Potential for microbially mediated redox transformations and mobilization of arsenic in uncontaminated soils

Surface soil samples, which had no significant As contamination, were examined for As(V) reduction, As(III) oxidation and As mobilization capability. All five soil samples tested exhibited microbial As(V)-reducing activities both in aerobic and anaerobic conditions. Under aerobic conditions when As(V) reduction had almost ceased, oxidation of As(III) to As(V) occurred, whereas only As(V) reduction was observed under anaerobic conditions. In cultures incubated with As(III), As(III) was oxidized by indigenous soil microbes only under aerobic conditions. These results indicate that microbial redox transformations of As are ubiquitous in the natural environment regardless of background As levels. Mobilization through microbially mediated As(V) and Fe(III) reduction occurred both in the presence and absence of oxygen. Significant variation in dissolved As occurred depending on the Fe contents of soils, and re-immobilization of As arose in the presence of oxygen, presumably as a consequence of dissolved As(III) and Fe(II) oxidation. There was no apparent correlation between dissolved Fe(II) and As, suggesting that reductive dissolution of Fe(III) minerals does not necessarily determine the extent of As release from soils.     

Destruction of lindane and atrazine using stabilized iron nanoparticles under aerobic and anaerobic conditions: effects of catalyst and stabilizer

Highly stable Fe-Pd bimetallic nanoparticles were prepared with 0.2% (w/w) of sodium carboxylmethylcellulose (CMC) as a stabilizer. The effectiveness of the stabilized Fe-Pd nanoparticles was studied for degradation of two chlorinated pesticides (lindane and atrazine) under aerobic and anaerobic conditions. Batch kinetic tests showed that under anaerobic condition the nanoparticles can serve as strong electron donors and completely reduce 1 mgl(-1) of lindane at an iron dose of 0.5 gl(-1) or 1mg l(-1) of atrazine with 0.05 gl(-1) iron with a trace amount (0.05-0.8% of Fe) of Pd as a catalyst. In contrast, under aerobic condition, the nanoparticles can facilitate Fenton-like reactions, which lead to oxidation of 65% of lindane under otherwise identical conditions. Under aerobic condition, the presence of CMC reduced the level of hydroxyl radicals generated from the nanoparticels by nearly 50%, and thus, inhibited the oxidation of the contaminants. While the particle stabilization greatly enhanced the anaerobic degradation, it did not appear to be beneficial under aerobic condition. The degradation rate was progressively enhanced as the Pd content increased from 0.05% to 0.8% of Fe, and the catalytic effect of Pd was more significant under anaerobic condition. Under anaerobic condition, lindane is degraded via dihaloelimination and dehydrohalogenation, whereas atrazine is by reductive dechlorination followed by subsequent reductive dealkylation. Under aerobic condition, reactive oxygen species and hydroxyl radicals from the iron nanoparticles are responsible for oxidizing the pesticides. Lindane is oxidized via dechlorination/dehydrohalogenation, whereas atrazine is destroyed through dealkylation of the alkylamino side chain.     

Mutagenicity of anaerobic fenitrothion metabolites after aerobic biodegradation

Previous studies have revealed that the mutagenicity of fenitrothion increases during anaerobic biodegradation, suggesting that this insecticide's mutagenicity could effectively increase after it pollutes anaerobic environments such as lake sediments. To investigate possible changes to the mutagenicity of fenitrothion under aerobic conditions after it had already been increased by anaerobic biodegradation, batch incubation cultures were maintained under aerobic conditions. The mutagenicity, which had increased during anaerobic biodegradation, decreased under aerobic conditions with aerobic or facultative bacteria, but did not disappear completely in 22 days. In contrast, it did not change under aerobic conditions without bacteria or under continued anaerobic conditions. These observations suggest that the mutagenicity of anaerobically metabolized fenitrothion would not necessarily decrease after it arrives in an aerobic environment: this would depend on the presence of suitable bacteria. Therefore, fenitrothion-derived mutagenic compounds may pollute the water environment, including our drinking water sources, after accidental pollution of aerobic waters. Although amino-fenitrothion generated during anaerobic biodegradation of fenitrothion was the principal mutagen, non-trivial contributions of other, unidentified metabolites to the mutagenicity were also observed.     

A microcosm test for potential mineralization of chlorinated compounds under coupled aerobic/anaerobic conditions

In this study, the feasibility of using a mineralization test under coupled aerobic/anaerobic conditions was demonstrated. The coupling of anaerobic methanogenic and aerobic methanotrophic conditions in a microcosm required the presence of both a carbon source for anaerobic metabolism and oxygen for aerobic metabolism. These requirements were fulfilled by using a slow hydrolyzing organic matter along with intermittent addition of oxygen to the bottle headspace. Perchloroethylene (PCE) mineralization tests confirmed the effectiveness of the proposed methodology as well as PCE mineralization under coupled conditions.     

Modeling of vapor intrusion from hydrocarbon-contaminated sources accounting for aerobic and anaerobic biodegradation

A one-dimensional steady state vapor intrusion model including both anaerobic and oxygen-limited aerobic biodegradation was developed. The aerobic and anaerobic layer thickness are calculated by stoichiometrically coupling the reactive transport of vapors with oxygen transport and consumption. The model accounts for the different oxygen demand in the subsurface required to sustain the aerobic biodegradation of the compound(s) of concern and for the baseline soil oxygen respiration. In the case of anaerobic reaction under methanogenic conditions, the model accounts for the generation of methane which leads to a further oxygen demand, due to methane oxidation, in the aerobic zone. The model was solved analytically and applied, using representative parameter ranges and values, to identify under which site conditions the attenuation of hydrocarbons migrating into indoor environments is likely to be significant. Simulations were performed assuming a soil contaminated by toluene only, by a BTEX mixture, by Fresh Gasoline and by Weathered Gasoline. The obtained results have shown that for several site conditions oxygen concentration below the building is sufficient to sustain aerobic biodegradation. For these scenarios the aerobic biodegradation is the primary mechanism of attenuation, i.e. anaerobic contribution is negligible and a model accounting just for aerobic biodegradation can be used. On the contrary, in all cases where oxygen is not sufficient to sustain aerobic biodegradation alone (e.g. highly contaminated sources), anaerobic biodegradation can significantly contribute to the overall attenuation depending on the site specific conditions.     

The digestibility of waste activated sludges.

Laboratory digestion studies using waste activated sludges (WAS) were conducted to compare the digestion performance between anaerobic and aerobic processes. Nine samples of WAS from seven wastewater treatment plants were collected and batch-digested under both anaerobic and aerobic conditions for 30 days at 25 degrees C. The cation content of wastewater (both floc and solution phases) and solution biopolymer (protein and polysaccharide) was measured before and after digestion and compared with volatile solids destruction data. The study revealed that each digestion process was associated with a distinct biopolymer fraction, which accounted for differences in volatile solids reduction under anaerobic and aerobic conditions. The anaerobic digestion data showed strong correlations between soluble protein generation, ammonium production, percent volatile solids reduction, and floc iron (Fe). These data suggest that the amount of volatile solids destroyed by anaerobic digestion depends on the Fe content of floc. In aerobic digestion, polysaccharide accumulated in solution along with calcium and magnesium. For aerobic digestion, correlations between divalent cation release and the production of inorganic nitrogen were found. This implies that divalent cation-bound biopolymer, thought to be lectin-like protein, was the primary organic fraction degraded under aerobic conditions. The results of the study show that the cation content in wastewater is an important indicator of the material that will digest under anaerobic or aerobic conditions and that some of the volatile solids will digest only under either anaerobic or aerobic conditions.     

Occurrence of carbon monoxide during organic waste degradation

The concentrations of carbon monoxide (CO) and other gases were measured in the emissions from solid waste degradation under aerobic and anaerobic conditions during laboratory and field investigations. The emissions were measured as room temperature headspace gas concentrations in reactors of 1, 30, and 150 L, as well as sucked gas concentrations from windrow composting piles and a biocell, under field conditions. The aerobic composting laboratory experiments consisted of treatments with and without lime. The CO concentrations measured during anaerobic conditions varied from 0 to 3000 ppm, the average being 23 ppm, increasing to 133 ppm when methane (CH4) concentrations were low. The mean/maximum CO concentrations during the aerobic degradation in the 2-L reactor were 101/194 ppm without lime, 486/2022 ppm with lime, and 275/980 ppm in the 150-L reactors. The presence of CO during the aerobic composting followed a rapid decline in O2 concentrations Significantly higher CO concentrations were obtained when the aerobic degradation was amended with lime, probably because of a more extreme depletion of oxygen. The mean/maximum CO concentrations under field conditions during aerobic composting were 95/1000 ppm. The CO concentrations from the anaerobic biocell varied from 20 to 160 ppm. The hydrogen sulfide concentrations reached almost 1200 ppm during the anaerobic degradation and 67 ppm during the composting experiments.     

Persistence of perfluoroalkylated substances in closed bottle tests with municipal sewage sludge

BACKGROUND, AIM, AND SCOPE: Perfluoroalkylated substances (PFAS) are chemicals with completely fluorinated alkyl chains. The specific properties of the F-C bond give PFAS a high stability and make them very useful in a wide range of applications. PFAS also pose a potential risk to the environment and humans because they have been recently characterized as persistent, bioaccumulative, and toxic. The objective of this work is to study the bacterial degradation of PFAS under aerobic and anaerobic conditions in municipal sewage sludge as a contribution toward understanding their environmental fate and behavior. MATERIALS AND METHODS: Bacterial communities from sewage sludge were exposed to a mixture of PFAS under aerobic or anaerobic conditions. Individual PFAS concentrations were determined in the experiment media at different exposure times using liquid chromatography-mass spectrometry analysis after extraction with solid-phase extraction. RESULTS: The PFAS analyses of samples of sludge showed repeatable replicate results, allowing a reliable quantification of the different groups of PFAS analyzed. No conclusive evidence for PFAS degradation was observed under the experimental conditions tested in this work. Reduction in concentrations, however, was observed for some PFAS in sludge under aerobic conditions. DISCUSSION: The largest concentration decrease occurred for the fluorotelomer alcohols (FTOHs), especially for the 8:2 FTOH, which have been described as biodegradable in the literature. However, this concentration decrease could be due to different causes: sorption to glass, septa, or matrix components, as well as bacterial activity. Therefore, it is not certain that biodegradation occurred. CONCLUSIONS: PFAS are very recalcitrant chemicals, especially when fully fluorinated. Although some decreases in concentration have been observed for some PFAS, such as the FTOHs, there is no conclusive evidence for biodegradation. It can be concluded that the PFAS tested in these experiments are non-biodegradable under these experimental conditions. RECOMMENDATIONS AND PERSPECTIVES: Since the presence of PFAS is ubiquitous in the environment and they can be toxic, more research is needed in this field to elucidate which PFAS are susceptible to biodegradation, the conditions required for biodegradation, and the possible routes followed. A possible inhibitory effect of PFAS on bacteria, the threshold concentrations, and conditions of inhibition should also be investigated.     

Occurrence of Carbon Monoxide during Organic Waste Degradation

Abstract

The concentrations of carbon monoxide (CO) and other gases were measured in the emissions from solid waste degradation under aerobic and anaerobic conditions during laboratory and field investigations. The emissions were measured as room temperature headspace gas concentrations in reactors of 1, 30, and 150 L, as well as sucked gas concentrations from windrow composting piles and a biocell, under field conditions. The aerobic composting laboratory experiments consisted of treatments with and without lime. The CO concentrations measured during anaerobic conditions varied from 0 to 3000 ppm, the average being 23 ppm, increasing to 133 ppm when methane (CH₄) concentrations were low. The mean/maximum CO concentrations during the aerobic degradation in the 2-L reactor were 101/194 ppm without lime, 486/2022 ppm with lime, and 275/980 ppm in the 150-L reactors. The presence of CO during the aerobic composting followed a rapid decline in O₂ concentrations Significantly higher CO concentrations were obtained when the aerobic degradation was amended with lime, probably because of a more extreme depletion of oxygen. The mean/maximum CO concentrations under field conditions during aerobic composting were 95/1000 ppm. The CO concentrations from the anaerobic biocell varied from 20 to 160 ppm. The hydrogen sulfide concentrations reached almost 1200 ppm during the anaerobic degradation and 67 ppm during the composting experiments. There is a positive correlation between the CO and hydrogen sulfide concentrations measured during the anaerobic degradation experiments.     

Biodegradation of triclosan and formation of methyl-triclosan in activated sludge under aerobic conditions

Triclosan is an antimicrobial agent which is widely used in household and personal care products. Widespread use of this compound has led to the elevated concentrations of triclosan in wastewater, wastewater treatment plants (WWTPs) and receiving waters. Removal of triclosan and formation of triclosan-methyl was investigated in activated sludge from a standard activated sludge WWTP equipped with enhanced biological phosphorus removal. The removal was found to occur mainly under aerobic conditions while under anoxic (nitrate reducing) and anaerobic conditions rather low removal rates were determined. In a laboratory-scale activated sludge reactor 75% of the triclosan was removed under aerobic conditions within 150 h, while no removal was observed under anaerobic or anoxic conditions. One percent of the triclosan was converted to triclosan-methyl under aerobic conditions, less under anoxic (nitrate reducing) and none under anaerobic conditions.     

PAH dissipation in a contaminated river sediment under oxic and anoxic conditions

A batch experiment was conducted to compare PAH degradation in a polluted river sediment under aerobic and anaerobic conditions, and to investigate whether input of fresh organic material (cellulose) could enhance such degradation. All measurements were checked against abiotic control treatments to exclude artifacts of sample preparation and non-biological processes like aging. Three- and four-ring PAHs could be degraded by the indigenous microbial community under aerobic conditions, but anaerobic metabolism based on iron and sulphate reduction was not coupled with PAH degradation of even the simplest 3-ring compounds like phenanthrene. Cellulose addition stimulated both aerobic and anaerobic respiration, but had no effect on PAH dissipation. We conclude that natural attenuation of PAHs in polluted river sediments under anaerobic conditions is exceedingly slow. Dredging and biodegradation on land under aerobic conditions would be required to safely remediate and restore polluted sites.     

14C]Pentachlorophenol mineralization in the rice rhizosphere with established oxidized and reduced soil layers

Flooded soils with rooted aquatic macrophytes have adjacent aerobic and anaerobic zones at the soil-water interface and rhizosphere where many common soil constituents undergo sequential oxidation and reduction reactions. To investigate whether pentachlorophenol (PCP) mineralization would also be enhanced under these conditions, a laboratory study was conducted to determine the conversion of [14C]PCP to 14CO2, 14CH4 and [14C]humic substances in soil microcosms with established aerobic-anaerobic zones at the soil-water interface and rice (Oryza sativa) rhizosphere. Contrary to what was expected, PCP was least rapidly degraded in rhizosphere-soil microcosms that contained the most extensive amounts of aerobic-anaerobic interfaces (63% PCP loss in 82 d) and was most rapidly degraded in soil microcosms that lacked redox interfaces in the soil profile (94% PCP loss in 82 d). Decreased PCP mineralization in the presence of aerobic-anaerobic interfaces was explained by (i) lack of sufficient O2 for aerobic PCP mineralization, due to the oxidation of other soil constituents in aerobic zones, and (ii) lack of an adequate supply of electron equivalents for reductive dechlorination of PCP, due to the reduction of other alternate electron acceptors in anaerobic zones. It was concluded that PCP mineralization is inhibited in flooded soils that contain extensive amounts of aerobic-anaerobic interfaces, due to redox cycling of other soil constituents that occur in these zones.     

Anaerobic and aerobic transformations affecting stability of dewatered sludge during long-term storage in a lagoon

The goal of this work was to study long-term behavior of anaerobically digested and dewatered sludge (biosolids) in a lagoon under anaerobic and aerobic conditions to determine the stability of the final product as an indicator of its odor potential. Field lagoons were sampled to estimate spatial and temporal variations in the physical-chemical properties and biological stability characteristics such as volatile solids content, accumulated oxygen uptake, and soluble protein content and odorous compound assessment. The analyses of collected data suggest that the surface layer of the lagoon (depth of above 0.15 m) undergoes long-term aerobic oxidation resulting in a higher degree of stabilization in the final product. The subsurface layers (depth 0.15 m below the surface and deeper) are subjected to an anaerobic environment where the conditions favor the initial rapid organic matter degradation within approximately the first year, followed by slow degradation.     

Biodegradation of polylactide in aerobic and anaerobic thermophilic conditions

Biodegradable polymers are designed to resist a number of environmental factors during use, but to be biodegradable under disposal conditions. The biodegradation of polylactide (PLLA) was studied at different elevated temperatures in both aerobic and anaerobic, aquatic and solid state conditions. In the aerobic aquatic headspace test the mineralisation of PLLA was very slow at room temperature, but faster under thermophilic conditions. The clear effect of temperature on the biodegradability of PLLA in the aquatic tests indicates that its polymer structure has to be hydrolysed before microorganisms can utilise it as a nutrient source. At similar elevated temperatures, the biodegradation of PLLA was much faster in anaerobic solid state conditions than in aerobic aquatic conditions. The behaviour of PLLA in the natural composting process was similar to that in the aquatic biodegradation tests, biodegradation starting only after the beginning of the thermophilic phase. These results indicate that PLLA can be considered as a compostable material, being stable during use at mesophilic temperatures, but degrading rapidly during waste disposal in compost or anaerobic treatment facilities.     

Biotic transformation of anticoccidials in soil using a lab-scale bio-reactor as a precursor-tool

Two anticoccidial agents, salinomycin and robenidine, heavily used in the worldwide veterinary meat production, were investigated for their potential biotic degradation by cultured soil bacteria. The degradation-study was performed in lab-scale bio-reactors under aerobic and anaerobic conditions incubated for 200 h with a mixed culture of soil bacteria. Samples were analyzed by LC-MS/MS and potential transformation products were tentatively identified. Salinomycin was degraded under aerobic conditions and traces could be found after 200 h, however, seems more persistent under anaerobic conditions. Four transformation products of salinomycin were discovered. Robenidine was degraded under aerobic and anaerobic conditions, however, traces of robenidine were observed after 200 h. Five biotic transformation products of robenidine were discovered.     

Microbial bioavailability of pyrene in three laboratory-contaminated soils under aerobic and anaerobic conditions

Changes in bioavailability of pyrene in three uncontaminated soils were examined under aerobic and anaerobic conditions. Three soils were aerobically aged with pyrene and [(14)C]pyrene for 63 days, then incubated with water, nitrate, or sulfate under aerobic or anaerobic conditions for one year. Under aerobic conditions, microorganisms in two soils mineralized 58-82% of the added [(14)C]pyrene. The two soils amended with nitrate were seen to have enhanced aerobic mineralization rates. In one of these soils, non-extractable pyrene was seen to decrease over the course of the study due to desorption and mineralization, nitrate amendment enhanced this effect. Under anaerobic conditions, generated with a N(2):CO(2)(g) headspace, two soils with nitrate or sulfate amendment showed an increase in extractable [(14)C]pyrene at 365 days relative to inhibited controls, presumably due to microbially mediated oxidation-reduction potential and pH alteration of the soil environment. These observations in different soils incubated under aerobic and anaerobic conditions have important implications relative to the impact of microbial electron acceptors on bioavailability and transport of non-polar organic compounds in the environment suggesting that, given enough time, under the appropriate environmental conditions, non-extractable material becomes bioavailable. This information should be considered when assessing site specific exposure risks at PAH contaminated locations.     

Impact of redox conditions on metolachlor and metribuzin degradation in Mississippi flood plain soils

The effect of soil redox conditions on the degradation of metolachlor and metribuzin in two Mississippi soils (Forrestdale silty clay loam and Loring silt loam) were examined in the laboratory. Herbicides were added to soil in microcosms and incubated either under oxidized (aerobic) or reduced (anaerobic) conditions. Metolachlor and metribuzin degradation under aerobic condition in the Forrestdale soil proceeded at rates of 8.83 ngd(-1) and 25 ngd(-1), respectively. Anaerobic degradation rates for the two herbicides in the Forestdale soil were 8.44 ngd(-1) and 32.5 ngd(-1), respectively. Degradation rates for the Loring soil under aerobic condition were 24.8 ngd(-1) and 12.0 ngd(-1) for metolachlor and metribuzin, respectively. Metolachlor and metribuzin degradation rates under anaerobic conditions in the Loring soil were 20.9 ngd(-1) and 5.35 ngd(-1). Metribuzin degraded faster (12.0 ngd(-1)) in the Loring soil under aerobic conditions as compared to anaerobic conditions (5.35 ngd(-1)).     

Denitrification with acrylamide by pure culture of bacteria isolated from acrylonitrile-butadiene-styrene resin manufactured wastewater treatment system

Acrylamide is widely used in industrial applications as cement binder and solidification agent. Due to its carcinogenicity and toxicity, discharge of acrylamide to the natural water and soil systems may lead to an adverse environmental impact on water quality and thus endanger public health and welfare. This study attempts to isolate and identify the denitrifying bacteria, which utilize acrylamide as the substrate from the acrylonitrile-butadiene-styrene resin manufactured wastewater treatment system. The performance of the denitrifying bacteria for treating different initial acrylamide concentrations was also investigated under aerobic and anaerobic conditions. The test results indicated that the Pseudomonas stutzeri could remove acrylamide at concentrations below 440 mg/l under aerobic conditions. The acrylic acid and ammonia intermediates were used as carbon and nitrogen sources, respectively. However, P. stutzeri did not show the capability of metabolizing acrylonitrile under aerobic conditions. Furthermore, the P. stutzeri could utilize both acrylamide and acrylic acid in the presence of nitrate (denitrification) and acrylamide could be removed completely from the wastewater.     

Field and laboratory studies of the fate and enantiomeric enrichment of venlafaxine and O-desmethylvenlafaxine under aerobic and anaerobic conditions

The stereoselectivity of R,S-venlafaxine and its metabolites R,S-O-desmethylvenlafaxine, N-desmethylvenlafaxine, O,N-didesmethylvenlafaxine, N,N-didesmethylvenlafaxine and tridesmethylvenlafaxine was studied in three processes: (i) anaerobic and aerobic laboratory scale tests; (ii) six wastewater treatment plants (WWTPs) operating under different conditions; and (iii) a variety of wastewater treatments including conventional activated sludge, natural attenuation along a receiving river stream and storage in operational and seasonal reservoirs. In the laboratory and field studies, the degradation of the venlafaxine yielded O-desmethylvenalfaxine as the dominant metabolite under aerobic and anaerobic conditions. Venlafaxine was almost exclusively converted to O-desmethylvenlafaxine under anaerobic conditions, but only a fraction of the drug was transformed to O-desmethylvenlafaxine under aerobic conditions. Degradation of venlafaxine involved only small stereoisomeric selectivity. In contrast, the degradation of O-desmethylvenlafaxine yielded remarkable S to R enrichment under aerobic conditions but none under anaerobic conditions. Determination of venlafaxine and its metabolites in the WWTPs agreed well with the stereoselectivity observed in the laboratory studies. Our results suggest that the levels of the drug and its metabolites and the stereoisomeric enrichment of the metabolite and its parent drug can be used for source tracking and for discrimination between domestic and nondomestic wastewater pollution. This was indeed demonstrated in the investigations carried out at the Jerusalem WWTP.     

Aerobic and anaerobic membrane bioreactors for municipal wastewater treatment.

An aerobic bioreactor and an anaerobic bioreactor, each coupled with a microfiltration membrane filter (MBR), were operated at different hydraulic retention times (HRTs) with primary effluent from the City of Elmhurst, Illinois, municipal-wastewater-treatment plant. The soluble chemical oxygen demand (COD) removal performance of the anaerobic MBR system was similar to that of the aerobic MBR under the same operational conditions, without the added cost of aeration. The results indicated that the solids deposition rate on the membrane surface was lower in the case of anaerobic MBR compared to the aerobic MBR, indicating possible lower loss in water-flux rates. This research found that an anaerobic MBR is a feasible and economical option for municipal-wastewater-treatment plants seeking COD removal by a biological process followed by a separate nitrification and denitrification system.