Simultaneous Cr(VI) reduction and phenol degradation in pure cultures of Pseudomonas aeruginosa CCTCC AB91095

Efficient removal and transformation of Cr(VI) from alkaline wastewater to form a ferrochromium spinel multiphase via a modified ferrite process

Chromium-containing wastewater causes serious environmental pollution due to the harmfulness of Cr(VI). The ferrite process is typically used to treat chromium-containing wastewater and recycle the valuable chromium metal. However, the current ferrite process is unable to fully transform Cr(VI) into chromium ferrite under mild reaction conditions. This paper proposes a novel ferrite process to treat chromium-containing wastewater and recover valuable chromium metal. The process combines FeSO4 reduction and hydrothermal treatment to remove Cr(VI) and form chromium ferrite composites. The Cr(VI) concentration in the wastewater was reduced from 1040 mg L-1 to 0.035 mg L-1, and the Cr(VI) leaching toxicity of the precipitate was 0.21 mg L-1 under optimal hydrothermal conditions. The precipitate consisted of micron-sized ferrochromium spinel multiphase with polyhedral structure. The mechanism of Cr(VI) removal involved three steps: 1) partial oxidation of FeSO4 to Fe(III) hydroxide and oxy-hydroxide; 2) reduction of Cr(VI) by FeSO4 to Cr(III) and Fe(III) precipitates; 3) transformation and growth of the precipitates into chromium ferrite composites. This process meets the release standards of industrial wastewater and hazardous waste and can improve the efficiency of the ferrite process for toxic heavy metal removal.

Evaluation of a Microbial Consortium and Selection of a Support in an Anaerobic Reactor Directed to the Bio-Treatment of Wastewater of the Textile Industry

The dyeing processes of the textile industry generate waste products such as unfixed dyes, phenolic surfactants and heavy metals. These constitute an environmental problem for the bodies receiving their wastewater due to the interruption of the lighting in the aquatic environment and the release of toxic molecules by the decomposition of the dyes. There are several treatment methods, of which biological methods are the most feasible. In the current study, the I5-ESPE microbial consortium was obtained and evaluated on the components of textile wastewater, in addition to the selection of a support for an anaerobic reactor that is directed to the treatment of effluents from the textile industry. Two microbial consortia were achieved by exposure to air in Pseudomonas culture medium modified with direct dyes Red 23 and Blue 106, evaluating their removal capacity of the reactive dyes Navy 171, Red 141 and Yellow 84. The consortium I5-ESPE was selected for its greatest action, yielding approximately 95% removal. Its tolerance to phenol was also determined; we reached 98% removal of chromium(VI) and 67% of total chromium under anaerobic conditions and some 25% zinc in aerobiosis. The reduction in the chemical oxygen demand (COD) was evaluated with (57.03%) and without (31.47%) aeration. The species Staphylococcus xylosus, Saccharomyces cerevisiae and Candida tropicalis were identified prior to treatment of textile wastewater, as well as Enterobacter cloacae and Bacillus megaterium after treatment. Bacillus subtilis was present throughout the process. We evaluated coconut shell as a support for an anaerobic reactor, and it demonstrated better physical characteristics than plastic and common rock, in addition to similar results in the reduction in COD of 50%, volatile suspended solids of 2545.46 mg/L and total suspended solids of 282.82 mg/L.

Concurrent anaerobic chromate bio-reduction and pentachlorophenol bio-degradation in a synthetic aquifer

Chromate [Cr(VI)] and pentachlorophenol (PCP) coexist widely in the environment and are highly toxic to public health. However, whether Cr(VI) bio-reduction is accompanied by PCP bio-degradation and how microbial communities can keep long-term stability to mediate these bioprocesses in aquifer remain elusive. Herein, we conducted a 365-day continuous column experiment, during which the concurrent removals of Cr(VI) and PCP were realized under anaerobic condition. This process allowed for complete Cr(VI) bio-reduction and PCP bio-degradation at an efficiency of 92.8 ± 4.2% using ethanol as a co-metabolic substrate. More specifically, Cr(VI) was reduced to insoluble chromium (III) and PCP was efficiently dechlorinated with chloride ion release. Collectively, Acinetobacter and Spirochaeta regulated Cr(VI) bio-reduction heterotrophically, while Pseudomonas mediated not only Cr(VI) bio-reduction but also PCP bio-dechlorination. The bio-dechlorinated products were further mineralized by Azospira and Longilinea. Genes encoding proteins for Cr(VI) bio-reduction (chrA and yieF) and PCP bio-degradation (pceA) were upregulated. Cytochrome c and intracellular nicotinamide adenine dinucleotide were involved in Cr(VI) and PCP detoxification by promoting electron transfer. Taken together, our findings provide a promising bioremediation strategy for concurrent removal of Cr(VI) and PCP in aquifers through bio-stimulation with supplementation of appropriate substrates.

NahAa can convert naphthalene and reduce chromate simultaneously and immobilized on functional multiwall carbon nanotubes for wastewater treatment

Pseudomonas brassicacearum LZ-4 is a facultative anaerobic bacterium, can efficiently degrade naphthalene and reduce chromate simultaneously. In this study, we showed that the naphthalene degradation enzyme NahAa from P. brassicacearum LZ-4 can reduce Cr(VI). Heterologous expression in E. coli S17-1 along with RNA interference of NahAa in strain LZ-4 showed the enzyme can reduce chromate in vivo. In vitro, purified NahAa was identified and can catalyze Cr(VI) reduction by 64.2%. Flavin adenine dinucleotide (FAD) was identified as a cofactor of NahAa, which Cr(VI) could obtain electrons from NADH through NahAa-associated FAD for reduction. Immobilized NahAa on functional multi walled carbon nanotubes via physical adsorption method to produce a stable, high efficient composite MWCNT-NahAa. The maximum efficiency of MWCNT-NahAa composite was obtained in enzyme concentrations of 6 mg/mL and 20 min immobilization time. The optical reaction conditions for MWCNT-NahAa were pH 7.0 and 30 °C, still retaining 50% of its initial activities after five consecutive cycles. Application of composites in wastewater can reduce 90.4% Cr(VI), higher than free NahAa that was 63.5%. To our best knowledge, this is the first report immobilized enzyme in polycyclic aromatic hydrocarbons-degradation pathway for Cr(VI) wastewater treatment, providing a new insights on combined pollution remediation.

Performance and microbial community dynamics relationship within a step-feed anoxic/oxic/anoxic/oxic process (SF-A/O/A/O) for coking wastewater treatment

A step-feed anoxic/oxic/anoxic/oxic (SF-A/O/A/O) was developed and successfully applied to full-scale coking wastewater treatment. The performance and microbial community were evaluated and systematically compared with the anoxic/oxic/oxic (A/O/O) process. SF-A/OA/O process exhibited efficient removal of COD, NH₄⁺-N, TN, phenols, and cyanide with corresponding average effluent concentrations of 317.9, 1.8, 46.2, 1.1, and 0.2 mg·L^-1, respectively. In particular, the TN removal efficiency of A/O/O process was only 7.8%, with an effluent concentration of 300.6 mg·L^-1. Furthermore, polycyclic aromatic hydrocarbons with high molecular weight were the dominant compounds in raw coking wastewater, which were degraded to a greater extent in SF-A/OA/O. The abundance in Thiobacillus, SM1A02, and Thauera could be the main reason why SF-A/O/A/O was superior to A/O/O in treating TN. The microbial community structure of SF-A/O/A/O was similar among stages in system (P ≥ 0.05, Welch's t-test) and was less affected by environmental factors, which may have been one of the important factors in the system's strong stability.

The conversion of the nutrient condition alter the phenol degradation pathway by Rhodococcus biphenylivorans B403: A comparative transcriptomic and proteomic approach

Highly toxic phenol causes a threat to the ecosystem and human body. The development of bioremediation is a crucial issue in environmental protection. Herein, Rhodococcus biphenylivorans B403, which was isolated from the activated sludge of the sewage treatment plant, exhibited a good tolerance and removal efficiency to phenol. The degradation efficiency of phenol increased up to 62.27% in the oligotrophic inorganic medium (MM) containing 500-mg/L phenol at 18 h. R. biphenylivorans B403 cultured in the MM medium showed a higher phenol degradation efficiency than that in the eutrophic LB medium. On the basis of the transcriptomic and proteomic analysis, a total of 799 genes and 123 proteins showed significantly differential expression between two different culture conditions, especially involved in phenol degradation, carbon metabolism, and nitrogen metabolism. R. biphenylivorans B403 could alter the phenol degradation pathway by facing different culture conditions. During the phenol removal in the oligotrophic inorganic medium, muconate cycloisomerase, acetyl-CoA acyltransferase, and catechol 1,2-dioxygenase in the ortho-pathway for phenol degradation showed upregulation compared with those in the eutrophic organic medium. Our study provides novel insights into the possible pathway underlying the response of bacterium to environmental stress for phenol degradation.

Biotreatment potential of co-contaminants hexavalent chromium and polychlorinated biphenyls in industrial wastewater: Individual and simultaneous prospects

Co-existence of polychlorinated biphenyls (PCBs) and hexavalent chromium (Cr(VI)) in the environment due to effluent from industries has aggravated the pollution problem. Both contaminants can alter chemical interactions, processes and impair enzymatic activities in the ecosystem that results in negative impacts on aquatic and terrestrial life. Previously, research has been performed for the fate and transfer of these contaminants individually, but simultaneous removal approaches have not received much attention. Cr(VI) exists in a highly toxic form in the environment once released, whereas location of chlorine atoms in the ring determines PCBs toxicity. Lower chlorinated compounds are easily degradable whereas as high chlorinated compounds require sequential strategy for transformation. Microorganisms can develop different mechanism to detoxify both pollutants. However, occurrence of multiple contaminants in single system can alter the bioremediation efficiency of bacteria. Use of metal resistance bacterial for the degradation of organic compounds has been widely used bioaugmentation strategy. Along with that use of sorbents/bio sorbents, biosurfactants and phytoremediation approaches have already been well reported. Bioremediation strategy with dual potential to detoxify the Cr(VI) and PCBs would be a probable option for simultaneous biotreatment. Application of bioreactors and biofilms covered organic particles can be utilized as efficient bioaugmentation approach. In this review, biotreatment systems and bacterial oxidative and reductive enzymes/processes are explained and possible biotransformation pathway has been purposed for bioremediation of co-contaminated waters.

Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

Chromium (Cr) (VI) is a well-known toxin to all types of biological organisms. Over the past few decades, many investigators have employed numerous bioprocesses to neutralize the toxic effects of Cr(VI). One of the main process for its treatment is bioreduction into Cr(III). Key to this process is the ability of microbial enzymes, which facilitate the transfer of electrons into the high valence state of the metal that acts as an electron acceptor. Many underlying previous efforts have stressed on the use of different external organic and inorganic substances as electron donors to promote Cr(VI) reduction process by different microorganisms. The use of various redox mediators enabled electron transport facility for extracellular Cr(VI) reduction and accelerated the reaction. Also, many chemicals have employed diverse roles to improve the Cr(VI) reduction process in different microorganisms. The application of aforementioned materials at the contaminated systems has offered a variety of influence on Cr(VI) bioremediation by altering microbial community structures and functions and redox environment. The collective insights suggest that the knowledge of appropriate implementation of suitable nutrients can strongly inspire the Cr(VI) reduction rate and efficiency. However, a comprehensive information on such substances and their roles and biochemical pathways in different microorganisms remains elusive. In this regard, our review sheds light on the contributions of various chemicals as electron donors, redox mediators, cofactors, etc., on microbial Cr(VI) reduction for enhanced treatment practices.

Response of Trametes hirsuta to hexavalent chromium promotes laccase-mediated decolorization of reactive black 5

The recalcitrant azo dyes combined with heavy metals constitute a major challenge for the bioremediation of industrial effluents. This study aimed to investigate the effect and mechanism of action of a white-rot fungus Trametes hirsuta TH315 on the simultaneous removal of hexavalent chromium [Cr(VI)] and azo dye (Reactive Black 5, RB5). Here, this study discovered that toxic Cr(VI) (1 mM) greatly promoted RB5 decolorization (from 57.15% to 83.65%) by white-rot fungus Trametes hirsuta with high Cr(VI)-reducing ability (>96%), resulting in the simultaneous removal of co-contaminants. On the basis of transcriptomic and biochemical analysis, our study revealed that the oxidative stress in co-contaminants mainly caused by Cr(VI), and a number of dehydrogenases and oxidases showed up-regulation in response to Cr(VI) stress. It was noteworthy that the oxidative stress caused by Cr(VI) in co-contaminants can both significantly induce glutathione S-transferase and laccase expression. Glutathione S-transferase potentially involved in antioxidation against Cr(VI) stress. Laccase was found to play a key role in RB5 decolorization by T. hirsuta. These results suggested that the simultaneous removal of co-contaminants by T. hirsuta could be achieved with Cr(VI) exposure. Overall, the elucidation of the molecular basis in details will help to advance the general knowledge about the fungus by facing harsh environments, and put forward a further possible application of fungi on environmental remediation.

Bioreduction of hexavalent chromium on goethite in the presence of Pseudomonas aeruginosa

The effective mineral absorption and bioreduction were considered as two preferred processes to alleviate the bioavailability and toxicity of toxic trace metals. In this study, the bioreduction of hexavalent chromium (Cr(VI)) on goethite (FeOOH) in the presence of Pseudomonas aeruginosa (P. aeruginosa) was investigated with different environmental factors, including carbon source concentrations, pH, temperature and initial Cr(VI) concentrations. The characterization of FeOOH-P. aeruginosa indicated that P. aeruginosa was surrounded by FeOOH, which could provide the essential iron for bacterial growth and reduce Cr(VI) to Cr(III). The optimal experimental conditions for Cr(VI) (initial concentration: 35 mg L^-1) absorption (∼46%) and bioreduction (∼54%) involved a temperature of 45 °C and pH of 5.5. Meanwhile, extracellular polymeric substances (EPS) secreted by P. aeruginosa and its functional groups played important roles in the reduction of Cr(VI). They could reduce Cr(VI) to Cr(III) and transform to Cr(OH)₃ or Fe_x-Cr_(1-x)(OH)₃ precipitation. These results of this study are of significant importance to better understand the environmental geochemical behavior of Cr(VI) with the interactions between soil minerals and microorganisms.

An overview on heavy metal resistant microorganisms for simultaneous treatment of multiple chemical pollutants at co-contaminated sites, and their multipurpose application

Anthropogenic imbalance of chemical pollutants in environment raises serious threat to all life forms. Contaminated sites often possess multiple heavy metals and other types of pollutants. Elimination of chemical pollutants at co-contaminated sites is imperative for the safe ecosystem functions, and simultaneous removal approach is an attractive scheme for their remediation. Different conventional techniques have been applied as concomitant treatment solution but fall short at various parameters. In parallel, use of microorganisms offers an innovative, cost effective and ecofriendly approach for simultaneous treatment of various chemical pollutants. However, microbiostasis due to harmful effects of heavy metals or other contaminants is a serious bottleneck facing remediation practices in co-contaminated sites. But certain microorganisms have unique mechanisms to resist heavy metals, and can act on different noxious wastes. Considering this significant, my review provides information on different heavy metal resistant microorganisms for bioremediation of different chemical pollutants, and other assistance. In this favour, the integrated approach of simultaneous treatment of multiple heavy metals and other environmental contaminants using different heavy metal resistant microorganisms is summarized. Further, the discussion also intends toward the use of heavy metal resistant microorganisms associated with industrial and environmental applications, and healthcare. PREFACE: Simultaneous treatment of multiple chemical pollutants using microorganisms is relatively a new approach. Therefore, this subject was not well received for review before. Also, multipurpose application of heavy metal microorganisms has certainly not considered for review. In this regard, this review attempts to gather information on recent progress on studies on different heavy metal resistant microorganisms for their potential of treatment of co-contaminated sites, and multipurpose application.

Enhanced biogeogenic controls on dichromate speciation in subsoil containment

In general, lab-based Cr (VI) reduction studies do not often corroborate the prevailing biogeochemical controls for on-site pollution abatement. To promulgate its importance, herein, we investigate the existing biogeogenic parameters of a contaminated site to attenuate the underground Cr (VI) toxicity. This study significantly assesses the speciation of dichromate by biogenic agents that are inherent and self-sustaining to treat the contaminated soil. Herein, a group of bacteria exposed to high concentrations of chromium (≥3500 mg/L) plays a vital role as an enhanced biogeogenic control for the detoxification of toxic Cr (VI). All identified bacteria were screened based on their ability to differentiate from extracellular speciation and harvested in a Cr (VI)-enriched molasses to achieve dichromate concentrations as low as 0.05 mg/L in 168 h. Under low O₂ condition, the bacterial growth rate and doubling time were monitored to establish the half-life period of Cr (VI) for adequate containment treatment. Furthermore, to understand the soil decontamination, Cr (VI) reactive transport was demonstrated to facilitate the contaminant reduction under both saturated and unsaturated groundwater conditions. Herein, Cr (VI) speciation to Cr (III) by the influence of abiogenic factors are unlikely or less probable as studied in existing geogenic conditions. Moreover, the evidence of biogenic reduction of Cr (VI) in microcosm suggests its effectiveness in enhanced detoxification of Cr (VI) up to ≤ 0.1 mg/L, within the reaction period of 144 h and 192 h, for saturated and unsaturated flow conditions, respectively.

Remediation potential of immobilized bacterial consortium with biochar as carrier in pyrene-Cr(VI) co-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) and potentially toxic trace elements (PTEs) soil contamination have become areas of concern. Bioaugmentation is regarded as an effective bioremediation method, however it is difficult to simultaneously degrade organic compounds and remove PTEs with individual microbial strains. Therefore, the objective of this study was to evaluate the feasibility of using immobilized microbial consortia, including two PAH-degrading bacterial strains (W1 and W2) and a Cr(VI)-reducing bacterium (Y2), for the remediation of pyrene-Cr(VI) co-contaminated soil. Three immobilization methods were investigated: (1) bacterial consortium adsorption onto biochar (BC), (2) bacterial consortium entrapment in alginate beads (AC), (3) bacterial consortium adsorption on biochar and sequential entrapment in alginate beads (BAC). In addition, a free bacterial consortium (FC) was also used for comparison. Ten treatments were designed to illustrate the bioremediation efficiency of the free and immobilized consortia. The results show that treatments AC and BAC resulted in more efficient Cr(VI) removal compared with BC and FC. Pyrene levels in AC and BAC microcosms were reduced from 42.33 ± 3.82 to 11.56 ± 1.37 and 7.48 ± 0.39 mg kg^-1, respectively. Bioavailable Cr (VI) in AC and BAC was significantly lower than that in other microcosms after 28 days' incubation. Both AC and BAC microcosms exhibited a higher level of dehydrogenase and fluorescein diacetate hydrolysis activity. Furthermore, soil microbial diversity was higher in AC and BAC microcosms compared with the others. Thus, the entrapped consortia may be useful for bioremediation of pyrene and Cr (VI) without compromising soil ecology.

Chromate detoxification potential of Staphylococcus sp. isolates from an estuary

Chromium (Cr) pollution is an emerging environmental problem. The present study was carried out to isolate Cr-resistant bacteria and characterize their Cr detoxification and resistance ability. Bacteria screened by exposure to chromate (Cr⁶⁺) were isolated from Mandovi estuary Goa, India. Two isolates expressed high resistance to Cr⁶⁺ (MIC ≥ 300 µg mL^-1), Cr³⁺ (MIC ≥ 900 µg mL^-1), other toxic heavy metals and displayed a pattern of resistance to cephalosporins and ß-lactams. Biochemical and 16 S rRNA gene sequence analysis indicated that both isolates tested belonged to the Staphylococcus genus and were closely related to S. saprophyticus and S. arlettae. Designated as strains NIOER176 and NIOER324, batch experiments demonstrated that both removed 100% of 20 and 50 µg mL^-1 Cr⁶⁺ within 4 and 10 days, respectively. The rate of reduction in both peaked at 0.260 µg mL^-1 h^-1. ATP-binding cassette (ABC) transporter gene involved in transport of a variety of substrates including efflux of toxicants was present in strain NIOER176. Through SDS-PAGE analysis, whole-cell proteins extracted from both strains indicated chromium-induced specific induction and up-regulation of 24 and 40 kDa proteins. Since bacterial ability to ameliorate Cr⁶⁺ is of practical significance, these findings demonstrate strong potential of some estuarine bacteria to detoxify Cr⁶⁺ even when its concentrations far exceed the concentrations reported from many hazardous effluents and chromium contaminated natural habitats. Such potential of salt tolerant bacteria would help in Cr⁶⁺ bioremediation efforts.

Alleviation of hexavalent chromium by using microorganisms: insight into the strategies and complications

Excessive industrialization and anthropogenic activities have resulted in widespread prevalence of heavy metals including hexavalent chromium in the environment. In addition to toxic properties, Cr(VI) possesses high stability and mobility, which in total makes it included in the list of priority heavy metals; thus it needs to be managed urgently. Among different methods available for remediation of Cr(VI), bioremediation is considered as one of the sustainable methods which could effectively be utilized for controlling Cr(VI) pollution. In this aspect, the treatment of Cr(VI)-containing wastewater originating from industries is noteworthy. The present review thus is an attempt to present a systematic overview dealing with studies on remediation of hexavalent chromium by using microorganisms and their application in treatment of Cr(VI)-containing industrial wastewaters. Various factors affecting the Cr(VI) removal and methods to enhance the bio-treatment are highlighted, which might act as a basis for researchers developing Cr(VI) bioremediation techniques.

Immobilization of Sphingomonas sp. GY2B in polyvinyl alcohol-alginate-kaolin beads for efficient degradation of phenol against unfavorable environmental factors

In this study, batch experiments were carried out to evaluate the biodegradation of phenol by Sphingomonas sp. GY2B, which were immobilized in polyvinyl alcohol (PVA)-sodium alginate-kaolin beads under different conditions. The optimal degradation performance was achieved by GY2B immobilized in beads containing 1.0% (w/v) of kaolin, 10% (w/v) of PVA, 0.3% (w/v) of sodium alginate, 10% (v/v) of biomass dosage, and exposed to an initial phenol concentration of 100 mg/L. The experimental results indicated that PVA-sodium alginate-kaolin beads can accelerate the degradation rate of phenol by reducing the degradation time and also improve degradation rate. The biodegradation rate of phenol by immobilized cells (16.79 ± 0.81 mg/(L·h)) was significantly higher than that of free cells (11.49 ± 1.29 mg/(L·h)) under the above optimal conditions. GY2B immobilized on beads was more competent than free GY2B in degradation under conditions with high phenol concentrations (up to 300 mg/L) and in strong acidic (pH = 1) and alkaline (pH = 12) environments. Higher phenol concentrations inhibit the biomass and reduce the biodegradation rate, while the lower biodegradation rate at low initial phenol concentrations is attributed to mass transfer limitations. The Haldane inhibitory model was in agreement with the experimental data well, revealing that phenol showed a considerable inhibitory effect on the biodegradation by Sphingomonas sp. GY2B, especially at concentrations higher than 90 mg/L. Intra-particle diffusion model analysis suggests that adsorption of phenol by immobilized beads was controlled by both rapid surface adsorption as well as pore diffusion mechanism. It's worth noting that the presence of 1 mg/L Cr(VI) enhanced the biodegradation of phenol by free cells, while Cr(VI) showed no obvious impact on the removal of phenol by immobilized cells. In addition, immobilized cells were reused 16 times and removed 99.5% phenol, and when stored at 4 °C for 90 days, more than 99% phenol was removed. These results showed that immobilized cells can significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. It is implied that PVA -sodium alginate-kaolin beads have great potential to be applied in a practical and economical phenolic wastewater treatment system.

What makes A. guillouiae SFC 500-1A able to co-metabolize phenol and Cr(VI)? A proteomic approach

Acinetobacter guillouiae SFC 500-1A is an environmental bacterium able to efficiently co-remediate phenol and Cr(VI). To further understand the molecular mechanisms triggered in this strain during the bioremediation process, variations in the proteomic profile after treatment with phenol and phenol plus Cr(VI) were evaluated. The proteomic analysis revealed the induction of the β-ketoadipate pathway for phenol oxidation and the assimilation of degradation products through TCA cycle and glyoxylate shunt. Phenol exposure increased the abundance of proteins associated to energetic processes and ATP synthesis, but it also triggered cellular stress. The lipid bilayer was suggested as a target of phenol toxicity, and changing fatty acids composition seemed to be the bacterial response to protect the membrane integrity. The involvement of two flavoproteins in Cr(VI) reduction to Cr(III) was also proposed. The results suggested the important role of chaperones, antioxidant response and SOS-induced proteins in the ability of the strain to mitigate the damage generated by phenol and Cr(VI). This research contributes to elucidate the mechanisms involved in A. guillouiae SFC 500-1A tolerance and co-remediation of phenol and Cr(VI). Such information may result useful not only to improve its bioremediation efficiency but also to identify putative markers of resistance in environmental bacteria.

Simultaneous biodegradation of bifenthrin and chlorpyrifos by Pseudomonas sp. CB2

The degradation of bifenthrin (BF) and chlorpyrifos (CP), either together or individually, by a bacterial strain (CB2) isolated from activated sludge was investigated. Strain CB2 was identified as belonging to genus Pseudomonas based on the morphological, physiological, and biochemical characteristics and a homological analysis of the 16S rDNA sequence. Strain CB2 has the potential to degrade BF and CP, either individually or in a mixture. The optimum conditions for mixture degradation were as follows: OD_600nm = 0.5; incubation temperature = 30°C; pH = 7.0; BF-CP mixture (10 mg L^-1 of each). Under these optimal conditions, the degradation rate constants (and half-lives) were 0.4308 d^-1 (1.61 d) and 0.3377 d^-1 (2.05 d) for individual BF and CP samples, respectively, and 0.3463 d^-1 (2.00 d) and 0.2931 d^-1 (2.36 d) for the BF-CP mixture. Major metabolites of BF and CP were 2-methyl-3-biphenylyl methanol and 3,5,6-trichloro-2-pyridinol, respectively. No metabolite bioaccumulation was observed. The ability of CB2 to efficiently degrade BF and CP, particularly in a mixture, may be useful in bioremediation efforts.

Influence of co-existed tetrabromobisphenol A (TBBPA) and hexavalent chromium on the cellular characteristics of Pycnoporus sanguineus during their removal and reduction

Simultaneous TBBPA removal and Cr(VI) reduction by Pycnoporus sanguineus together with the effect of these co-existed pollutants on the fungal cellular characteristics were investigated in this study, aiming at illuminating the mechanism involved in the interactions between contaminants and microbial cells. The results revealed that Cr(VI) reduction and TBBPA removal declined from 92.5%, 75.4-30.6%, 44.8% when Cr(VI) concentration increased from 5 to 40mg/L, respectively. The removal efficiencies for Cr(VI) and TBBPA reached 61.4% and 94% separately under the optimum concentration of TBBPA at 10mg/L. Subsequent analyses indicated that the negative effect of Cr(VI) of high concentrations on Cr(VI) reduction and TBBPA removal was mainly attributed to the inhibition of fungal growth, intracellular proteins synthesis, cell viability and ATP enzyme activity. Compared with the moderate impact of TBBPA, the cell membrane of P. sanguineus was impaired severely and the surface morphology and intracellular structure changed dramatically in the presence of high concentration of Cr(VI) (above 10mg/L). This study also suggested that high level of TBBPA (15 and 20mg/L) promoted the synthesis of intracellular proteins and improved ATP enzyme activity within the first 48h of the reaction for enhancing the transportation and transformation of TBBPA.

Dual bioremediation of phenol and Cr(VI) by mixed microbial cultures in the presence of molasses

Simultaneous phenol and Cr(VI) bioremoval by two different mixed cultures, from petroleum-contaminated soil (PS) and boron-contaminated wastewater (BW), was investigated in regard to different culture media, pH levels (6-8), initial phenol (25-100 mg/L) and Cr(VI) (15-50 mg/L) concentrations. The optimum medium was found to be mineral salt medium tested, which contained 1% (v/v) molasses (MSM). Optimum pH values were 6 for PS and 8 for BW. All of the phenol present in the samples was mineralized regardless of its concentrations tested, Cr(VI) bioremoval was enhanced by the increase in phenol concentrations, and molasses also exerted a positive effect on Cr(VI) removal, and the yields reached 100% for both pollutants, even at 13.1 mg/L Cr(VI) and 91.1 mg/L phenol concentration in PS samples. In MSM containing PS samples approximate efficiency was 100% for phenol removal; but Cr(VI) removal ratios were 64.9% and 41.7% at 25.8 mg/L and 41.3 mg/L concentrations, respectively. Finally it can be concluded that molasses stimulated Cr(VI) bioremoval at elevated phenolic conditions in the mixed microbial culture, and molasses might be of use for the bioremediation of phenol and Cr(VI) polluted wastewaters.

Enhanced treatment performance of coking wastewater and reduced membrane fouling using a novel EMBR

A novel EMBR (electric field applied in MBR) by placing stainless steel mesh cathode inside a flat membrane module and stainless steel mesh anode outside the module was built and operated to enhance the treatment performance of coking wastewater containing phenol, pyridine and quinoline and reduce the membrane fouling. The degradation rates of COD, phenol, pyridine and quinoline in EMBR with electric field (reactor A) were significantly higher than the sum of EMBR without electric field (reactor B) and only electro-catalytic degradation during the long-term treatment, confirming that a coupling effect was existed between biodegradation and electro-catalytic degradation process. Illumina sequencing data revealed that bacterial community was richer and more diverse in reactor A. Comamonas strain JB as the inoculums was the most dominant genus in each reactor and electric field applied in reactor A further improved the abundance of strain JB. The membrane fouling in reactor A was reduced.

Bioaugmentation: an effective commercial technology for the removal of phenols from wastewater

Phenol represents a huge problem in industrial wastewater effluents and needs to be removed due to its toxic and carcinogenic nature. The removal of phenol from the wastewater is often both expensive and time consuming; there is therefore a requirement for a more effective, sustainable solution for the removal of phenol from wastewaters. Bioaugmentation or the addition of phenol degrading microorganisms to contaminated effluents is one such sustainable approach being considered. Here, we describe how bioaugmentation has been applied for the biological treatment of phenol in industrial wastewaters.

A novel Pseudomonas gessardii strain LZ-E simultaneously degrades naphthalene and reduces hexavalent chromium

Combined pollutants with polycyclic aromatic hydrocarbons (PAHs) and heavy metals have been identified as toxic and unmanageable contaminates. In this work, Pseudomonas gessardii strain LZ-E isolated from wastewater discharge site of a petrochemical company degrades naphthalene and reduces Cr(VI) simultaneously. 95% of 10mgL(-1) Cr(VI) was reduced to Cr(III) while 77% of 800mgL(-1) naphthalene was degraded when strain LZ-E was incubated in BH medium for 48h. Furthermore, naphthalene promotes Cr(VI) reduction in strain LZ-E as catechol and phthalic acid produced in naphthalene degradation are able to reduce Cr(VI) abiotically. An aerated bioreactor system was setup to test strain LZ-E's remediation ability. Strain LZ-E continuously remediated naphthalene and Cr(VI) at rates of 15mgL(-1)h(-1) and 0.20mgL(-1)h(-1) of 800mgL(-1) naphthalene and 10mgL(-1) Cr(VI) addition with eight batches in 16days. In summary, strain LZ-E is a potential applicant for combined pollution remediation.

Simultaneous Cr(VI) removal and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) biodegradation by Pseudomonas aeruginosa in liquid medium

Simultaneous Cr(VI) removal and 2,2',4,4'-tetra brominated diphenyl ether (BDE-47) biodegradation by Pseudomonas aeruginosa in liquid medium were investigated in this study, with the goal of elucidating the interaction between concomitant pollutants Cr(VI) and BDE-47 during microbial remediation. The experimental results revealed that the degradation efficiency of 1 mg L(-1) BDE-47 by 60 mg L(-1) biomass achieved 51.3% within 7 d when 2 mg L(-1) Cr(VI) coexisted. The degradation efficiency was accelerated at low concentrations of Cr(VI) (≤5 mg L(-1)), but inhibited at higher levels (≥10 mg L(-1)). Cr(VI) of 2 mg L(-1) facilitated the secretion of rhamnolipid from the strain, altered cell surface hydrophobicity and cell membrane permeability, and promoted intracellular BDE-47 accumulation, thus improving BDE-47 biotransformation. In addition, the stimulation of intracellular enzyme synthesis by 2 mg L(-1) Cr(VI) contributed to more BDE-47 elimination in the cells. The achievement of BDE-47 biodegradation was coupled with cell growth, enzyme extraction, cell membrane permeability change, and ATPase activity increase. The study also indicated that the improvement of Cr(VI) removal in BDE-47/Cr(VI) co-contaminated condition was mostly due to the increasing synthesis of extracellular enzyme in the presence of low concentrations of BDE-47. The whole study demonstrated that P. aeruginosa was available for the removal of toxic Cr(VI) and degradation of BDE-47 simultaneously in the liquid.

A simple Cr(VI)-S(IV)-O2 system for rapid and simultaneous reduction of Cr(VI) and oxidative degradation of organic pollutants

Hexavalent chromium (Cr(VI)), a heavy-metal contaminant, can be easily reduced to less toxic trivalent chromium (Cr(III)) by sulfite ions (S(IV)). However, S(IV) has not drawn as much attention as the ferrous ion has. We report herein a novel Cr(VI)-S(IV)-O2 system containing sulfite ions that rapidly and simultaneously reduces Cr(VI) and oxidize organic pollutants in the presence of oxygen in aqueous solutions. This Cr(VI)-S(IV)-O2 system contains the initiator Cr(VI), the reductant S(IV), and the oxidant O2, which produce oxysulfur radicals (mainly SO4(-) and SO5(-)) and hydroxyl radicals (OH). The Cr(VI)/S(IV) molar ratio, pH, and oxygen content play important roles in the entire reaction system. Acidic conditions (pH 3.0) facilitated degradation of organic compounds and reduction of Cr(VI) as well. In addition, experiments of rapid degradation of several kinds of organic pollutants such as azo dye (acid orange 7, AO7), aniline, phenol, bisphenol A etc were also conducted. Preliminary results show that the removal rates of the analogs of phenols or aromatic amines in this Cr(VI)-S(IV)-O2 system have a relationship with the electronic parameters (Hammett constant, σ) of the substituted groups. Thus, the Cr(VI)-S(IV)-O2 system, provides an excellent strategy of "waste control by waste" for removing multiple industrial contaminants.

Community Analysis and Recovery of Phenol-degrading Bacteria from Drinking Water Biofilters

Phenol is a ubiquitous organic contaminant in drinking water. Biodegradation plays an important role in the elimination of phenol pollution in the environment, but the information about phenol removal by drinking water biofilters is still lacking. Herein, we study an acclimated bacterial community that can degrade over 80% of 300 mg/L phenol within 3 days. PCR detection of genotypes involved in bacterial phenol degradation revealed that the degradation pathways contained the initial oxidative attack by phenol hydroxylase, and subsequent ring fission by catechol 1,2-dioxygenase. Based on the PCR denatured gradient gel electrophoresis (PCR-DGGE) profiles of bacteria from biological activated carbon (BAC), the predominant bacteria in drinking water biofilters including Delftia sp., Achromobacter sp., and Agrobacterium sp., which together comprised up to 50% of the total microorganisms. In addition, a shift in bacterial community structure was observed during phenol biodegradation. Furthermore, the most effective phenol-degrading strain DW-1 that correspond to the main band in denaturing gradient gel electrophoresis (DGGE) profile was isolated and identified as Acinetobacter sp., according to phylogenetic analyses of the 16S ribosomal ribonucleic acid (rRNA) gene sequences. The strain DW-1 also produced the most important enzyme, phenol hydroxylase, and it also exhibited a good ability to degrade phenol when immobilized on granular active carbon (GAC). This study indicates that the enrichment culture has great potential application for treatment of phenol-polluted drinking water sources, and the indigenous phenol-degrading microorganism could recover from drinking water biofilters as an efficient resource for phenol removal. Therefore, the aim of this study is to draw attention to recover native phenol-degrading bacteria from drinking water biofilters, and use these native microorganisms as phenolic water remediation in drinking water sources.

Enhanced degradation of phenol by Sphingomonas sp. GY2B with resistance towards suboptimal environment through adsorption on kaolinite

The effects of clay minerals on microbial degradation of phenol under unfavorable environmental conditions were investigated. Degradation of phenol by Sphingomonas sp. GY2B adsorbed on kaolinite, montmorillonite, and vermiculite were evaluated in comparison with free bacteria under optimal conditions. Kaolinite was found to be the most effective in accelerating degradation rate (reducing the degradation time) as well as improving degradation efficiency (increasing the percentage of phenol degraded), with GY2B/kaolinite complex achieving a degradation efficiency of 96% within 6 h. GY2B adsorbed on kaolinite was more competent than free GY2B in degradation under conditions with high phenol concentrations and at alkaline pH. Kaolinite reduced the time required for degradation by 8-12 h and improved the degradation efficiency by as much as 82% at high phenol concentrations. Meanwhile, the GY2B/kaolinite complex reduced the degradation time by 24 h and improved the degradation efficiency by 46% at pH 12. The improvement was partially due to the buffering effects of kaolinite. It was also shown that Cr(VI) and kaolinite synergistically enhanced the degradation by GY2B, with Cr(VI) and kaolinite both increasing the degradation rate and kaolinite being primarily responsible for enhanced degradation efficiency. These results showed one of the common clay minerals, kaolinite, is able to significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. Kaolinite can collaborate with Cr(VI) to further improve the microbial degradation performance. It is implied that clay minerals have great potential to be applied in enhancing the biodegradation of phenol.

Removal of mixed contaminants, crystal violet, and heavy metal ions by using immobilized stains as the functional biomaterial

A new functional biomaterial based on Burkholderia vietnamiensis C09V (C09V) was immobilized on beads and used for simultaneous removal of both heavy metals and crystal violet (CV).

Optimization of simultaneous removal of Cr (VI) and phenol by a native bacterial consortium: its use for bioaugmentation of co-polluted effluents

AIMS

This study was designed to isolate, identify and characterize micro-organisms or mixed cultures capable of simultaneously removing Cr (VI) and phenol in the surrounding area of a tannery localized in Elena, Córdoba, Argentina. In addition, nutritional and physical factors were optimized in order to improve the removal efficiency in a real effluent.

METHODS AND RESULTS

The consortium SFC 500-1, composed of two bacterial strains belonging to Acinetobacter and Bacillus genus, was isolated from the heavily polluted wastewater discharge channel of a local tannery. SFC 500-1 was able to remove phenol at environmentally relevant concentrations (1000 mg l(-1) ) and reduce Cr (VI) to Cr (III), which was immobilized in the bacterial biomass. The consortium simultaneously removed these contaminants under a wide range of physicochemical conditions and different growth media, even in a tannery effluent.

CONCLUSION

The ability of SFC 500-1 to simultaneously reduce Cr (VI) and degrade phenol in different synthetic growth media and even in the effluent from which it was isolated with high efficiency makes this consortium a potential candidate for the biotreatment of effluents.

SIGNIFICANCE AND IMPACT OF THE STUDY

This finding is important, taking into account that industrial effluents present complex mixtures of toxic substances as well as native flora which often affect the bioremediation process. Considering the ecological advantages of using native bacteria for bioremediation, as well as the high efficiency of the consortium SFC 500-1 to simultaneously remove Cr (VI) and phenol, this could be a suitable biological system to improve the biotreatment of polluted effluents through a bioaugmentation strategy.

Biochemical and molecular mechanisms involved in simultaneous phenol and Cr(VI) removal by Acinetobacter guillouiae SFC 500-1A

Bioremediation has emerged as an environmental friendly strategy to deal with environmental pollution. Since the majority of polluted sites contain complex mixtures of inorganic and organic pollutants, it is important to find bacterial strains that can cope with multiple contaminants. In this work, a bacterial strain isolated from tannery sediments was identified as Acinetobacter guillouiae SFC 500-1A. This strain was able to simultaneously remove high phenol and Cr(VI) concentrations, and the mechanisms involved in such process were evaluated. The phenol biodegradation was catalized by a phenol-induced catechol 1,2-dioxygenase through an ortho-cleavage pathway. Also, NADH-dependent chromate reductase activity was measured in the cytosolic fraction. The ability of this strain to reduce Cr(VI) to Cr(III) was corroborated by detection of Cr(III) in cellular biomass after the removal process. While phenol did not affect significantly the chromate reductase activity, Cr(VI) was a major disruptor of catechol dioxygenase activity. Nevertheless, this activity was high even in presence of high Cr(VI) concentrations. Our results suggest the potential application of A. guillouiae SFC 500-1A for wastewaters treatment, and the obtained data provide the insights into the removal mechanisms, dynamics, and possible limitations of the bioremediation.

Polyvinyl alcohol-immobilized Phanerochaete chrysosporium and its application in the bioremediation of composite-polluted wastewater

A novel biosorbent, polyvinyl alcohol (PVA)-immobilized Phanerochaete chrysosporium, was applied to the bioremediation of composite-polluted wastewater, containing both cadmium and 2,4-dichlorophenol (2,4-DCP). The optimum removal efficiency achieved was 78% for Cd(II) and 95.4% for 2,4-DCP at initial concentrations of 20 mg/L Cd(II) and 40 mg/L 2,4-DCP. PPBs had significantly enhanced the resistance of P. chrysosporium to 2,4-DCP, leading to the degradation rates of 2,4-DCP beyond 90% with varying initial 2,4-DCP concentrations. This research demonstrated that 2,4-DCP and secreted proteins might be used as carbon and nitrogen sources by PVA-immobilized P. chrysosporium beads (PPBs) for Cd(II) removal. Fourier transform infrared spectroscopy analysis showed that hydroxyl and carboxyl groups on the surface of PPBs were dominant in Cd(II) binding. The mechanism underlying the degradation of 2,4-DCP into fumaric acid and 1-hexanol was investigated. The adsorption-desorption studies indicated that PPBs kept up to 98.9% of desorption efficiency over three cycles.

Biotreatment of simulated tannery wastewater containing Reactive Black 5, aniline and CrVI using a biochar packed bioreactor

Azo dyes and CrVI in tannery wastewater can be treated by redox active bacteria. Dye decolorization and CrVI reduction are simultaneous under anaerobic conditions. Biochar is an effective support matrix for packed bed bioreactors used to treat dyes and CrVI.

Chromium (VI) remediation by a native strain: effect of environmental conditions and removal mechanisms involved

A native bacterial strain with high capability for Cr (VI) removal was isolated from tannery sediments located in Elena (Córdoba Province, Argentina). The strain was characterized by amplification of 16S rRNA gene and identified as Serratia sp. C8. It was able to efficiently remove different Cr (VI) concentrations in a wide range of pHs and temperatures. The addition of different carbon sources as well as initial inoculum concentration were analyzed, demonstrating that Serratia sp. C8 could reduce 80 % of 20 mg/L Cr (VI) in a medium containing glucose 1 g/L, at pH 6-7 and 28 °C as optimal conditions, using 5 % inoculum concentration. The mechanisms involved in Cr (VI) removal were also evaluated. The strain was capable of biosorpting around 7.5-8.5 % of 20 mg/L Cr on its cell surface and to reduce Cr (VI). In addition, approximately a 54 and 46 % of total Cr was detected in the biomass and in the culture medium, respectively, and in the culture medium, Cr (III) was the predominant species. In conclusion, Serratia sp. C8 removed Cr (VI) and the mechanisms involved in decreasing order of contribution were as follows: reduction catalyzed by intracellular enzymes, accumulation into the cells, and biosorption to the microbial biomass. This strain could be a suitable microorganism for Cr (VI) bioremediation of tannery sediments and effluents or even for other environments contaminated with Cr.

Cr(VI) reduction and Cr(III) immobilization by Acinetobacter sp. HK-1 with the assistance of a novel quinone/graphene oxide composite

Cr(VI) biotreatment has attracted a substantial amount of interest due to its cost effectiveness and environmental friendliness. However, the slow Cr(VI) bioreduction rate and the formed organo-Cr(III) in solution are bottlenecks for biotechnology application. In this study, a novel strain, Acinetobacter sp. HK-1, capable of reducing Cr(VI) and immobilizing Cr(III) was isolated. Under optimal conditions, the Cr(VI) reduction rate could reach 3.82 mg h(-1) g cell(-1). To improve the Cr(VI) reduction rate, two quinone/graphene oxide composites (Q-GOs) were first prepared via a one-step covalent chemical reaction. The results showed that 2-amino-3-chloro-1,4-naphthoquinone-GO (NQ-GO) exhibited a better catalytic performance in Cr(VI) reduction compared to 2-aminoanthraquinone-GO. Specifically, in the presence of 50 mg L(-1) NQ-GO, a Cr(VI) removal rate of 190 mg h(-1) g cell(-1), which was the highest rate obtained, was achieved. The increased Cr(VI) reduction rate is mainly the result of NQ-GO significantly increasing the Cr(VI) reduction activity of cell membrane proteins containing dominant Cr(VI) reductases. X-ray photoelectron spectroscopy analysis found that Cr(VI) was reduced to insoluble Cr(III), which was immobilized by glycolipids secreted by strain HK-1. These findings indicate that the application of strain HK-1 and NQ-GO is a promising strategy for enhancing the treatment of Cr(VI)-containing wastewater.

Measurement of biochemical oxygen demand from different wastewater samples using a mediator-less microbial fuel cell biosensor

Microbial fuel cells (MFCs) have attracted considerable attention as potential biosensors. A MFC biosensor for rapid measurement of biochemical oxygen demand (BOD) has been recently studied. However, a standardized bacterial mixture inoculated in the MFC biosensor for BOD measurement is unavailable. Thus, the commercial application of a MFC biosensor is limited. In this study, a mediator-less MFC biosensor inoculated with known mixed cultures to quickly determine BOD concentration was tested. Optimal external resistance, operating temperature and measurement time for the MFC biosensor were determined to be 5000 omega, 35 degrees C and 12h, respectively. A good relationship between BOD concentration and voltage output, high reproducibility and long-term stability for the MFC biosensor was observed. The newly developed MFC biosensor was inoculated with a mixture of six bacterial strains (Thermincola carboxydiphila, Pseudomonas aeruginosa, Ochrobactrum intermedium, Shewanella frigidimarina, Citrobacter freundii and Clostridium acetobutylicum) capable of degrading complex organic compounds and surviving toxic conditions. The described MFC biosensor was able to successfully measure BOD concentrations below 240 mg L(-1) in real wastewater samples.

Simultaneous Cr(VI) reduction and phenol degradation using Stenotrophomonas sp. isolated from tannery effluent contaminated soil

This study presents simultaneous hexavalent chromium (Cr(VI)) reduction and phenol degradation using Stenotrophomonas sp., isolated from tannery effluent contaminated soil. Phenol was used as the sole carbon and energy source for Cr(VI) reduction. The optimization of different operating parameters was done using Placket-Burman design (PBD) and Box-Behnken design (BBD). The significant operating variables identified by PBD were initial Cr(VI) and phenol concentration, pH, temperature, and reaction time. These variables were optimized by a three-level BBD and the optimum initial Cr(VI) concentration, initial phenol concentration, pH, temperature, and reaction time obtained were 16.59 mg/l, 200.05 mg/l, 7.38, 31.96 °C and 4.07 days, respectively. Under the optimum conditions, 81.27 % Cr(VI) reduction and 100 % phenol degradation were observed experimentally. The results concluded that the Stenotrophomonas sp. could be used to decontaminate the effluents containing Cr(VI) and phenol effectively.

Pentachlorophenol dechlorination and simultaneous Cr6+ reduction by Pseudomonas putida SKG-1 MTCC (10510): characterization of PCP dechlorination products, bacterial structure, and functional groups

It is the first report in which a novel psychrotrophic Pseudomonas putida SKG-1 strain was evaluated for simultaneous bioremediation of pentachlorophenol and Cr(6+) under various cultural and nutritional conditions. Pentachlorophenol (PCP) dechlorination products, bacterial structure, and functional groups were characterized by gas chromatography and mass spectrometry (GC-MS), scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDS), and Fourier-transform infrared (FTIR) techniques. The strain was extremely tolerant to excessively higher individual concentration of PCP (1,400 mg l(-1)) and Cr(6+) (4,300 mg l(-1)). Increasing concentration of PCP and Cr(6+) exerted inhibitory effect on bacterial growth and toxicants' removal. The strain exhibited growth, and concomitantly remediated both the pollutants simultaneously over a broad pH (7.0-9.0) and temperature (28-32 °C) range; maximum growth, PCP dechlorination (87.5%), and Cr(6+) removal (80.0%) occurred at optimum pH 8.0 and 30 °C (from initial PCP 100 mg l(-1) and Cr(6+) 500 mg l(-1)) under shaking (150 rpm) within 72 h incubation. Optimization of agitation (125 rpm) and aeration (0.4 vvm) in bioreactor further enhanced PCP dechlorination by ~10% and Cr(6+) removal by 2%. A direct correlation existed between growth and bioremediation of both the toxicants. Among other heavy metals, mercury exerted maximum and cobalt minimum inhibitory effect on PCP dechlorination and Cr(6+) removal. Chromate reductase activity was mainly associated with the supernatant and cytosolic fraction of bacterial cells. GC-MS analysis revealed the formation of tetrachloro-p-hydroquinone, 2,4,6-trichlorophenol, and 2,6-dichlorophenol as PCP dechlorination products. FTIR spectrometry indicated likely involvement of carbonyl and amide groups in Cr(3+) adsorption, and SEM-EDS showed the presence of chromium on P. putida surface. Thus, our promising isolate can be ecofriendly employed for biotreatment of various industrial wastes contaminated with high PCP and Cr(6+) concentrations.

Reduction of Cr(VI) by Escherichia coli BL21 in the presence of redox mediators

Anthraquinone-2,7-disulfonate (2,7-AQDS), anthraquinone-1-sulfonate (α-AQS), anthraquinone-2-sulfonate (AQS), anthraquinone-2,6-disulfonate (AQDS) and anthraquinone-1,5-disulfonate (1,5-AQDS) were selected as redox mediators for Cr(VI) reduction by Escherichia coli BL21. In the presence of 0.8mmoll(-1) AQS, the Cr(VI) reduction efficiency was 98.5% in 7.5h, whereas it was only 21-34% in the absence of a mediator or in the presence of α-AQS, 1,5-AQDS, AQDS, 2,7-AQDS. A linear correlation, k=0.768C(AQS)+1.5531 (R(2)=0.9935), was found for the reaction constant, k (mg Cr(VI) g(-1) dry cell weight h(-1)) and the AQS concentration (C(AQS)). The Arrhenius equation described the Cr(VI) reduction in the tested temperature range, and the pre-exponential factor A was 13.249mg Cr(VI) g(-1) dry cell weight h(-1),and the activation energy Ea was 28.01kJmol(-1). Glucose was the best carbon sources, and the optimum pH was 6.0. The Cr(VI) reduction rate obtained with AQS is a significant improvement over low conventional anaerobic reduction rates.

Responses of Phanerochaete chrysosporium to toxic pollutants: physiological flux, oxidative stress, and detoxification

The white-rot fungus Phanerochaete chrysosporium has been widely used for the treatment of waste streams containing heavy metals and toxic organic pollutants. The development of fungal-based treatment technologies requires detailed knowledge of the relationship between bulk water quality and the physiological responses of fungi. A noninvasive microtest technique was used to quantify real-time changes in proton, oxygen, and cadmium ion fluxes following the exposure of P. chrysosporium to environmental toxic (2,4-dichlorophenol and cadmium). Significant changes in H(+) and O(2) flux occurred after exposure to 10 mg/L 2,4-dichlorophenol and 0.1 mM cadmium. Cd(2+) flux decreased with time. Reactive oxygen species formation and antioxidant levels increased after cadmium treatment. Superoxide dismutase activity correlated well with malondialdehyde levels (r(2) = 0.964) at low cadmium concentrations. However, this correlation diminished and malondialdehyde levels significantly increased at the highest cadmium concentration tested. Real-time microscale signatures of H(+), O(2), and Cd(2+) fluxes coupled with oxidative stress analysis can improve our understanding of the physiological responses of P. chrysosporium to toxic pollutants and provide useful information for the development of fungal-based technologies to improve the treatment of wastes cocontaminated with heavy metals and organic pollutants.