser is manufactured bythe GermanIKA company. The Model 500 spinning drop interfacial tensiometer isobtained from the Texas Corporation, USA. The Brookfield DV-II viscometeris purchased from the Brookfield Company in the United States. TheOlympus IX73 electron microscope is received from the Japanese OlympusCompany. The Turbiscan Lab stability analyzer is purchased from theFrench Formulaction Company.4.2Thesimulated oil used in the experiment was a mixture of crude oil, inthe combined station of the B oil production plant of Daqing Oilfield,and kerosene in a volume ratio of 5:1. At 45 °C, and it had aviscosity of 10 mPa·s. The purpose of using the simulated oilwas to make its viscosity consistent with the formation conditions.Although the change in the oil phase composition will affect the emulsifyingability and reduce the oil–water interfacial tension to a certainextent, the effect of this change is much smaller than that of addinga surfactant and an alkali to the water phase. Besides, the same simulatedoil was used in each experiment, so the influence of kerosene on theexperimental results can be ignored.4.3The interfacial tension was measured by the spinning drop method.In the experiments, the temperature was set to 45 °C, and therotational speed was set to 5000 rpm. After 2 h of starting the test,equilibrium was reached, and the interfacial tension no longer changedand was recorded this time.4.4Preparation of the emulsion: 50 mL of oil-displacing agent andsimulated oil were taken in a beaker at a volume ratio of 1:1, preheatedin a water bath at 45 °C for 10 min, and stirred at 4000 rpmfor 5 min to obtain the emulsion shown in Determination of the particle size of the emulsion:one drop ofthe emulsion on a glass slide was taken, the type of the emulsionwas observed through an electron microscope, the uniformity of thedistribution of the emulsion droplets was recorded, and the averageparticle size of the emulsion droplets was measured, as shown in Emulsionstability testing: the emulsion was taken into a samplebottle and analyzed with a stability analyzer, resulting in an outputof the backscattered light intensity curve and TSI, as shown in z and cumulative emulsification stabilityindex Z from the water separation rate were recorded,as shown in Determinationof the emulsification stability index of the emulsion:20 mL of emulsion was taken into a glass-graduated cylinder, the waterseparation rate was recorded every 1 h, and the step-length emulsificationstability index 4.5Scheme1 was a one-component system composed of HPAM solution, which wasused for comparison with composite oil displacement agents.Scheme 2 was a binary system. The emulsifying ability of the systemwas changed by changing the surfactant content. Therefore, two schemeswith different surfactant contents were designed: Scheme 2a is a binarysystem L1 composed of HPAM solution and 0.15% (w) petroleum sulfonatesolution, and Scheme 2b was a binary system L2 composed of HPAM solutionand 0.30% (w) petroleum sulfonate solution.Scheme 3 was a ternarysystem. The emulsifying ability of the systemwas changed by changing the content of the surfactant and alkali.Therefore, three schemes with different contents of surfactant andalkali were designed, respectively: Scheme 3a was a ternary systemN1 composed of HPAM solution, 0.15% (w) petroleum sulfonate solution,and 1.2% (w) sodium carbonate solution. Scheme 3b was a ternary systemN2 composed of HPAM solution, 0.30% (w) petroleum sulfonate solution,and 1.20% (w) sodium carbonate solution. Scheme 3c was a ternary systemN3 composed of HPAM solution, 0.30% (w) petroleum sulfonate solution,and 0.60% (w) sodium carbonate solution.In the above schemes,the viscosity of the systems was controlledat 40 mPa·s (a temperature of 45 °C and a shear rate of6.0 rpm) by adjusting the content of HPAM.


The linear dependence of the degree of polymerization on time confirms the conduct of radical polymerization in a controlled mode. The VT conversion was over 98% and the PVT number average molecular weight ranged from 11 to 61 kDa. The polydispersity of the synthesized polymers reached 1.16. The occurrence of the controlled radical polymerization was confirmed by monitoring the degree of polymerization over time.Narrow dispersed poly (PVT) was synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization of 1-vinyl-1,2,4-triazole (VT). AIBN as the initiator and dithiocarbamates, xanthates, and trithiocarbonates as the chain transfer agents (CTA) were used. Dithiocarbamates proved to be the most efficient in VT polymerization. Gel permeation chromatography was used to determine the molecular weight distribution and polydispersity of the synthesized polymers. The presence of the CTA stabilizing and leaving groups in the PVT was confirmed by  The datCarrying out the controlled radical polymerization of VT, in contrast to free radical polymerization, led to a decrease in the average molecular weights and the formation of narrowly dispersed polymers . The higThe effect of the natures of the RAFT agent, solvent, molar ratio of the initiator AIBN and CTA on the monomer conversion, molecular weight, and polydispersity of the resulting poly were studied .The use of methanol and DMF was due to the good solubility of the PVT and RAFT agents in these solvents. The molar ratio of [AIBN]:[CTA] ranged from 1:1 to 1:10. Regardless of the CTA used and the polymerization conditions, the polymer conversion was more than 98%, and the average molecular weight of the PVT varied in the range from 11 to 61 kDa . The useIn order to control the molecular weight of PVT, studies were carried out at different ratios of [M]:[CTA] in the range from 100 to 400 at a constant ratio of [AIBN]:[CTA] = 1:2.5 . Accordi2C≡N), so the efficiency of the reinitiation step for both chain transfer agents is close. The difference between CTA1 and CTA2 lies in the stabilizing group (Z), which ensures the stabilization of the macromolecular chain in the inactive (sleeping) state. Based on this, the difference in the molecular weight and dispersion of PVT is due to the influence of this fragment.The obtained results indicate that CTA2 is a more efficient RAFT agent in the controlled radical polymerization of VT compared to CTA1. CTA1 and CTA2 have the same leaving group  bond and easier attachment of the growing macroradical to polyCTA2. As a result, polyCTA2 had higher activity and a higher transfer coefficient compared to polyCTA1, which led to a decrease in the growth reaction rates and a decrease in M1H and 13C NMR spectroscopy. The 1H NMR spectrum of the poly obtained at [AIBN]:[CTA2] = 1:10 in DMF is shown in 1H NMR spectrum of the homopolymer. New broadened signals showed up in the region of 4.20–3.34 and 2.34–1.94 ppm, which were assigned to the proton resonance in the methyne and methylene groups in the polymer backbone, respectively. The signals at 7.87–7.29 ppm belonged to the protons of the triazole ring. In addition, the 1H NMR spectrum contained signals at 8.37–8.14 and 6.94 ppm, which were related to the protons of the pyridine ring of CTA2. The methyl proton signals of the dithiocarbamate group of CTA2 were visible at 3.80 ppm. The signal attributable to the methylene protons of the NC–CH2 R-group was detected at 2.43 ppm. Such signals were not observed in the 1H NMR spectrum of the PVT synthesized by free radical polymerization  and indicate that the polymer chain end is capped by CTA fragments as expected, according to the general mechanism of the RAFT process.Kinetic studies of VT radical polymerization in the presence of [AIBN]:[CTA2] = 1:2 in DMF at 60 °C were carried out in order to confirm the controlled nature of the polymerization. The conversion and molecular weight characteristics of PVT from the time of polymerization were controlled. The conversion, average molecular weight, and polydispersity of the homopolymer in the reaction mixture were determined by GPC.Monomer conversion and the ratio of the monomer concentration over time as a function of reaction time is shown in The dependence of the average molecular weight and polydispersity on the monomer conversion is shown in An important criterion for proving the controlled nature of polymerization is the ability to further increase the polymer chain, which is in an inactive state. For this purpose, the resulting and isolated polymer PVT , 16 was 1H and 13C NMR experiments revealed that the PVT chains contain CTA functional groups. The retention of activity of the PVT to chain transfer synthesized by the RAFT polymerization method was confirmed by successful chain extension.The controlled radical polymerization of 1-vinyl-1,2,4-triazole in the presence of AIBN as an initiator and dithiocarbamates, xanthates, and trithiocarbonates as the chain transfer agents was studied. Dithiocarbamates—cyanomethyl methyl(phenyl)dithiocarbamate and cyanomethyl methyl(pyridine-4-yl)dithiocarbamate—proved to be the most effective chain transfer agents. The use of methanol as a medium compared to DMF led to polymers with a narrower polydispersity. The study of RAFT polymerization at various [M]:[CTA] ratios indicates a linear dependence of the molecular weight, which confirms the controlled mode of VT polymerization. Regardless of the polymerization conditions, the monomer conversion was greater than 98%. The average molecular weight of the synthesized PVT was in the range from 61,000 to 11,000 Da while the polydispersity reached 1.16. The structural analysis performed via the


To maintain the temperature and settlement stability of a subgrade, a combination of graded crushed rock layer and insulation layer may be applied to optimize pavement structures. This study verifies a proposed numerical model of pavement and subgrade design in permafrost regions and evaluates temperature and settlement characteristics at different particle size and thickness of graded crushed rock layer and different thickness and location of insulation layer. The results show that the temperature and settlement of the combination of graded crushed-rock layer and insulation layer decrease significantly as the particle diameter and thickness of graded crushed-rock layer increase, and vary little when the thickness of insulation layer is more than 0.15 m. The location of installation layer has significant influence on the temperature of the subbase layer, but has little influence on the temperature of the subgrade. The maximum settlement of the pavement structure and subgrade decreases when the installation layer varies from the top of the subbase layer to the bottom of the subbase layer. The optimal combination of graded crushed-rock layer and insulation layer is that the 0.15 m-thickness installation layer is at the bottom of the 0.50 m-thickness graded crushed-rock layer with the particle size of 6–8 cm. This study provides a theoretical basis for the design, construction, operation, maintenance, and safety management of airport runways in permafrost regions. The thermal stability of permafrost is poor, and its settlement frequently causes the cracking, deformation, subsidence, and collapse of engineered structures , 2. HencThe crushed-rock subgrade method uses crushed-rock to replace shallow permafrost, which promotes subgrade stability. For example, 1.5 m-thick crushed-rock subgrade was used in the Alaska Arctic Coastal Plain Airport, 1.8 m-thick crushed-rock subgrade was used in the Brookes Mountain Area Airport, and 3–10 m thick crushed-rock subgrade was used in the Mohe Gulian Airport of China and Yichun Airport of China . Qin andThe insulation subgrade method employs insulation materials to reduce heat transfer from the outside to the permafrost to slow permafrost temperature changes and degradation, which is beneficial for maintaining the temperature field stability of the subgrade. The first insulation subgrade was utilized at Kotzebee Airport and Inigok Airport in Alaska, with extruded polystyrene foam used as the insulation material . Both thCrushed-rock and insulation subgrades exhibit many advantages for ensuring permafrost subgrade stability. However, crushed-rock subgrade is not suitable for a wide distribution and thick layer of permafrost owing to the limits of excavation, backfill, earthwork volume, and construction costs. The insulation subgrade method prevents the outward transfer of internal heat, but the permeability, strength, thickness, and durability of the insulation material also affect permafrost subgrade stability. In China, the large airport is called “Hub airport”, which refers to the airport with dense international and domestic air routes, the node of the central air route network, and also the distribution center of air passenger and cargo transport. The main features of the large airport are a high proportion of transit operations and efficient flight connectivity, where passengers can easily transfer to other airports. Hence, the large airport needs to meet 4F-class airport standards, can take off and land the aircraft of A380-800. And the 4F-class airport is an airport with an available runway length of 3600 m or more, a wingspan of 65–80 m for the largest aircraft available, and a distance of 14-16m from the outer wheels of the main landing gear under standard conditions. Therefore, it is necessary to determine the optimal combination of crushed-rock and insulation subgrades in the large airport. This study established and verified a runway model for large airports and analyzed the influence of crushed-rock layer thickness and particle diameter, and insulation layer thickness and location on subgrade stability. Finally, this paper proposed optimization parameters for combined crushed-rock and insulation subgrade in permafrost regions. The research findings provide valuable information informing the design, construction, operation, maintenance, safety, and management of airports in permafrost regions.C is the heat capacity, T is the temperature, t is the time, L is the transformed latent heat of water, 334560 J (m)-3, ρi is the density of ice, 0.917×103 kg (m)-3, wi is the volume fraction of ice, and kx, ky, and kz are components of thermal conductivity.The runway is disturbed by solar radiation and precipitation, geological lithology, and the water content of its structural layer and its lower soil layer. Therefore, to optimize the model, improve its computational efficiency, and ensure the effectiveness of the results, the following practical assumptions are made: 1) The layers of the pavement, natural surface, and subgrade are uniform and isotropic. (2) The boundary of each structural layer does not permit moisture migration. (3) The pavement, natural surface, and subgrade layers obey the law of energy conservation and feature only the effects of the heat transfer. Harlan and Taylor propose an equation for the material migration during freezing and thawing. Three-dimensional (3D) unsteady heat conduction can be expressed by Eq -3; Kx, Ky, and Kz are the components of hydraulic conductivity; φ is the total potential energy, equal to ϕ and h; ϕ is the volumetric potential energy; and h is the gravitational potential, which is ignored.During the freezing and thawing of soil, 3D mass transfer can be expressed by Eq  when evaThe content of unfrozen water is the mass ratio of unfrozen water to soil particles at a certain negative temperature, as shown in Eq :∂wu∂t=Eq  can be oThe volumetric potential of unfrozen water at different temperatures can be determined according to the relationship between temperature and content of unfrozen water and the characteristic curve of water, as shown in Eq :∂ϕ∂t=∂δ is the differential capacity of water, D is the coefficient of diffusion of water, and K is the hydraulic conductivity.Eq  can be oC(T) is the equivalent heat capacity, and λx(T), λy(T), and λz(T) are the equivalent thermal conductivities.Finally, Eq  can be tT0 is the mean annual ground temperature of the boundary layer, taken as the mean annual air temperature; ΔT is the increment in the temperature of the boundary layer, which is set to 2.5°C for the natural surface and 4.5°C for the pavement; a is the amplitude of variation in temperature, which is set to 12°C for the natural surface and 15°C for the pavement; t is the time in hours; b is the initial phase, equal to zero at the initial set time of April 1 in northeast China; and α is the increment in the global temperature over the next 30 years, which is set to 1.5°C.The first boundary condition is established based on the surface temperature of the permafrost region and is applied to the surface in the numerical models, as shown in Eq  18].T.T18].The second boundary condition is an adiabatic boundary condition that is applied on both sides of the numerical models, as shown in Eq  30]:∂:∂30]:The third boundary condition is a constant temperature gradient of 0.03°C (m). This is applied at the bottom of the numerical models, as shown in Eq  31]..31].The configuration of the main landing gear is shown in As shown in E is the elastic modulus; ν is the Poisson’s ratio; c is the cohesion; θ is the friction angle; and a1, a2, a3, a4, b1, b2, b3, and b4 are the regression coefficients. When T is not less than zero, b1, b2, b3, and b4 are all equal to zero. m is the index, which is set at 0.6.The calculation time was 10 years. The boundary conditions of the numerical model were determined using Eqs , 14), a, a14), aOwing to a lack of monitoring data on runways, the reliability of the numerical model was verified through a comparison with previously proposed models in terms of the temperature field, frozen layer depth, and settlement without considering aircraft load. Transient thermal analysis of the runway was conducted over 10 years based on the initial temperature field. The temperature field after 10 years of operation in northeast China is shown in th day, after the air temperature had reached its maximum value at the end of March in the second year. The appearance time of the maximum depth of the frozen pavement layer in th day after the air temperature had reached its maximum value in the middle of August. Maximum settlement was observed for the pavement and natural surface at 0.023 m and 0.098 m, respectively, in runway engineering. The maximum settlement characteristics and temporal regularity in As shown in As shown in As shown in As shown in When the particle sizes of the subbase layers were 6–8 cm and 10–15 cm, the evolution laws of temperature-time and temperature-depth curves were similar to those shown in Figs When the 0.10 m-thickness installation layer is at the bottom of the subbase layer and the particle size of the subbase layer is 6–8 cm, the time-dependent temperature curves at different thickness of the subbase layer are shown in Both the temperature and temperature range of the pavement center decreased as subbase layer thickness increased. When the subbase layer thickness varied from 0.10 m to 0.50 m, the maximum temperature at the bottom of the subbase layer decreased by 4.7°C, and the minimum temperature at the bottom of the subbase layer decreased by 3.5°C. As the subbase layer thickness increased from 0.10 m to 0.50 m, the temperature amplitude below the subbase layer varied by decreasing amounts as depth increased. When the depth was 5 m below the subgrade, the maximum and minimum temperatures changed by 0.6°C and 0°C respectively as the subbase layer thickness increased from 0.10 m to 0.50 m. Hence, the increase in the thickness of the graded crushed-rock maintained a reduced temperature of the subgrade, and the cooling effect of the graded crushed-rock gradually diminished as depth increased. Hence, the optimization thickness of the subbase layer was 0.50 m, which was beneficial to maintain the temperature stability of the subgrade and ensure the settlement of replacement construction.When the installation layer is at the bottom of the subbase layer and the 0.50 m-thickness subbase layer is the particle size of 6–8 cm, the time-dependent temperature curves at different thickness of installation layer are shown in When the thickness of installation layer is 0.15 m and the 0.50 m-thickness subbase layer is the particle size of 6–8 cm, the time-dependent temperature curves at different location of installation layer are shown in As shown in As shown in In When the particle sizes of the subbase layer were 6–8 cm and 10–15 cm, the evolution laws of the settlement-time and settlement-depth curves were similar to those shown in Figs When the 0.10 m-thickness installation layer is at the bottom of the subbase layer and the particle size of the subbase layer is 6–8 cm, the time-dependent settlement curves at different thickness of the subbase layer are shown in When the installation layer is at the bottom of the subbase layer and the 0.50 m-thickness subbase layer is the particle size of 6–8 cm, the time-dependent settlement curves at different thickness of installation layer are shown in When the thickness of installation layer is 0.15 m and the 0.50 m-thickness subbase layer is the particle size of 6–8 cm, the time-dependent settlement curves at different location of installation layer are shown in As shown in As shown in The settlement of the pavement center shown in As shown in When the particle size of the subbase layer was 6–8 cm and 10–15 cm, the evolution laws of the settlement-time and settlement-depth curves were similar to those shown in Figs When the 0.10 m-thickness installation layer is at the bottom of the subbase layer and the particle size of the subbase layer is 6–8 cm, the time-dependent settlement curves at different thickness of the subbase layer are shown in When the installation layer is at the bottom of the subbase layer and the 0.50 m-thickness subbase layer is the particle size of 6–8 cm, the time-dependent settlement curves at different thickness of installation layer are shown in When the thickness of installation layer is 0.15 m and the 0.50 m-thickness subbase layer is the particle size of 6–8 cm, the time-dependent settlement curves at different location of installation layer are shown in In this study, a numerical model of the structure of the pavement and subgrade in permafrost regions is developed through a comparison with previous models in terms of the characteristics of the temperature field, frozen layer depth, and settlement without considering aircraft load. This study also analyzes the temperature and settlement of different pavement structures. The main conclusions are as follows:When the combination of graded crushed-rock layer and insulation layer is included in the subgrade, the temperature amplitudes of the pavement and natural surface gradually decrease with some phase delay as depth increases. The temperature amplitudes of the pavement at the bottom of the combination of graded crushed-rock layer and insulation layer vary significantly and are smaller than those at the bottom of the base layer. The temperature ranges of the pavement and natural surface decrease with increasing depth and tend to be constant. The cooling effect of the combination of graded crushed-rock layer and insulation layer is enhanced with an increase in the particle diameter and thickness of graded crushed-rock layer and the thickness of insulation layer. Moreover, the location of installation layer has significant influence on the temperature of the subbase layer, but has little influence on the temperature of the subgrade.The combination of graded crushed-rock layer and insulation layer can significantly reduce the settlement range of the time-dependent curve and maintain the settlement stability of the subgrade. The settlement range of the pavement center decreases as the particle diameter and thickness of graded crushed-rock layer and the thickness of insulation layer increases. When the depth exceeds 2.45 m, pavement settlement is a positive value due to the effect of frost deformation. The maximum settlement of the pavement structure and subgrade decreases when the installation layer varies from the top of the subbase layer to the bottom of the subbase layer.The evolution of the settlement under the static load of the aircraft is similar to that of the no-aircraft case. The settlements at the pavement and natural surface centers decrease with increasing depth and tend to zero. The settlement decreases with increasing the particle diameter and thickness of graded crushed-rock layer and the thickness of insulation layer. The maximum settlement of the pavement structure and subgrade decreases when the installation layer varies from the top of the subbase layer to the bottom of the subbase layer. However, the graded crushed-rock layer particle size of 10–15 cm is not suitable for construction and leveling in runway engineering and increasing the porosity and cooling effect of the subbase layer slightly. And the time-dependent temperature and settlement curves are similar at the installation layer thickness of 0.15 m and 0.20 m. The optimization particle size of the subbase layer is 6–8 cm, the optimization thickness of the subbase layer is 0.5 m, the optimization thickness of the installation layer is 0.15 m, and the optimization location of installation layer is at the bottom of the subbase layer.


Background and objectives: Occlusal overloads produce a series of manifestations in teeth, especially attrition and non-carious cervical lesions (NCCL). Optical Coherence Tomography (OCT) can highlight and evaluate tooth lesions. The aim of this study was to examine the changes of dental hard tissues in the cervical area because of occlusal overload by macroscopic examination and using in vitro Swept Source OCT examination. Materials and Methods: The study was performed on 21 extracted teeth with occlusal trauma. After macroscopic and OCT examination, the 2D OCT images were transformed into 3D images using ImageJ software. Statistical analysis of macroscopic and OCT images was performed with Statistical Package for Social Sciences. Results: On 21 teeth, 88 cervical lesions (cracks) were identified. Upper premolars with an occlusal Smith and Knight tooth wear score of 2 had the most NCCL. Statistical analysis revealed significant differences in the median widths of cervical lesions between teeth with score 1 and score 3. Additionally, we obtained statistically significant differences in median widths between the buccal and oral surfaces. Conclusions: These cracks can be considered precursors of NCCL. NCCL can be located on dental surfaces in the cervical area other than the buccal one. A 3D reconstruction of OCT images emphasized that cracks are located especially at enamel level, evolving towards the enamel–dentin junction, with multiple ramifications. Occlusal overloads produce a series of manifestations in teeth, of which a special place is occupied by attrition and non-carious cervical lesions (NCCL). In terms of attrition, the mechanism of hard tissue loss seems easy to understand , whereasIn 1991, Grippo used the term “abfraction” to define NCCL and considered them a consequence of excessive occlusal forces . He descIn 2019, a group of 15 experts from the European Dental Caries Research Organization and the Cariology Research Group of the International Association for Research in Dental Medicine (IADR) met at a workshop in Frankfurt to define the terminology associated with erosive dental wear and dental caries. They unanimously agreed that the term “abfraction” is not recommended to be used because there is not enough information to show that this form of dental wear is caused only by excessive occlusal forces . CurrentOptical Coherence Tomography (OCT) is an advanced biomedical imaging technique that allows visualization of the internal biological structure in a non-invasive manner and has multiple applications in numerous medicine fields . The firCurrently a higher number of publications describe the applications of OCT and the advantages of this method in highlighting and evaluating tooth lesions ,13. AmonThe aim of this study was to highlight the changes of dental hard tissues in the cervical area as a consequence of occlusal teeth overload, using in vitro Swept Source Optical Coherence Tomography (SS-OCT), to determine which teeth are most affected, the association of cervical lesions with the degree of occlusal wear, and to identify the most affected axial surfaces. Furthermore, the study aimed to assess more accurately the lesions in the hard tissues by tridimensional reconstruction of images using the ImageJ program.The study was performed on 21 teeth without endodontic treatments, fillings or carious lesions in the cervical areas, represented by 7 upper molars, 8 lower molars, 4 upper premolars and 2 lower premolars. The study was approved by the Ethics Committee of University of Medicine and Pharmacy from Craiova, Romania (no. 20/12 February 2021), and it is in accordance with relevant guidelines and regulations. Patients provided written informed consent for dental treatment and participation in the study.The teeth included in the study were extracted for various reasons from 13 patients over the age of 60, who presented for diagnostic and treatment in Dental Prosthetics Clinic of the Faculty of Dentistry, University of Medicine and Pharmacy of Craiova, during March–April 2021.The inclusion criteria in the study for the patients were: (1) informed consent to participate in the study, (2) diagnosis of extended partial edentulism, with multiple occlusal imbalances  established following clinical examination, examination of casts and radiological examination (orthopantomogram), and (3) teeth to be extracted showed low support capacity or various odonto-periodontal diseases in which conservative treatments could not be performed and could not be taken into account for a prosthetic rehabilitation.Of these, teeth that showed conclusive signs of occlusal trauma  were selected for this study.All teeth selected for this study had antagonist teeth, while they were in function in the oral cavity. Thereby, these teeth could be considered to have been subjected to occlusal overloads because the masticatory forces were supported by a smaller number of teeth in the functional processes of mastication and swallowing.The examination of patients and teeth extractions were performed by 6 dentists specialized in general dentistry and dental prosthetics, authors of the study from the Department of Prosthetic Dentistry and Oral Rehabilitation, according to conventional techniques, as little traumatic as possible, to avoid formation of additional cracks .The extracted teeth were immersed in hydrogen peroxide solution 10% for 10 min to remove organic residues. Subsequently, the teeth were scaled and brushed and kept in saline solution NaCl 0.9% until examination, to prevent dehydration and formation of additional cracks.Selected teeth were examined macroscopically, and occlusal tooth wear was evaluated according to the Smith and Knight tooth wear score . The preTooth samples were prepared for SS-OCT examination according to a protocol used in other studies . The teeThe macroscopic examination of teeth was performed using photographs taken with Canon DSLR 600EOS .The SS-OCT examination was performed using a system developed by Thorlabs  with a laser beam characterized by a central wavelength of 1310 nm, a spectral band of 100 nm and an average power of 12 mW. The system was used for 2D in vitro scanning of dental surfaces, and its resolution was 12 µm for the axial resolution and 15 µm for the lateral one. The system allowed the examination of samples measuring 6 mm × 5 mm × 1.5 mm  in about 30 s using the charge-coupled device type detector .The scan was performed in the cervical area on all axial faces of teeth, obtaining approximately 500 2D images for each scanned surface. For the quantitative evaluation, the refractive index of 1.58 was used, representing an average between the refractive index of enamel (1.63) and dentin (1.54) . RepreseCracks in the dental hard tissues and areas of structural alteration appeared as signals of high intensity, differentiated by the enamel and dentin mass. The high intensity signal from the cracks was determined by a higher refraction due to the interruption of the tissue continuity. The high intensity signal from structural alteration areas was determined by multiple reflections as a result of the signal destructuring. In these areas, tissue damage was caused by demineralization and stress concentration.p < 0.05 represented the statistically significance threshold.Tooth data were first grouped using Microsoft Excel. The same program was used for the basic descriptive analysis. For group comparisons, continuous variables were expressed as mean ± STDEV (standard deviation). We used Statistical Package for Social Sciences (SPSS), version 20 (IBM Corp.) to apply statistical tests upon our parameters. Correlations were analyzed based on Chi-square test. Mann–Whitney U and Kruskal–Wallis H tests were used for group distributions, based on the results of the Shapiro–Wilk normality test. Post hoc analysis was based on Dunn’s (1964) procedure with a Bonferroni correction for multiple comparisons, and the value Three-dimensional reconstruction ensures the assessment of the disposition of the cracks in the hard dental tissues. Three-dimensional images provide information on changes in hard dental structures from multiple angles along the 3 axes .The 2D OCT images (JPEG image format) were further transformed into 3D images and 3D volume viewer images using ImageJ software.ImageJ was developed on Mac OSX using its built-in editor and Java compiler.The source code is freely available . The author, Wayne Rasband, is a Special Volunteer at the National Institute of Mental Health, Bethesda, MD, USA 1997). This program does geometric transformations such as scaling, rotation and flips [97. This The 21 teeth included in the study were represented by 10 teeth from the mandibular arches and 11 teeth from the maxillary arches. In other words, the study was performed on 15 molars  and 6 premolars .Following direct examination and macroscopic images analysis of the 21 teeth, the diagnosis of occlusal wear of various degrees was established for all teeth as well as presence of NCCL .According to From all the images obtained for this study, macroscopic images of an upper first premolar (PM1), an upper second premolar (PM2) and a lower second molar (m2) will be presented.In the area of the buccal cusp of PM1, the occlusal Smith and Knight tooth wear score had a value of 2. In the buccal cervical area, an NCCL of medium depth, wedge-shaped, at the enamel–cement junction, was identified by visual examination a.In the case of PM2, the occlusal Smith and Knight tooth wear score had a value of 2, and no NCCL was identified by visual examination a.Tooth m2 presented an occlusal Smith and Knight tooth wear score of 3, and no NCCL was diagnosed by visual examination a.Following SS-OCT examination, besides the 4 NCCL described in the macroscopic examination, another NCCL on the oral face of an upper premolar and 83 cracks with various locations and widths were identified, resulting in a total of 88 cervical lesions . Of thesThe distribution of cervical lesions according to the Smith and Knight tooth wear score was as follows: 48 cervical lesions were recorded on teeth with an occlusal Smith and Knight tooth wear score of 1 with an average of 4.36 lesions per tooth, 15 cervical lesions on teeth with an occlusal Smith and Knight tooth wear score of 2 with an average of 3.71 lesions per tooth and 25 cervical lesions on teeth with an occlusal Smith and Knight tooth wear score of 3 with an average of 4.16 lesions per tooth .The most affected dental surfaces were the buccal ones, with 40 cervical lesions, followed by the mesial surfaces with 19 cervical lesions, the oral faces with 15 cervical lesions and the distal ones with 14 cervical lesions. Each surface presented either unique lesions or multiple lesions. A lesion was considered unique when it was the only lesion present on one side; a lesion was considered as part of a set of multiple lesions when there were at least two lesions present on the same side. Our study lot comprised 42 multiple lesions (representing 47.73%) and 46 unique lesions (52.27%).Depending on the degree of damage to the hard dental tissues; 76 cervical lesions were in the enamel, 7 cervical lesions were located at the enamel–dentin junction and 5 were located in the cementRegarding the width of cracks, the situation is presented in From all the 2D OCT images obtained for this study, those of PM1, PM2 and m2 will be presented.In the case of PM1, the 2D OCT images of buccal cervical area highlighted the existence of a concave fissure, located coronary from the NCCL, in the enamel, which continues at the enamel–dentin junction, corresponding to the red b and bluIn the case of PM2, the 2D OCT images of the buccal cervical area highlighted the existence of a straight crack at the enamel–dentin junction b. InitiaFor tooth m2, the 2D OCT examination of the buccal cervical area highlighted the existence of several cracks, positioned at the enamel–dentin junction and others with a radial appearance, located in the enamel b. On thiThe statistical results are based on the macroscopic examination of the 2D OCT images.Intra-rater reliability involved the analysis of two persons’ measurements of all cracks, following a second measurement process after a 2-week interval. ICC analysis showed a very good intra-rater agreement . Inter-class correlation coefficient analysis indicated also a very good inter-rater agreement  when comparing the measurements of all 4 persons involved in this phase of the study. The final values represented the average measurements of all 4 raters.p = 0.035).A Chi-square test was conducted between the presence of multiple lesions and tooth surfaces. All expected cell frequencies were greater than five. There was a moderately strong association between these variables (Cramer’s V = 0.313), which was statistically significant (p > 0.05).Similar tests were conducted to identify potential correlations between the presence of multiple cracks and tooth type , tooth position (maxillary and mandible) and the degree of tooth wear , but no statistically significant associations were obtained , but not between any other group combination.The distribution of crack width according to the degree of occlusal tooth wear showed that the teeth with an occlusal Smith and Knight tooth wear score of 2 presented the largest cervical lesions, with a mean of 0.176 ± 0.162. Those were followed by teeth with an occlusal Smith and Knight tooth wear score of 3, with a mean of 0.168 ± 0.192, and teeth with an occlusal Smith and Knight tooth wear score of 1, with a mean of 0.108 ± 0.129. For teeth with an occlusal Smith and Knight tooth wear score of 1, cervical lesions seem to be more uniform in width, while for teeth with scores 2 and 3, cervical lesions present various widths. For groups of teeth defined by the occlusal wear score, we obtained statistically significant differences in cracks’ size . Thus, wp < 0.0083 level (for the four possible cracks’ location). This post hoc analysis revealed significant differences in median widths between the buccal and oral sides (p = 0.007), but not between any other group combination.Regarding crack location on dental surfaces, buccal dental surfaces are more likely to have multiple cervical lesions (22), followed by mesial surfaces (10), distal (6) and oral surfaces (4). There are statistically significant differences in cracks’ width between these groups of teeth . Thus, wp > 0.05.There was no statistically significant difference regarding the width of cracks from different locations , The 3D reconstruction made using ImageJ program, on the 3 axes of the 2D OCT images, confirmed the presence of the cervical lesions and revealed their location and orientation in space.In the case of PM1, the 3D reconstruction revealed a buccal cervical lesion with a “wedge” appearance, from the level of which towards the occlusal was observed the propagation of a crack in the thickness of the hard tissues, with multiple ramifications. e,fIn the case of PM2, the 3D reconstruction revealed a surface crack, in the thickness of the hard tissues, with a semicircular appearance, going from the enamel–cement junction to the occlusal and from surface into depth c,d.In the case of m2, the 3D reconstruction revealed multiple radial cracks, oriented from surface into depth, stopping at the level of the enamel–dentin junction. At the enamel–dentin junction, another crack was noticed, parallel to the surface of the enamel. The 3D image brings together all the aspects recorded in the 2D OCT examination c,d.This study aimed to highlight the effects of occlusal overloads on hard tissues in the cervical area of teeth with varying degrees of occlusal wear. For this, a macroscopic examination and 2D OCT examination were performed. The additional objective of this study was to process OCT images from 2D to 3D with the ImageJ program, for a more accurate assessment of the distribution and orientation of the detected cervical lesions. Volumetric reconstructions and 2D image processing techniques are commonly employed in various medical fields in order to increase the accuracy of content analysis or object detection ,21,22.The effects of occlusal overloads highlighted in the form of dental wear (attrition and NCCL) ,24, in tThe present study was performed on 21 extracted teeth with occlusal wear of various degrees. The quantification of occlusal wear was performed using the Smith and Knight tooth wear score, a classic index used in many research studies to assess the degree of tooth wear regardless of the etiology involved. NCCL were identified through macroscopic and OCT examination and cracks were identified using only OCT examination. Along with NCCL as a direct consequence of occlusal overloads in the dental hard tissues, a series of cracks in the form of bright areas were highlighted, on a gray background. The diagnosis of dental cracks by current methods is difficult to achieve due to their location. Shimada showed that SS-OCT was an effective diagnostic method for dental cracks  and presAlthough the study initially aimed to highlight NCCL in teeth subjected to occlusal overloads, the large number of cracks and their morphology foreshadowing future NCCL, led to their inclusion in the effects of occlusal overloads and referred to them during the study as of “cervical lesions”. In fact, Grippo, in 1991, described NCCL as “hairline lesions” that can be located on all sides of the teeth . Prior tThere are other studies in literature that focused on the association between occlusal wear and the presence of lesions in the cervical area of the respective teeth. Most studies are performed by Finite Element Analysis (FEA) and show that the less the occlusal morphology is affected by wear, the higher the stress concentration in the cervical areas of the teeth, especially on the buccal surfaces ,24.The present study revealed the highest number of cervical lesions to be in teeth with an occlusal Smith and Knight tooth wear score of 1. The explanation could be given by the presence of premature contacts and occlusal interferences specific to teeth with primary or slightly modified occlusal morphology. The same explanation is given by Troia in 2021  and ChanIn contrast, the study showed a slight increase in the number of cervical lesions in teeth with an occlusal Smith and Knight tooth wear score of 3 compared to teeth with an occlusal Smith and Knight tooth wear score of 2. A possible explanation would be that score 2 occlusal wear has an adaptive character, whereas in score 3 occlusal wear, clenching and grinding can be invoked in addition to excessive occlusal forces ,34. The Although this is not a study focused on establishing the prevalence of cervical lesions, it showed that the most affected teeth were premolars. The result overlaps with studies on the prevalence of NCCL that have shown a preferential impairment of premolars ,40,41.Regarding the degree of damage to the axial faces, most manifestations of occlusal stress were identified in the buccal cervical area, followed by the mesial, oral and distal cervical area, respectively. This result is consistent with the preferential location of NCCL on the buccal surfaces of the teeth. Classical forms of abfraction lesions have been present mainly on the buccal aspects of teeth, although manifestations of occlusal overloads have been located in other cervical areas, which shows that there are several factors involved. The distribution of cervical lesions suggests the presence of morphological features of the enamel in these areas and the fact that several factors are involved in the genesis of NCCL.Regarding the width of these cervical lesions, mandibular teeth showed the highest variety of damage. Hughes analyzed the cracks in the cervical enamel and demonstrated in a 2009 study  that theIn the last part of the study presented, the 2D OCT images were transformed into 3D images and 3D volume viewer images, using ImageJ software. This 3D format allows a visualization of the lesions in all dental structures. To our knowledge, there are no studies in which the reconstruction of 3D images and 3D volume viewer of 2D OCT images was performed.The limitations of the study are represented by the small number of teeth examined.The study allowed the identification by macroscopic and OCT examination of the effects of occlusal overloads in the cervical areas of teeth in the form of NCCL and cracks located mostly on the vestibular surfaces of teeth.The present study performed a complete assessment of the lesions in the cervical area of teeth subjected to occlusal overloads and found that occlusal factors may be associated with NCCL. The similarity of some of the dental cracks to that of the NCCL has been highlighted, so that these cracks can be considered precursors of NCCL. The study confirmed the possibility of NCCL on dental surfaces in the cervical area other than the buccal one.A 3D reconstruction of OCT images performed using the ImageJ software application showed that cracks are present on all axial sides, especially in dental enamel, with an evolution towards the enamel–dentin junction, and with multiple ramifications.