Synergistic Treatment of Mixed 1,4-Dioxane and Chlorinated Solvent Contaminations by Coupling Electrochemical Oxidation with Aerobic Biodegradation.

Biodegradation of the persistent groundwater contaminant 1,4-dioxane is often hindered by the absence of dissolved oxygen and the co-occurrence of inhibiting chlorinated solvents. Using flow-through electrolytic reactors equipped with Ti/IrO2-Ta2O5 mesh electrodes, we show that combining electrochemical oxidation with aerobic biodegradation produces an overadditive treatment effect for degrading 1,4-dioxane. In reactors bioaugmented by Pseudonocardia dioxanivorans CB1190 with 3.0 V applied, 1,4-dioxane was oxidized 2.5 times faster than in bioaugmented control reactors without an applied potential, and 12 times faster than by abiotic electrolysis only. Quantitative polymerase chain reaction analyses of CB1190 abundance, oxidation-reduction potential, and dissolved oxygen measurements indicated that microbial growth was promoted by anodic oxygen-generating reactions. At a higher potential of 8.0 V, however, the cell abundance near the anode was diminished, likely due to unfavorable pH and/or redox conditions. When coupled to electrolysis, biodegradation of 1,4-dioxane was sustained even in the presence of the common co-contaminant trichloroethene in the influent. Our findings demonstrate that combining electrolytic treatment with aerobic biodegradation may be a promising synergistic approach for the treatment of mixed contaminants.

Advances in bioremediation of 1,4-dioxane-contaminated waters.

1,4-Dioxane is a contaminant of emerging concern that has been found widespread in groundwater, surface water, and drinking water environments. Many states are implementing lower regulatory advisory levels based on the toxicological profile of 1,4-dioxane and the potential public health risks. However, the unique chemical properties of 1,4-dioxane, such as high water solubility, low Henry's law constant, and importantly, the co-occurrence with chlorinated solvents and other contaminants, increase the challenges to efficiently cleanup 1,4-dioxane. This review summarizes currently available chemical and physical 1,4-dioxane treatment technologies and focuses on recent advances in bioremediation and monitoring tools. We also include laboratory studies and field applications to propose the next steps in 1,4-dioxane bioremediation research. It is important to provide useful references to change the industrial and regulatory perception of 1,4-dioxane biodegradability, to understand treatment mechanisms especially in contaminant mixtures, and to direct research for meeting practical needs.

Biodegradation Kinetics of 1,4-Dioxane in Chlorinated Solvent Mixtures.

This study investigated the impacts of individual chlorinated solvents and their mixtures on aerobic 1,4-dioxane biodegradation by Pseudonocardia dioxanivorans CB1190. The established association of these co-occurring compounds suggests important considerations for their respective biodegradation processes. Our kinetics and mechanistic studies demonstrated that individual solvents inhibited biodegradation of 1,4-dioxane in the following order: 1,1-dichloroethene (1,1-DCE) > cis-1,2-diochloroethene (cDCE) > trichloroethene (TCE) > 1,1,1-trichloroethane (TCA). The presence of 5 mg L(-1) 1,1-DCE completely inhibited 1,4-dioxane biodegradation. Subsequently, we determined that 1,1-DCE was the strongest inhibitor of 1,4-dioxane biodegradation by bacterial pure cultures exposed to chlorinated solvent mixtures as well as in environmental samples collected from a site contaminated with chlorinated solvents and 1,4-dioxane. Inhibition of 1,4-dioxane biodegradation rates by chlorinated solvents was attributed to delayed ATP production and down-regulation of both 1,4-dioxane monooxygenase (dxmB) and aldehyde dehydrogenase (aldH) genes. Moreover, increasing concentrations of 1,1-DCE and cis-1,2-DCE to 50 mg L(-1) respectively increased 5.0-fold and 3.5-fold the expression of the uspA gene encoding a universal stress protein. In situ natural attenuation or enhanced biodegradation of 1,4-dioxane is being considered for contaminated groundwater and industrial wastewater, so these results will have implications for selecting 1,4-dioxane bioremediation strategies at sites where chlorinated solvents are present as co-contaminants.

Identification and quantification of Thiothrix eikelboomii using qPCR for early detection of bulking incidents in a full-scale water reclamation plant.

This study found that the ratio of Thiothrix eikelboomii to total bacterial concentrations (TH/TB) (%) was a better indicator of bulking incidents affecting effluent quality compared to absolute T. eikelboomii abundance alone. This was determined using a genus-specific Thiothrix quantitative PCR primer and probe set, which was developed in this study to monitor specific Thiothrix populations over a 1-year period. T. eikelboomii was identified as the source of bulking incidents based on sequencing of the 16S rRNA gene at a nitrifying-denitrifying wastewater treatment plant. Peak T. eikelboomii concentrations observed in March, April, and July 2009 were 2.32 × 10(10), 2.64 × 10(10), and 1.84 × 10(10) cells/l, respectively. The highest fraction of T. eikelboomii to total bacterial population was measured at 0.24% in March, and a ratio >0.19% caused increases of suspended solids and biochemical oxygen demand in the secondary effluent. Additionally, food/mass ratios, dissolved oxygen concentrations in the anoxic selector, and ammonium ion concentrations in the primary effluent were three parameters displaying statistically significant correlations (r = 0.40, r = 0.50, and r = 0.32, respectively) to Thiothrix spp. abundance in an aeration tank. No bulking events caused by T. eikelboomii occurred when the dissolved oxygen concentrations in the anoxic selector was maintained at lower than 0.12 mg/l and the TH/TB ratios were <0.10%.

Identification of biomarker genes to predict biodegradation of 1,4-dioxane.

Bacterial multicomponent monooxygenase gene targets in Pseudonocardia dioxanivorans CB1190 were evaluated for their use as biomarkers to identify the potential for 1,4-dioxane biodegradation in pure cultures and environmental samples. Our studies using laboratory pure cultures and industrial activated sludge samples suggest that the presence of genes associated with dioxane monooxygenase, propane monooxygenase, alcohol dehydrogenase, and aldehyde dehydrogenase are promising indicators of 1,4-dioxane biotransformation; however, gene abundance was insufficient to predict actual biodegradation. A time course gene expression analysis of dioxane and propane monooxygenases in Pseudonocardia dioxanivorans CB1190 and mixed communities in wastewater samples revealed important associations with the rates of 1,4-dioxane removal. In addition, transcripts of alcohol dehydrogenase and aldehyde dehydrogenase genes were upregulated during biodegradation, although only the aldehyde dehydrogenase was significantly correlated with 1,4-dioxane concentrations. Expression of the propane monooxygenase demonstrated a time-dependent relationship with 1,4-dioxane biodegradation in P. dioxanivorans CB1190, with increased expression occurring after over 50% of the 1,4-dioxane had been removed. While the fraction of P. dioxanivorans CB1190-like bacteria among the total bacterial population significantly increased with decrease in 1,4-dioxane concentrations in wastewater treatment samples undergoing active biodegradation, the abundance and expression of monooxygenase-based biomarkers were better predictors of 1,4-dioxane degradation than taxonomic 16S rRNA genes. This study illustrates that specific bacterial monooxygenase and dehydrogenase gene targets together can serve as effective biomarkers for 1,4-dioxane biodegradation in the environment.

Interaction of operational and physicochemical factors leading to Gordonia amarae-like foaming in an incompletely nitrifying activated sludge plant.

The overgrowth of Gordonia amarae-like bacteria in the mixed liquor of an incompletely nitrifying water reclamation plant was inversely correlated with temperature (r = -0.78; P < 0.005) and positively correlated with the solids retention time (SRT) obtained a week prior to sampling (r = 0.67; P < 0.005). Drops followed by spikes in the food-to-mass ratio (0.18 to 0.52) and biochemical oxygen demand concentrations in primary effluent (94 to 298 mg liter(-1)) occurred at the initiation of G. amarae-like bacterial growth. The total bacterial concentration did not increase as concentrations of G. amarae-like cells increased, but total bacterial cell concentrations fluctuated in a manner similar to that of G. amarae-like bacteria in the pseudo-steady state. The ammonium ion removal rate (percent) was inversely related to G. amarae-like cell concentrations during accelerated growth and washout phases. The dissolved oxygen concentration decreased as the G. amarae-like cell concentration decreased. The concentrations of G. amarae-like cells peaked (2.47 × 10(9) cells liter(-1)) approximately 1.5 months prior to foaming. Foaming occurred during the late pseudo-steady-state phase, when temperature declines reversed. These findings suggested that temperature changes triggered operational and physicochemical changes favorable to the growth of G. amarae-like bacteria. Fine-scale quantitative PCR (qPCR) monitoring at weekly intervals allowed a better understanding of the factors affecting this organism and indicated that frequent sampling was required to obtain statistical significance with factors changing as the concentrations of this organism increased. Furthermore, the early identification of G. amarae-like cells when they are confined to mixed liquor (10(7) cells liter(-1)) allows management strategies to prevent foaming.

Cometabolic biotransformation of 1,4-dioxane in mixtures with hexavalent chromium using attached and planktonic bacteria.

Biological treatment of 1,4-dioxane, a probable human carcinogen and a recalcitrant contaminant of concern, is often complicated by the presence of inhibitory co-contaminants. Due to its use as a solvent, wetting agent, and stabilizer for chlorinated solvents employed in metal vapor degreasing, 1,4-dioxane has often been found to occur with a variety of co-contaminants, including heavy metals such as hexavalent chromium [Cr(VI)]. Cr(VI) also occurs naturally in groundwater due to geological formations, but also has sources that can coincide with 1,4-dioxane from anthropogenic activities such as metal vapor degreasing. Biodegradation of 1,4-dioxane can be accomplished by microbes that use it as a source of carbon or energy as well as those that cometabolize it after growth on other organic substrates. A propanotroph, Mycobacterium austroafricanum JOB5, was grown in planktonic pure cultures and biofilms to determine its ability to cometabolize 1,4-dioxane in the presence of varying concentrations of Cr(VI). 1,4-Dioxane cometabolism by JOB5 planktonic cells was uninhibited by Cr(VI) at levels up to 10 mg/L, while biofilms were only mildly inhibited at 10 mg/L. As an important part of the biofilms commonly found in subsurface aquifers and engineered systems, extracellular polymeric substances (EPS) were found to play an important role in preventing Cr(VI) exposure to cells. We observed that soluble EPS were able to bind to Cr(VI) and theorize that biofilm-associated EPS additionally served to impede penetration of the biofilm structure by Cr(VI), thus mitigating exposure and toxicity. These findings suggest that bioremediation would be a viable treatment strategy for 1,4-dioxane-contaminated waters that contain elevated levels of Cr(VI) in natural and built environments.

Monitoring, assessment, and prediction of microbial shifts in coupled catalysis and biodegradation of 1,4-dioxane and co-contaminants.

Microbial community dynamics were characterized following combined catalysis and biodegradation treatment trains for mixtures of 1,4-dioxane and chlorinated volatile organic compounds (CVOCs) in laboratory microcosms. Although a few specific bacterial taxa are capable of removing 1,4-dioxane and individual CVOCs, many microorganisms are inhibited when these contaminants are present in mixtures. Chemical catalysis by tungstated zirconia (WOx/ZrO2) and hydrogen peroxide (H2O2) as a non-selective treatment was designed to achieve nearly 20% 1,4-dioxane and over 60% trichloroethene and 50% dichloroethene removals. Post-catalysis, bioaugmentation with 1,4-dioxane metabolizing bacterial strain,Pseudonocardia dioxanivorans CB1190, removed the remaining 1,4-dioxane. The evolution of the microbial community under different conditions was time-dependent but relatively independent of the concentrations of contaminants. The compositions of microbiomes tended to be similar regardless of complex contaminant mixtures during the biodegradation phase, indicating a r-K strategy transition attributed to the shock experienced during catalysis and the subsequent incubation. The originally dominant genera Pseudomonas and Ralstonia were sensitive to catalytic oxidation, and were overwhelmed by Sphingomonas, Rhodococcus, and other catalyst-tolerant microbes, but microbes capable of biodegradation of organics thrived during the incubation. Methane metabolism, chloroalkane-, and chloroalkene degradation pathways appeared to be responsible for CVOC degradation, based on the identifications of haloacetate dehalogenases, 2-haloacid dehalogenases, and cytochrome P450 family. Network analysis highlighted the potential interspecies competition or commensalism, and dynamics of microbiomes during the biodegradation phase that were in line with shifting predominant genera, confirming the deterministic processes guiding the microbial assembly. Collectively, this study demonstrated that catalysis followed by bioaugmentation is an effective treatment for 1,4-dioxane in the presence of high CVOC concentrations, and it enhanced our understanding of microbial ecological impacts resulting from abiotic-biological treatment trains. These results will be valuable for predicting treatment synergies that lead to cost savings and improve remedial outcomes in short-term active remediation as well as long-term changes to the environmental microbial communities.

Development of a quantitative PCR method to differentiate between viable and nonviable bacteria in environmental water samples.

Ethidium monoazide bromide (EMA) treatment of pure culture and environmental waters at low concentrations (1.0-7.5 microg/ml) indicated effective enumeration of viable and viable but nonculturable Escherichia coli in pure cultures, creek waters, and secondary activated sludge effluent samples by quantitative polymerase chain reaction (qPCR) amplification of the uidA and fliC gene targets at turbidity values < 10 NTU. However, EMA treatment was not effective in primary clarifier and secondary trickling filter effluents where turbidities were > or = 10 NTU. In viable pure cultures, rapidly dividing and senescent cells were most affected by increasing EMA concentrations. Amplification of heat-killed pure bacterial cultures decreased 4 to 6 logs depending on EMA concentration and culture age. The greatest difference was observed in 5-h cultures using 7.5 microg/ml EMA. Turbidity (> or = 100 NTU) in environmental samples inhibited EMA effectiveness on viability discrimination. Enumeration of E. coli in certain wastewaters using EMA-qPCR was similar to culture suggesting that EMA treatment could be incorporated into qPCR assays for the quantification of viable bacteria increasing assay time no more than 30 min. Our results indicate that EMA can be used in routine qPCR assays, but optimum conditions for exposure must be identified for each sample type due to sample matrix effects such as turbidity.

Response and recovery of microbial communities subjected to oxidative and biological treatments of 1,4-dioxane and co-contaminants.

Microbial community dynamics were characterized following combined oxidation and biodegradation treatment trains for mixtures of 1,4-dioxane and chlorinated volatile organic compounds (CVOCs) in laboratory microcosms. Bioremediation is generally inhibited by co-contaminate CVOCs; with only a few specific bacterial taxa reported to metabolize or cometabolize 1,4-dioxane being unaffected. Chemical oxidation by hydrogen peroxide (H2O2) as a non-selective treatment demonstrated 50-80% 1,4-dioxane removal regardless of the initial CVOC concentrations. Post-oxidation bioaugmentation with 1,4-dioxane metabolizer Pseudonocardia dioxanivorans CB1190 removed the remaining 1,4-dioxane. The intrinsic microbial population, biodiversity, richness, and biomarker gene abundances decreased immediately after the brief oxidation phase, but recovery of cultivable microbiomes and a more diverse community were observed during the subsequent 9-week biodegradation phase. Results generated from the Illumina Miseq sequencing and bioinformatics analyses established that generally oxidative stress tolerant genus Ralstonia was abundant after the oxidation step, and Cupriavidus, Pseudolabrys, Afipia, and Sphingomonas were identified as dominant genera after aerobic incubation. Multidimensional analysis elucidated the separation of microbial populations as a function of time under all conditions, suggesting that temporal succession is a determining factor that is independent of 1,4-dioxane and CVOCs mixtures. Network analysis highlighted the potential interspecies competition or commensalism, and dynamics of microbiomes during the biodegradation phase, in line with the shifts of predominant genera and various developing directions during different steps of the treatment train. Collectively, this study demonstrated that chemical oxidation followed by bioaugmentation is effective for treating 1,4-dioxane, even in the presence of high levels of CVOC mixtures and residual peroxide, a disinfectant, and enhanced our understanding of microbial ecological impacts of the treatment train. These results will be valuable for predicting treatment synergies that lead to cost savings and improved remedial outcomes in short-term active remediation as well as long-term changes to the environmental microbial communities.

Abiotic and bioaugmented granular activated carbon for the treatment of 1,4-dioxane-contaminated water.

1,4-Dioxane is a probable human carcinogen and an emerging contaminant that has been detected in surface water and groundwater resources. Many conventional water treatment technologies are not effective for the removal of 1,4-dioxane due to its high water solubility and chemical stability. Biological degradation is a potentially low-cost, energy-efficient approach to treat 1,4-dioxane-contaminated waters. Two bacterial strains, Pseudonocardia dioxanivorans CB1190 (CB1190) and Mycobacterium austroafricanum JOB5 (JOB5), have been previously demonstrated to break down 1,4-dioxane through metabolic and co-metabolic pathways, respectively. However, both CB1190 and JOB5 have been primarily studied in laboratory planktonic cultures, while most environmental microbes grow in biofilms on surfaces. Another treatment technology, adsorption, has not historically been considered an effective means of removing 1,4-dioxane due to the contaminant's low Koc and Kow values. We report that the granular activated carbon (GAC), Norit 1240, is an adsorbent with high affinity for 1,4-dioxane as well as physical dimensions conducive to attached bacterial growth. In abiotic batch reactor studies, 1,4-dioxane adsorption was reversible to a large extent. By bioaugmenting GAC with 1,4-dioxane-degrading microbes, the adsorption reversibility was minimized while achieving greater 1,4-dioxane removal when compared with abiotic GAC (95-98% reduction of initial 1,4-dioxane as compared to an 85-89% reduction of initial 1,4-dioxane, respectively). Bacterial attachment and viability was visualized using fluorescence microscopy and confirmed by amplification of taxonomic genes by quantitative polymerase chain reaction (qPCR) and an ATP assay. Filtered samples of industrial wastewater and contaminated groundwater were also tested in the bioaugmented GAC reactors. Both CB1190 and JOB5 demonstrated 1,4-dioxane removal greater than that of the abiotic adsorbent controls. This study suggests that bioaugmented adsorbents could be an effective technology for 1,4-dioxane removal from contaminated water resources.

Differential Sensitivity of Wetland-Derived Nitrogen Cycling Microorganisms to Copper Nanoparticles.

Metallic nanoparticles (NPs), the most abundant nanomaterials in consumer and industrial products, are the most probable class to enter the environment. In this study, wetland-derived microcosms were incubated with copper nanoparticles (Cu-NP) and ionic CuCl2 to investigate acute (10 days) and chronic (100 days) exposure towards nitrogen cycling microorganisms. The microbial ecology of wetlands play a crucial role in balancing nitrogen in pristine environments as well as in areas impacted by high nutrient loads (e.g., at wastewater effluent discharges). Gene abundance and expression changes were monitored using the GeoChip 5.0 high throughput functional gene microarray and metatranscriptomic shotgun sequencing (RNA-seq), respectively. After 10 days, the Cu-NP impacted microbial communities experienced structural shifts within microorganisms associated with dissimilatory nitrogen reduction accompanied by lower nitrate removal as compared to the unexposed controls. By day 100, these differences were largely resolved and nitrate removal was similar to the unexposed control. Furthermore, the Cu-NP exposed microcosms tolerated copper and were more resilient and adaptive than the unexposed controls based on the abundance and expression of other functions, including electron transfer, metal homeostasis, and stress response. These findings suggest sudden influxes of Cu-NPs into wetland systems may impair nitrogen removal initially, but long-term microbial shifts and functional redundancy would promote the net flux of total nitrogen out of the wetlands.

Transition metals and organic ligands influence biodegradation of 1,4-dioxane.

1,4-Dioxane, a contaminant increasingly detected in water supplies, is a public health concern because it is classified as a possible human carcinogen. 1,4-Dioxane can be biodegraded by aerobic bacteria via monooxygenase-catalyzed reactions. While these metalloenzymes require trace metals as cofactors in their catalytic sites, these metals may be toxic at elevated concentrations. In this study, the effects of transition metals on 1,4-dioxane biodegradation by Pseudonocardia dioxanivorans CB1190, a monooxygenase-expressing bacterium, were investigated. Dose-dependent inhibition of 1,4-dioxane biodegradation by Cd(II), Cu(II), and Ni(II) was observed, whereas Zn(II) had no measurable effect on biodegradation rates. 1,4-Dioxane biodegradation in cultures exposed to 2 mg/L Cu(II) was restored in the presence of 0.005, 0.05, and 0.5 mM alginin, 0.05, and 0.5 mM cysteine, and 0.005 mM tannin. These results indicated that specific ligands bind with transition metals and alleviate bacterial toxicity. In parallel experiments, tannin and cysteine inhibited 1,4-dioxane biodegradation, but alginin, BSA, and SRNOM did not affect the biodegradation rates. Thus, monooxygenase-catalyzed biodegradation rates are subject to interactions among transition metals and natural organic ligands in the environment. Mechanistic insights and quantitative data obtained in this study will be useful for designing bioremediation strategies at sites simultaneously contaminated with metals and organic pollutants.

Influence of physicochemical and operational parameters on Nitrobacter and Nitrospira communities in an aerobic activated sludge bioreactor.

To understand how to optimize performance of a partially nitrifying plant, the dynamics of Nitrospira and Nitrobacter abundance were studied over a 1 year period using quantitative polymerase chain reaction (qPCR) and their relative contributions to nitrite oxidation assessed including the affects of temperature and dissolved oxygen (DO). Correlation coefficients linking shifts in the community composition of nitrite-oxidizing bacteria (NOB) to operational or environmental variables indicated Nitrospira was significantly and negatively correlated to nitrite concentrations (r = -0.45, P < 0.01) and DO (r = -0.46, P < 0.01), while temperature showed a strong positive correlation (r = 0.59, P < 0.0001). However, the Nitrobacter portion of the total NOB populations showed a positive correlations with DO (r = 0.38, P < 0.01) and hydraulic retention time (HRT) (r = 0.33, P < 0.05), as well as being negatively correlated with temperature (r = -0.49, P < 0.001) suggesting specific niche adaptations within the NOB community. Nitrospira was dominant being better adapted to the low DO and shorter sludge retention times (SRT) of this plant, while Nitrobacter increased in abundance during the winter months, when temperatures were lower and DO concentrations higher. Principal component analysis (PCA) results supported these findings by the close proximity of Nitrospira and temperature biplots of PC1 and PC2 as well as grouping Nitrobacter, NO(2)(-)-N, HRT, and DO in the loadings together. The clustering of samples from specific dates also exhibited a strong seasonality.

Microbial source tracking in a small southern California urban watershed indicates wild animals and growth as the source of fecal bacteria.

Three independent microbial source tracking (MST) methods were applied to a small urban subwatershed in Orange County, California. Fifty-seven water samples collected over summer 2002 were analyzed for human adenovirus and enterovirus. Enterococci and E. coli were isolated for antibiotic resistance analysis (ARA) and for PCR identification of human- and animal-specific toxin genes, respectively. All water samples were PCR negative for human enteroviruses and E. coli human-specific toxin gene. E. coli toxin markers revealed the presence of toxin genes specific to bird, rabbit, and cow. Enterococci ARA results supported this conclusion and indicated that fecal bacteria from bird and wild animal feces as well as soil were the predominant source found in the watershed. An E. coli, isolated from the watershed and inoculated back into the heat-sterilized storm drain water, increased 4 log units within 6 days. Collectively, these results suggest that bird and wild animal feces, soil amendments, and/or fecal coliform growth in the storm drain are the major contributors to the fecal bacterial pollution in downstream areas. However, human adenoviruses were detected on two occasions. Fecal bacterial concentrations were not elevated on these two occasions, suggesting that the elevated levels of fecal indicator bacteria in this small watershed could be unrelated to the source of human adenovirus.