Clostridioides difficile infections (CDIs) are the most common cause of acquired diseases in hospitalized patients. Effective surface disinfection, focused on the inactivation of the spores of this pathogen, is a decisive factor in reducing the number of nosocomial cases of CDI infections. An efficient disinfection procedure is the result of both the properties of the biocidal agent used and the technology of its implementation as well as a reliable, experimental methodology for assessing the activity of the biocidal active substance based on laboratory models that adequately represent real clinical conditions. This study reviews the state of knowledge regarding the properties and biochemical basis of the action mechanisms of sporicidal substances, with emphasis on chlorine dioxide (ClO2). Among the analyzed biocides, in addition to ClO2, active chlorine, hydrogen peroxide, peracetic acid, and glutaraldehyde were characterized. Due to the relatively high sporicidal effectiveness and effective control of bacterial biofilm, as well as safety in a health and environmental context, the use of ClO2 is an attractive alternative in the control of nosocomial infections of CD etiology. In terms of the methods of assessing the biocidal effectiveness, suspension and carrier standards are discussed. The One Health approach recognizes that human health is closely connected to the health of animals and the natural environment. The paradigm of One Health is based on the observation that health is a continuous, combined, global, and interdependent series of causes and effects occurring within ecosystems as well as in human and animal populations ,2,3. Thegenera Salmonella, Campylobacter, and Clostridium, as well as Escherichia coli, which are the cause of food toxico-infections [To face the challenges of a changing world, intensive cooperation among veterinarians, medical doctors, environmentalists, chemists, and biologists is crucial. Emerging new infections require action to develop effective drugs, but also special precautions to prevent the spread of infections. It should also be noted that an equally important issue in contemporary infectiology is the existence of species that have managed to develop over the course of their evolution effective mechanisms of high resistance to biocides. These include enteropathogenic bacteria of the fections . The devClostridioides difficile (CDI) are the most common causes of intestinal diseases acquired during hospitalization. This phenomenon is associated with the use of antibiotics and chemotherapy, as well as with ineffective decontamination of the hospital environment [In North America and Europe, infections with ironment . On averironment . In thisironment , with abironment ,12. The ironment . In Germironment . It was ironment . AccordiClostridioides difficile (CD) was first isolated in 1935 from the stool of a healthy infant [Clostrioides difficile A (TcdA) toxin and Clostrioides difficile B (TcdB) toxin, which are large multidomain proteins with a molecular weight of 308 and 270 kDa, respectively [The bacterium y infant . In the y infant . It beloy infant . This paectively ,21.According to the latest estimates, more than half of the CDI cases are associated with healthcare facilities . Since C− without biocidal properties. Application forms of preparations based on active chlorine are usually aqueous solutions containing a complex, equilibrium system of several forms of chlorine, with concentrations resulting from the pH of the solution, i.e., elemental chlorine (Cl2), chloric acid (HClO), chlorate ions (I) (ClO−), as well as small amounts of complex trichloride (Cl3−) ions [The commonly used term “active chlorine”, adopted from the terminological area of the analytical chemistry of sodium chlorate (I) solutions, is used to refer to preparations containing chlorine with oxidation states 0 and +1, in contrast to chloride ions Cl3−) ions ,29. In vN-chlorine derivatives of amines, such as sodium dichloroisocyanurate (NaDCC) or chloramines [Active chlorine solutions used in disinfection are generally obtained from preparations containing active chlorine-releasing substances , including sodium hypochlorite (formerly “sodium hypochlorite”) and selected oramines ,31.Commercially available sodium hypochlorite solutions are produced by absorption of elemental chlorine in sodium hydroxide solution (1):A by-product of Reaction (1) is sodium chloride, some amounts of which are present in sodium hypochlorite solutions, also due to the partial decomposition of sodium hypochlorite (2):Under the conditions of an excess of hydroxide ions (pH > 7) in an aqueous solution, sodium chlorate (I) undergoes electrolytic dissociation according to Equation (3):Lowering the content of hydroxyl ions leads to the production of poorly dissociated chloric acid (I) (4), considered as a form of active chlorine, which mainly determines the biocidal properties  (4):(4)CFurther reduction of the pH of the solution leads to the opposite reaction (1) and the production of molecular chlorine.- ions with lower biocidal effectiveness increases.The course of the equilibrium curves presented in N-chlorinated derivatives, the source of chloric acid (I) is the hydrolysis reaction of sodium diisocyanurate or chloramine, according to Equations (5) and (6). As mentioned earlier, HOCl mainly determines the biocidal properties.In the case of using 2Cl) has been investigated as early as in the 1970s. Authors Shih and Lederberg [B. subtilis DNA under the influence of several dozen µmol/L HOCl solutions. Studies conducted with the use of isolated E. coli RNA nucleotides  showed significant changes in their molecular structure, confirmed by UV spectrophotometry. Other authors [2O2, to the production of HO· radicals, the interaction of which with DNA leads to degradation.The biocidal mechanism of chloric acid (I) action on microbial cells consists of the disruption of metabolic pathways essential for the functioning of the cell and the degradation of genetic material. The influence of HOCl from chloramine (NHederberg  showed t authors  showed tThe strong influence of chloric acid (I) on oxidative phosphorylation pathway disruption as well as on other processes involving the cell membrane has been demonstrated ,36. The N-chloro derivatives > 1000 mg/L) [The most frequently used preparations containing active chlorine with sporicidal properties are sodium hypochlorite  and sodi00 mg/L) ,41,42.The decisive stage in the mechanism of the sporicidal action of active chlorine seems to be the increase in the permeability of the spore coating (cortex), manifested by the release of dipicolinic acid (DPA) . The mecLowering the concentration to 500 mg/L resulted in the reduction of the most infectious CD isolate ribotype R027 to L = 1.2–2.4-LOG. In addition, the use of active chlorine concentrations below the recommended levels may affect the hydrophobicity of spores and, thus, their ability to adhere to the surface, which in turn may favor the spread of the pathogen . HoweverA significant environmental issue related to the use of preparations based on active chlorine is their ability to chlorinate organic matter and produce disinfection by-products (DBPs), which potentially harm the environment and human health ,47. PrevThe critical stage in the mechanism of the biocidal action of aldehydes is the denaturation of proteins and the degradation of RNA and DNA . This isThe most popular aldehyde to combat CD is glutaraldehyde (GA). The mechanism of action of bifunctional glutaraldehyde is the formation of imide bonds with lipopeptides and peptidoglycan of bacterial cell walls, causing their deformation. Glutaral also reduces dipicolinic acid formation, which is characteristic of spores and determines their external factor resistance . The advo-phthalaldehyde, the disinfection results were poorer [Glutaraldehyde has a high sporicidal activity. A 1% GA solution, with a contact period of 15 min, can reduce CD spores at the L = 1.03-LOG level, and a 6% solution can reduce such spores at the L = 2.05-LOG level. The discussed results were obtained using the “four-field” method according to the EN 16615 standard . Howevere poorer . In this2O2) is a strongly oxidizing, odorless substance with strong biocidal properties in liquid and gaseous form. Low concentrations of gaseous H2O2 are more effective than liquid forms [Hydrogen peroxide  by Bioquell, VHP (vapor hydrogen peroxide) by Steris, and aHP (aerosolized hydrogen peroxide) by Sterinis [Techniques of surface disinfection with gaseous Hnd 1990s . There aSterinis ,63.2O2 with the addition of a silver cation. In the case of 0.5% sodium hypochlorite solution (5 mg/L active chlorine), the effectiveness of the disinfection process was noticed in 50% of the disinfected rooms. By testing the disinfection effectiveness of the same products in vitro on polyvinyl chloride or laminate carriers, imitating floors and furniture in hospital rooms, spore reductions of L = 4.18 ± 0.8-LOG for H2O2 solution and L = 4.32 ± 0.35-LOG for sodium hypochlorite were obtained [The HPV and aHP systems have been tested in the decontamination of hospital wards affected by CDI. The HPV system introduced to hospitals for two periods of 10 months reduced the amount of CDI by 53% compared to the control . In the obtained .2O2 largely depends on the type of the disinfected surface. Significant differences were found in the effectiveness of decontamination of B. subtilis spores, depending on surface porosity. Within 20 min and at a concentration >1000 mg/L H2O2 on porous surfaces of industrial flooring and pine wood, the level of pathogen reduction, respectively, L = 1.6-LOG and L = 2.2-LOG. On non-porous glass or cardboard surfaces, spore reduction levels were L = 7.5-LOG and L = 7.6-LOG [Decontamination with H 7.6-LOG .Peracetic acid (PAA) is a colorless, clear liquid with an acetic odor. It is a strong oxidant, with an oxidation potential comparable to that of ozone .The essence of PAA’s biocidal activity lies in its ability to homolyze, with the formation of highly reactive hydroxyl radicals (10) :2O2 is its resistance to decomposition by peroxidases, which allows it to remain active [These, in turn, interact with organic matter, analogously to hydrogen peroxide. The advantage of peracetic acid over Hn active . As a ren active .In the EN 16615 carrier method against CD, the expected reduction of L ≥ 4-LOG spores was obtained during a contact period of 15 min for a solution with a PAA concentration of 4% .2 is an alternative to commonly used preparations based on active chlorine and other biocides. The strong oxidizing properties of ClO2, combined with the selectivity of the biocidal action, and the inability to form harmful by-products of disinfection justify the increased interest in this chemical compound as an active ingredient in disinfectants [2 directly result from its unusual molecular structure, presented in the form of resonance structures in Due to the lack of the ability to chlorinate organic matter and, thus, to produce ecotoxic chlorine-based disinfection byproducts, ClOfectants ,69. The 2 molecule is a free radical where the unpaired electron is not located at a specific atom but is part of a covalent three-electron bond. This explains the stability of the ClO2 molecule and the lack of a tendency to dimerize to form Cl2O4, unlike other simple inorganic radicals with similar symmetry. The ClO2 is a yellow-brown gas with a characteristic acrid odor. At 1 atm pressure, ClO2 boils at 11 °C and melts at −59 °C. At higher concentrations, both gaseous and liquid ClO2 have strong explosive properties. Hence, in practical use, ClO2 is not compressed but generated in situ in aqueous solutions at concentrations not exceeding 3 g/L. It can also be released as a gas at concentrations below the explosive limit [The ClOve limit .2 in aqueous solutions have shown the possibility of effective and quick reactions with various functional groups by free radical oxidation [Studies on the chemical activity of ClOxidation ,74,75,762 can therefore be explained by the reactions with numerous molecules of key importance for the organism under attack, at different levels of the cell structure  and virus . Because of its strong oxidizing properties, ClO2, especially in aqueous solutions, exhibits biocidal activity by influencing the cellular equilibrium of electron transfer processes.The non-specific mechanism of the bactericidal and virucidal action of ClO2 is based on a reaction with six amino acids: cysteine, tryptophan, tyrosine, proline, hydroxyproline, and histidine; reactivity with the first three is extremely high [The mechanism of protein denaturation via ClOely high .2 molecule gives a transient Cys-ClO2 adduct. At high pH values, reaction with another cysteine thiol radical leads to the formation of the aforementioned dimer (cystine); at a low pH, cysteic sulfonic acid is generated (11) and (12) [In the case of cysteine, degradation and loss of biochemical functions is the result of dimerization of this amino acid, with the formation of a disulfide bond . The preand (12) .2 with the participation of amine nitrogen atoms is the production of a radical precursor of tryptophan oxidation. The diagram shows one of the two alternative pathways of the radical attack of the ClO2 molecule directed at the indole nitrogen atom, leading to the formation of a radical cation and, after proton cleavage, a resonance-stabilized radical, the extreme mesomeric forms of which are shown in Equation (13) [An example of the degradation of an amino acid under the influence of ClOion (13) :N-formylokinurenine, formed as a result of the attack of the ClO2 radical on the 3-yl carbon atom of the indole moiety [2, tyrosine is oxidized to 3,4-dihydroxyphenylalanine (DOPA) or 2,4,5-trihydroxyphenylalanine [The radical presented in the above scheme is a precursor in the reaction of formation of among others e moiety . Under tlalanine .2 on living organisms, is the strong ClO2 interference in redox processes, determining electrochemical equilibria in mitochondria and cell membranes, in particular with regard to the NADH/NAD + redox system responsible for cellular respiration and mediation in ATP synthesis [One interesting finding, shedding light on the possible mechanism of the influence of ClOynthesis ,85).2. At the amino acid level, TcdA and TcdB are approximately 45% identical [In the context of amino acid composition, it is worth analyzing the potential mechanism of CD toxin inactivation against ClOdentical . They hadentical . Both Tcdentical . After edentical ,89,90. Tdentical ,92. Thisdentical , resulti2 with CD can therefore take place on several levels. The APD auto-processing domain is a protease containing cysteine and histidine residues in the active center, most likely responsible for the binding of zinc ions, facilitating the proper release of the GTD domain into the cytosol [2 may influence the key stages of the TcdA and TcdB mechanisms in the cell and, thus, inhibit the cytotoxic effect of host proteins.According to the available literature, the interaction of ClO cytosol . At the  cytosol . Oxidati2 reactions with elements of biologically active molecule structures presented above are mainly the result of studies using isolated, pure forms of biologically active target compounds. Unfortunately, reports describing the results of studies on the mechanisms of biocidal activity in vivo, based on observations of changes in living organisms, are few, and the obtained conclusions are not consistent. For example, the results of Zhu et al. indicate that ClO2 in concentrations higher than 100 mg/L damages DNA in Saccharomyces cerevisiae [2. Young and Setlow reported that B. subtilis spores treated with ClO2 showed no tendency to accumulate DNA damage [2.The possible paths of ClOrevisiae . This dorevisiae . SimilarA damage . The occ2 was observed for spores lacking the coat protein, examined with chemical methods or by mutation of genes encoding respective proteins. Although no release of dipicolinic acid (DPA) was found in the ClO2-treated spores; the spores released DPA much more easily after sub-lethal heat treatment than untreated ones. The above observations lead us to the conclusion that the critical process of the mechanism of action of the sporicidal ClO2 solution against B. subtilis spores is not DNA damage, but the damage to the cortex layer composed of, among others, DPA.Increased sensitivity to ClO2 has been described elsewhere [Bacillus thuringiensis spores exposed to the ClO2 solution with a concentration of 750 mg/L. The study of molecular structure changes was carried out using Raman spectroscopy and the optical laser tweezer (LTRS) technique. Changes in the structure of spores were determined via scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Although a high degree of spore reduction was observed under the influence of the ClO2 solution (5-6-LOG was obtained), no visible changes were found in the Raman spectra, both for the bands characteristic for DPA and DNA as well as for amide bands related to possible changes in the structure of amino acids. There were also no significant changes in the SEM and TEM images of the spores under the influence of ClO2.An attempt to create a molecular basis for explaining the mechanism of the sporicidal action of ClOlsewhere . The stu2-based preparations are scarce, the estimated sporicidal properties of ClO2 should be considered attractive, in particular in relation to the low risks to human health and the environment. Foegeding et al. [2 on the survival of Bacillus cereus T, B. cereus F4810/72, Bacillus stearothermophilus ATCC 1518, and Clostridium perfringens NCTC 8798 spores in the environment of a relatively low concentration of ClO2 (20–80 ppm) at pH 4.5 and 8.5, using various sporulation methods.Although studies on the effectiveness of ClOg et al.  studied B. cereus T sporulation method on survival. In the case of C. perfringens spores, a decrease in survival was observed at higher pH. At a concentration of 50 mg/L, the level of 4-LOG reduction at pH 4.5 was achieved for 15–30 min for B. cereus spores (depending on the sporulation method), 20 min for B. subtilis, and 80 min for C. perfringens. The same level of reduction at pH 8.5 was achieved after 45 min for C. perfringens. The influence of the pH on the survival of the remaining spores was insignificant. In another study [B. pumilus SAFR-032 and B. subtilis ATCC 6051 model strains for C. difficile, resistant to disinfection with hydrogen peroxide, under unloaded conditions and in ClO2 aqueous solutions were investigated. For the concentration of 47 mg/L and period of 10, 60, and 24 min, reduction levels of 1-LOG and 2-LOG were obtained, respectively. Complete reduction was only achieved after 24 h. However, increasing the ClO2 concentration to 187 mg/L achieved complete spore reduction within 10 min. In 2005, Perez et al. demonstrated that a solution with a concentration of 600 mg/L ClO2 reduced CD spores to the level of L = 6 LOG within 15–30 min, depending on the strain and the condition of the microorganisms. The tests were carried out in unloaded (clean) conditions with the use of steel disc tests [2 during 10 min without organic load on sterile glass carriers [Comparison of sporicidal properties showed the effect of er study , spores sc tests . In anotcarriers .2 under clean conditions and a contact period of 5 min.The suspension tests of the authors of this publication, carried out in accordance with the EN 17126 standard, showed the effectiveness in controlling CD at the level of 4.49-LOG for a solution with a concentration of 100 mg/L ClOAs already mentioned, an important element in the control of CDI is surface disinfection, especially the so-called “tactile”. Producers of disinfectants demonstrate their sporicidal activity through suspension and/or carrier tests.Bacillus subtilis and Bacillus cereus spores. However, the responsible implementation of biocides requires further Phase 2 research.Until 2018, the standards EN 14347:2005 and EN 13704:2018-09 ,104 wereBacillus subtilis spores and for Bacillus cereus spores and Clostridium sporogenes. Products placed on the market and used in medical areas were mostly tested according to the described standard but under unclean conditions, with an increased organic load .The suspension standard EN 13704:2018-09 describes Phase 2, Step 1 tests, which consist of determining the effectiveness parameters, i.e., concentration and contact period under the conditions of use of the preparation. Mandatory tests are performed in clean and unclean conditions for Since 2018, the suspension standard EN 17126:2018-01  has beenBacillus subtilis spores in accordance with EN 13697:2015 [Currently, there are no approved carrier standards for liquid disinfectants for the control of spores in medical areas. Some manufacturers of sporicidal disinfectants specify the effectiveness of their preparations against CD or 697:2015 . Gemein 697:2015 . The metThe red polygon arrow line shows the trajectory of the disinfectant tissue, moved along the four fields, starting from infected field A through uninfected fields B, C, D, and back. After rubbing the remaining fields, the degree of pathogen spread is determined.Bacillus subtilis ATCC 6633. In addition, it facilitates testing the effectiveness against any pathogen, including CD.One interesting aspect in the context of the assessment of sporicidal activity is the use of the carrier standard EN 17272:2020, approved and published in 2020 . The staBiocides used in clinical disinfection for the control of bacteria resistant to disinfection treatments, in particular spore-forming bacteria, are usually simple, low-molecular-weight chemical compounds with strong oxidants  or electrophiles with high affinity for atoms with non-binding electron pairs .oxidation of thiol groups with the formation of disulfide bridges or derivatization of amine compounds by radical oxidation (oxidants);formation of imine bonds (Schiff compounds) by condensation of amino groups of amino acids with carbonyl groups .The mechanism of the biocidal action of the above compounds mainly consists of the denaturation of proteins by generating irreversible structural changes at the level of functional groups of individual amino acids, such as:2), may be an important step in the mechanism of the killing action. Despite the natural ability of spores to produce proteins that protect DNA against genotoxic effects , the factor determining the resistance of spores to the action of the discussed substances, including ClO2 or HClO, is their protein shell (coat).The disruption of intracellular redox processes, which constitute steps in metabolic pathways (oxidants, in particular ClOAmong the discussed biocidal compounds effective in controlling vegetative forms and CD spores, one attractive alternative is chlorine dioxide, because of its high biocidal effectiveness and low risks for human health and the environment. Although the underlying mechanism has not been fully elucidated, this compound shows a relatively high sporicidal activity. The way in which it is carried out experimentally plays a key role in assessing the effectiveness of the sporicidal disinfectant.The key condition for the reliability of the assessment of effectiveness, affecting the final test result, is the adequacy of the mapping of the real object, which is a fragment of a diverse, usually non-standard clinical environment, by artificially created model conditions of a laboratory method. The approximation of laboratory conditions to real conditions is achieved through the implementation of subsequent phases and stages of biocidal effectiveness assessment.The suspension standard EN 17126:2018-01 is an example of the procedure in Phase 2 of Step 1 of the assessment of sporicidal activity of chemical disinfectants. The next stage of approaching the real clinical environment is the designed carrier standards in Phase 2 of Step 2. The carrier standards simulate the conditions occurring during surface disinfection; they can be divided into those with and without the use of a mechanical factor. The four-field carrier test, included in the EN 16615 standard and intended for the evaluation of sporicidal activity, allows the evaluation of the degree of spore reduction on the surface with the use of a chemical and mechanical agent, to determine whether the preparation has a prolonged effect and thus can be used for periods of up to 1 h, and estimate the effect of transferring spores to other surfaces during e disinfection. The use of a vehicle test, applying a mechanical factor will be the largest step in assessing the sporicidal activity of chemical disinfectants.


In order to effectively utilize aluminum industrial waste—red mud and bauxite tailings mud—and reduce the adverse impact of waste on the environment and occupation of land resources, a red mud–bauxite tailings mud foam lightweight soil was developed based on the existing research results. Experiments were conducted to investigate the mechanical properties and microscopic characteristics of the developed materials with different proportions of red mud and bauxite tailings mud. Results show that with the increase in red mud content, the wet density and fluidity of the synthetic sample was increased. With 16% red mud content, the water stability coefficient of the synthetic sample reached its maximum of 0.826, as well as the unconfined compressive strength (UCS) of the sample cured for 28 d (1.056 MPa). SEM images reveal that some wastes of the sample without red mud were agglomerated, the peripheral hydration products were less wrapped, and when the amount of red mud was 16%, the hydration products tightly wrapped the waste particles and increased the structural compactness. The final concentration of alkali leaching of samples increased with the addition of red mud. The maximum concentration of alkali leaching was 384 mg/L for the group with the addition of red mud of 16%. Based on the obtained mechanical strength and alkali release analysis, the sample B24R16 was selected as the optimum among all tested groups. This study explored a way to reuse aluminum industrial waste, and the results are expected to be applied to roadbed and mining filling. Red mud and bauxite tailings mud are aluminum industrial wastes. Bauxite tailings mud is the water-bearing residue of bauxite raw ore  after grinding and washing . Bauxite2O)/(SiO2 + Al2O3) = 0.88, the UCS of road base materials meets the strength requirements of highways. Additionally, the ion leaching concentration meets the drinking water standard 3− with the OH− and water in the system. [Al(OH)6]3− was further combined with Ca2+ and SO42− to form C-S-H and ettringite [tringite . The resCorresponding to the XRD test, three groups, B40R0, B36R4, and B24R16, were selected for curing for 28 days, and the microstructure and product shape were observed by scanning electron microscopy under conditions of 50 and 5000 times.2, and a small amount of needle-like ettringite can be seen in each group. When cement, bauxite tailings mud, red mud, and other materials were mixed in each group, cement hydration reaction with water generated C-S-H, CH, Aft, and other cementation products. Meanwhile, Al2O3 and SiO2 rich in red mud and bauxite tailings mud reacted with Ca+ in volcanic ash to generate C-S-H, which improved the strength of the samples. The bauxite tailings mud content of the sample B40R0 group was the largest, and some waste particles agglomerated in the hydration process, and the agglomerates were only partially wrapped by hydration products outside the body, which made the strength of the sample low after curing for 28 d, which is also the reason why the unconfined compressive strength of the sample in this group was only 0.41 MPa. The sample B36R4 group added 4% of red mud because bauxite tailings mud mixed with still more. There were still some samples after particles in water clouds appeared, but because red mud contains many Na2O, can provide a hydration process with hydroxyl, and promotes the hydration process, to generate a more mottled gelling material wrap in most of the areas, the integral structure was made more compact. Therefore, the unconfined compressive strength of this group of specimens was nearly 50% higher than that of B40R0 specimens. No agglomeration particles were found in the B24R16 group samples, and a large number of C-S-H and CH generated by hydration reaction tightly wrapped the red mud and bauxite tailings mud particles in the system that were not involved in the hydration reaction. Moreover, as red mud was added to this group the most, part of the soluble basic ions in red mud accelerated the hydration reaction process, significantly increasing the density of the structure. Therefore, the UCS strength of the combination was the highest among all combinations, and the water stability coefficient was also the largest.+ leaching concentration and time is shown in The change in NaIn this study, aluminum industrial waste was used to prepare foam lightweight soil from red mud–bauxite tailings mud. The test mainly analyzed the physical and mechanical properties, microscopic characteristics, and alkali environmental effects of foam lightweight soil from red mud–bauxite tailings mud, and explored a way to reuse aluminum industrial waste, the results of which can be applied to the needs of roadbed and filling. The main conclusions of this chapter are as follows:When the red mud content increased from 0% to 20%, both wet density and fluidity increased with the increase in red mud content. When the red mud content was between 4% and 20%, the fluidity of the foam light soil of red mud–bauxite tailings mud was between 168 mm and 177 mm, which meets the requirements of the specification and is conducive to filling.When the red mud content was 0–16%, with the increase in red mud content, the unconfined compressive strength of 7 d and 28 d samples increased greatly and reached the maximum values of 0.872 MPa and 1.056 MPa, respectively, when the red mud content was 16%, which increased 192.6% and 157.6% compared with the group without red mud content, respectively. However, the water stability coefficient increased with the increase in red mud content and reached the maximum value of 0.892 when the red mud content was 16%.The microscopic test revealed that some wastes of the samples without red mud were agglomerated, and the surrounding hydration products were less wrapped, resulting in a lower structural strength of the samples. When the red mud content reached 16%, there were more hydration products, and the red mud and bauxite tailings mud particles that were not involved in the hydration reaction were tightly wrapped so that the sample structure was dense and the strength was the highest.The final concentration of alkali leaching increased with the addition of red mud. When the addition amount was 16%, the concentration of alkali leaching was still lower than the four types of water limit specified, with a mixing amount of 20%. The maximum alkali leaching concentration was 460 mg/L, which exceeded the limit value of the four types of groundwater. According to UCS and alkali release analysis results, the B24R16 group had the highest UCS intensity, and the alkali leaching amount of this group did not exceed the four water limits, so it belongs to the optimal group.


Gait stability has been measured by using many entropy-based methods. However, the relation between the entropy values and gait stability is worth further investigation. A research reported that average entropy (AE), a measure of disorder, could measure the static standing postural stability better than multiscale entropy and entropy of entropy (EoE), two measures of complexity. This study tested the validity of AE in gait stability measurement from the viewpoint of the disorder. For comparison, another five disorders, the EoE, and two traditional metrics methods were, respectively, used to measure the degrees of disorder and complexity of 10 step interval (SPI) and 79 stride interval (SI) time series, individually. As a result, every one of the 10 participants exhibited a relatively high AE value of the SPI when walking with eyes closed and a relatively low AE value when walking with eyes open. Most of the AE values of the SI of the 53 diseased subjects were greater than those of the 26 healthy subjects. A maximal overall accuracy of AE in differentiating the healthy from the diseased was 91.1%. Similar features also exists on those 5 disorder measurements but do not exist on the EoE values. Nevertheless, the EoE versus AE plot of the SI also exhibits an inverted U relation, consistent with the hypothesis for physiologic signals. Maintaining walking stability requires stable gaits. The cost of falls due to unstable gait is severe, especially for the elderly . TherefoIn gait stability measurement, stride interval (SI) and step interval (SPI) time series are important parameters that are often used. Specifically, the SI is defined as the time from a heel strike of one foot to the next heel strike of the same foot. Similar to SI, the SPI is defined as the time from a heel strike of one foot to the next heel strike of the other foot . The sumNumerous entropy-based measures of disorder and complexity were proposed and applied to gait analysis. However, some inconsistencies or limitations in finding the relation between the complexity or disorder measurement and gait stability were still recognized and are worth further investigation ,3.For example, sample entropy (SE) is a widely used measure of disorder in terms of irregularity , which aOn the other hand, Costa et al. proposed a multiscale entropy (MSE) analysis to measure the complexity of a physiologic time series by measuring the SE value of the time series on a multiple-time-scale basis. Subsequently, many multiscale-based entropy methods for complexity were developed ,14,15. AHowever, entropy of entropy (EoE)  and averIn the application of the AE to static standing postural stability, the AE values of the center-of-pressure trajectory time series of each of the individuals in testing was found to increase from stable to unstable balance conditions . The stuIn this study on walking stability, we apply the EoE and the AE to three gait databases to investigate whether the disorder is better than the complexity to measure gait stability. The stable versus unstable conditions in the three gait databases are as follows: (1) healthy subjects walking with eyes open versus closed; (2) healthy subjects versus patients with Parkinson’s disease (PD); (3) healthy subjects versus patients with lateral sclerosis (ALS), Huntington’s disease (HT), and PD. For comparison, the AE values of all the SI and the SPI time series from the three databases are to be compared with those measured by using the SE, the FE, the DE, the FDE, and the DistE. The corresponding means and the standard deviations (SD) of the time series were presented to show the difference between the traditional metrics and the entropy-based method in gait analysis.Three databases of 10 SPI and 79 SI time series were used for the study of walking stability. These databases also provide the acceleration data of individuals walking continuously on an obstacle-free path, from which the SPI and the SI time series were derived.The SPI time series of the first database (D1) were collected from 10 healthy participants (36.1 ± 18.3 years old). Specifically, each participant walked three laps of a 400-meter-long athletic field with his/her eyes open and closed, respectively. All participants walked at their preferred gait velocities from the same starting point. They took enough rest between their walks with eyes open and closed, individually. When they walked with their eyes closed, every one of them was accompanied by a laboratory staff to prevent from falling or deviating from the track by verbal instructions. An accelerometer  was secured tightly at the sacrum of each of the participants by using a bandage. The acceleration measurement range of the accelerometer is ±3 g with a resolution of 3 mg, where g is the abbreviation of the acceleration of gravity. The acceleration data were sampled at 100 Hz and saved in a memory card on a programmed Arduino UNO board. The SPI time series were derived from the acceleration data for analysis ,26,27. AThe SI time series of the other two databases were downloaded from the online databases on PhysioNet . One is ix} = {x1, …, Nx} of length N, the algorithms of the AE and EoE methods consist of three steps. The first two steps are the same for both entropies. The first step is to divide a time series for analysis into consecutive and non-overlapping windows with an equal length of τ, referred to as a scale factor. Each window is in the form of jwτ)( = {xj−1)τ+1τ+τ and the minimal (minT) values among them. The range between maxT and minT in amplitude was divided into s1 slices of equal width such that each slice represents a state. Over each window, the probability to find a data in each of the slices was obtained. The probability jkp for a certain data point ix over window jw(τ) to occur in slice k is thus obtained in the form ofk is the slice index ranging from 1 to s1. Accordingly, the Shannon entropy value of the data in each window was derived from the distribution of the probabilities over the slices. The Shannon entropy value jyτ)( of each window jwτ) and the minimal (minSE) values among them. The range between maxSE and minSE was divided into s2 slices of equal width. The probability of finding data in each of the slices over the new sequence was obtained. The probability lp for a certain jyτ}{ over the sequence {jyτ) were tuned to improve the capability in differentiating the healthy from the pathologic groups. As the number of classes in FDE was set equal to the bin number in DistE, 512, the overall performance under the new set of input parameters P2I is better than that under P1D, which is commonly used. The differences between the P2I and the P1D were listed as follow: (1) SE: The similarity threshold was changed to 0.0015; (2) FE: The width of the fuzzy exponential function was changed to 0.003; (3) DE: The number of classes was changed to 128; (4) FDE: The number of classes was changed to 512. For additional details about the algorithms, please refer to ,12,30,31DAcc1, Recall, Precision, and F score according to the results obtained by applying the traditional metrices of mean and SD, as well as the entropy analyses of AE, SE, FE, DE, FDE, and DistE to D1, D2 and D3, respectively. For database D1, the accuracy was obtained in the formdN is the total number of subjects of the database and trendn is the number of the participants who exhibit a relatively high entropy value when walking with eyes closed and a relatively low entropy value when walking with eyes open, individually.To quantify the performances of these entropy methods, we make use of the following performance indices accuracy TP, FP, and FN mean true positive, false positive, and false negative, respectively.For databases D2 and D3, quadratic discriminant analysis (QDA) was applied to classify the entropy values of the SI time series of the healthy and pathologic groups . In the Besides, the values of the performance indices for the various groups in D2 and D3 were calculated for comparison based on the sample size guideline of equal group probability for two-group discriminant analysis . Specifiτ = 10, respectively. Each of the 10 participants exhibited a relatively high AE value, labeled in red, when walking with eyes closed and a relatively low AE value in green when walking with eyes open, respectively. The trend of the change due to the visual feedback between eyes closed and open is completely consistent on the AE values for the 10 participants, individually. However, the trend is not completely consistent on the EoE values since 2 of the 10 participants exhibited an opposite change, as shown in τ = 10, respectively. The 15 subjects were composed of 10 healthy individuals and 5 patients with PD. In τ = 10, respectively. The 64 subjects consisted of 16 healthy individuals and 48 patients with ALS, HD, and PD. In Similar to th = 1.06, the dashed line in the figure, is optimal to differentiate the healthy from the diseased. Note that only 1 out of the 53 high AE values in red is below the threshold, with 20 out of the 26 low AE values in green. Thus, the overall accuracy of 91.1% (=72/79) is maximal in differentiating the healthy from the diseased.Applying the same threshold of AE = 1.06 as the criterion of stability into DAcc1, Recall, Precision, and F obtained by applying the traditional metrices of mean and SD, as well as the analyses of AE, SE, FE, DE, FDE, and DistE to D1, D2, and D3, respectively. As expected, the overall performances of the 5 disorder entropies under the new set of input parameters P2I are better than those under P1D, which is commonly used. By comparison, the AE and the DistE exhibit the best and the second-best performances for all D1, D2, and D3, respectively. Yet, the overall performances of the mean and the SE are relatively poor.Second only to the AE analysis, the DistE exhibited the best performance under P1D among the 5 disorder measurements of SE, FE, DE, FDE, and DistE; the DistE exhibits the best performance under P1D. As we tuned the number of classes in FDE equal to the bin number in DistE, 512, the overall performances of the 5 disorder measurements under the new set of input parameters P2I are significantly improved in comparison with those under P1D, which is commonly used. Besides, it is worth noting the relative change of the DE and FDE values for the healthy and the pathologic groups under P1D and P2I. This finding is consistent with the results in the previous studies of gait in children. The values obtained by using FE and DistE decreased from the younger to the older children ,12, whilThe two traditional metrices of SD and mean are not as good as the AE in differentiating the healthy from the diseased groups in D1, D2, and D3. The main difference between them is the lack of the information on the sequential order of a given time series in the traditional metrices. Recall that the AE method applies the multiscale technique to extract the randomness of a series , while tAn inverted U relation between the complexity and the disorder measurements of a series is a characteristic of a physiological time series. The feature was first conceptually proposed by Huberman and Hogg in 1986 . In 2019The AE, a measure of disorder, has been demonstrated to be a good measure of static standing postural stability . This stDAcc1, the Recall, the Precision, and the F. Among them, AE, DE, and DistE exhibited better performances than SE, FE, and FDE. On the contrary, the EoE, a complexity measure, could not measure gait stability.The results of the 10 SPI and the 79 SI time series in gait showed that every one of the 10 participants exhibited a relatively high AE value of the SPI time series when walking with eyes closed while a relatively low AE value when walking with eyes open. The trend is completely consistent on the AE rather than the EoE values. As to the 26 healthy and the 53 diseased subjects, most of the AE values of the SI time series of the diseased subjects were higher than those of the healthy subjects. For comparison, other disorder measures such as mean, SD, SE, FE, DE, FDE, and DistE also show good performances in terms of the accuracy Therefore, the results support that disorder measurement is also valid in gait stability as in static standing postural stability because of the nonautonomically controlled nervous system. Furthermore, the EoE versus AE plot of the 79 SI time series in gait also exhibits an inverted U curve. The shape is another example of the complexity versus disorder relation hypothesized for physiologic signals.


The experimental studies presented aim to analyze the capacity to inhibit the development of mold type Aspergillus and Penicillium on the surface of composite materials with nano-TiO2 content and the identification of the optimal range of nanomaterial addition. The identification and analysis of the inhibition halo  confirmed the biocidal capacity of the cementitious composites, but also indicated the possibility that an excess of TiO2 nanoparticles in the mixture could induce a development of cell resistance, which would be unfavorable both in terms of behavior and in terms of cost.The development of mold films on the cement surfaces of buildings is a health and safety problem for the population, aesthetic but also in terms of their durability. The use of specific performance of cementitious composites containing TiO Worldwide, there is a change in the lifestyle of the population, with many of the daily activities moving from outside to inside . At the Ochratoxin (OCT), aflatoxin B1, Trichothecene [Aspergillus and Penicillium genera and are genotoxic, immunotoxic, hepatotoxic, mutagenic and potentially carcinogenic [It is currently known that the development of microorganisms  on the surfaces of buildings has negative effects on the health of the population, especially if the development takes place on the surfaces of indoor living spaces, on the sustainability and safety in operation of buildings and on the degree of environmental pollution. The overall negative impact on the health of users is recognized worldwide as ‘sick building syndrome (SBS)’, manifesting itself in the population operating, partially or totally, inside buildings affected by micro-organisms deposits, as a result of degradation of indoor air quality by contamination with spores and toxins ,4,5,6,7.othecene ,12,13,14inogenic ,15. Epidinogenic . On the inogenic ,18,19. ACladosporium, Acremonium, Alternaria, Periconia, Curvularia, Stemophylium, Penicillium, Aspergillus [Penicillium and Aspergillus were found in more than 50% of the cases of commercial buildings and residential buildings analyzed, especially in conditions of high humidity and low direct solar radiation [After plastics, concrete is the building material most commonly affected by mold . Accordiergillus ,7,20. A adiation ,22. 2 nanoparticles proposes a simple and promising technology for inhibiting the development of mold film on the surface of cementitious materials. Thus, by simply exploiting sunlight, it becomes an alternative to the use of chemical disinfectants [Therefore, it is desirable to identify solutions for increasing the degree of indoor air hygiene, durability of constructions and printing a self-maintenance capability. Harnessing the photocatalytic process of TiOfectants ,25,26,272 nanoparticles in their matrix, acquire and show self-cleaning capacity under the action of environmental factors . Currently, there is research reported in the literature indicating that, even under low–intensity light irradiation conditions (the situation of the interior surfaces of buildings), a natural light intensity of ∼10 MW cm−2 or a simple neon bulb is sufficient to provide a sufficient amount of UV activation energy to allow photoactivation and therefore the self-cleaning effect of the composite cementitious surface [These cementitious composites, intended for the construction sector, become “intelligent” by embedding TiO surface .2 content is the sum of two phenomena, both due to the behavior of TiO2 nanoparticles under UV radiation: on the one hand, a superhydrophilicity of the cementitious surface develops which, when in contact with water, allow for the formation of a continuous film that will wash away the more effective the particles deposited on the surface, and, on the other hand, are catalyzed oxidation reactions in the molecules of the organic in nature, they are transformed into the products, the organic molecule is smaller and more easily washed off, and more easily destroyed in turn by means of a new process for the oxidation to CO2 and H2O [2 nanoparticles, alone, lose their hydrophilicity influence property as soon as the action of UV radiation ceases, but in combination with SiO2 in cement, the UV-activated effect extends even more days of darkness .The self-cleaning capacity of cementitious composites with nano-TiO and H2O ,35,36,37 and H2O  indicate2 nanoparticles under conditions of exposure to the action of UV rays can be explained on the basis of the increase in hydroxyl groups (OH−), phenomenon identified by X–ray photoemission spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) or nuclear magnetic resonance (MRI) [−) and holes (h+). Electrons tend to reduce the Ti (IV) cation to Ti (III) ions, and holes oxidize O2− anions. This process will release oxygen creating gaps on the surface of titanium dioxide, gaps that give the possibility of binding water molecules with the release of hydroxyl (OH−) groups. In the case of cementitious composite surfaces containing TiO2, the literature also indicates [+) increase the length of the bonds within the TiO2 network bringing the surface to a metastable state that allows the adsorption of molecular water, simultaneously with the formation of new hydroxyl groups and the release of a proton. Research believes that these generated hydroxyl groups are less thermodynamically stable, therefore the surface will allow flattening of the water drop to cover a larger area for stabilization purposes [The mechanism underlying the increase in hydrophilicity of cementitious composite surfaces with TiOce (MRI) ,38,39,40ndicates ,41 that purposes ,41,42. 2, electron pairs (e−) and voids (h+) are generated, which, react with O2 and H2O forming anionic radicals (O2−) and (OH−). These oxidative species  and (OH−)) are all highly reactive and contribute to the destruction of the cells of microorganisms [+) is greater than the electron reduction capacity (e−), and on the surface of the photocatalyst there is a single layer of adsorbed H2O molecules, hydroxyl groups (OH−) are formed. These highly oxidizing hydroxyl groups react with organic molecules producing peroxyl free radicals, which will react with molecular oxygen in a chain of reactions up to the final products CO2 and H2O and contribute to cell membrane rupture [−) reduce oxygen to the free radical O2− which will react with the resulting peroxide molecules during the reaction between the hydroxyl groups and the organic molecules, ultimately also leading to a chain of reactions up to the final products CO2 and H2O [2 photoactivation incident radiation that produces strong destruction at the cellular level in the range of 320–400 nm [As for the mechanism of oxidation of organic molecules, with energy supplied by UV radiation, greater than the valence band difference of TiOrganisms ,44. Sinc rupture ,46,47. O and H2O ,52,53,540–400 nm ,57,58,590–400 nm ,61,62,632 nanoparticles have been known since 1921 [2 is evident on 11 genera of filamentous fungi, 3 yeasts, 2 amoeba, 1 Apicomplexan, 1 diplomonad, 1 ciliate and 7 algae, including 1 diatom, fungal spores being generally more resistant than vegetative forms [Although the potential benefits of TiOnce 1921 , the abince 1921 ,66,67. Cve forms ,76,77,78As a result of the above presented, it is appreciated that it is of major interest to develop solutions to increase and improve the resistance of the surface of the constructions to the development of mold, thus contributing to the increase in the durability and sustainability of the constructions, whit the aim to achieve the goals of the concept of Sustainable Development.2 nanoparticles addition (up to 6%), and to identify the range of the concentration of nanoparticles in relation to the amount of cement, which provides effectiveness, from the point of view of the resistance of biological tissue.Therefore, the aim of this study is to assess the capacity of the increase in the resistance to the action of mold of white Portland cement cementitious composites, with various amounts of TiO2 nanoparticles addition, was prepared and conditioned according to 2 content). The TiO2 nanoparticles used were commercial AEROXIDE® TiO2 P25 by Evonik Degussa Industries AG, Hanau, Germany. According to the manufacturer’s Data Sheet, these TiO2 nanoparticles are characterized by an average particle size of 21 nm, with a specific surface of 35–65 m2/g, 99.5% purity, containing more than 70% anatase, with a minor amount of rutile and a small amount of amorphous phase anatase and rutile crystallites, both phases playing an important role in industrial applications and contribute to the photoactivation mechanism [Cementitious composites paste, with TiOechanism .2 nanoparticles have a very small density, which causes a large volume of material added to the initial volume of cement. It is therefore not possible to obtain a cementitious paste enriched with TiO2 nanoparticles under conditions of constant preservation of the amount of preparation water, without affecting the consistency and workability of the fresh material and, implicitly, the properties of the hardened material. Accordingly, the standard consistency of the paste, determined with the Tetmayer probe, was established as a constant parameter, and depending on it, the mixing water was determined for each individual cement/TiO2 nanoparticle ratio.Research carried out previously and in accordance with some specifications in the literature ,20,61,63The cementitious composite paste was poured into patterns, obtaining rectangular plates from which samples were extracted in the form of discs with a diameter of 17.4 mm, respectively, plates with dimensions 24 mm × 30 mm.These samples were subjected to photoactivation by holding for 24 h under the action of UV rays, using a light source with emission in the 400–315 nm spectrum, corresponding to the UVA band, located at a distance of 10 cm above the surface of the samples, which determined a luminous flux intensity of 860 lux.Aspergillus niger and the rectangular samples to an environment contaminated with Penicillium notatum spores.After photoactivation, the circular samples were exposed to an environment contaminated with In the laboratory, Petri dishes, φ 9 cm, were prepared, in which a nutrient subtract of Potato Dextrose Agar (PDA) was placed, known as a medium conducive to the growth of mold crops. The nutrient PDA substrate was prepared by dissolving the dehydrated substance in hot water (39 g/l) and pouring the resulting solution into the Petri dish. After cooling and curing of the PDA solution, the Petri dishes were sterilized 24 h under the action of UV rays.Aspergillus niger (FAg18003) and Penicillium notatum (Fag19002) have been used as a source of inoculum in Petri dish contamination experiments. Solutions of spores of Penicillium notatum, respectively, of Aspergillus niger were prepared form mold cultures by introducing 2 loops of 10 µL of biological material in 1 mL of distilled water. These types of mold were chosen for the study because of the high frequency with which they are encountered on the surface of the built environment, both inside and outside buildings, and because of the toxicity of emanated aflatoxins and the high frequency with regard to the reporting of population diseases arising from exposure to them [For testing the resistance of the cementitious composites to colonization with molds, two species of mold were used, extracted from selected homes. Both species were isolated, purified and maintained in the collection of microorganisms of the Microbiology discipline of the Faculty of Agriculture within USAMV Cluj–Napoca, Romania. Pure cultures of  to them ,16,20,21In each Petri dish with sterilized PDA nutrient substrate, 1.5 mL of mold spore suspension was applied and distributed so that the entire surface was covered with PDA, after which the photoactivated cementitious composite sample with nanoparticle addition was centrally placed under handling conditions that did not allow cross-contamination of the system. Subsequently, on the cementitious composite sample, 0.5 mL of spore suspension was applied, and the Petri dish lid was placed, the entire system was isolated on the edge with sealing tape to prevent cross-contamination.For each mold species, a growth system was also prepared that did not contain a cementitious composite sample. By continuously and evenly distributed growth of the mold film that has covered the entire surface of the nutrient medium, they constitute the viability control systems of the spore solutions used.®, Wetzlar, Germany).The growth systems thus prepared were placed in laboratory conditions, (23 ± 2 °C), (65 ± 5%) RH, natural lighting conditions. At regular intervals (24 h) the samples were examined visually and microscopically to identify signs of growth/development of the biological material and the development of the inhibition halo  was followed, recording its diameter (D), as an average of at least 5 measurements , using a2 shows in an environment contaminated with P. notatum spores, vs. environment contaminated with A. niger spores, eliminating the variable introduced by the size of the composite sample.Due to the difference in shape between the two sets of samples, the distance from the edge of the composite sample to the outer limit of the inhibition halo (d) was also measured simultaneously with the measurement of the diameter of the inhibition halo. This distance (d), expressed as average of minimum of five measurements, was considered a useful indicator in the resistance comparison test, expressed by the radius of action of the mold growth inhibition effect, which each cementitious composition with the addition of nano-TiO2 the following indicators were calculated:The percentage value, relative to the control sample, which represents the larger the diameter of the inhibition halo compared to the control’s inhibition diameter, (CPCM) calculated according to Equation (1):2 at 2, respective 3 days exposure in contaminated environment; 2, at 2, respectively 3 days exposure in contaminated environment; 2 at 2 days exposure in contaminated environment; 2 at i > 2 days exposure in contaminated environment.Reduction in the diameter of the inhibition halo over time (RDT) calculated according to Equation (2):For each exposure time and for each mixture of cementitious composite containing nano–TiOp < 0.05. This permits the usage of both means ± s.e., followed by letters which indicate the significant differences based on international standards for post-hoc tests. The data synthesis was exported in format.csv based on the functions available in the “broom” package. For the analysis of the specific resistance potential of each cementitious composite combination to colonization with both species of fungi, the main Component Analysis (PCA) based on the functions of the “vegan” package was applied [The data analysis was performed with different packages available in the RStudio software, on the R platform. The basic statistics were performed with the “psych” package, the averages and the standard error observed in each experimental variant analyzed were extracted. To assess the presence of significant differences between variants, the ANOVA test from the “agricolae” package was applied. Positive ANOVA tests allowed post-hoc exploration with the LSD test available in the same package. LSD analysis was applied dynamically; completely contaminated mold variants were removed from the analysis. This approach wanted to highlight the real differences between the tested mixtures that were successful in blocking the development of fungi. We preferred the LSD test for its potential to compare multiple variants, based on their differences at  applied ,81,82,832 in an environment contaminated with P. notatum and A. niger spores, respectively, showed that:A. niger spores in the control sample (0% TiO2) and in samples with 1% TiO2 and 2% TiO2, respectively, the diameter of the inhibition halo (D) decreases, completely disappearing after 5 days of exposure. The extinction of the inhibition halo was also observed on P8 sample (6% TiO2) after 6 days of exposure in the contaminated environment. In the case of samples containing 3.6%; 4%; 5% TiO2 in the cementitious matrix, the inhibition halo is maintained throughout the evaluation (28 days) in the case of contamination with A. niger spores (In case of exposure to an environment contaminated with r spores a.2), the diameter of the inhibition halo (D) decreases, completely disappearing after 3 days of exposure, in case of exposure to environment contaminated with P. notatum spores , the diameters of the inhibition halo (D) recorded for all nano-TiO2-containing cementitious samples are significantly higher, regardless of the duration of exposure in the contaminated environment, indicating good biocidal activity in both mold cases. Relative to the diameter of the control inhibition halo, it is observed that the diameters of the inhibition halo of all samples containing nano-TiO2 are greater by 28–38% at 2 days and by 40–50% at 3 days of exposure in the environment contaminated with P. notatum spores and by 18% at 2 days and by 15% at 3 days of exposure in the environment contaminated for cementitious samples containing 3–6% nano-TiO2, in the case of an environment contaminated with A. niger spores  or after 6 days , highlighting the composite samples with 3,6–5% nano–TiO2 showing the maintenance of the inhibition halo throughout the evaluation (28 days);With regard to the evolution over time of the inhibition halo, their diameter decreases for all tested specimens, reducing, compared to the values recorded after exposure 2 days in a contaminated environment, by 2–5% after 3 days, 10–17% after 4 days, up to 27–33% after 28 days exposure in environment contaminated with ver time c. In casver time c, evolveP. notatum, and isolated points with signs of initiation of mold growth after maintenance at least 7 days in an environment contaminated with A. niger;In the visual analysis, with the naked eye, under the incidence of natural light, on the surface of none of the samples of cementitious material tested there were no traces of mold development, in case of contamination with spores of ◦The inhibition zone extending circularly around the cementitious composite sample to a maximum distance equal to the diameter of the inhibition halo (D). In this area, the degree of contamination corresponds to the characterization “sterile” or maximum “1–10 colonies of microorganisms”◦The transition zone in which the biological charge, the density of mold colonies, increases as the distance from the edge of the cementitious composite specimen increases◦The area of intense growth, in the extremity of the analyzed system, in which the biological load, the density of mold colonies, is so great that independent units can no longer be identified, all being confluent with each other.Microscopic analysis of the surface of the samples, the inhibition halo, the medial areas and the areas removed from the composite sample within the entire test system (Petri dish with PDA growth medium and cementitious composite sample), revealed the presence of three major areas of contamination and growth of the biological material :◦The inhExperimental results on the behavior of the cementitious composites with the addition of TiOA. niger spores, for the same ratio of TiO2 introduced in the cementitious matrix , it was found that, in general, the measurable indicator (d) has a lower value in the case of the environment contaminated with s matrix . This fiTherefore, it is considered that the shape and dimensions of the tested samples can influence to some extent the quantitative indicators, but certainly cannot influence qualitatively the proof of the mold growth inhibition effect. By correlation with the literature, it is considered desirable to have a disc shape samples, especially for easier measurement of the dimensions characteristic of the inhibition halo, but even samples with other shapes can be tested for a qualitative proof of the anti–mold effect. This hypothesis is supported by the circular shape of the inhibition halo even in the case of rectangular shaped cementitious composite samples.A. niger (p < 0.001) at the beginning of the experiment and is significantly maintained until the 14th day . Transposed into average values of the halo, the range of variation is 7 mm between variants, with a maximum for P4–P8 mixtures, compared to P1–P3 mixtures. The differences between these two groups were significant. The same trend is maintained on the third day of experimentation, with an insignificant reduction in the diameter recorded. Starting from the fourth day of experimentation, significant differences can be observed between the tested samples. A halo of more than 30 mm can be observed only for P4–P7 mixtures, the others having values below 28 mm. The differences recorded are significant only when comparing the two groups with each other. An interesting case is mixture P8, which shows a reduction to 27.56 mm in diameter of the halo on this day. From the 5th day of experimentation, samples P1–P3 are completely affected by mold, similarly P8. Analysis of the capacity to restrict the development of the species A. niger  highligh2 in the cementitious matrix to ensure biocidal efficiency, i.e., the quantity of nanoparticles impressing the self–cleaning effect shall be sufficiently large to ensure an obvious and lasting biocidal effect, but not more than the concentration limits to ensure the possibility of homogeneous dispersion in the composite matrix and not induce a possible resistance reaction of the cell. The halo reduction dynamics at this point of the experiment only indicate mixture P7 capable of maintaining the halo above 31 mm, followed by P5 and P6 mixtures, with halos in the range 26–28 mm. Mixture P8 is placed between P5–P7 and P1–P4 mixtures as the level of maintaining the value of the halo.This observation contributes to the support of the hypothesis expressed above indicating the need to identify an optimal concentration range of nano–TiOA. niger. On this day, the P6 sample makes the transition between the P5 and P6 compositions, with significant differences only between these two mixtures. On the 7th day of experimentation, the P7 sample maintains its ability to stop the growth of fungi, but decreases over the next 7 days (day 14) by 5 mm. In the case of P5 and P6 mixtures, the observed restrictions on the diameter of the halo are much smaller and are maintained at a level below 1 mm in an interval of 7 days. From the 21st day of experimentation, no significant differences are observed between the mixtures, all of which maintain the halo at a level above 23–25 mm.From the 6th day, only three mixtures maintain their ability to repel A. niger, in the case of P. notatum there is a lower aggressiveness  the halo reduction trend is 1–2 mm, maintaining the differences between the experimental variants. From the 4th day of experimentation, mixture P1 is completely affected by fungi. The differences between the E variants keep small, the meanings being visible only when comparing mixtures P7–P8 with P5. On the 5th day, P7 maintains its repellency capacity, with significant differences from most mixtures except P2. The same mixture shows a sharp 8 mm reduction in the halo in the 24–hour interval between days 5–6, reaching the level of the other mixtures. 2.The differences between the experimental variants are significant only when comparing P5 with P8. On the 7th day of experimentation, only mixture P2 undergoes an average reduction in the halo by 5mm. In the case of the other mixtures the reduction is 1–2 mm, but without significant differences. The reductions remain insignificant, generally below the value of 0.5–1 mm/7 days, which indicates the performance of cementitious mixtures in the long term, regardless of the percentage of TiO2 particles integrated in the cementitious composite. The variance explained by both axes totals 98.57%, with a greater share of Axis 1 (91.39%) compared to Axis 2 (7.19%). In the case of P. notatum, the lack of TiO2 does not block colonization, the location on the PCA ordering being grouped in the basal part and at approximately equal distance from both axes. This aspect supports the lack of toxicity of cement to the installation of fungi. In the case of the species A. niger, the mixtures P5–P7, with high capacity to maintain the non-colonized surface, are highlighted. These three concentrations have the ability to block colony expansion and maintain this mechanism over a period of 4 weeks. Superimposed over Axis 2, in the case of the same species, concentrations of P1–P3 are observed, with reduced ability to block the mechanism of fungal expansion and loss of this property in the first 48–72 h after inoculation.The principal components’ analysis  highlighA. niger, but which lose this property after a week after inoculation. In the case of P. notatum, any concentration of TiO2 acts to block colony development up to a diameter of 20–25 mm around the colony. The differences between the concentrations are much smaller in this case, being defining as differentiation the rate of reduction in the protection area.In the upper part of the ordering are the concentrations of P4 and P8, both of which have an average capacity to block the development of The similarity between the concentrations of P2 and P7 is given by the ability to maintain the reduction in the halo in the same percentage range, from day to day. The concentrations P3–P4, P6 and P8, respectively, are located in the same area of the ordering; in each of them a value similar to P5 is observed.2 and to identify the concentration range of nanoparticles, in relation to the amount of cement, which provides an effective effect from the point of view of biological resistance. For this purpose, two species of mold, Aspergillus niger and Penicillium notatum, were used for colonization. Based on the presented results, the following can be said:All test systems showed three major zones of contamination and growth of biological material: the zone of inhibition halo ; the transition zone in which the biological load, the density of mold colonies, increases as the distance from the edge of the cementitious composite specimen increases and the zone of intense growth .P. notatum mold development were observed on the surface of any of the tested cementitious material samples. The surface of the cementitious composites exposed in an environment contaminated with A. niger showed isolated spots with signs of mold growth initiation, after conditioning for at least 7 days of testing.No traces of 2, the dimensions of the inhibition halo change to reduce them. Thus, in the case of A. niger it disappears completely after 5 days of testing for the control sample (P1) and for the mixtures P2 and P3  and after 6 days of testing for the sample P8 (6% TiO2). For P3, P4 and P5 composites  the inhibition halo is maintained throughout the testing period (28 days), showing dimensional reductions in the first 3–4 days, after which a relative stabilization is observed. In case of exposure to P. notatum spores contaminated environment the control sample P1 (0% TiO2) loses the inhibition halo after 3 days of testing but all TiO2-containing cementitious composites (P2–P8) the inhibition halo is maintained throughout the test.As the duration of exposure of the cementitious samples in the contaminated environment increases, depending on the content of nano–TiO2 content, respectively P1 (0% nano–TiO2) and P8 (6% nano–TiO2) following several hypotheses:◦2).Thus, (I) the hypothesis of the biocidal effect of photoactivation of nanoparticles in the cementitious matrix was confirmed based on the comparison of the characteristics of inhibition haloes compared to the control sample, P1 (0% nano-TiO◦2 in the cementitious matrix (II) was disproved by identifying the maximum functionality threshold, respectively, P7 (5% nano–TiO2), and by the less efficient behavior of the composite P8 (6% nano–TiO2). The behavior of this excess nanoparticle composite can be accepted on the basis of two hypotheses extracted in accordance with the specifications of the literature and which will be developed in future studies: (1) the difficulty of homogeneous dispersion of a large amount of nanoparticles in the cementitious matrix which results in the inhomogeneity of the composite with the existence of agglomeration areas of nanoparticles and areas with insufficient nano–TiO2 content and (2) the possibility that, some known biocidal treatment solutions, too high a concentration causes the cell to become insensitive. Analyzing CPCM and RTD in the case of P. notatum, a slight increase in this indicator for the analyzed mixtures was observed when using 6% nano-TiO2 addition, compared to 5%. However, it was assessed that this increase in the efficiency of the biocide effect is not necessarily sufficiently motivating for an increase in the concentration of nano–TiO2 to 6%, which also attracts an increase in production costs. Moreover, it can be said that for different species of mold, the effectiveness of the addition of TiO2 nanoparticles reacts differently and detailed research is needed for each individual case.The hypothesis of increasing the proportional and continuous biocidal effect, with the increase in the content of nano–TiO◦2 into the cementitious matrix automatically induces a capacity for resistance to mold growth, regardless of its species Type (III) is disproved by two observations as follows: (1) an insufficient amount of nanoparticles does not ensure the maintenance of the inhibition halo (see behavior of mixtures P2 (1% TiO2), P3 (2% TiO2) exposed in a contaminated environment with A. niger) and therefore does not ensure the durability of the biocidal effect and (2) the resistance to mold development differs according to its species, as demonstrated by comparing the behavior of composites with the same content of nano-TiO2 exposed in each of the two contaminating media.In addition, the hypothesis that the introduction of some amount of nano–TiOThe mix–design of cementitious composites mixtures included two extreme variants of nano–TiOThe differentiation of the shape/dimensions of the tested samples contributed to the evaluation of the acceptability of the hypothesis (IV) that considers that the geometric aspects of the tested cementitious composite sample are defining for the quantitative and qualitative indicators of evaluation of the biocidal effect. In this sense, it can be said that the geometric aspects influence to some extent the quantitative indicators, but, certainly, cannot influence qualitatively the proof of the effect of inhibition of mold growth, a statement supported by the circular shape of the inhibition halo  even in the case of cementitious composite samples with rectangular shape. However, in order to facilitate and increase the accuracy of measurements and quantitative evaluation, a disc shape of the test specimens was considered desirable.Statistical analysis of quantitative performance evaluation indicators  was a useful tool for supporting decisions to confirm or refute the previously mentioned hypotheses. The results obtained experimentally and analyzed statistically open a new direction in the continuation of experimental researches aimed at maintaining the ability to inhibit the development of fungi even after the action of the aging process, the small concentrations having the chance of not inducing resistance to biocide action over time.The aim of this work was to analyze the mold inhibition capacity presented by cementitious composites based on white Portland cement with the addition of nano–TiO2 content, in addition to the self-cleaning effect demonstrated by numerous researches reported in the literature, the increased and lasting resistance to mold development is a proven property, which, however, is dependent on both the compositional characteristics of the material and the mold species. As such, it is considered necessary to continue the development of the experimental research in this direction, which are both types of cement, and the nanoparticles are different from those used in the present study, as well as other species of fungi, algae, fungi, etc., the development of which it is commonly found on the surface of the built environment, all of which contribute to the increase in the safety and health of the population, as well as to increase the sustainability of the construction industry and, consequently, to the reduction in the pollution of the environment.As a result of those presented, it can be appreciated that in the case of cementitious composites with nano-TiO


Aiming at the problem of highly toxic Nitrogenous disinfection by-products (N-DBPs) produced by disinfection in the process of drinking water, two-point influent activated carbon-quartz sand biofilter, activated carbon-quartz sand biofilter, and quartz sand biofilter are selected. This study takes typical N-DBPs Dichloroacetonitrile (DCAN) as the research object and aromatic amino acid Tyrosine (Tyr), an important precursor of DCAN, as the model precursor. By measuring the changes of conventional pollutants in different biofilters, and the changes of Tyr, the output DCAN formation potential of the biofilters, this article investigates the control of DCAN generation of the two-point influent activated carbon-quartz sand biofilter. The results show that the average Tyr removal rate of the three biofilters during steady operation is 73%, 50%, and 20%, respectively, while the average effluent DCAN generation potential removal rate is 78%, 52%, and 23%, respectively. The two-point influent activated carbon-sand biofilter features the highest removal rate. The two-point water intake improves the hypoxia problem of the lower filter material of the activated carbon-quartz sand biofilter, and at the same time, the soluble microbial products produced by microbial metabolism can be reduced by an appropriate carbon sand ratio, which is better than traditional quartz sand filters and activated carbon-quartz sand biofilters in the performance of controlling the precursors of N-DBPs. The disinfectant used in the process of drinking water disinfection will react with most natural organic matter as well as producing harmful Disinfection by-products (DBPs) . DCAN, aIn recent years, the application of biological filtration in the advanced treatment of drinking water has gradually risen. The effectiveness of biologically active filtration for denitrification and the removal of DBPs precursors has been confirmed in most studies , but theThe test device is shown in As the biofilter adopts the method of inoculation and film hanging, the inoculated sludge is taken from the secondary sedimentation tank of the municipal sewage plant. Each filter column is inoculated with 1 L sludge, and the sludge concentration during inoculation is 2 g MLVSS/L. The experiment makes use of artificial water distribution, and the water quality of the experiment refers to the effluent from the sedimentation tank of The Ningbo Water Plant. Gu et al.  found th4+-N is measured by Nessler’s reagent photometric method; NO2−-N is measured by N-(1-naphthyl)-ethylenediamine photometric method; NO3−-N is measured by UV spectrophotometry; Total nitrogen (TN) is measured by alkaline potassium persulfate digestion UV spectrophotometry; Chemical oxygen demand (COD) is measured by standard potassium dichromate method; Dissolved oxygen (DO) and pH value are measured by portable analyzer; turbidity is measured by turbidity meter. The biomass is determined by the phospholipid method [Collect influent and effluent samples of three biofilters every day. The water sample is filtered with 0.45 μm fiber membrane before analysis, and each water sample is measured 3 times. NHd method  and the Tyr analysis is measured by Hitachi L8900 automatic amino acid analyzer. Put 50 mL of the water sample into a centrifuge tube, pretreat the water sample with a rotary evaporator, concentrate it for 10 times, inject the mixed amino acid standard working solution and sample determination solution of the same volume into the amino acid automatic analyzer, and calculate the Tyr concentration in the sample determination solution by the external standard method through the peak area.The DCAN formation potential is measured by a fully chlorinated method , ShimadzC—Cl2 dosage, mg/L;Among them: C1—DOC, mgC/L;C2—NH3 concentration, mgN/L.3 buffer, store it at 25 °C away from light and at a constant temperature for 24 h, and then add ascorbic acid to remove the residual chlorine in the water sample. Then take 50 mL of water sample with a 50 mL centrifuge tube, add 5 g of anhydrous sodium sulfate, put it on the vibrator for full shaking for 1 min, add 5 mL of extractant methyl tert butyl ether for liquid-liquid extraction and enrich DCAN in the water sample. The chromatographic column was used for DCAN detection. The formation potential of DCAN was measured by the modified EPA551.1 method. The sample inlet is 200 °C, the detector is 290 °C, the temperature rise procedure is 35 °C, hold for 10 min, then raise the temperature to 145 °C at 10 °C/min for 2 min, and then raise the temperature to 260 °C at 20 °C/min for 5 min.Fully mix after chlorination, adjust the solution to pH = 7 with NaHCOMicroorganisms were analyzed by high-throughput sequencing . On the 4+-N concentration on the inlet and outlet water of the biofilter. The effluent NH4+-N concentration of the biofilter gradually stabilizes in about 30 days, and the effluent NH4+-N concentration is between 0.14 and 0.47 mg/L, while the NH4+-N removal rate is above 60%. The average removal rate of TN in the biofilter is shown in p < 0.05), and filter C possesses the best nitrogen removal effect. Denitrification produces N2, organic nitrogen or inorganic nitrogen, which is used and transformed by microorganisms into N element in microbial cells for microbial growth and reproduction, which are all possible ways to remove TN.During the test period, After filtration, the turbidity of the effluent from the three filters was significantly reduced c, and thMn in the effluent of the biofilter are shown in p < 0.05). The Tyr concentration of biofilter effluent is lower than that of influent, which is inconsistent with the conclusion made by Liu et al. [Mn removal rate is consistent with that of average effluent Tyr removal rate. The CODMn removal rate can reflect the removal of organic matter in the biofilter. Tyr is an organic matter, and its molecular structure contains reducing phenolic hydroxyl and amino groups, which can be oxidized by potassium permanganate. Therefore, the CODMn removal rate can also be applied as the basis of Tyr removal. Meanwhile, except for the influent mode, other conditions of filter B and C are the same, but the organic matter removal effect of filter C is significantly better than that of filter B, indicating that the two-point influent improves the organic matter removal rate of biofilter.The average removal rates of Tyr and CODu et al. , who rec4+-N, NO3−-N and NO2−-N in water are also important sources of nitrogen in N-DBPs. Therefore, the SMPS produced by the internal microbial action of the biofilter and other organic matter in the effluent and even NO3−-N and NO2−-N may be the precursors of DCAN, affecting the effluent DCAN formation potential.The formation potential for DCAN in the influent and effluent of the biofilter is shown in S produced by microorganisms will accumulate and release. The adsorption performance of activated carbon is stronger than that of quartz sand, and the number and activity of microorganisms in the activated carbon-quartz sand biofilter are also stronger than that of quartz sand biofilter. Therefore, the impact of continuous operation on activated carbon-quartz sand biofilter is higher than that of quartz sand biofilter.Backwashing will also impact the formation potential for DCAN in the effluent of biofilter. S released by bacteria [S is also the reason for the increase in Tyr concentration in the lower layer of the filter. The influent of filter C at the depth of 20 cm brings in DO, which increases the DO at 20 cm depth , which is consistent with the removal rate of CODMn. The utilization of organic matter by the biofilter increases with the increase of DIN loss, indicating that the DIN loss phenomenon in the reaction is related to filter denitrification [Nitrogen in drinking raw water mainly exists in the form of NHnitrogen . Most offication .2, and microbial growth in the filter consumes some N elements, which will cause DIN loss. At the same time, organic nitrogen conversion will make up for DIN loss to a certain extent. There is a certain linear correlation between the variation of Tyr in the effluent of the three biofilters and the nitrogen loss in the filter, and the correlation coefficients of the biofilters are: Filter A (0.44), Filter B (0.63) and Filter C (0.73). The correlation coefficients of biofilters are between 0.3 and 0.8, indicating that there is a certain correlation between the loss of DIN and the change of Tyr in the three biofilters. Some scholars have confirmed that the amount of DIN loss is positively correlated with NH4+-N concentration, and increases with the increase of NH4+-N concentration [4+-N. it is speculated that Tyr will be degraded by ammoniation in the biofilter to produce NH4+-N. It is confirmed from the side that part of Tyr is removed by ammoniation. In the meantime, it is only correlated but not strongly correlated, indicating that Tyr can also be removed by other means. Among the three types of filters, filter C has the strongest correlation, and filter A has the weakest correlation.The reactions related to nitrogen transformation in the biofilter mainly include nitrification, denitrification, ammoniation, and so on. The oxygen in the upper part of the filter is sufficient, and the nitrification reaction is mainly carried out in the upper part of the filter. The oxygen in the lower part of the filter is insufficient, and the denitrification reaction is mainly carried out in the lower part of the filter. The ammoniation of Tyr degradation can occur in all stages along the biofilter, and the reaction generates ammonia nitrogen to realize the transformation from organic nitrogen to inorganic nitrogen. Denitrification produces Nntration . From thIt’s shown in Proteobacteria, Planctomycetes, Bacteroidetes, Firmicutes, Chloroflexi, Actinobacteria, and Chlorobi, among which, Proteobacteria can use organic matter as nutrition [Bacteroidetes is also considered to be very important to the degradation process of organic matter [Actinobacteria can also remove nitrogen-containing organic matter, so it is speculated that they are related to the degradation and removal of Tyr. The bacterial phylum involved in the removal of Tyr in the sample is discussed and analyzed separately, as shown in The microbial community structure of the sample of the phylum level is shown in utrition , particiutrition . Bacteroc matter . Studies4+-N and turbidity) and organic pollutants (CODMn and Tyr); the average NH4+-N removal rate is 80%, turbidity is 80%, CODMn is 49%, and Tyr is 73%. The two-point influent activated carbon-quartz sand biofilter has the best control effect on the formation of DCAN. The removal of Tyr in the biofilter is concentrated on 0~30 cm in the upper part of the filter. DO decreases along the upper part of the filter, and then stabilizes, and the total biomass of the two-point influent charcoal-sand biofilter is the largest. The correlation coefficient between DIN loss and Tyr change in the two-point influent activated carbon-quartz sand biofilter is 0.73, which possesses the highest correlation, and its biochemical property is the highest, which is beneficial to the removal of precursors. The total abundance of bacteria related to Tyr removal in two-point influent activated carbon-quartz sand biofilter is the highest among the three filters.The two-point influent activated carbon-quartz sand biofilter is superior to other filters in removing conventional pollutants (NH