Minimizing N-Nitrosodimethylamine Formation During Disinfection of Blended Seawater and Wastewater Effluent.

Augmenting seawater with wastewater has the potential to reduce the energy demand and environmental impacts associated with seawater desalination. Alternatively, as wastewater reuse becomes more widespread, augmenting wastewater with seawater can increase the available water supply. However, the chemistry of disinfecting a blended stream has not been explored. Toxic byproducts, including N-nitrosodimethylamine (NDMA), are expected to form during disinfection, and the extent of formation will likely be a function of which stream is chlorinated and whether disinfection happens before or after blending. In this work, three blending-disinfection scenarios were modeled and experimentally evaluated in bench-scale systems treating synthetic and authentic waters. Modeling results suggested that chlorinating preblended wastewater and seawater would produce the most NDMA because it yielded the highest concentrations of bromochloramine, which was previously found to promote NDMA formation. However, chlorinating wastewater prior to blending with seawater, which modeling indicated would form the most dichloramine, produced the most NDMA in experiments. When seawater was disinfected prior to blending with wastewater, bromide likely converted most chlorine to free bromine. Bromamines formed after blending, however, did not lead to an elevated level of NDMA formation. Therefore, to minimize NDMA formation when disinfecting blended wastewater-seawater, seawater should be disinfected prior to introducing wastewater.

Chloramination of Nitromethane: Incomplete Chlorination and Unexpected Substitution Reaction.

Ozone is commonly used as a predisinfectant in potable water reuse treatment trains. Nitromethane was recently found as a ubiquitous ozone byproduct in wastewater, and the key intermediate toward chloropicrin during subsequent secondary disinfection of ozonated wastewater effluent with chlorine. However, many utilities have switched from free chlorine to chloramines as a secondary disinfectant. The reaction mechanism and kinetics of nitromethane transformation by chloramines, unlike those for free chlorine, are unknown. In this work, the kinetics, mechanism, and products of nitromethane chloramination were studied. The expected principal product was chloropicrin, because chloramines are commonly assumed to react similarly to, although more slowly than, free chlorine. Different molar yields of chloropicrin were observed under acidic, neutral, and basic conditions, and surprisingly, transformation products other than chloropicrin were found. Monochloronitromethane and dichloronitromethane were detected at basic pH, and the mass balance was initially poor at neutral pH. Much of the missing mass was later attributed to nitrate formation, from a newly identified pathway involving monochloramine reacting as a nucleophile rather than a halogenating agent, through a presumed SN2 mechanism. The study indicates that nitromethane chloramination, unlike chlorination, is likely to produce a range of products, whose speciation is a function of pH and reaction time.

Ipso Substitution of Aromatic Bromine in Chlorinated Waters: Impacts on Trihalomethane Formation.

Parabens and salicylates were examined as disinfection byproduct (DBP) precursors to explore the possible influence of ipso substitution (i.e., halogen exchange) on the yield and speciation of trihalomethanes (THMs) formed during water chlorination. Substoichiometric conversion of C-Br bonds into C-Cl bonds was confirmed for several parabens and salicylates. The co-occurrence of (mono)brominated and nonhalogenated precursors in the presence of free chlorine (but in the absence of added Br-) generated polybrominated THMs, implicating ipso substitution. The THM molar yield, bromine incorporation, and bromine recovery from brominated and nonhalogenated precursor mixtures were commensurate with those observed from equimolar additions of NaBr, indicating efficient displacement of aromatic bromine by free chlorine followed by reincorporation of liberated HOBr into DBP precursors. The THM molar yield from brominated precursors was enhanced by a factor of ≤20 relative to that from nonhalogenated precursors. Trends in THM molar yields and bromine incorporation differed between brominated parabens and brominated salicylates, suggesting that the influence of ipso substitution on THM formation varies with the structure of the organic precursor. Collectively, these results provide new evidence of the often-overlooked role ipso substitution can play in promoting halogen exchange and bromine enrichment among DBPs in chlorinated waters.

Out of Thin Air? Catalytic Oxidation of Trace Aqueous Aldehydes with Ambient Dissolved Oxygen.

Water reuse is expanding due to increased water scarcity. Water reuse facilities treat wastewater effluent to a very high purity level, typically resulting in a product water that is essentially deionized water, often containing less than 100 µg/L organic carbon. However, recent research has found that low-molecular-weight aldehydes, which are toxic electrophiles, comprise a significant fraction of the final organic carbon pool in recycled wastewater in certain treatment configurations. In this manuscript, we demonstrate oxidation of trace aqueous aldehydes to their corresponding acids using a heterogeneous catalyst (5% Pt on C), with ambient dissolved oxygen serving as the terminal electron acceptor. Mass balances are essentially quantitative across a range of aldehydes, and pseudo-first-order reaction kinetics are observed in batch reactors, with kobs varying from 0.6 h-1 for acetaldehyde to 4.6 h-1 for hexanal, while they are low for unsaturated aldehydes. Through kinetic and isotopic labeling experiments, we demonstrate that while oxygen is essential for the reaction to proceed, it is not involved in the rate-limiting step, and the reaction appears to proceed primarily through a base-promoted ß-hydride elimination mechanism from the hydrated gem-diol form of the corresponding aldehyde. This is the first report we are aware of that demonstrates useful abiotic oxidation of a trace organic contaminant using dissolved oxygen.

Ozonation of organic compounds in water and wastewater: A critical review.

Ozonation has been applied in water treatment for more than a century, first for disinfection, later for oxidation of inorganic and organic pollutants. In recent years, ozone has been increasingly applied for enhanced municipal wastewater treatment for ecosystem protection and for potable water reuse. These applications triggered significant research efforts on the abatement efficiency of organic contaminants and the ensuing formation of transformation products. This endeavor was accompanied by developments in analytical and computational chemistry, which allowed to improve the mechanistic understanding of ozone reactions. This critical review assesses the challenges of ozonation of impaired water qualities such as wastewaters and provides an up-to-date compilation of the recent kinetic and mechanistic findings of ozone reactions with dissolved organic matter, various functional groups (olefins, aromatic compounds, heterocyclic compounds, aliphatic nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, carbanions, ß-diketones) and antibiotic resistance genes.

Antibiotic transformation in an anaerobic membrane bioreactor linked to membrane biofilm microbial activity.

Although extensive research to date has focused on enhancing removal rates of antibiotics from municipal wastewaters, the transformation products formed by anaerobic treatment processes remain understudied. The present work aims to examine the possible roles that the different microbial communities of an anaerobic membrane bioreactor (AnMBR) play in the transformation of antibiotics during wastewater treatment. As part of this work, sulfamethoxazole, erythromycin, and ampicillin were added in separate stages to the influent of the AnMBR at incremental concentrations of 10, 50, and 250 µg/L each. Antibiotic-specific transformation products detected during each stage, as identified by high resolution LC-MS, are reported herein. Results suggest that both isoxazole (sulfamethoxazole) and ß-lactam (ampicillin) ring opening could be facilitated by the AnMBR's bioprocess. Microbial community analysis results indicated that relative activity of the system's suspended biomass consistently shifted towards syntrophic groups throughout the duration of the experiment. Notable differences were also observed between the suspended biomass and the AnMBR's membrane biofilms. Membrane-attached biofilm communities showed high relative activities of several specific methanogenic (Methanothrix and Methanomethylovorans), syntrophic (Syntrophaceae), and sulfate-reducing (Desulfomonile) groups. Such groups have been previously identified as involved in the formation of the antibiotic degradation products observed in the effluent of the AnMBR. The activity of these communities within the biofilms likely confers certain advantages that aid in the biotransformation of the antibiotics tested.

Formation and Fate of Nitromethane in Ozone-Based Water Reuse Processes.

Ozonation is widely used in wastewater reclamation treatment trains, either for micropollutant control or as a disinfectant and preoxidant in certain reuse processes. We recently found that ozonation of secondary effluent produces nitromethane, which can be efficiently transformed to genotoxic halonitromethanes by chlorination. In this work, the fate of nitromethane through water reuse treatment trains was characterized by analyzing samples from five reuse operations employing ozone. Nitromethane was poorly (<50%) rejected by reserve osmosis (RO), not removed by, and in some cases, increased by ultraviolet/advanced oxidation processes (UV/AOP). Sufficient nitromethane remained after advanced treatment that when chlorine was added to mimic secondary disinfection, halonitromethane formation was consistently observed. In contrast, biological activated carbon removed most (>75%) nitromethane. Bench-scale experiments were conducted to verify low removal by RO in clean systems and with wastewater effluent and to quantify the kinetics of direct and indirect photolysis of nitromethane in UV/AOP. An explanation for increasing nitromethane concentration during AOP is proposed. These results indicate that nitromethane presents a unique hazard to direct potable reuse systems, due to its ubiquitous formation during wastewater ozonation, poor removal by RO and UV/AOP, and facile conversion into genotoxic halonitromethanes upon chlorine addition.

Evaluation of Histidine Reactivity and Byproduct Formation during Peptide Chlorination.

The covalent modifications resulting from chlorine reactions with peptide-bound amino acids contribute to pathogen inactivation and disinfection byproduct (DBP) formation. Previous research suggested that histidine is the third most reactive of the seven chlorine-reactive amino acids, leading to the formation of 2-chlorohistidine, 2-oxohistidine, or low-molecular-weight byproducts such as trihalomethanes. This study demonstrates that histidine is less reactive toward formation of chlorine transformation products (transformation time scale of hours to days) than five of the seven chlorine-reactive amino acids, including tyrosine (transformation time scale of minutes). Chlorine targeted tyrosine in preference to histidine within peptides, indicating that chlorine reactions with tyrosine and other more reactive amino acids could contribute more to the structural modifications to proteins over the short time scales relevant to pathogen inactivation. Over the longer time scales relevant to disinfection byproduct formation in treatment plants or distribution systems, this study identified ß-cyanoalanine as the dominant transformation product of chlorine reactions with peptide-bound histidine, with molar yields of ∼50% after 1 day. While a chlorinated histidine intermediate was observed at lower yields (maximum ∼5%), the cumulative concentration of the conventional low-molecular-weight DBPs (e.g., trihalomethanes) was ≤7%. These findings support the need to identify the high-yield initial transformation products of chlorine reactions with important precursor structures to facilitate the identification of unknown DBPs.

Transformation of N-Methylamine Drugs during Wastewater Ozonation: Formation of Nitromethane, an Efficient Precursor to Halonitromethanes.

Potable reuse of wastewater is expanding, and ozonation for water reuse is becoming more common, either as a preoxidant before membranes or as part of ozone/biological activated carbon (O3/BAC) systems. However, previous research has demonstrated that ozone drastically increases the formation potential of genotoxic halonitromethanes (HNMs), including during O3/BAC. Chloropicrin, the most common HNM, is synthesized by chlorinating nitromethane, suggesting that nitromethane may be the immediate precursor of chloropicrin, although nitromethane is unlikely to occur naturally in wastewater. We hypothesized that wastewater ozonation forms nitromethane, which would be the key intermediate toward HNMs. Ozonation of wastewater effluent was shown to form abundant nitromethane, which explained the majority (in one case, all) of subsequent chloropicrin formation. Next, we investigated a suspected category of nitromethane precursor: stimulant drugs, such as ephedrine and methamphetamine, and certain antidepressants. These drugs all feature N-methylamine functional groups, and certain N-alkylamines have been shown to produce primary nitroalkanes upon ozonation. Ozonation of N-methylamine drugs ubiquitously formed nitromethane, typically at >50% yield. Subsequent chlorination converted nitromethane to chloropicrin. The reaction mechanism was investigated to understand the variation in nitromethane yield between different precursors. These results suggest that nitromethane fate during reuse and nitromethane control should be investigated.

Summation of disinfection by-product CHO cell relative toxicity indices: sampling bias, uncertainty, and a path forward.

The cyto- and genotoxic potencies of disinfection by-products (DBPs) have been evaluated in published literature by measuring the response of exposed Chinese hamster ovary cells. In recent publications, DBP concentrations divided by their individual toxicity indices are summed to predict the relative toxicity of a water sample. We hypothesized that the omission or inclusion of certain DBPs over others is equivalent to statistical sampling bias and may result in biased conclusions. To test this hypothesis, we removed or added actual or simulated DBP measurements to that of published studies which evaluated granular activated carbon as a treatment to reduce the relative toxicity of the effluent. In several examples, it was possible to overturn the conclusions (i.e., activated carbon is detrimental or beneficial in reducing toxicity) by preferentially including specific DBPs. In one example, removing measured haloacetaldehydes caused the predicted cytotoxicity of a treated sample to decrease by up to 47%, reversing the initial conclusion that activated carbon increased the toxicity of the water. We also discuss measurements of statistical error, which are rarely included in publications related to predicted toxicity, but strongly influence the outcomes. Finally, we discuss future research needs in the light of these and other concerns.

Reverse Osmosis Shifts Chloramine Speciation Causing Re-Formation of NDMA during Potable Reuse of Wastewater.

UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH4+ promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H+ ↔ NHCl2 + NH4+. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.

Ozone Promotes Chloropicrin Formation by Oxidizing Amines to Nitro Compounds.

Chloropicrin formation has been associated with ozonation followed by chlorination, but the reaction pathway and precursors have been poorly characterized. Experiments with methylamine demonstrated that ozonation converts methylamine to nitromethane at ∼100% yield. Subsequent chlorination converts nitromethane to chloropicrin at ∼50% yield under the conditions evaluated. Similarly high yields from other primary amines were limited to those with functional groups on the ß-carbon (e.g., the carboxylic acid in glycine) that facilitate carbon-carbon bond cleavage to release nitromethyl anion. Secondary amines featuring these reactive primary amines as functional groups (e.g., secondary N-methylamines) formed chloropicrin at high yields, likely by facile dealkylation to release the primary nitro compound. Chloropicrin yields from tertiary amines were low. Natural water experiments, including derivatization to transform primary and secondary amines to less reactive carbamate functional groups, indicated that primary and secondary amines were the dominant chloropicrin precursors during ozonation/chlorination. Ozonation followed by chlorination of the primary amine side chain of lysine demonstrated low yields (∼0.2%) of chloropicrin, but high yields (∼17%) of dichloronitrolysine, a halonitroalkane structural analogue to chloropicrin. However, chloropicrin yields increased and dichloronitrolysine yields decreased in the absence of hydroxyl radical scavengers, suggesting that future research should characterize the potential occurrence of such halonitroalkane analogues relative to natural radical scavenger (e.g., carbonate) concentrations.

Formation Pathways and Trade-Offs between Haloacetamides and Haloacetaldehydes during Combined Chlorination and Chloramination of Lignin Phenols and Natural Waters.

In vitro bioassays have indicated that haloacetamides and haloacetaldehydes exhibit the highest cytotoxicity among DBP classes. Previous research has focused on their potential formation from the chlorination or chloramination of aliphatic compounds, particularly nonaromatic amino acids, and acetaldehyde. The present work found that acetaldehyde served as a relatively poor precursor for trichloroacetaldehyde and dichloroacetamide, generally the most prevalent of the haloacetaldehydes and haloacetamides, during chlorination or chlorination/chloramination. Using phenolic model compounds, particularly 4-hydroxybenzoic acid, as models for structures in humic substances, we found significantly higher formation of trichloroacetaldehyde and dichloroacetamide from prechlorination followed by chloramination. Evaluation of the stoichiometry of chlorine reactions with 4-hydroxybenzoic acid and several intermediates indicated that seven successive Cl[+1] transfers, faster with chlorination than chloramination, can form 2,3,5,5,6-pentachloro-6-hydroxy-cyclohexa-2-ene-1,4-dione via chlorophenol and chlorobenzoquinone intermediates. Formation of 2,3,5,5,6-pentachloro-6-hydroxy-cyclohexa-2-ene-1,4-dione may serve as a key branching point, with chloramines promoting the formation of dichloroacetamide and chlorination promoting the formation of trichloroacetaldehyde. The behavior of 4-hydroxybenzoic acid with respect to yields of dichloroacetamide and trichloroacetaldehyde during chlorination followed by chloramination was similar to the behavior observed for model humic acids and several surface waters, suggesting that phenolic structures in natural waters may serve as the predominant, and common pool of precursors for haloacetamides and haloacetaldehydes. Experiments with natural waters indicated that the branching point is reached over prechlorine exposures (100-500 mg-min/L) relevant to drinking water utilities using chlorine as a primary disinfectant and chloramines for maintenance of a distribution system residual.

Determinants of disinfectant pretreatment efficacy for nitrosamine control in chloraminated drinking water.

Utilities using chloramines need strategies to mitigate nitrosamine formation to meet potential future nitrosamine regulations. The ability to reduce NDMA formation under typical post-chloramination conditions of pretreatment with ultraviolet light from a low pressure mercury lamp (LPUV), free chlorine (HOCl), ozone (O3), and UV light from a medium pressure mercury lamp (MPUV) were compared at exposures relevant to drinking water treatment. The order of efficacy after application to waters impacted by upstream wastewater discharges was O3 > HOCl ≈ MPUV > LPUV. NDMA precursor abatement generally did not correlate well between oxidants, and waters exhibited different behaviors with respect to pH and temperature, suggesting a variety of source-dependent NDMA precursors. For wastewater-impacted waters, the observed pH dependence for precursor abatement suggested the important role of secondary or tertiary amine precursors. Although hydroxyl radicals did not appear to be important for NDMA precursor abatement during O3 or MPUV pretreatment, the efficacy of MPUV correlated strongly with dissolved organic carbon concentration (p = 0.01), suggesting alternative indirect photochemical pathways. The temperature dependences during pre- and post-disinfection indicated that NDMA formation is likely to increase during warm seasons for O3 pretreatment, decrease for HOCl pretreatment, and remain unchanged for MPUV treatment, although seasonal changes in source water quality may counteract the temperature effects. For two waters impacted by relatively high polyDADMAC coagulant doses, pretreatment with HOCl, O3, and MPUV increased NDMA formation during post-chloramination. For O3 pretreatment, hydroxyl radicals likely led to precursor formation from the polymer in the latter tests. MPUV treatment of polymer-impacted water increased subsequent NDMA formation through an indirect photochemical process. Many factors may mitigate the importance of this increased NDMA formation, including the low polyDADMAC doses typically applied, and simultaneous degradation of watershed-associated precursors.

Formation, precursors, control, and occurrence of nitrosamines in drinking water: a review.

This review summarizes major findings over the last decade related to nitrosamines in drinking water, with a particular focus on N-nitrosodimethylamine (NDMA), because it is among the most widely detected nitrosamines in drinking waters. The reaction of inorganic dichloramine with amine precursors is likely the dominant mechanism responsible for NDMA formation in drinking waters. Even when occurrence surveys found NDMA formation in chlorinated drinking waters, it is unclear whether chloramination resulted from ammonia in the source waters. NDMA formation has been associated with the use of quaternary amine-based coagulants and anion exchange resins, and wastewater-impaired source waters. Specific NDMA precursors in wastewater-impacted source waters may include tertiary amine-containing pharmaceuticals or other quaternary amine-containing constituents of personal care products. Options for nitrosamine control include physical removal of precursors by activated carbon or precursor deactivation by application of oxidants, particularly ozone or chlorine, upstream of chloramination. Although NDMA has been the most prevalent nitrosamine detected in worldwide occurrence surveys, it may account for only ≈ 5% of all nitrosamines in chloraminated drinking waters. Other significant contributors to total nitrosamines are poorly characterized. However, high levels of certain low molecular weight nitrosamines have been detected in certain Chinese waters suspected to be impaired by industrial effluents. The review concludes by identifying research needs that should be addressed over the next decade.

Role of lysine during protein modification by HOCl and HOBr: halogen-transfer agent or sacrificial antioxidant?

Although protein degradation by neutrophil-derived hypochlorous acid (HOCl) and eosinophil-derived hypobromous acid (HOBr) can contribute to the inactivation of pathogens, collateral damage to host proteins can also occur and has been associated with inflammatory diseases ranging from arthritis to atherosclerosis. Though previous research suggested halotyrosines as biomarkers of protein damage and lysine as a mediator of the transfer of a halogen to tyrosine, these reactions within whole proteins are poorly understood. Herein, reactions of HOCl and HOBr with three well-characterized proteins [adenylate kinase (ADK), ribose binding protein, and bovine serum albumin] were characterized. Three assessments of oxidative modifications were evaluated for each of the proteins: (1) covalent modification of electron-rich amino acids (assessed via liquid chromatography and tandem mass spectrometry), (2) attenuation of secondary structure (via circular dichroism), and (3) fragmentation of protein backbones (via sodium dodecyl sulfate-polyacrylamide gel electrophoresis). In addition to forming halotyrosines, HOCl and HOBr converted lysine into lysine nitrile (2-amino-5-cyanopentanoic acid), a relatively stable and largely overlooked product, in yields of up to 80%. At uniform oxidant levels, fragmentation and loss of secondary structure correlated with protein size. To further examine the role of lysine, a lysine-free ADK variant was rationally designed. The absence of lysine increased yields of chlorinated tyrosines and decreased yields of brominated tyrosines following treatments with HOCl and HOBr, respectively, without influencing the susceptibility of ADK to HOX-mediated losses of secondary structure. These findings suggest that lysine serves predominantly as a sacrificial antioxidant (via formation of lysine nitrile) toward HOCl and as a halogen-transfer mediator [via reactions involving ε-N-(di)haloamines] with HOBr.

Disinfection byproduct formation in reverse-osmosis concentrated and lyophilized natural organic matter from a drinking water source.

Drinking water treatment and disinfection byproduct (DBP) research can be complicated by natural organic matter (NOM) temporal variability. NOM preservation by lyophilization (freeze-drying) has been long practiced to address this issue; however, its applicability for drinking water research has been limited because the selected NOM sources are atypical of most drinking water sources. The purpose of this research was to demonstrate that reconstituted NOM from a lyophilized reverse-osmosis (RO) concentrate of a typical drinking water source closely represents DBP formation in the original NOM. A preliminary experiment assessed DBP formation kinetics and yields in concentrated NOM, which demonstrated that chlorine decays faster in concentrate, in some cases leading to altered DBP speciation. Potential changes in NOM reactivity caused by lyophilization were evaluated by chlorination of lyophilized and reconstituted NOM, its parent RO concentrate, and the source water. Bromide lost during RO concentration was replaced by adding potassium bromide prior to chlorination. Although total measured DBP formation tended to decrease slightly and unidentified halogenated organic formation tended to increase slightly as a result of RO concentration, the changes associated with lyophilization were minor. In lyophilized NOM reconstituted back to source water TOC levels and then chlorinated, the concentrations of 19 of 21 measured DBPs, constituting 96% of the total identified DBP mass, were statistically indistinguishable from those in the chlorinated source water. Furthermore, the concentrations of 16 of 21 DBPs in lyophilized NOM reconstituted back to the RO concentrate TOC levels, constituting 86% DBP mass, were statistically indistinguishable from those in the RO concentrate. This study suggests that lyophilization can be used to preserve concentrated NOM without substantially altering the precursors to DBP formation.

Novel thermally stable poly(vinyl chloride) composites for sulfate removal.

BaCO(3) dispersed PVC composites were prepared through a polymer re-precipitation method. The composites were tested for sulfate removal using rapid small scale column test (RSSCT) and found to significantly reduce sulfate concentration. The method was extended to synthesize barium carbonate-loaded silica aero-gels-polyvinyl chloride (PVC) polymer composites. The PVC composites were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray mapping, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and inductively coupled plasma mass spectrometry (ICP-MS) analysis. The method has advantages over conventional sulfate precipitation (sulfate removal process) using BaCO(3) wherein clogging of the filter can be avoided. The method is environmentally friendly and does not interfere with natural organic matter as the conventional resin does. Some of the composites were thermally more stable as compared with the pure PVC discussed in the literature.