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Agricultural soils have been identified as sinks for microplastic fibers; however, little information is available on their long-term fate in these soils. In this study, polyester and nylon fibers were precisely cut to relevant environmental lengths, using novel methodology, and their behavior in sand columns was studied at environmental concentration. The longer fibers (50 μm) accumulated in the upper layers of the sand, smaller fibers were slightly more mobile, and nylon showed marginally higher mobility than polyester. Previous studies have overlooked changes in microplastic morphology due to transport in soil. Our study is the first to show that fibers exhibited breakage, peeling, and thinning under flow conditions in soil, releasing smaller, more mobile fragments. Furthermore, the peelings exhibited different adsorption properties compared to the core fiber. This suggests that microplastic fibers can become a source of smaller micro(nano)plastics and potential vectors for certain molecules, risking continuous contamination of nearby soils, surfaces, and groundwater.

A multi-functional, self-regenerating material was designed to adsorb and biodegrade formaldehyde from water in a simple, one-step process. The material is based on montmorillonite clay, polyethyleneimine and formaldehyde-degrading Pseudomonas putida, and has three unique functions which facilitate bioremediation: a. selectively adsorbs formaldehyde to reduce cytotoxicity, b. buffers the solution to allow efficient biodegradation, and c. self-cleans through slow release of formaldehyde and subsequent degradation by the attached bacteria, allowing regeneration and long-term use of the material. A polyethyleneimine-clay composite was optimized to carry positive surface charges and a high concentration of functional amine groups, which facilitated formaldehyde adsorption and bacterial adhesion. Formaldehyde binding was specific, yet reversible and pH dependent; binding fitted the Langmuir model and had a qmax of 62 mg·g−1 composite. A formaldehyde-degrading Pseudomonas putida strain was then immobilized on the positively charged composite through electrostatic interactions. The efficiency of the resulting bio-composite was demonstrated for multiple successive treatment cycles, with degradation rates as high as 1600 mg·L−1·FA·h−1. This self-regenerating one-step process is a promising solution to the challenging drawbacks of formaldehyde remediation and could also help design other adsorption-degradation platforms for wastewaters that demand complicated treatment strategies.

In this study, a comparative activity assessment of several activated carbon (AC) and AC-Fe

Iron-clay-cyclodextrin composites were designed as sorbent catalysts to adsorb and oxidize pollutants from water. The clay-iron backbone served as a mechanical support and as a heterogeneous Fenton catalyst, and the cyclodextrin monomers or polymers cross-linked with polyfluorinated aromatic molecules were used to accommodate adsorption of the pollutants. The composite based on iron-clay-cyclodextrin-polymers (Fe-MMT-βCD-DFB) exhibited superior adsorption and degradation of the model pollutants, bisphenol A (BPA), carbamazepine (CBZ), and perfluorooctanoic acid (PFOA), compared to the monomer-based composite and the native iron clay. The variety of adsorption sites, such as the polyfluorinated aromatic cross-linker, cyclodextrin toroid, and iron-clay surface, resulted in high adsorption affinity toward all pollutants; BPA was primarily adsorbed to the cyclodextrin functional groups, CBZ showed high affinity toward the Fe-MMT surface and the Fe-MMT-βCD-DFB composite, whereas PFOA was adsorbed mainly to the βCD-DFB polymer. Degradation, using H2O2, was highly efficient, reaching over 90% degradation in 1 h for BPA and CBZ and ∼80% for PFOA. The composite also showed excellent degradation efficiency in a multicomponent system with all three model pollutants. Furthermore, the composite's activity remained steady for five consecutive cycles of adsorption and degradation. The ability to remediate a broad range of pollutants, and the high overall removal exhibited by this novel material, demonstrates the potential for future application in water remediation technologies.

Fenton-like reactions at near neutral pHs are limited by the slow reduction of ferric species. Enhancing generation of from solid peroxides is a promising strategy to accelerate the rate-limiting step. Herein, the H

The properties of clays and oxides govern many environmental processes, consequently, ongoing effort is invested in developing non-destructive, in-situ analytical tools that reflect these properties. Herein, the physicochemical properties of montmorillonite (MMT) and iron-oxide coated montmorillonite (FeOx-MMT) were characterized using common analytical techniques, and the results were compared to spectral induced polarization (SIP) measurements. FeOx-MMT particles showed a lower CEC, higher pH dependency of the surface charge, and lower suspension stability. Also, the size of the primary particles increased following iron-oxide deposition. SIP measurements over a range of salinities showed that the effective polarization length of the clays was in the order of several microns, suggesting the measurements of aggregates (not primary particles). Moreover, FeOx-MMT particles were more compact than MMT, and their size decreased with increasing salinity due to compaction of the EDL and arrangement of primary particles in the aggregate. The SIP-response to pH changes agreed with zeta potential measurements; at low pH values, MMT exhibited higher polarization due to the higher CEC. However, at a high pH, the differences diminish due to deprotonation of the Fe-OH surface groups. These findings suggest that SIP is a sensitive method that can detect changes in the surface chemistry of soil particles.

Removal and separation of cyanobacteria is of interest from both environmental and industrial standpoints. Flocculation and sedimentation using clay minerals can be advantageous, however, long-term effects such as resuspension of live bacteria or membrane damage, can be detrimental to these processes. In this respect, the effect of cocultivation of clays with cyanobacteria (CB) on aggregation trends and viability and consequently on separation processes is still largely unknown. In this study, Anabaena PCC 7120 was cultivated in the presence of relevant types of clays and clay composites, to observe their impact on growth, activity, and clay-CB complexation over time. Growth and activity of CB were monitored by looking at chlorophyll content and ammonia production. Clay-CB aggregation trends, extent, and morphology were assessed by measuring the decline of optical density over time, monitoring changes in zeta potential, and characterization using light and electron microscopy. The results revealed that CB grown in the presence of native Ca-montmorillonite and kaolinite suffer only a minor hindrance in growth rate and activity but undergo rapid sedimentation. Humic acid coated clay only slightly hindered growth yet inhibited sedimentation significantly. In contrast, chitosan and iron oxide coating caused damage to the cell membrane and CB death after several days. In terms of sedimentation, chitosan coated clays produced large flocs (up to 400 µm) and achieved high sedimentation rates of 46% after 3 min. Iron-oxide coated clays created the largest apparent aggregates (∼600 µm floc size) and exhibited the fastest sedimentation rates, 73% after 3 min and 87% after 30 min. The results stress the importance of looking at cocultivation with the different particles, since viability is not a priori hindered by aggregation, as in the case of native and humic-acid coated clays. On the other hand, chitosan and iron coated clays were both bactericidal and excellent flocculants. Thus, these findings can advance and improve the design of CB separation and removal strategies in natural and engineered systems.

E. coli cells overexpressing the enzyme atrazine chlorohydrolase were coated using layer-by-layer self-assembly. The polymeric coating was designed to improve the surface properties of the cells and create positively charged, ecologically safe, bio-hybrid capsules that can efficiently degrade the herbicide atrazine in soils. The physio-chemical properties of the bacteria/polymer interface were studied as a function of the polymeric composition of the shell and its thickness. Characterization of cell viability, enzyme activity, morphology, and size of the bio-capsules was done using fluorescence spectroscopy, BET and zeta potential measurements and electron microscopy imaging. Out of several polyelectrolytes, the combination of polydiallyldimethylammonium chloride and polysodium 4-styrenesulfonate improved the surface properties and activity of the cells to the greatest extent. The resulting bio-hybrid capsules were stable, well-dispersed, with a net positive charge and a large surface area compared to the uncoated bacteria. These non-viable, bio-hybrid capsules also exhibited a kinetic advantage in comparison with uncoated cells. When added to soils, they exhibited continuous activity over a six-week period and atrazine concentrations declined by 84%. Thus, the concept of layer-by-layer coated bacteria is a promising avenue for the design of new and sustainable bioremediation and biocatalytic platforms.

In the following study the tetrameric enzyme, aldehyde dehydrogenase (ALDH - 228 kDa), was immobilized on montmorillonite using polyethyleneimine (PEI) as a bridging agent. Previous studies have shown that small enzymes such as laccases and peroxidases exhibit increased stability and enhanced activity over time when immobilized on the surface of clay minerals. However, low-cost immobilization methods for high MW, multimeric enzymes, are lacking because these enzymes are prone to disassociation and deactivation upon adsorption. Herein, ALDH was successfully immobilized by pre-stabilization with a polyelectrolyte prior to adsorption on the surface of montmorillonite. The resulting complex was characterized in terms of enzyme conformation and loading using zeta potential, SEM, FTIR, and TGA measurements. Aldehyde transformation activity was measured by following benzaldehyde transformation to benzoic acid and NADH formation. An optimal ALDH:PEI ratio of 4:1 (w/w) was identified, yielding the highest activity at the adsorbed state due to conformational stability. The adsorption isotherm best fit the dual Langmuir-Freundlich model and revealed a significantly high loading capacity of 6.2 mg protein per mg montmorillonite. Rate experiments showed that although activity was maintained at the adsorbed state, the immobilization slowed aldehyde transformation, probably due to diffusion limitations caused by aggregation and heterogeneity of the material. Overall, the results suggest that this method has the potential to efficiently immobilize large multimeric proteins. This in turn can help solve separation issues and advance the design of efficient platforms for bio-catalysis and bioremediation technologies.

Fenton-like reactions at near neutral pHs are limited by the slow reduction of ferric species. Enhancing generation of from solid peroxides is a promising strategy to accelerate the rate-limiting step. Herein, the H2O2 release and Fenton-like reactions of four solid peroxides, MgO2, CaO2, ZnO2 and urea hydrogen peroxide (UHP), were investigated. Results indicated that UHP can release H2O2 instantly and show a similar behavior as H2O2 in the Fenton-like reactions. MgO2 released H2O2 quickly in phosphate buffered solutions, which was comparable to CaO2 but faster than ZnO2. Metal peroxides induced higher initial phenol degradation rates than UHP and H2O2 when the same theoretic H2O2 dosages and Fe(III)-EDTA were used. MgO2 displayed a superior performance for phenol degradation at pH 5, resulting in more than 93% phenol reduction at 1.5 h. According to kinetic analyses, the generation rate of in the MgO2 system was 18 and 3.4 times higher than those in ZnO2 and CaO2 systems, respectively. The addition of MgO2 significantly promoted H2O2 based Fenton-like reactions by increasing production of , and the mixture of MgO2 and H2O2 had an improved utilization efficiency of active oxygen than the MgO2 system. The findings suggested the critical roles of metal peroxides in favoring Fenton-like reactions and inspired strategies to simultaneously accelerate Fenton-like reactions and improve utilization efficiency of active oxygen.

Catalyzed hydrogen peroxide propagation (CHP) processes are widely applied for the remediation of petroleum hydrocarbon contaminated soils, but greatly limited by the rapid decomposition of H2O2. Although phosphate stabilizer can extend the lifetime of H2O2 in the soil systems, it is unclear about the effect of stabilizers on the processes with different exogenous iron species that are frequently added to accelerate the Fenton-like reactions. Herein, calcium superphosphate (CAP) was used as a H2O2 stabilizer in the modified-Fenton treatment of the diesel spiked soil with two exogenous iron species, a citrate chelated ferric complex (IC) and an iron mineral (γ-Fe2O3 immobilizing on montmorillonite, IB). A ratio of CAP to soil (RCS) at 1/10 can retain 49% of H2O2 within 24 h in the soil. The diesel removal efficiency in the IC based process reached 70% at 10 h after adding 480 mM H2O2 when IC and RCS were 90 mM and 1/10, which is much higher than that in the IB based process. In the latter system, only 23% diesel removal can be achieved at 48 h after adding the same dosage of H2O2 and CAP. This can be attributed to the higher concentration of hydroxyl radicals produced in the former process. The O2 detection showed that CAP can effectively retard H2O2 decomposition into O2 in the both processes. A relatively high dosage of CAP should be applied in the IC process to retain H2O2 and extend ·OH production for diesel degradation, while a relatively low dosage of CAP can promote the diesel removal by altering the O2 production through a superoxide radical mediated pathway.

Adsorption and redox reactions between organic matter and natural reactive surfaces have a significant impact on pollutant sequestration and transformation, and on the effectivity of water and soil remediation practices. Herein, the interactions between an organic phenolic acid, gallic acid (GA), and clay coated with iron oxides (FeOx-MMT), were explored. Adsorption and desorption experiments revealed that GA has a higher affinity for FeOx-MMT than for native clay. The adsorption to FeOx-MMT was irreversible and only slightly affected by salinity, suggesting strong inner-sphere complexation. The GA-FeOx-MMT complex was characterized using cyclic-voltammetry, UV–Vis spectroscopy, FTIR, and XPS measurements. The results showed oxidation and transformation of GA on the surface and a considerable reduction of the surface iron. The resulting GA-FeOx-MMT complex had increased catalytic properties, enhancing hydrogen peroxide decomposition, and creating significantly more radicals than FeOx-MMT and raw clay. This led to the destruction of GA on the surface of the clay-iron complex, resulting in loss of activity over time. Our findings suggest a correlation between overall GA adsorption, consequent iron reduction and oxidant decomposition. This means that in systems where such constituents are present, these types of interactions need to be taken into consideration in terms of predicting the fate of pollutants in the environment, and for properly evaluating soil and water chemical treatment processes.

The adsorption of organic pollutants to a novel adsorbent–polyvinyl-pyridine- co -styrene–montmorillonite nanocomposite was quantified and modeled. To elucidate the adsorption mechanisms, experimental methods and QSAR analysis were combined, searching for correlations between the pollutant-nanocomposite adsorption coefficient ( k d ) and pollutant chemical–physical properties. The adsorption isotherms at a wide range of concentrations were fitted to the Freundlich equation and the log k d values were extracted at a low, environmentally significant, concentration. A significant regression was achieved with QSAR, predicting adsorption affinity by four meaningful descriptors: adsorption was positively correlated to heat of formation, number of hydrogen acceptor groups and the partitioning coefficient, and was negatively correlated to molecular mass. The resulting model predicted log k d for test pollutants with an average deviation of only 0.77 log units from the experimental values. Consequently, this method could be applied to better understand adsorption mechanisms and to screen for compatibility between pollutants and a variety of novel and commonly used adsorbents.

Biodegradation by cells encapsulated in silica gel is an economical and environmentally friendly method for the removal of toxic chemicals from the environment. In this work, recombinant E. coli expressing atrazine chlorohydrolase (AtzA) were encapsulated in organically modified silica (ORMOSIL) gels composed of TEOS, silica nanoparticles (SNPs), and either phenyltriethoxysilane (PTES) or methyltriethoxysilane (MTES). ORMOSIL gels adsorbed much higher amounts of atrazine than the hydrophilic TEOS gels. The highest amount of atrazine adsorbed by ORMOSIL gels was 48.91×10-3μmol/mlgel, compared to 8.71×10-3μmol/mlgel by the hydrophilic TEOS gels. Atrazine biodegradation rates were also higher in ORMOSIL gels than the TEOS gels, mainly due to co-localization of the hydrophobic substrate at high concentrations in close proximity of the encapsulated bacteria. A direct correlation between atrazine adsorption and biodegradation was observed unless biodegradation decreased due to severe phase separation. The optimized PTES and MTES gels had atrazine biodegradation rates of 0.041±0.003 and 0.047±0.004μmol/mlgel, respectively. These rates were approximately 80% higher than that measured in the TEOS gel. This study showed for the first time that optimized hydrophobic gel material design can be used to enhance both removal and biodegradation of hydrophobic chemicals.

The presence of nitrate and other redox-active anionic contaminants in terrestrial ecosystems poses a significant risk to humans and other forms of life on Earth. The purpose of the present study was to test a potential in situ system, using poly-(D) glucosamine (chitosan) adsorbed to mineral surfaces under redox-active conditions in order to degrade nitrate to lower oxidation states. Chitosan is a linear polysaccharide derived from the chitin found in the shells of shrimp and other shellfish. Five different loadings of chitosan (0, 0.075, 0.25, 0.50, and 1.0 g/L; labeled C0, C1, C2, C3, and C4, respectively) were adsorbed to ferruginous smectite (SWa-1) to form chitosan-SWa-1 composites (CSC) in the pH range 5.8–4. The CSC was then reduced by Na2S2O4 in a citrate-bicarbonate buffered dispersion and washed free of excess salts under inert-atmosphere conditions. Upon addition of the nitrate, the solution pH remained slightly acidic, ranging from 5.5 to 4.7. Samples were analyzed for Fe(II) content, reacted with a NaNO3 solution, and then re-analyzed for structural Fe(II) content. Supernatant solutions were analyzed for nitrate, nitrite, and ammonium. In samples C1 to C4, extensive concentrations of nitrite were observed in the supernatants with a corresponding increase in the reoxidation of structural Fe(II), proving that a coupled redox reaction had occurred between the nitrate and the structural Fe in the clay mineral. The most efficient loading, defined as the largest percentage of adsorbed nitrate reduced to nitrite, occurred in sample C1. The total amount of nitrate reduced and Fe(II) reoxidized followed the trend 0 = C0 < C2 < C3 < C4 ≈ C1. Chitosan showed the potential to reverse the surface charge of constituent clay minerals, thereby enabling the CSC to remove nitrate anions from aqueous mineral systems via redox reactions with structural Fe(II) in clay minerals.

Curli are amyloid fibrils that polymerize extracellularly from curlin, a protein that is secreted by many enteric bacteria and is important for biofilm formation. Presented here is a systematic study of the effects of curli on bacteria-clay interactions. The aggregation trends of curli-producing and curli-deficient bacteria with clay minerals were followed using gradient-sedimentation experiments, Lumisizer measurements, bright-field and electron microscopy. The results revealed that curli-producing bacteria auto-aggregated into high-density flocs (1.23 g/cm3), ranging in size from 10 to 50 μm, that settle spontaneously. In contrast, curli-deficient bacteria remained relatively stable in solution as individual cells (1–2 μm, 1.18 g/cm3), even at high ionic strength (350 mM). The stability of clay suspensions mixed with curli-deficient bacteria depended on clay type and ionic strength, the general trends being consistent with the classic DLVO theory. However, suspensions of curli-producing bacteria mixed with clays were highly unstable regardless of clay type and solution chemistry, suggesting extensive interactions between the clays and the bacteria-curli aggregates. SEM measurements revealed interesting differences in morphologies of the aggregates; montmorillonite particles coated the bacterial auto-aggregates whereas the kaolinite platelets were embedded within the larger curli-bacteria aggregates. These new observations regarding the densities, aggregation trends, and morphologies of bacteria-curli and bacteria-curli-clay complexes make it clear that production of surface appendages, such as curli, need to be considered when addressing the fate, activity and transport of bacteria - particularly in aquatic environments.

Pyrene removal by polycation-montmorillonite (MMT) composites and granulated activated carbon (GAC) in the presence of humic acid (HA) was examined. Pyrene, HA, and sorbent interactions were characterized by FTIR, fluorescence and zeta measurements, adsorption, and column filtration experiments. Pyrene binding coefficients to the macro- molecules were in the order of PVPcoS (poly-4-vinylpiridine-co-styrene) > HA > PDADMAC (poly diallyl-dimethyl-ammonium-chloride), correlating to pyrene-macromolecules compatibility. Electrostatic interactions explained the high adsorption of HA to both composites (∼100%), whereas HA adsorption by GAC was low. Pyrene removal by the composites, unlike GAC, was enhanced in the presence of HA; removal by PDADMAC-MMT increased from ∼50 (kd = 2.2 × 10 3 kg/L) to ∼70% (kd = 2.4 × 10 3 kg/L) in the presence of HA. This improvement was attributed to the adsorption of pyrene-HA complexes. PVPcoS-MMT was most efficient in removing pyrene (kd = 1.1 × 10 4 kg/L, >95% removal) which was explained in terms of specific π donor−π acceptor interactions. Pyrene uptake by column filters of GAC reached ∼50% and decreased to ∼30% in the presence of HA. Pyrene removal by the PVPcoS-MMT filter was significantly higher (100−85% removal), exhibiting only a small decrease in the presence of HA. The utilization of HA as an enhancing agent in pollutant removal is novel and of major importance in water treatment.

Removal of humic acid (HA) from water by octadecyltrimethyl-ammonium (ODTMA) micelle–montmorillonite (MMT) composites and by granulated activated carbon (GAC) was studied in dispersion and by filtration. FTIR measurements emphasized that the ODTMA micelle–clay-mineral composite differs from the ODTMA monomer-clay-mineral one. HA adsorption by GAC in dispersion was moderately reduced from 100% initially to 75% with an increase in HA concentrations. In contrast, the fractions adsorbed by the composite increased monotonically with HA concentrations from very low adsorption up to 80%. This effect was explained by the presence of a small concentration of ODTMA monomers in dispersion, which adsorbed on the negatively charged HA and partially neutralized it, or caused charge reversal, which in turn inhibited HA adsorption by the positively charged composite. This effect was verified by mobility measurements and was found to be more pronounced at low HA concentrations. This trend of increase in HA removal with an increase in HA concentration (3 and 10 ppm) was also observed in filtration (50% and 85% removal, respectively), when employing columns of the composite mixed with sand (to improve flow). Throughout the experiment the removal of high HA concentration (10 ppm) by the composite filter remained ~ 80% whereas, the removal by the GAC filter decreased from an initial 80% removal to a complete recovery of the HA (no removal) after the passage of 20 L (200 pore volumes). Upon applying sand of higher quality in the columns the removal of low HA concentrations was nearly complete by the composite column while the GAC only slightly contributed to its removal (for a passage of 100 L (1000 pore volumes)).

A systematic study was carried out to characterize the adsorption of organic cations as monomers, micelles, or polymers on montmorillonite by monitoring zeta potential (ξ) as a function of cation loading on the clay. In general, the clay's ξ became less negative as cation loading increased. A fairly good linear correlation between adsorption of organic cations on the clay, up to the cation exchange capacity (CEC) of the clay, and ξ potential of the composites was fitted. However, when the adsorption of the larger cation exceeded the CEC, a nonlinear increase in ξ was measured. The degree of this increase corresponds to the cation size and affinity to the clay (in the order surfactant

article i nfo Phenolic compounds pose health and environmental hazards. This study focused on two priority pollutants, trinitrophenol (picric acid—PA) and trichlorophenol (TCP), which were detected in rivers, lakes and water reservoirs. Polycation-clay mineral nanocomposites were characterized and designed for the removal of these pollutants from water. The adsorption kinetics of polydiallyl dimethylammonium chloride (PDADMAC) and poly-4-vinylpyridine-co-styrene (PVPcoS) on montmorillonite (MMT) was significantly faster (2- 4h ) than on sepiolite (3-4 days), which was explained by the latter's porous structure. Consequently, polycation-MMT composites were chosen to test pollutant adsorption. Both PA (anionic) and TCP (non- ionic) showed higher affinity to the less charged polycation PVPcoS (40% of the monomers charged) than to the highly charged polycation PDADMAC. However, PA removal by the PVPcoS-MMT composite was nearly complete whereas TCP removal reached 40 to 60% of the added amounts. The adsorption isotherms of the pollutants suggested that the binding to PVPcoS-MMT was driven mainly by hydrophobic interactions, but also by electrostatic interactions in the case of PA. Differences were also seen in the binding kinetics of PA and TCP to dried and wet composites. The hydration properties of PA enhanced its binding to wet composites whereas the hydrophobic properties of TCP enhanced its binding to dehydrated composites. The results of this study emphasize the importance of better understanding pollutant-adsorbent interactions to enable more efficient tailoring of polymer-clay mineral composites for water treatment.

Atrazine removal from water by two polycations pre-adsorbed on montmorillonite was studied. Batch experiments demonstrated that the most suitable composite poly (4-vinylpyridine-co-styrene)-montmorillonite (PVP-co-S90%-mont.) removed 90-99% of atrazine (0.5-28 ppm) within 20-40 min at 0.367% w/w. Calculations employing Langmuir's equation could simulate and predict the kinetics and final extents of atrazine adsorption. Column filter experiments (columns 20x1.6 cm) which included 2g of the PVP-co-S90%-mont. composite mixed with excess sand removed 93-96% of atrazine (800 ppb) for the first 800 pore volumes, whereas the same amount of granular activated carbon (GAC) removed 83-75%. In the presence of dissolved organic matter (DOM; 3.7 ppm) the efficiency of the GAC filter to remove atrazine decreased significantly (68-52% removal), whereas the corresponding efficiency of the PVP-co-S90%-mont. filter was only slightly influenced by DOM. At lower atrazine concentration (7 ppb) the PVP-co-S90%-mont. filter reduced even after 3000 pore volumes the emerging atrazine concentration below 3 ppb (USEPA standard). In the case of the GAC filter the emerging atrazine concentration was between 2.4 and 5.3 microg/L even for the first 100 pore volumes. Thus, the PVP-co-S90%-mont. composite is a new efficient material for the removal of atrazine from water.

A novel controlled release formulation (CRF) of the herbicide imazapyr (IMP) was designed to reduce its leaching,which causes soil and water contamination. The anionic herbicide IMP was bound to polydiallyldimethylammonium-chloride (PDADMAC)-montmorillonite composites. PDADMAC adsorption reached a high loading of polymer, which resulted in charge reversal of the clay and promoted IMP binding. The composites were characterized by Fourier transform infrared, zeta potential, and X-ray diffraction measurements, indicating electrostatic interactions of the polycation with the surface, polycation intercalation in the clay and suggesting a configuration as loops and tails on the surface at high loadings. IMP binding to the composites is affected by polycation loading and flocculation. Upon adding high concentrations of IMP to a composite of 0.16 g/g, we obtained high herbicide loadings (66% active ingredient). IMP release from the CRFs applied on a thin layer of soil was substantially slower than its release from the commercial formulation (Arsenal). Accordingly, soil column bioassays indicated reduced herbicide leaching (nearly 2-fold) upon applying the CRFs while maintaining good herbicidal activity. The new PDADMAC-clay formulations are promising from the environmental and weed control management points of view.

Chlorinated isocyanuric acids are widely used water disinfectants that generate hypochlorite, but with repeated application, they build up cyanuric acid (CYA) that must be removed to maintain disinfection. 3-Aminopropyltriethoxysilane (APTES)-treated Escherichia coli cells expressing cyanuric acid hydrolase (CAH) from Moorella thermoacetica exhibited significantly high CYA degradation rates and provided protection against enzyme inactivation by hypochlorite (chlorine). APTES coating or encapsulation of cells had two benefits: (i) overcoming diffusion limitations imposed by the cell wall and (ii) protecting against hypochlorite inactivation of CAH activity. Cells encapsulated in APTES gels degraded CYA three times faster than nonfunctionalized tetraethoxysilane (TEOS) gels, and cells coated with APTES degraded CYA at a rate of 29 µmol/min per mg of CAH protein, similar to the rate with purified enzyme. UV spectroscopy, fluorescence spectroscopy, and scanning electron microscopy showed that the higher rates were due to APTES increasing membrane permeability and enhancing cyanuric acid diffusion into the cytoplasm to reach the CAH enzyme. Purified CAH enzyme was shown to be rapidly inactivated by hypochlorite. APTES aggregates surrounding cells protected via the amine groups reacting with hypochlorite as shown by pH changes, zeta potential measurements, and infrared spectroscopy. APTES-encapsulated E. coli cells expressing CAH degraded cyanuric acid at high rates in the presence of 1 to 10 ppm hypochlorite, showing effectiveness under swimming pool conditions. In contrast, CAH activity in TEOS gels or free cells was completely inactivated by hypochlorite. These studies show that commercially available silica materials can selectively enhance, protect, and immobilize whole-cell biocatalysts for specialized applications., IMPORTANCE Hypochlorite is used in vast quantities for water disinfection, killing bacteria on surfaces, and washing and whitening. In pools, spas, and other waters, hypochlorite is frequently delivered as chlorinated isocyanuric acids that release hypochlorite and cyanuric acid. Over time, cyanuric acid accumulates and impairs disinfection and must be removed. The microbial enzyme cyanuric acid hydrolase can potentially remove cyanuric acid to restore disinfection and protect swimmers. Whole bacterial cells expressing cyanuric acid hydrolase were encapsulated in an inert silica matrix containing an amine group. The amine group serves to permeabilize the cell membrane and accelerate cyanuric acid degradation, and it also reacts with hypochlorite to protect against inactivation of cyanuric acid hydrolase. Methods for promoting whole-cell biocatalysis are important in biotechnology, and the present work illustrates approaches to enhance rates and protect against an inhibitory substance.

Nitrate is linked to chronic human illness and to a variety of environmental problems, and continues to be a contaminant of concern in soils and natural waters. Improved methods for nitrate abatement, thus, are still needed. The purpose of this study was to assess the potential for redox-modified, iron-bearing clay minerals to act as nitrate decontamination agents in natural environments. The model clay mineral tested was ferruginous smectite (sample SWa-1) exchanged with either sodium (Na+) or polydiallyldimethylammonium chloride (poly-DADMAC). Structural iron (Fe) in SWa-1 was in either the oxidized or reduced state. Little nitrate uptake was observed in the Na+-SWa-1, which was attributed to coulombic repulsion between the basal surfaces of the smectite and the nitrate anion. The addition of the DADMAC to the SWa-1 reversed the electrostatic charge manifested at the smectite surface from negative to positive, as measured by the zeta (ζ) potential. The positively charged poly-DADMAC-SWa-1 yielded high nitrate uptake due to coulombic attraction in both the oxidized and reduced states of the Fe in the SWa-1. The presence of reduced structural Fe(II) in the positively charged poly-DADMAC-SWa-1 enabled a chemical reduction reaction with the nitrate to produce nitrite. The amounts of nitrite found in solution, however, failed to account for all of the Fe(II) oxidized, so other N reduction products may also have formed or perhaps nitrite was also present in the adsorbed phase. The effects of other complexities, such as polymer configuration at the surface, also need further investigation. The results do clearly establish abiotic nitrate reduction to nitrite and possibly other reduction products. The combination of bacterial activity in soils and sediments, which is known to reduce structural Fe in smectites, and the abundance of organic cations in soil organic matter creates an environment where reversed-charge smectite could exist in nature. This represents a potentially effective system for mitigating harmful effects of nitrate in soils, sediments, groundwater, and surface water.

Trace concentrations of heavy metals cause health and environmental hazards. Specifically, trace concentrations of iron induce biofilm formation which is of great concern in water systems. To remove the iron, protein–polycation–clay composites were designed based on the hypothesis that the adsorbed apo-ferredoxin (apo-mFd: mFd protein without the 2Fe–2S cluster) chelates iron. Fe2+ chelation by apo-mFd protein was established by optical spectroscopy and gel electrophoresis. To reduce its biodegradation, apo-mFd was adsorbed to montmorillonite and these composites were characterized by X-ray diffraction, zeta potential and adsorption isotherms. The apo-mFd–montmorillonite did not chelate iron with high efficiency; however, when a polycation–apo-mFd complex was adsorbed to the clay, the protein retained its chelating characteristics and specific interactions of iron with the biocomposite were established. Results present the innovative tailoring of bioactive protein–polycation–clay composites which may be applicable in many fields, e.g., protein immobilization, drug delivery and water treatment.