A multi-species, individual-based, pore-scale model is developed and parameterized with data from 3 Arthrobacter sp. strains, known to be, respectively, competitive, versatile, and poorly competitive. In the simulations, bacteria of each strain are distributed in a 3D computed tomography (CT) image of a real soil and three water saturation levels  and spatial heterogeneity levels  in the distribution of the soil organic matter are considered. High and intermediate heterogeneity levels assume, respectively, an amount of particulate organic matter (POM) distributed in a single (high heterogeneity) or in four (intermediate heterogeneity) randomly placed fragments. POM is hydrolyzed at a constant rate following a first-order kinetic, and continuously delivers dissolved organic carbon (DOC) into the liquid phase, where it is then taken up by bacteria. The low heterogeneity level assumes that the food source is available from the start as DOC. Unlike the relative abundances of the 3 strains, the total bacterial biomass and respiration are similar under the high and intermediate resource heterogeneity schemes. The key result of the simulations is that spatial heterogeneity in the distribution of organic matter influences the maintenance of bacterial biodiversity. The least competing strain, which does not reach noticeable growth for the low and intermediate spatial heterogeneities of resource distribution, can grow appreciably and even become more abundant than the other strains in the absence of direct competition, if the placement of the resource is favorable. For geodesic distances exceeding 5 mm, microbial colonies cannot grow. These conclusions are conditioned by assumptions made in the model, yet they suggest that microscale factors need to be considered to better understand the root causes of the high biodiversity of soils.There is still no satisfactory understanding of the factors that enable soil microbial populations to be as highly biodiverse as they are. The present article explores  During the last decade, soils have become increasingly central to a number of crucial debates on issues of great societal concern e.g., . Because10 bacterial cells and 5 × 104 species  mineralization in soils that have a pH above 5.5. SOC mineralization continues at the same rate, after fumigant removal, once the initial decomposition flush is over  imaged at a resolution of 68 μm, suitable to visualize meso- and macro-pores.In this general context, the key objective of the present article is to explore the hypothesis that the heterogeneous distribution of the basic nutrient resources used by bacteria in soils can account to some extent for their diversity. The spatial distribution of organic matter in soils is known to be highly heterogeneous. Incorporation of plant residues by tillage results in patchy distribution at the centimeter scale e.g.,  while at3 voxels size out of the set of segmented CT images. The voxel-resolution of the image is 68 μm, so that the pore space explored in this study encompasses most of the structural porosity made of meso- and macro-pores. This image corresponds to a volume size of about 314 mm3, and it has a porosity of 18.82%. This number is undoubtedly smaller than the actual porosity of the soil, because of the fact that sub-resolution pores are ignored  Albeluvisol . 3D imag ignored .wS (the proportion of the pore space filled with water), is calculated using a two-phase two-relaxation-times (TRT) lattice-Boltzmann model (LBM) as described by wS = 1.00, wS = 0.50, and wS = 0.25. After a visual inspection of the 3D distribution of the gas phase in the images, we selected a few of the smallest visible pores containing gas and recalculated from the Young-Laplace law a rough estimate of the matric potential for wS = 0.25 and wS = 0.50. The matric potentials estimated in this manner are about -0.6 and -0.3 kPa, respectively. Therefore, even though a water saturation level of 0.25 would suggest that the soil is relatively dry, the fact that this number refers only to the CT-visible pore space means that the scenarios reported in the present contribution correspond to wet conditions.The localization of the fluid and gas voxels corresponding to a given water saturation index, The image offers a tradeoff between resolution and sample size (constrained by X-ray computed tomography). It is a compromise that presents the advantage of reproducing the millimeter-scale variability of the microbial activity, as reported by The description below of the Ib-LBioS-Comp model follows the overview, design concepts, and details (ODD) protocol , 2010, wIb-LBioS-Comp, which stands for Individual-based LBM for biodegradation affected by soil structure and competition, is a pore scale modeling approach developed to study the impact of the soil structure or, more appropriately, architecture  of up to three different species or strains, dissolved organic carbon or DOC (abiotic lattice-Boltzmann populations), and particulate organic matter . Bacterial cells and DOC are distributed in the 3D volume of the soil pore volume and POM is distributed in the 3D volume of the soil solid matrix. Enzymatic hydrolysis of POM is assumed to continuously supply DOC to the liquid phase. Then DOC diffuses through the liquid phase toward the microenvironments where it is taken up by bacteria and used as nutrient source. The diffusion and uptake of oxygen are not accounted for explicitly in the model at the moment and are assumed not to limit microbial activity.The simulated space is divided into a regular 3D grid made of cubic voxels that can be either solid or filled with a fluid (air or water).iI) is defined by the variables Πi, identifying its position in the domain, its species ij, its mass im (mg C), its specific uptake rate υDOC,i (tu-1), and its mass at reproduction R,im (mg C). All masses in Ib-LBioS-Comp are expressed in terms of mass of carbon. Letting P = I(t) denote the number of bacteria at time t, one obtains for the state of the population at time t:A bacterial cell or individual  the total number of cells at time t.where lA) is defined by a variable indicating its position in the domain, Πl, and its carbon mass, POM,lm (mg C). Letting A(t) denote the number of POM agents, the POM population state at time t is:A POM agent (l is the index of the POM agents and m(t) the total number of POM agents at time t.where qf, that are microscopic solute entities defined in the Q microscopic directions at each liquid node of the 3D grid. The Q directions are defined by the unit microscopic velocity vectors, d is the dimension of the grid or lattice. We used the model D3Q7.The DOC solute is simulated by microscopic lattice-Boltzmann populations, DOCC (t) (mg C lu-3) can be calculated at each liquid node of the grid as the sum of the qf populations:The DOC concentration in the liquid phase, xyzV the volume of one voxel expressed in lu3 where lu is the spatial unit of the lattice, in our case determined by the scanning resolution so that 1 lu = 68 μm.with ΔThe temporal evolution of the system is divided into equal intervals associated with time steps or units (tu) of a time step length dictated by the lattice-Boltzmann submodel. The temporal extent of the simulations was set to 10 days according to previous simulations made by Figure 1): (i) the initialization of the simulated system, (ii) the time step loop, which is repeated until the end of the defined time steps, and (iii) the model output section, where the system-level (aggregated) and individual-level (non-aggregated) data are saved in files. Initialization of the system includes: reading of model parameters, initialization of the bacterial agents, and initialization of the LBM parameters and DOC populations. The time step loop includes, chronologically: (ii.i) storage of the simulation state in temporary data structures, (ii.ii) the POM agents actions loop, (ii.iii) the bacterial actions loop , and (ii.iv) the lattice-Boltzmann actions. Output files of aggregated and state variables are created from the temporary data structures saved previously.Global simulation comprises three sections  are defined at the microscopic level of the Q directions of the lattice, and the solute behavior (diffusion) emerges from the interactions among the solute lattice-Boltzmann populations.Bacterial processes  are defined at a single-cell level and the population or system level behavior emerges from the interactions among individuals and between the individuals and the media. The main population-level emerging characteristics are the population density (bacteria present in the media), the population biomass, the DOC taken up by the population, the COBacteria are considered to be immobile but they compete directly for space through the maximum carrying capacity of a voxel. Therefore, the presence of other bacterial cells in the local space can directly affect the fate of new-born bacteria. Indirect interactions among individual bacteria arises from competition for the DOC available in the local environment.Randomness is considered when the rules are applied to individuals by using probabilistic distributions to deal with or manage individual events. Random processes or events include the assignment of the position of new-born bacteria in the physical domain near the mother when the grid element of the mother reached maximum occupancy, and the occurrence for cell death. The sequence of actions of the simulated bacteria changes randomly at each time step to avoid privileging one over the others. The model can also introduce further stochasticity when setting the mass of the initial individuals, the individual specific uptake rate, and the mass at reproduction of the individual bacteria using folded normal distributions, but this is not considered in the current study.2 produced in the media, and, for each of the three bacterial species, the number of bacteria, and total bacterial biomass. The state of all the individual bacteria is saved at sampling times. These single-cell data include the position within the domain, species, mass, uptake rate, and mass at reproduction of the individuals. The carbon mass and position of all the POM spots (abiotic agents) are also saved at sampling times. The DOC concentration of the liquid voxels holding at least one bacterium is also recorded at sampling times. The final DOC concentration of all the liquid grid cells of the domain is recorded at the end of the simulation.Global and single-cell outputs are recorded at the beginning of the simulation, at regular intervals during the simulation, as well as at the end of the simulation. Global variables calculated at the scale of the entire domain include: mass of DOC, POM, and CODOC,iv), and the reproduction mass  of the initial individuals  are assumed to be specific for each jth species. For the individuals of each species j, these properties are set using the model parameters im) is initialized according to the model parameters The specific uptake rate  that, in turn, are randomly chosen, with replacement, from the liquid voxels having one or more solid neighbors.Since it is generally assumed that bacteria in soil microenvironments tend to be sorbed to, or be at least very near, solid surfaces, the model assumes that bacteria can be located only in liquid voxels having at least one solid neighbor. What defines a neighbor here is the particular lattice-Boltzmann connectivity that is adopted in the calculations (D3Q7 in this case). The initial The POM agents are situated in the solid matrix of the soil. The initial POM agents are randomly distributed among solid voxels that have at least one liquid neighbor.0, is distributed homogeneously among the liquid voxels of the image.An initial amount of dissolved organic carbon, DOCThe model uses soil structural data as described in see Section Soil Image.Several separate submodels describe quantitatively the uptake, metabolism, reproduction, and mortality, respectively, of individual bacteria.Uptake submodel, the uptake (iU) of carbon substrate by bacterium i, belonging to the species ij = j, is given by the equation depending on the mass im (t) of the bacteriumIn the DOC,iv is the specific uptake rate of the ith bacterium (tu-1), and the parameter -3) of the jth species.where Metabolism submodel, the mass of carbon taken up is used by the cell to create new biomass. Since catabolic reactions need energy, due to the respiration process, a fraction of the carbon that is taken up is released again to the media in the form of CO2 emissions. Accordingly, the growth of the bacterial cell is modeled using the following equation:In the -1) of the species j. Equations (4) and (5) assume that growth respiration  and maintenance respiration  are not distinguished.where The Reproduction submodel adopts a simple bipartition condition , the reproduction mass of the ith individual. If im(t + 1) > R,im, the mass of the bacterium is halved, and simultaneously a daughter cell of the same mass is created. If the number of bacteria occupying the voxel of the mother cell is less than VOXN, the maximum carrying capacity of a voxel, the cell is created in the current voxel. Otherwise, the simulator chooses randomly a voxel that has not attained the maximum carrying capacity. The searching algorithm looks progressively to neighbors situated at increasing distances (in voxels) from the mother’s voxel of origin, until all the tridimensional space is inspected. If all the voxels reach the maximum carrying capacity, the simulation stops. The daughter cell remains active but does not act until the next time step is reached. The specific uptake rate of the new-born individual  and its mass at reproduction  are inherited from the mother.ondition  accordinthe Mortality submodel accounts for bacterial cell death derived from internal and external events . The cell cannot survive anymore due to internal events when the cell size decreases below the minimal cell size characteristic of its species j,pr with pr is a random realization coming from a uniform distribution between 0 and 1. If Finally, POMk. The underlying hypothesis is that exo-enzymes are ubiquitous in soil  along:in which the collision and propagation steps are described, respectively, by the two first terms of right hand side and left hand side of (7), respectively. The sink/source term of DOC, → =−c→q¯ . During Both parameters must be comprised between -2 and 0 for stability. The rescaling of lattice Boltzmann time units (tu) in real time units [T] is made through the relation:LBMT and LBML are the space and time in lattice units  and RT and RL are their corresponding time and space units in real units [respectively (T) and (L)].where Arthrobacter sp. (see Table 1) were taken from the literature. The specific uptake rate, Typical parameters for the three different strains 3R, 7R, and 9R of VOXN, was calculated from the volume of a single image voxel (683 μm3) and the mean cell volume of a bacterial cell. The mean volume of an Arthrobacter cell was calculated to be 0.418 μmł according to data from Arthrobacter sp. The mean reproduction diameter  was also estimated from Arthrobacter cell size distributions  and the value for the reproduction mass, 3, a ratio of dry to wet cell weight of 0.25, and a carbon content of 0.47 g C per gram of dry cells  stem residues. These authors found “optimal decomposition conditions similar to those obtained with ground material” for fragments of POM of 0.02 cm length. Assuming a density of POM of 0.12 g cm-3 , located at the solid/liquid interface . When the POM hydrolyses, the DOC produced is included in the neighboring fluid site.The value of the decay rate of the POM agents, 2 g cm-3  and a vo2tu-1  the three strains systematically co-exist in the same bacterial spot, so that only 230 bacterial spots were generated. The local micro-environments of these bacterial spots were modified by introducing heterogeneity in the placement of the resource (POM and DOC) in the medium. The water content level was also modified. Figure 3a). Ten replicated simulations were performed with the position of POM fragments controlled by a random seed. The positions of the 690 bacterial spots were left unchanged for the ten replicated simulations. The water saturation level, wS, was 0.50.The initial 690 bacteria were distributed among 690 randomly selected liquid voxels neighboring the soil solid matrix. Four POM fragments were randomly distributed in the medium . Bacteria were located in the same 690 positions as for scenario S1 and the same water saturation level, Sw = 0.50, was adopted. Ten replicated simulations were again performed with the position of POM fragments controlled by a random seed Comparison of scenario 1 and 2 made it possible to assess the effect of the degree of spatial heterogeneity of POM.The four fragments of POM were gathered in one fragment made of 2 × 2 × 3 voxels with the base 2 × 2 voxels being contiguous solid sites neighboring 2 × 2 fluid sites  involved 3 bacteria, one of each strain, in selected 230 bacterial spots. In S4a, we took one particular repetition of scenario S2 in which the three strains had a noticeable growth (repetition S2r2) and we classified the 690 spots according to the amount of biomass growth of the colony in a descending order. The first 230 bacterial spots were selected and used to place the initial bacteria. In S4b, we took the repetition S2r2 but we just selected the 230 bacterial positions occupied by the less competitive strain (9R). In each of these spots, we placed initially 3 bacteria, one of each strain.These scenarios are identical to scenario S2 except for the water saturation level that was fixed to 1.00 (S5) and 0.25 (S6). Because the positions of the 690 bacterial spots are left unchanged, in scenario S6 there were 165 bacterial spots that were found to be in the gas phase, and thus did not grow. In the 525 spots still placed in water filled grid cells, the three strains were found to be equally distributed as 178 cells of strain 3R, 172 cells of strain 9R and 175 cells of strain 7R.POMk = 0.25 d-1, about 92% of the initial mass of carbon of the POM fragments is hydrolyzed at the end of the simulations. The predicted time evolutions of the POM, DOC, total biomass (B), and CO2 are shown in Figure 4. At the beginning of the simulations, the carbon hydrolyzed from the POM particles cannot be totally consumed and accumulates in the liquid phase. After one day, when exponential growth of bacteria starts, the major part of the dissolved organic carbon is metabolized by the cells. At the end of the simulations, the CO2 emitted has not yet reached a plateau although the slope of its cumulated increase begins to decrease. Except for one repetition of scenario S2, no differences are observed in the time evolutions of the POM, DOC, total biomass, and CO2 between the two POM distributions.Simulation scenarios S1 and S2 assume that the soil organic matter is found in a number of POM fragments that are distributed (S1) or aggregated (S2). In the proposed scenarios, the hydrolysis rate of POM is set to a constant value, so that for Figure 4, right). When the POM is fragmented into 4 pieces, the less competitive strain 9R cannot grow significantly . The fastest growing strain 3R experiences an exponential growth up to two days before starting to decline. The more generalist strain 7R has a much smoother exponential increase compared to 3R, and even surpasses the biomass of 3R after five days, before starting to decline after about the day seven. When the POM fragments are gathered into a single piece, 3R has the same overall dynamics, with comparable mean abundances but with higher dispersion between replicates. The coefficient of variation (CV) of the abundance peak is 0.03 for S1 and 0.10 for S2. The strain 7R has also the same dynamics as in scenario S1 but with a lower mean abundance peak that does not exceed 78% of the 7R mean abundance peak observed for the scenario S1. Again, the CV is highest in scenario S2 compared to S1 with the values of 0.24 and 0.10, respectively. On the contrary, the strain 9R shows a much higher growth variation among replicates when the POM is aggregated in a single piece of POM. In particular, two replicates (S2r2 and S2r5) show growth kinetics similar to those of strain 7R. In three other replicates, 9R grows without exceeding the abundance of the other species. In the last five replicates, 9R presents a similar growth as in the case of POM fragmented. The S2 replicate with lower global total biomass and emitted CO2 (S2r9) corresponds to the lowest abundances of the strains 3R and 9R, and to the highest abundance of 7R. In that case, the highest abundance of 7R does not compensate the low abundances of strains 3R and 9R, while compensation is observed for the other replicates at the scale of the whole soil sample.Although the global model outputs are similar for both spatial distributions of POM, differences in the strains abundance are observed . The global growth of the total biomass is much faster  with a maximum peak reached at day one. The value of the peak is 4.5 times higher than the peaks reached by the total biomass in scenarios with POM fragments. The higher amount of DOC available initially permits a higher bacterial uptake that translates into a faster growth of the bacteria. As a result, the amount of DOC quickly decreases within the same time interval (one day) and the cumulated CO2 emitted is higher, with values of about 72%  and 91% , respectively. The different picture shown by the biodegradation kinetics has relevant implications for the species abundance . The most competitive 3R strain dominates from the very beginning. The high value of its maximal uptake rate (Table 1) makes 3R cells benefit more from the larger initial DOC concentration, and experience a quick and large exponential growth. This strain shows a more pronounced decline phase than in scenarios with POM fragments. Only when DOC becomes scarcer, the more generalist strain 7R with the lowest DOCk values succeeds to grow at about the same extent as observed in previous scenarios with POM fragments. The strain 9R with intermediate growth rate but with a higher DOCk value is not competitive enough to grow. A probable explanation is that, after two days, the DOC concentration at the local microbial habitat of strain 9R remains always lower than in the case of the POM fragments. In the latter case, some microbial habitats of strain 9R that are located close to the POM fragments can still benefit from a sufficient DOC concentration for them to grow. On the contrary, the more generalist strain 7R is not impacted by the lower DOC concentrations. Figure 5 also shows that the position of the bacterial spots does not affect the predicted model outputs, and the ten replicated simulations almost overlap. Simulation scenario 3 is consistent with the nutritional state of the soil after a sudden flush of nutrients, which is typical of the anthropic addition of fertilizers to agricultural land, or as observed after rainfall following a period of drought.A very different biodegradation kinetics is observed when the DOC is homogeneously distributed in the pore space . In both scenarios, a few spots containing cells of the less competitive strain 9R can surpass spots of strain 3R and 7R and even be the most active spots . When POM is fragmented, some spots containing 9R cells also end up with an amount of biomass that is similar to what is found with the strains 3R and 7R  showing that the global, per strain representation displayed in the graphic at right in Figure 4 hides the very large dispersion of kinetics at the local scale .The spatial distribution of the abundances of the different strains in the scenarios S1 and S2 reveals a number of interesting patterns. In terms of the biomass in each of the 690 spots, we observe that the maximum peak abundance reached in the spots is 2.43 ± 1.01 higher in the case of scenario S2 compared to scenario S1 . In our scenarios, since the POM hydrolysis is constant and independent of the spatial position of bacteria, a lower amount of dissolved organic carbon is produced locally compared to the aggregated POM fragments when there are 4 fragments. Even if the probability of having more spots closer to these local sources of DOC is higher with dispersed POM, the available DOC concentration remains lower. The general trend suggested by these results is that when POM is gathered into one piece, significantly fewer microbial habitats  are prone to grow, and a larger dispersion of the abundance is found compared to scenarios in which POM is fragmented. Therefore, under these conditions, it is not surprising that similar biomass growth is observed at the scale of a soil sample , however, when comparing the repetitions within a scenario it appears that spots where growth is maximum (S1r2) has a longer or similar minimal geodesic distance than spots having lower growth (S1r9 and S1r4). A large number of spots that do not have significant growth can have a very large range of geodesic distance values , which is an unexpected result. In some cases, the geodesic distance can even be close to the shortest values. However, when geodesic distances are longer than about 5000 μm in the case of S1 and about 7500 μm in the case of S2, the spots do not noticeably grow. When POM fragments are dispersed, the geodesic distances are shorter but also the DOC concentration that is emitted from the POM spots is lower.Using an algorithm developed by 13C have been reported to hold the sites of higher microbial assimilation and referred as “residusphere” . To test this hypothesis, we chose one replicate of the scenario S2 (S2r2) in which a few 9R microbial habitats experienced growth, and we initially placed three cells in now 230 spots, one of each strains. The global outputs of the model are similar , but the strain abundances are very different . When the three strains co-exist in the same microbial habitat, the strain 9R cannot grow, even when it is located in the spots close to the POM fragments. The most competitive strain 3R grows to a much higher extent and the strain 7R has a delayed growth. There are no prominent differences observed between scenario S4a and S4b.Simulation scenarios S1, S2, and S3 suggest that when the strain 9R is closely competing with 3R or 7R, growth of 9R can occur only when it is located in an advantageous point with respect to a sufficient source of DOC . As mentioned in Section Entities, State Variables, and Scales, oxygen limitations are not yet considered in Ib-LBioS-Comp, so that the different water saturation levels do not impact the role of oxygen in the bacterial activity in these scenarios. Furthermore matric potentials considered in the scenarios S2 and S6 are very close  so that oxygen limitations are not expected to happen under the tested conditions. Since the local positions of the aggregated POM fragments and the 690 microbial habitats are not changed, the only effect of the higher water saturation is to decrease the DOC concentrations. However, the diffusive transport of DOC is also accelerated because all the pore space is now connected. The strain abundances are rather similar although this environment is comparatively more favorable for the generalist strain 7R, which becomes the most abundant strain after day 6. The establishment on the system for the simulations showing a noticeable growth of the less competing strain appear mostly driven by the spatial heterogeneity of POM distribution.The role of the water saturation level of the pore space on the carbon dynamics was investigated in the scenarios S5 and S6. The global model outputs are similar when the pore space is fully saturated with water (wS = 0.50 to wS = 0.25), 525 of the original bacterial spots are still in the aqueous phase. In spite of that, five of the replicates  produced global model outputs similar to the ones observed for higher water saturation levels . In one replicate (S6r1), the aggregated POM fragments are located in solid voxels whose neighbors are disconnected from the aqueous phase, preventing the release of DOC, and thus bacterial growth . In three other replicates  one of the four gathered solid voxels containing the aggregated POM fragments also has a dry neighbor voxel. Furthermore, for two of them (S6r7 and S6r9), and for the replicate S6r8, no bacterial growth is recorded, resulting in the accumulation of DOC in the liquid phase . In these three last situations, spatial disconnections between the microbial spots and the POM fragments are made possible by the aqueous phase fragmentation. Spatial disconnections are also observed in the repetition S6r3 where total biomass growth is very small . The strain abundances in the active spots are very similar to those observed when the water saturation is 0.50. In one repetition, the growth of strain 9R of all microbial spots surpasses the growth of strain 7R .When the water saturation level decreases, the pore space filled with air increases and more disconnected aqueous regions appear. Consequently, some POM spots may not hydrolyze resource to the liquid phase, and, some bacterial microhabitats may not have access to the DOC hydrolyzed by the connected POM agents. In particular, when the water saturation is divided by two (from wS = 0.25), our scenarios do not show a clearly improved establishment of the less competing strain. Another study , four fragments of organic matter (intermediate heterogeneity), and a single fragment of organic matter (high heterogeneity).A number of results can be highlighted from the modeling scenarios performed: (i) In general terms, the greater the spatial heterogeneity of the location of the resource, the greater the variability in the output at the level of the soil volume imaged; (ii) When the resource is found as particulate organic matter, the fastest growing strain tends to dominate at first but then, when the resources becomes scarcer, it is overtaken by the generalist strain, showing that the spatial distribution of organic matter affects bacterial succession; (iii) the global bacterial growth is faster when the nutrient resource is available in the liquid phase at the beginning of the simulation. Under these circumstances, the fastest growing strain is able to reach much higher relative abundances, having a negative effect on biodiversity; (iv) When the resource is present as particulate organic matter, the total biomass created does not differ noticeably between the intermediate and high spatial heterogeneity schemes but in contrast the species abundance is impacted; (v) The least competing strain, which does not reach noticeable growth for the low and intermediate resource spatial heterogeneity schemes, is able to grow appreciably in the absence of direct competition, if the position of the nutrient resource is favorable. According to this observation, heterogeneity of the spatial distribution of the organic matter in soil would promote microbial diversity; (vi) the geodesic distance among the nutrient resources and the bacteria alone is not sufficient to explain this phenomenon; and, (vii) In the scenarios tested, the water saturation level does not seem to change much the observed biodiversity.As a cautionary note, one needs to remember that the various predictions made in this article emanate from a relatively simple model, which ignores many different aspects of soils. In actual soils, microbial diversity and growth are potentially affected by a myriad of factors . In particular, bacterial motility and the diffusion of oxygen in the pore space are likely to have a significant influence on microbial activity. Subresolution pores, too small to be visible in X-ray CT images, are most probably playing a role in this context as well, especially in the dry range of the hydrological regime of soils. Future research will determine if the relationship between bacterial diversity and the spatial heterogeneity in resource distribution, highlighted in the present article, still holds when some of the assumptions of the model are lifted. It is possible that the same relationship will be observed, or that other, more complex behaviors will unfold.https://doi.org/10.17862/cranfield.rd.6744158.Data underlying this paper can be accessed at XP implemented the models. XP and VP ran simulations and analyzed the data. All authors conceived, designed the study, and contributed to the writing of the 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.


In dentistry, one of the most common surgical procedures is the removal of retained third molars. This surgery generates great morbidity to the participants for causing pain, edema, and trismus due to surgical trauma. The objective of the present study is to evaluate the efficacy of photobiomodulation with light emitting diode (LED) in the control of pain, facial edema, trismus, and quality of life resulting from the extraction of retained lower third molars.A randomized, double-blind, placebo-controlled clinical trial involving 38 adult participants, who meet the criteria of eligibility and agree to participate in the study. Before the surgeries are performed, the facial and mouth opening measures of all the participants will be taken. Immediately after the surgeries, participants will be randomized into 2 groups. In the LED group, participants will receive LED applications  in the immediate postoperative, first and second days after the surgical procedure. In the control group, the participants will be attended in the same way as in the LED group, however, the person in charge of the application will simulate the irradiation. Pain (EVA and NRS-101), postoperative edema, trismus, temperature, dysphagia, and hematoma will be evaluated after 1, 2, 5, and 7 days. The oral health impact profile (OHIP-14 Questionnaire) and anxiety analysis (Beck anxiety inventory -BAI) questionnaires will be applied preoperatively and 7 days after treatment. The appropriate statistical tests will be applied for each specific analysis in a significance level of 5%.Although the use of low-power laser in the postoperative has shown good results in the control of postoperative sequelae, this is the first study on the efficacy of the use of LED in this situation. Different clinical situations require different PBM protocols. Most of the research on PBM in dentistry was carried out with low power/intensity lasers and some protocols are already well established using these lasers. However, few studies in dentistry were developed using LEDs, and most of them were performed to prevent/treat oral mucositis.Photobiomodulation (PBM) is an emerging technique using red or near infrared light (low-power laser or light emitting diode [LED]) to modulate inflammation, accelerate wound healing, and reduce pain and discomfort in different clinical situations.–6 However, the near-infrared light in the 850 nm range has been shown to be capable of promoting vasodilation and the production of growth factors, as well as angiogenesis, leading to wound healing.,8Some studies have demonstrated a beneficial effect of LED (670 nm) on the incidence and severity of oral mucositis in participants undergoing oncological treatment.,9 This surgery generates great morbidity to the participants by causing pain, edema, and trismus due to surgical trauma.,10,11 In recent years, several studies have shown beneficial effects of low intensity laser therapy in the postoperative period of lower third molar extractions.–14. Despite the beneficial effects of LEDs on pain control and repair described in the literature, no studies were found to evaluate the effect of the use of LEDs in the postoperative period of third molar surgery. This is a relatively new technology and it is still under investigation especially in clinical trials.In dentistry, one of the most common surgical procedures is the removal of retained third molars.The objective of the present study is to evaluate the efficacy of LED photobiomodulation in pain control, facial edema, trismus, temperature, dysphagia, hematomas, and quality of life after the extraction of retained lower third molars.22.1A randomized, double-blind, placebo-controlled clinical trial will be conducted to determine the efficacy of diode-emitting diode (LED) PBM on the adverse effects of extraction of retained lower third molars. The study will be conducted at the Faculty of Dentistry of UFRGS, Department of Surgery and Orthopedics (DCO), from May 2018 to May 2019.The study will be conducted in accordance with the guidelines of good clinical practice and has been approved by the Research Ethics Committee of UFRGS under process number 82570818.0.0000.5347. It follows the 466/2012 resolution of the National Health Council. After clarification and authorization of participants  they shall sign a Free and Informed Consent Form.The protocol is in accordance with the 2013 SPIRIT  Statement. The SPIRIT checklist can be found as an additional file and Figure 2.2https://clinicaltrials.gov/ct2/show/NCT03442166Clinicaltrials.gov as NCT03442166, first posted February 22, 2018 and last updated May 17, 2018; 2.3 based on the pain analysis of the participants on the 3rd postoperative day evaluated by a visual analog scale (VAS) was performed. Using a power of 80% and level of significance of 5%, a minimum sample size of 17 cases per group was obtained, making a total of 34 participants for the study. Winpepi software version 10.5 was used for this calculation. Considering a loss of 10%, based on the study that was used for the sample calculation, a loss of 2 participants per group should be predicted. Therefore, the total number of participants to be selected will be 38 individuals.A sample calculation based on the parameters of variability of the article of Eshghpour, Ahrari Inclusion criteria:Need of surgical removal of retained lower third molars;Agree to participate in the study after reading and signing the Informed Consent Term;Participants with indication for extraction of lower third molars  or professional written indication, healthy patients , systolic blood pressure lower than 140 mm Hg, and diastolic blood pressure lower than 90 mm Hg and heart rate values of 70 ± 20 beats/minute. The upper and lower central incisor teeth must be present.Exclusion criteria:Systemic diseases, chronic pain or neurological and psychiatric disorders;Smokers;Using anti-inflammatories, analgesics or bisphosphonates in the last 15 days;Present active pericoronarite;Pregnant;Breastfeeding;Severe temporomandibular disorders;Photosensitivity history;Allergic to any drug used in the research ;Participants presenting radiolucent images associated with the teeth to be extracted;Participants who present any type of complication during surgery , as these cases are not in the standard expected for third molar surgeries. In this case, the central action analgesic will be prescribed. These data will not be part of the statistical analysis but will be described and discussed.2.4Thirty-eight participants of both genders referred to the Faculty of Dentistry of UFRGS who need to perform the removal of lower third molars will be selected. Participants will be approached by means of an oral invitation to be conducted after verifying the eligibility criteria of the subject for the research.To randomly distribute the subjects in the 2 experimental groups, a draw will be made with numbers. As the numbers are drawn, they will compose the experimental groups. Opaque envelopes will be identified with each number and inside it a sheet containing the information of the corresponding experimental group will be inserted according to the order obtained in the draw. The envelopes will be sealed and will remain sealed in numerical order in a safe place until the time of the surgeries. The drawing and preparation of the envelopes will be performed by a person who is not involved in the study.Participants will be evaluated by the surgeon and when they meet all eligibility criteria previously described, they will be included in the study. All will be submitted to the same surgical protocol. Immediately after the surgeries, the researcher responsible for applying the LED will remove and open one envelope  and perform the indicated procedure.The 38 participants will be allocated in the experimental groups as follows:LED group n = 19): Participants will receive 3 applications of intraoral LEDs with 660 nm and extraoral with 850 nm  in the immediate postoperative, first and second days after the surgical procedure. The intraoral irradiation will be performed with a 6 red LED cluster and in the extraoral site a 36 infrared LED cluster will be used. The parameters of red/infrared LED are describe in Table 9: ParticControl group (n = 19)—Participants will be attended in the same way as the LED group. The person in charge of the application will simulate the intraoral and extraoral irradiation by positioning the LED in the same locations described for the LED group, but the equipment will be kept off. So that the patient does not identify the sound of activation of the device (beep), it will be recorded, and connected at the time of application.33.13.1.1Measurements of the distances between the corner of the eye and the angle of the mandible, between the tragus and the labial commissure, and between the tragus and the pogonium of each patient will be taken before the surgical procedure.3.1.2,16The opening of the mouth will be measured by the distance between the incisal edges of the upper and lower central incisors using a 150 mm hand-operated caliper  as previously described.3.2The procedures will be performed by a surgeon specializing in maxillofacial surgery. The surgical material and the operative technique will be determined according to protocol for removal surgeries of retained third molars from School of Dentistry of UFRGS. The following procedures will be performed in each surgery: extra and intraoral antisepsis, infiltrative anesthesia by block and infiltrative terminal of the tooth and attached structures, isolation and drying of the operative field with gauze, incision with proximal extension of the teeth involved in order to allow access to the exposure surgical removal of the gingival flap, osteotomy for access (when necessary), muco-periosteal detachment, ostectomy, odontosection with electric motors (when necessary), aspiration of blood and liquids used for irrigation and washing of the operative field, detachment and removal of the gingival flap, avulsion of the dental element, irrigation and suture.All participants will receive the following medications: Codeine 30 mg, paracetamol 500 mg to be used every 6 hours, in the first 24 hours. Then, they will use paracetamol 750 mg every 6 hours for the duration of the painful symptomatology. They will be asked for information on the amount of medicine ingested. The data of these participants will only be described, but not included in the analysis of the results. Such exclusion shall not prejudice the treatment.3.3At the end of the surgeries, the maxillofacial surgeon will record the following: the position of the retained tooth, the degree of difficulty of the procedure, the number of anesthesia tubes used, the occurrence of hemorrhage during surgery and during suturing and the duration of the surgery (from the first incision to the end of the suture). and by Pell and Gregory.The position of the included tooth will be determined based on the classifications proposed by Winter which classifies the surgical procedure as follows: grade 1=extraction with only a forceps; grade 2=extraction with osteotomy; grade 3=extraction with osteotomy and coronal section; and grade 4=complex extraction.The degree of difficulty of the surgery will be evaluated by the Prant scale modified by Amarillas-Escobar et al,3.4After the suture is completed, the researcher responsible for applying the LED will open the envelope containing the information from the experimental group in which the patient will be inserted and proceed to the experiment. A single examiner will run the LED application and will not perform any type of evaluation. Surgical procedures will be performed by the same surgeon. The preoperative and postoperative evaluations  will be done by an examiner who will not be aware of the group in which each patient is allocated. The information that will be obtained in the evaluations will be written in the evaluator's file. Participants will not be aware of whether or not they received LED irradiation because the person responsible for applying the LED will position the insert in the irradiation sites in all participants and will only trigger light when and where predicted in the specific experimental group. The characteristic sound of the device will be triggered by recording in the control group.3.5In this project, we intend to apply 2 scales: the VAS and NRS-101. The VAS will be printed on the patient evaluation form and the subjects will be instructed by the evaluator to mark a point on the 10 cm line, indicating the intensity of their pain after 1.2, 5, and 7 days of the surgeries For the NRS-101 scale, the evaluators will ask participants to assign a number between 0 (no pain) and 100 (worst possible pain) that best represents the pain they are currently experiencing after 1, 2, 5, and 7 days of surgeries.3.6 of each patient 1, 2, 5, and 7 days after surgery.The evaluator will measure the distances between the corner of the eye and angle of the mandible, between tragus and labial commissure, and between tragus and pogonium3.7This result is usually evaluated by measuring the distance between the incisal edges of the upper and lower central incisors, using a caliper rule. In the present study, the evaluator will measure the opening of the mouth in each patient 1, 2, 5 and 7 days after surgery.3.8The temperature will be measured locally and systemically in each patient 1, 2, 5, and 7 days after surgery. The local measurement will be done with a digital thermometer , in the region of the mandibular angle, 2 cm above the lower border of the mandible and 3 cm for mesial of the branch of the mandible, both on the operated side and on the opposite side. The systemic temperature will be measured in the frontal region of the patient in the median position 3 cm above the glabella in the same time frames.3.9The evaluation of dysphagia will be performed through a numerical scale in which: (0) total absence of dysphagia; (1) dysphagia to solid foods; (2) dysphagia to any liquid or solid food. The patients will respond to the questioning on days 1, 2, 5, and 7 days after surgery.3.10The presence of hematoma/ecchymosis will be evaluated by measuring the largest diameter of colorimetric changes in the skin of the jugal and submandibular region at 1, 2, 5, and 7 days after surgery. The measure will be performed by the evaluator who will classify the occurrence of this result into 4 categories: none; larger diameter smaller than 4 cm; greater diameter between 4 and 10 cm, and larger diameter >10 cm.3.11The oral health impact profile (OHIP-14) is a simplified form of the original OHIP questionnaire that is used to assess the impact of oral health on subjects’ quality of life. The items are distributed among the following subscales: functional limitation, pain, psychological discomfort, physical disability, psychological deficiency, social incapacity and disability. The questionnaire will be applied by the evaluator in the preoperative period and 7 days after surgery.3.12 The inventory consists of 21 items that are descriptive statements of the symptoms common in anxiety pictures and that should be evaluated by the individual with reference to himself in the period of one week in a scale of 4 points that reflect levels of increasing severity of each symptom, whose alternatives are: absolutely not; lightly: It did not bother me much; moderately: It was very unpleasant, but I could bear it; seriously: I could hardly bear it. At the end, the items are summed and the total score can vary from 0 to 63. All participants will respond to this questionnaire in the preoperative period and at 7 days postoperatively.The analysis of anxiety will be done through Beck's inventory of anxiety that evaluates, by quantitative approximation, anxiety symptoms. The questionnaire contains 21 aspects that reflect somatically, cognitively and affectively the characteristic symptoms of anxiety. The questionnaire also presents high reliability, high internal consistency and moderate validity, both for psychiatric participants and for general population samples.3.13Initial descriptive analyses will be performed considering all variables measured in the study, both quantitative (mean and standard deviation) and qualitative (frequencies and percentages). Later, the appropriate statistical tests will be applied for each specific analysis. In all tests, the significance level of 5% probability or the corresponding p-value will be adopted. All analyses will be performed using the statistical software SAS for Windows, version 9.1.3.4–14 this is the first study on the efficacy of the use of LED in this situation. Besides this, recently it was suggested that the accurate combination of irradiation site and PBM wavelength could optimize the postoperative results of this therapy after third molar removal surgeries. The best match would be the use of intraoral red light and extraoral infrared light. This study will evaluate whether the combination of 2 wavelength LEDs used intra and extraorally will bring benefits to the post-operative of third molar removal surgeries.The removal of retained third molars is a very common procedure that causes pain, edema, and trismus due to surgical trauma. Although the use of low-power laser in the postoperative has shown excellent results in the control of postoperative sequelae,55.1The study will be conducted in accordance with the guidelines of good clinical practice and has been approved by the Research Ethics Committee of UFRGS under process number 82570818.0.0000.5347. It follows the 466/2012 resolution of the National Health Council. After clarification and authorization of participants  they shall sign a Free and Informed Consent Form. The identity of all individuals will be preserved in all stages of the research. Changes in the study will be reported to the committee. This will guarantee the confidentiality of each patient's data. The individual who does not attend the scheduled session will be excluded from the study.5.2The authors were previously trained to collect data and perform the surgeries. All authors are qualified in photobiomodulation therapy. All data will be entered electronically. The participants’ files will be stored in numerical order in a safe place and accessible only to the authors of this study.5.3The application of LEDs offers minimal risk, however, if during treatment, some participants report increased pain or display an infectious condition, measures such as the use of analgesics and/or antibiotics will be adopted according to clinical tolerance and individual assessment. These participants will be excluded from the study and will be followed up by the surgical team until resolution of the condition.5.4All information collected from the participants will be transcribed into a database replacing the individuals’ names with the registration number of the evaluation form. The datasets generated and analysed during the present study are available from the corresponding author at reasonable request. After the analysis of the data, volunteers will be invited to a meeting and the results will be shared and they will become public.Conceive and design the study: KPSF, SKB, MDM; will perform the experiment: CAT, JJCF, MATM; will analyze the data: MLLG, DFTS, RAMF, KPSF, SKB; will perform the statistical analysis: DFTS, RAMF; write the paper: CAT, MDM, MLLG, KPSF.Conceptualization: Manoela Domingues Martins, Sandra Kalil Bussadori, Kristianne Porta Santos Fernandes.Data curation: Marcela Leticia Leal Gonçalves, Daniela de Fátima Teixeira da Silva, Sandra Kalil Bussadori.Formal analysis: Marcela Leticia Leal Gonçalves, Daniela de Fátima Teixeira da Silva, Raquel Agnelli Mesquita-Ferrari, Sandra Kalil Bussadori, Kristianne Porta Santos Fernandes.Investigation: Carlos Alberto Tenis, João Julho da Cunha Filho, Marco Antonio Trevizani Martins.Methodology: Carlos Alberto Tenis, João Julho da Cunha Filho, Marco Antonio Trevizani Martins.Software: Daniela de Fátima Teixeira da Silva.Supervision: Kristianne Porta Santos Fernandes.Writing – original draft: Carlos Alberto Tenis.Writing – review & editing: Manoela Domingues Martins, Marcela Leticia Leal Gonçalves, Kristianne Porta Santos Fernandes.


Swimming pool water was treated using an ultrafiltration process using ceramic and polymer membranes for comparison. It was determined that the efficiency of the process depended on the type of membrane used. The polymer membrane decreased the absorbance and concentration of combined chlorine in the pool water to a greater extent than the ceramic membrane. In the case of a ceramic membrane, the concentration of combined chlorine in the permeate exceeded the limit values. During the ultrafiltration process, the permeate flux decreased, causing the blockage of membrane pores. The extent of this phenomenon was similar for both tested membranes. In the case of the ceramic membrane, flushing it with water could significantly restore its initial performance. For both tested membranes, a high regeneration efficiency was observed during chemical treatment with an alkaline solution. SEM photos of the polymer membrane showed low resistance of this polymer to the chlorine present in the swimming pool water. Swimming pool users introduce fragments of the epidermis, sweat, urine, and microorganisms into the water, including pathogenic microorganisms which thrive in such an environment. Therefore, swimming pool water is a mixture of water added to a closed circulation system  and water from a swimming pool that is constantly being treated and disinfected.The main factors affecting the quality of water in the pool, ensuring health and safety and the comfort of bathers, are primarily modern technologies for water treatment, with a high efficiency of disinfection and filtering and the selection of appropriate chemicals. These factors guarantee that the pool water meets strict requirements in terms of physicochemical and bacteriological parameters ,2,3.Due to the fact that disinfection byproducts (DBP) were proven to pose a threat to bathers’ health, it is now standard practice to support conventional treatment methods  with processes that boost the chlorination process, for instance, irradiating the flux of water with ultraviolet (UV) light or ozonization. Equally effective in the area of pool water treatment technology, other methods include hydrogen peroxide biocides, mixtures of chlorine and chlorine dioxide, titanium dioxide, silver nanoparticles, and heterogeneous catalysts. Introducing these solutions to swimming pool water treatment systems allows reducing the amount of chlorine that is added at the final stage of the disinfection process. This, in turn, allows lowering the concentration of chloro-nitrogen compounds that cause allergies and irritation of the upper respiratory and digestive systems, and those that are also mutagenic and responsible for the characteristic unpleasant smell of swimming pool water ,5,6,7,8.Alternatively to swimming pool water treatment technologies, one can also use hybrid systems that combine filtration with advanced oxidation processes ,10.Currently, another method that is considered to be an effective swimming pool technology is membrane water treatment, including specifically the ultrafiltration process. Ultrafiltration captures fine solids, colloids, bacteria, and viruses. The transport mechanism is a sieve-like structure which does not allow solids larger than the pore diameter to pass through. The process transmembrane pressures fall within the range of 0.1–1.0 MPa. These membranes are made of ceramic and polymer materials ,12. ConsThe main disadvantages of the membrane processes are the lowered hydraulic performance of the membrane caused by adverse effects of the filtration process , development of a gel layer on the surface of the membrane, accumulation of dirt on the surface of the membrane or inside its pores (fouling), and precipitation of salts poorly soluble in water that create inorganic sediments  . These pThe water that is being treated may contain compounds that are damaging to the membrane, such as chlorine . BecauseDuring in-house research, two ultrafiltration membrane types were selected for comparison and used to support the sports swimming pool water treatment system in a chosen indoor facility. The effectiveness of the pool water treatment, the intensity of the adverse effects, and the possibility of cleaning the membranes were assessed.3/h, filtering speed: 30 m/h). The dimensions of the swimming pool basin (25 m × 12.5 m × (1.1–1.8) m) allow for approximately 30 persons to swim comfortably. Water deficits that are the result of evaporation, splashing, and the need to flush filter beds are replenished by drawing water from the mains into the retention tank. A closed circulation system with an active overflow is the basic requirement for correct circulation of swimming pool water (2SO4), UV irradiation , and final disinfection (14% solution of NaOCl), it is directed to the swimming pool through heat exchangers. Before the filters, a coagulant solution is applied . The swimming pool water treatment system has two pressure filters with a 1.2-m-high multi-layered sand–anthracite filter bed.The subject of research involved water samples taken from a sports and leisure swimming pool basin, using a vertical water flow system , and retentate. The analyzed parameters of swimming pool water quality were pH, turbidity, color, absorbance of UV® 740 laboratory multi-parameter meter manufactured by WTW. The absorbance was measured at 254 nm, using a UV–visible light (UV–Vis) Cecil 1000 . To determine the turbidity of samples, a Turbidimeter TN-100  was used. Color measurements were performed with a UV–Vis Spectroquant® Pharo 300  at 340 nm. Concentrations of total and free chlorine were determined with a colorimetric method using a portable Pocket Colorimeter II DeviceTM . The concentrations of ammonia nitrogen and nitrate nitrogen were determined with a Photolyser 400 tester .The general parameters were measured with an inoLab2, an intermediate tank with a volume of 15 dm3, a high-pressure pump with a capacity between 0.5 and 3.0 m3/h (type CRN 3) produced by Grundfos, and a control and measurement apparatus. The picture of the first filtration system is shown in The membrane filtration was conducted in two circuits operating in a cross-flow system using pipe membranes made of different materials . The fir3/h (type CRN 1) produced by Grundfos.The second filtration circuit had a structure similar to the first, but this one was adjusted to have ceramic membranes. This circuit had a low-pressure pump of capacity between 1.50 and 3.50 mMembrane filtration tests were carried out in the following order: membrane conditioning with deionized water, pool water filtration, and an attempt to clean the membranes. The process was conducted at 0.1 MPa transmembrane pressure conditions for the ceramic membrane, and at 0.2 MPa for the polymer membrane. These pressures were selected on the basis of preliminary tests.The temperature of the filtered water was kept at a constant level of 20 ± 2 °C. The filtration process was carried out to the maximum degree of feed volume reduction ratio , which did not cause hydraulic disturbances in the system. This was determined visually based on the evaluation of the water table in the feed tank.3 acid (cycle 2) and a 1% solution of NaOH (cycle 3).The process of cleaning the membranes was a multistage one and consisted of flushing them with deionized water (cycle 1), and chemical cleaning with a 0.3% solution of HNOvJ (wJ) is the volumetric permeate flux (m3/m2∙s) for swimming pool water (for deionized water), V is the volume (m3), F is the membrane area (m2), and t is the time (s).R is the retention (%), pC is the concentration in permeate (mg/dm3), and fC is the concentration in feed (mg/dm3).To determine the effectiveness of the membrane process, it was necessary to establish its performance by calculating the permeate flux volume (Equation (1)) and the retention/reduction (Equation (2)) of the chosen pollutants or the general indicators associated with the presence of particular groups of pollutants.wJ) and after the pool water treatment (vJ).The phenomenon of blocking the membrane surface was determined by calculating its relative permeability (Equation (3)), with a quotient of fluxes  specified for a new membrane during its conditioning with deionized water (v(cleaned)J is the volumetric permeate flux for the cleaned membrane (m3/m2∙s), and v(fouled)J is the volumetric permeate flux for the fouled membrane (m3/m2).The effectiveness of membrane cleaning was determined by calculating the so-called recovery ratio (Equation (4)).The stability and degree of contamination were evaluated via imaging with the SEM Phenom proX microscope .−6 m3/m2·s, and that of the polymer membrane was 17.0 × 10−6 m3/m2·s. This is mainly due to the characteristics of the used membranes, including the materials (contact angle) they were made of  was evaluated. The parameters of permeate and swimming pool water quality were compared against limit values specified in World Health Organization (WHO) guidelines , DIN 196The ultrafiltration process completely removed the water color. The elimination of other contaminants was dependent upon both the membrane type and the filtration time . The polOn the other hand, the ceramic membrane eliminated water turbidity to a greater extent than the polymer one. The effectiveness of lowering this ratio by the ceramic membrane increased with filtration time. This was caused by the condensation conditions that allowed for better separation of the contaminants. On the other hand, the concentration of nitrogen compounds in the permeate, including primarily the ammonium nitrogen, was close to or higher than the values specified for the water for treatment. A higher concentration of ammonium nitrogen in the permeate may indicate the occurrence of additional reactions during the water treatment process, including releasing this contaminant from complex compounds. The mechanisms for removing contaminants during the ultrafiltration process were presented in Reference . In the It was determined that flushing the ceramic membrane with water cycle 1,  may signThe chemical cleaning of membranes with an alkaline solution, performed at a later stage, caused a significant increase in the initial performance of both tested membranes (cycle 3). The polymer membrane was regenerated to 98% and the ceramic membrane to almost 100% . The higCleaning membranes with chemicals gives, in the majority of instances, better results than flushing them with water, and it increases the chance of restoring the membranes’ initial performance . It is tStudies on the use of ultrafiltration in swimming pool water treatment systems showed some limitations in the use of this process. This research demonstrated that the effectiveness of swimming pool water treatment is significantly influenced by both the type of the membrane and the time of filtration. The polymer membrane decreased the absorbance and concentration of bound chlorine in the swimming pool water to a greater extent than the ceramic membrane. In the case of the ceramic membrane, the concentration of bound chlorine in the permeate exceeded the limit values. Chlorine present in the swimming pool water damaged the polymer membrane structure, which may decrease its total operation time. Over time, this phenomenon may also reduce the effectiveness of the membrane in the elimination of pollutants from the swimming pool water. During the ultrafiltration process of the swimming pool water, the permeate flux decreased due to the blocked membrane pores. The extent of this phenomenon was similar for both tested membranes. In the case of the ceramic membrane, this adverse effect was partially reversible. For both tested membranes, a high regeneration efficiency was observed following chemical treatment with an alkaline solution. This means that the swimming pool water under treatment was contaminated to a more significant extent with organic substances than with inorganic ones.


Concerning this volatilisation of NH3, the process parameters of pH and air temperature are crucial. During a period of approximately 10 years, systematic measurements of NH3 losses originating from a large variety of different livestock houses were made. One of the problems with NH3 emissions is the large variation in the measured data due to the season, the production of the animals, the manure treatment, type of livestock house, and the manure storage. Generally speaking, prevention and control of NH3 emission can be done by control of N content in the manure, moisture content, pH, and temperature[1]. In houses for growing pigs, a combination of simple housing measures can be taken to greatly reduce NH33 emissions[2]. In houses for laying hens, the control of the manure drying process determines the emission of NH3[1]. Monteny[3] has built an NH3 production model with separate modules for the emission of the manure storage under the dairy house and the floor in the house. Manure spreading is also a major source of NH3 emission and is dependent on slurry composition, environmental conditions, and farm management. The effects of these factors have been employed in a model[4]. Losses via NO, N2O, and N2 are important in husbandry systems with solid manure and straw. The number of experimental data is, however, very limited. As N2O is an intermediate product of complex biochemical processes of nitrification and denitrification, optimal conditions are the key issues in N2O reduction strategies. We may expect that in the near future the emission of greenhouse gases will get the same attention from policy makers as NH3. Sustainable livestock production has to combine low emissions of gaseous N compounds with acceptable odour emissions, low emissions of greenhouse gases, and acceptable standards of animal welfare. For the entrepreneur, the strategy must be built on the regulations, the special conditions of his farm, and what is reasonably achievable.Nitrogen (N) losses from livestock houses and manure storage facilities contribute greatly to the total loss of N from livestock farms. Volatilisation of ammonia (NH


This study presents a novel construction pre-supporting system for large underground space excavation with shallow depth, Steel Tube Slab system (STS), in which adjacent steel pipes are connected by a couple of flanges, bolts and concrete for flexural capacity and lateral stiffness of the whole structure. The STS method is employed for the first time for the construction of the ultra-shallow buried and large span subway station in China, during which ground settlement and structural deformation are monitored. A numerical model for the subway station is established with reliability verified by monitored data comparison from numerical results and investigation on the effect of large span underground excavation on surrounding soil surrounding soil and existing buildings in soft soils. Unlike traditional methods, the STS method can effectively control and reduce the ground settlement during construction, thereby rendering it ideally suited for application in soft soils. While stress redistribution of the surrounding soils around the excavation face can cause great damage without an effective supporting system ,2, the get al. .Typical features such as ultra-shallow buried excavation, complicated upper building environments and large spans in underground excavation projects in urban districts are responded to in the design and construction of underground structures for excavation-induced ground settlement and structural stability . As a reThe New Tubular Roof (NTR) Method is one of the new methods developed for the design and construction of subway stations . The perAnother new kind of pre-supporting system, referred to as the Concrete Arch Pre-supporting System, was proposed by Dadizadeh and Sadaghiani for construction of subway stations . This meIn addition, the Central Beam Column (CBC) system has also been proposed for the construction of the Tehran Subway . The maiIn response to the limitations mentioned above, this paper proposes a novel technique, i.e. STS, as a pre-supporting system for underground excavations, adopted in the Northeastern Street station of line #10 in Shenyang Subway. The ground surface settlement and structural deformation for large span subway station using the STS method were monitored and analysed and the influences of some key parameters such as construction sequence and temporary steel supports on the ground settlement control are investigated. This paper begins with a discussion on techniques for underground excavations and is followed by a description of the STS technique. Numerical analysis of subway station construction using STS structure and an engineering project are presented, along with discussions on future work.2.The STS structure originates in the traditional pipe-roofing supporting system. Considering the weak connection in the transverse bearing capacity, the adjacent steel tubes are connected by flange plates, steel bolts and concrete –19, as s(a)The designed steel tubes are jacked into the soil layer by the mechanical equipment, and then the soil is cleaned both inside and outside of the steel tubes.(b)The transverse steel bolts are installed in the specified location, and self-compacting concrete is casted in the tubes by the reserved grouting holes.(c)The pilot tunnels (PT1 and PT2) are constructed first, then the steel column (SC1) is constructed. The rest of the gradients  are completed using identical construction sequences.(d)The subway hall and the platform floor, respectively, are constructed.In general, the STS structure combined with the PBA method is used to perform underground excavation. The main construction steps are described as follows and the construction sketch diagrams are depicted in 3.There are few studies on STS structure as this method is being used for construction of an ultra-shallow-buried subway station for the first time. A three-dimensional finite-element model is used to investigate the influence of construction sequences on ground settlement and STS structure deformation.3.1.3.1.1.(a)The soil was modelled as a linear plastic material yielding according to the Mohr–Coulomb failure criteria. Soil in the same layer has an elastic plastic property which can be treated as homogeneous and isotropic.(b)The effect of groundwater seepage is not considered because the groundwater drainage is completed before construction.(c)The elastic model is adopted for the calculation of the structure of the lining and beam-column system, in which elastic deformation is the only factor considered. The weight of the soil and the main structure together with the ground overload are considered.3.1.2.3D. The size of the numerical model is 120 × 9 × 50 m, as shown in A three-dimensional finite difference model is established to study the surface settlement and structural deformation of the proposed supporting system using FLACBeam and pile elements were deployed to simulate the temporary steel supports and feet-lock bolt, respectively. Line and shell elements were applied to simulate the steel columns and the primary lining, respectively. Meanwhile, the Mohr–Coulomb model was adopted to define the behaviour of soil, and the soil properties are shown in 3.1.3.(1) Stage 1: Construction of the left-bottom pilot tunnel (PT2);(2) Stage 2: Construction of the left-top pilot tunnel (PT1);(3) Stage 3: Construction of the left cylindrical steel column (SC1);(4) Stage 4: Construction of the right-bottom pilot tunnel (PT4);(5) Stage 5: Construction of the right-top pilot tunnel (PT3);(6) Stage 6: Construction of the right cylindrical steel column (SC2);(7) Stage 7: Construction of the top plate at mid-span;(8) Stage 8: Construction of the station hall; and(9) Stage 9: Construction of the platform layer.The main construction simulation was divided into nine stages, as follows:3.2.3.2.1.It can be seen from 3.2.2.The vertical deformation curve of the horizontal STS structure is shown in It can be seen from the figure that the construction of the mid-span buckle arch has the greatest influence on the settlement of the STS structure, and the construction of the mid-span increases the settlement of the STS structure while reducing the settlement of the side-span. The excavation of the station hall has little effect on the settlement of the mid-span, has a great influence on the left and right cross-span and has no significant impact on the overall settlement.3.2.3.In the traditional PBA method, the side piles are generally used as the lateral supporting structure when the main structure is excavated, and the deformation of the lateral retaining structure directly affects the stability and safety of the entire structure. The STS method is applied as the lateral enclosure structure.It can be seen from the numerical results that the deformation of the left STS structure is slightly larger. The horizontal deformation of the vertical STS structure on the left side is analysed, because it is necessary to study the stability and safety of the lateral support structure during the excavation period. From 3.3.Section 3.2 shows that the construction of the pilot tunnel and the mid-span buckle arch causes most of the total settlement. Combined with the construction experience, the excavation sequence of the pilot piles through the PBA method has a multi-cavern effect, and the stratum settlement can be significantly different using different excavation sequences. Therefore, it is of great significance to study the excavation sequence of the pilot tunnel in the STS method combined with the PBA method. The design schemes are shown in The ground settlement curve after construction of each scheme is depicted in 3.4.3.4.1.To study the influence of the construction sequences of the station hall on the ground settlement, the following two schemes are analysed: (i) scheme 1: first mid-span then side-span and (ii) scheme 2: first side-span then mid-span.Based on the analysis of the excavation sequences of the two station halls, the maximum settlement of the ground surface is concentrated near the centre line of the station. The settlements of different construction stages are shown in According to the excavation sequence of scheme 2, numerical simulation is carried out for each construction stage, and the ground settlement curve is shown in In general, ground settlement increases slightly during the construction of the side-span while it has no major impact on the total deformation. During the excavation of the mid-span, the settlement increases by 1.64 mm and the excavation of the station hall has no impact on the total ground settlement.3.4.2.The vertical deformation of the STS structure caused by the excavation of the station hall in scheme 2 is shown in 3.5.3.5.1.In the excavation sequences of the station hall, a temporary steel support is set at the corner of the STS structure to reduce the lateral calculation length of the whole space and improve the bearing capacity and stability of the STS structure, which is shown in 3.5.2.The calculation span of the side-span can be shortened, and vertical load can be shared by the horizontal stiffness of the STS structure. As a result, the ground settlement and STS structure deformation can be significantly reduced by installing temporary steel supports. The ground settlement caused by each scheme is shown in 3.5.3.It can be seen from 3.5.4.It can be seen from 3.6.8 N · m2 when the flange plate is un-welded, and the stiffness is 1.91 × 108 N · m2 when the flange plate is welded.Unlike the traditional pipe-curtain method, a lateral joint is installed in the STS structure which can effectively eliminate the need for complicated temporary supports and control the ground settlement. The lateral stiffness of the STS structure can directly reflect the deformation characteristics of the structure, and subsequently affects the deformation of the soil. Based on the laboratory experiment and numerical simulation, the load versus deformation curve is calculated and analysed. It can be concluded that the stiffness of the STS structure is 1.05 × 10b is 0.5 m, the design strength of concrete is C30, and the elastic modulus E is reduced to 0.8 times, about 24 GPa. The calculation result is shown in To simplify the lateral stiffness of the STS structure, the lateral stiffness is the same as concrete. The calculation formula of the rectangular section stiffness isIn the field construction process of the STS structure, the influence of the pore-forming quality, the bolt installation and the flange plate welding on the stiffness of the STS structure means the lateral stiffness is not as perfect as in laboratory conditions. In the calculation process, it is necessary to reduce the lateral stiffness to different degrees according to the quality of the construction. According to the simplified results of the STS structure provided by Jia , the stiIn terms of ultra-shallow-buried tunnels and underground stations, the settlement of the vault caused by excavation is predicted by the ground settlement, which means ground settlement control is one of the important factors during construction. The ground settlement for different STS structure stiffness is shown in 4.Subway stations in Shenyang (line 10) are constructed by the traditional PBA method that has some challenges when used in Northeastern Street station (located west of the intersection of Beihai street and Northeastern Road) due to the complexity of the existing structures and heavy traffic load. As a result, considering the geographical location and geological properties of the subway station, a combination of STS and PBA methods, as discussed in the previous section, is used to design and construct this station.The total length of the station is 225.95 m, the width of a standard cross section is 24.7 m, and the buried depth of the bottom floor of the station is 17.5 m, with an overburden layer of about 3.4 m. For construction, the station is divided into three sections: north of the station for which covered excavation is used; south of the station for which the open surface method is adopted and the middle section of the station in which a combination of the STS and PBA methods is adopted considering the intensity of the surrounding structures and heavy surface traffic load. The length of the southern, middle and the northern segments of the station are 68.65 m, 114.4 m, 42.9 m, respectively. The engineering details of the Northeastern Street station are illustrated in The soil stratum at the station location was determined from geological investigations. Accordingly, the field can be classified into five layers based on the mechanical properties and formation lithology, as shown in 5.The bolt stress is changed by the deformation of the STS structure during the construction process. In this research, the stress gauges were installed at the bolt location to monitor the stress change. According to the site condition, the monitoring points between 5# and 6# steel tubes and between 9# and 10# steel tubes are selected, which was shown in (1)Construction of pilot tunnel: It can be seen from (2)Construction of the beam-column system: at this stage, the value was basically maintained in a stable state by monitoring the stress gauges, but the overall trend was increasing, and the data reached a constant, which was related to the multiple disturbance of the soil during the construction of the pilot tunnel.Research results in chapter 3 shows the construction of the pilot tunnel had a great influence on the deformation of the STS structure and the ground settlement. Therefore, the influence of construction of pilot tunnel on the changing rule of bolt stress is investigated. Two stages of construction sequences are analysed under the site construction condition: tunnel excavation and beam-column system construction. Let's take the case of the steel tubes 5#-6#.6.6.1.3D software (FLAC3D 5.0). The dimensions of the numerical model were 120 × 39 × 50 m to eliminate the boundary conditions [X-, Y- and Z-directions. The front and back side were fixed in X- and Y-directions. The left and right side were fixed in X-and Y-directions. The top surface was free to move in all directions. A surcharge of 20 kPa was applied on the top surface to simulate surface loads. The diameter of the cylindrical steel columns is 0.8 m, the distance between cylindrical steel columns is 8.5 m, the length of the feet-lock bolt is 2.5 m and the distance between the feet-lock bolts is 1.0 m in the model, in accordance with the real structure.A large span underground subway station is treated as a three-dimensional model. A full three-dimensional model of the station construction was established using FLACnditions , as showBeam and pile elements are adopted to simulate the temporary steel supports and feet-lock bolt, respectively. Different materials were assigned to the different soil layers and different components of the STS structure as shown in (1) Stage 1: Construction of the side pilot tunnels PT5 and PT6;(2) Stage 2: Construction of the pilot tunnels PT1 and PT2 and cylindrical steel column SC1;(3) Stage 3: Construction of the pilot tunnels PT3 and PT4 and cylindrical steel column SC2;(4) Stage 4: Construction of the top plate at mid-span;(5) Stage 5: Construction of the station hall; and(6) Stage 6: Construction of the platform layer.In accordance with the construction sequence of Northeastern Road subway station, the whole construction simulation was divided into six stages, as follows:6.2.The longitudinal displacement profile of the pilot tunnel Z1 was investigated. The step length was assumed to be 3 m in the numerical simulations in accordance with the realities of construction.As for the ground settlement of the pilot tunnel, the simulation and monitored results showed similar settlement profiles when pilot tunnel PT1 was excavated, and the largest difference of both was within 10%, as shown in 6.3.The Dongbei Damalu Station is adjacent to the viaduct near Beihai Street. The horizontal distance between the viaduct and subway station is only about 4 m. Therefore, it is necessary to strictly control the settlement and horizontal displacement of the viaduct during the construction of the subway station. The photo of the viaduct is shown in 6.3.1.During the buried excavation process of the subway station, the settlement of the bridge piles cap is shown in 6.3.2.The horizontal deformation of the bridge pile after the main body construction is shown in 6.4.6.4.1.Scheme 1: The side of the pilot tunnel was grouted to reinforce soil, and the spacing of steel supports was 0.5 m.Scheme 2: The side of the pilot tunnel was grouted to reinforce soil, and the spacing of steel supports was 2.0 m.Scheme 3: The side of the pilot tunnel was grouted to reinforce soil, and steel supports had not been installed.Scheme 4: There is no need to reinforce soil and install the steel supports in the construction of the pilot tunnel.To analyse the influence of concrete grouting on the side of the pilot tunnel and the spacing of temporary support on the deformation of the bridge pile, the following four schemes were used for the simulation calculation, and the characteristic monitoring points were shown in 6.4.2.It can be seen from 6.4.3.The maximum horizontal displacement of four schemes is shown in 7.(1)The STS structure can effectively control the deformation of ground and adjacent structures by connecting the steel pipes in a transversal direction and can be widely used in large span underground engineering in soft soil areas.(2)The STS method and PBA method are combined to construct the subway station in Shenyang. The ground settlement is mainly accumulated during the construction of pilot tunnels and the secondary lining of mid-span. The construction of the main structure has little influence on the ground settlement, while it can cause horizontal deformation of STS structures.(3)As for construction of the station hall, the ground settlement of different construction sequences, i.e. rear-span to mid-span and mid-span to rear-span, can be reduced by 22%. Temporary supports can effectively reduce the deformation of the vertical STS structure, as well as controlling the deformation of the horizontal STS structure. The optimum spacing of temporary supports is 2 m.(4)The side pilot tunnel has a significant effect on the deformation of the bridge pile, and the surrounding soil of pilot tunnel needs to be reinforced during the construction process.This study introduces the STS method that has been applied for the first time to construct an ultra-shallow-buried and large span subway station. Based on the numerical simulation and monitoring data, surface settlement and structural deformation in a large span subway station using the Steel Tube Slab were investigated. As a result, conclusions were drawn as follows:


Mandatory and recommended vaccination in the EU, Iceland and Norway: results of the VENICE 2010 survey on the ways of implementing national vaccination programmes’ by M Haverkate, et al. published on 31 May 2012, the modalities of implementation of the childhood vaccination programme for Latvia were corrected in Tables 1 and 2. The affected numbers in the text were also corrected accordingly. These corrections were made on 3 July 2019, upon request of the authors.In the article ‘