Anoxic System Research Articles

Staphylococcus aureus Strain Newman Photoinactivation and Cellular Response to Sunlight Exposure.

Sunlight influences microbial water quality of surface waters. Previous studies have investigated photoinactivation mechanisms and cellular photostress responses of fecal indicator bacteria (FIB), including Escherichia coli and enterococci, but further work is needed to characterize photostress responses of bacterial pathogens. Here we investigate the photoinactivation of Staphylococcus aureus (strain Newman), a pigmented, waterborne pathogen of emerging concern. We measured photodecay using standard culture-based assays and cellular membrane integrity and investigated photostress response by measuring the relative number of mRNA transcripts of select oxidative stress, DNA repair, and metabolism genes. Photoinactivation experiments were performed in both oxic and anoxic systems to further investigate the role of oxygen-mediated and non-oxygen-mediated photoinactivation mechanisms. S. aureus lost culturability much faster in oxic systems than in anoxic systems, indicating an important role for oxygen in photodecay mechanisms. S. aureus cell membranes were damaged by sunlight exposure in anoxic systems but not in oxic systems, as measured by cell membrane permeability to propidium iodide. After sunlight exposure, S. aureus increased expression of a gene coding for methionine sulfoxide reductase after 12 h of sunlight exposure in the oxic system and after 6 h of sunlight exposure in the anoxic system, suggesting that methionine sulfoxide reductase is an important enzyme for defense against both oxygen-dependent and oxygen-independent photostresses. This research highlights the importance of oxygen in bacterial photoinactivation in environmentally relevant systems and the complexity of the bacterial photostress response with respect to cell structure and transcriptional regulation.IMPORTANCEStaphylococcus aureus is a pathogenic bacterium that causes gastrointestinal, respiratory, and skin infections. In severe cases, S. aureus infection can lead to life-threatening diseases, including pneumonia and sepsis. Cases of community-acquired S. aureus infection have been increasing in recent years, pointing to the importance of considering S. aureus transmission pathways outside the hospital environment. Associations have been observed between recreational water contact and staphylococcal skin infections, suggesting that recreational waters may be an important environmental transmission pathway for S. aureus However, prediction of human health risk in recreational waters is hindered by incomplete knowledge of pathogen sources, fate, and transport in this environment. This study is an in-depth investigation of the inactivation of a representative strain of S. aureus by sunlight exposure, one of the most important factors controlling the fate of microbial contaminants in clear waters, which will improve our ability to predict water quality changes and human health risk in recreational waters.

The Synthesis of NZVI and Its Application to the Removal of Phosphate from Aqueous Solutions

Nanoscale zero valent iron (NZVI) was synthesized by the reduction of natural limonite under hydrogen conditions. The adsorption performance of the as-prepared NZVI on phosphate was evaluated through batch and column experiments. The removal of phosphate (PO4 3−) significantly decreased with an increase of pH from 2.0 to 11, whereas a remarkable increase of PO4 3− removal was observed in the presence of SO4 2− and S2O3 2−. In addition, Cl− and NO3 − also improved phosphate removal at concentrations of more than 0.2 mmol/L. Kinetic studies indicated that the removal process of PO4 3− on NZVI can be easily followed with the pseudo-second-order kinetic model. The removal of phosphate from the oxic system was significantly higher than that of the anoxic system, which was attributed to the formation of the secondary phase by the further oxidization of Fe2+. The adsorption capacity of the as-prepared NZVI of the oxic system was 16 mg/g, and the pH was 6.3. The column experiments further demonstrated that the as-prepared NZVI presented a high removal capacity for PO4 3−-P. These findings indicated that the as-prepared NZVI displayed an excellent ability to remove phosphate from aqueous solutions.

Genetic diversity of nitrate reducing bacteria in marine and brackish water nitrifying bacterial consortia generated for activating nitrifying bioreactors in recirculating aquaculture systems

Nitrate reducing potency of 88 bacterial isolates segregated from marine and brackish water nitrifying bacterial consortia (NBC), generated for activation of nitrifying bioreactors, was confirmed by determining the nitrate reducing capability under aerobic conditions as maintained in nitrifying bioreactors. All the isolates had the potential to be used as bio-augmentors for activating nitrate dissimilation in recirculating aquaculture system. The existence of nitrate reducers with nitrifiers in NBC and in the reactor configuration negates the requirement of integrating anoxic denitrifying system for effective removal of NO3−-N. Phylogenetic analyses of representative isolates from each cluster of the dendrograms generated based on phenotypic characterization and amplified ribosomal DNA restriction analysis revealed profound diversity of nitrate reducing bacterial flora in the NBC. They were composed of Streptomyces enissocaesilis, Marinobacter sp., Pseudomonas sp., Microbacterium oxydans, Pelagibacterium halotolerans and Alcanivorax dieselolei from marine NBC and Streptomyces tendae, Nesterenkonia sp., Bacillus cereus, Microbacterium oxydans and Brevibacterium sp. from brackish water NBC. The diversity indices of the consortia were calculated using Mega 5.0, primer 7 and VITCOMIC softwares. Marine NBC exhibited higher Shannon wiener diversity and mean population diversity than brackish water NBC. The study delineated higher species richness and diversity in marine NBC than in its brackish water counterpart, a possible reflection of the higher biodiversity of marine systems, and hence, the former is more promising to be used as start-up cultures for the activation of nitrifying bioreactors after appropriate acclimatization to the desired salinity.

Correlation between cervical cancer and vaginal microbes

Cervical cancer is a serious disease endangering the health of women, which is next only to breast cancer and colon cancer. There are nearly 130 000 new cases of cervical cancer arise in China each year, accounting for 1/5 of the total number of new cases in the world. Epidemiological survey has found that cervical cancer is related to various factors, such as human papilloma virus infection, multiple sexual partners, smoking, premature sexual life, sexually transmitted diseases, economic status and immunosuppression. Cervical cancer is pathologically characterized by cervical dysplasia cervical atypical hyperplasia (mild, moderate, severe) to carcinoma in situ and to infiltrating carcinoma. Female vagina is a relatively anoxic and unique dynamic micro ecological system colonized with a large number of bacteria. And the vaginal microflora is the kernel of maintaining vaginal micro ecological balance. The uterine cervix is directly exposed to the vagina, and is closely related to vaginal microbes. However, there are few reports on the direct relationship between cervical cancer and vaginal microbes. In this review, the roles and significance of vaginal microbial imbalance and common vaginal infections in cervical cancer will be discussed from different angles. Key words: Cervical cancer; Vaginal microbe; Human papilloma virus; Vaginal infection

The abiotic degradation of methyl parathion in anoxic sulfur-containing system mediated by natural organic matter

Although the kinetics and transformation of methyl parathion have been investigated extensively, its abiotic degradation mechanism in anoxic sulfur-containing groundwater system is still not clear. In this work, the abiotic degradation of methyl parathion in anoxic sulfur-containing system mediated by natural organic matter (NOM) was investigated in batch experiments. It was found that the removal of methyl parathion (up to 80.7%) was greatly improved in sulfide containing NOM compared to those in sulfide alone (with 15.5%) and in NOM alone (almost negligible). Various sulfur species presented significant differences in behaviors methyl parathion degradation, but followed by the pseudo-first-order model well. No facilitated degradation of methyl parathion was observed in sulfite (SO32-) or thiosulfate (S2O32-) containing NOM such as anthraquinone. Although elemental sulfur (S0) and cysteine could further improve the degradation rate of methyl parahtion, their impacts was very limited. The removal efficiency of methyl parathion in anoxic sulfur-containing system were related remarkably with NOM concentration and solution pH. Based on the transformation products identified by gas chromatography-mass spectrometer (GC/MS) and liquid chromatography high resolution mass spectrometer (LC/HRMS), both the nitro group reduction and hydrolysis (SN@C) processes by sulfide (HS−) were further proved to be two predominant reaction mechanisms for the abiotic degradation of methyl parathion in anoxic sulfur-containing system. The results of this study help to understand the natural attenuation of methyl parathion under anoxic sulfide-containing groundwater system mediated by NOM.

Mercury methylation in paddy soil: source and distribution of mercury species at a Hg mining area, Guizhou Province, China

Abstract. Rice paddy plantation is the dominant agricultural land use throughout Asia. Rice paddy fields have been identified as important sites for methylmercury (MeHg) production in the terrestrial ecosystem and a primary pathway of MeHg exposure to humans in mercury (Hg) mining areas. We compared the source and distribution of Hg species in different compartments of the rice paddy during a complete rice-growing season at two different typical Hg-contaminated mining sites in Guizhou province, China: an abandoned site with a high Hg concentration in soil but a low concentration in the atmosphere and a current-day artisanal site with a low concentration in soil but a high concentration in the atmosphere. Our results showed that the flux of new Hg to the ecosystem from irrigation and atmospheric deposition was insignificant relative to the pool of old Hg in soil; the dominant source of MeHg to paddy soil is in situ methylation of inorganic Hg (IHg). Elevated MeHg concentrations and the high proportion of Hg as MeHg in paddy water and the surface soil layer at the artisanal site demonstrated active Hg methylation at this site only. We propose that the in situ production of MeHg in paddy water and surface soil is dependent on elevated Hg in the atmosphere and the consequential deposition of new Hg into a low-pH anoxic geochemical system. The absence of depth-dependent variability in the MeHg concentration in soil cores collected from the abandoned Hg mining site, consistent with the low concentration of Hg in the atmosphere and high pH of the paddy water and irrigation water, suggested that net production of MeHg at this site was limited. We propose that the concentration of Hg in ambient air is an indicator for the risk of MeHg accumulation in paddy rice.

Possible role of antioxidants and nitric oxide inhibitors against carbon monoxide poisoning: Having a clear conscience because of their potential benefits

Carbon monoxide poisoning is one of the important emergency situations manifested by primarily acute and chronic anoxic central nervous system (CNS) injuries and other organ damages. Current descriptions and therapeutic approaches have been focused on the anoxic pathophysiology. However, this point of view incompletely explains some of the outcomes and needs to be investigated extensively. Considering this, we propose that reactive oxygen species (ROS) including especially nitric oxide (NO) are likely to be a key concept to understand the emergency related to CO poisoning and to discover new therapeutic modalities in CO toxicity. If we consider the hypothesis that ROS is involved greatly in acute and chronic toxic effects of CO on CNS and some other vital organs such as heart, it follows that the antioxidant and anti-NO therapies might give the clinicians more opportunities to prevent deep CNS injury. In support of this, we review the subject in essence and summarize clinical and experimental studies that support a key role of ROS in the explanation of pathophysiology of CO toxicity as well as new treatment modalities after CO poisoning.

Total, chemical, and biological oxygen consumption of the sediments in the Ziya River watershed, China.

Sediment oxygen demand (SOD) is a critical dissolved oxygen (DO) sink in many rivers. Understanding the relative contributions of the biological and chemical components of SOD would improve our knowledge of the potential environmental harm SOD could cause and allow appropriate management systems to be developed. A various inhibitors addition technique was conducted to measure the total, chemical, and biological SOD of sediment samples from 13 sites in the Ziya River watershed, a severely polluted and anoxic river system in the north of China. The results showed that the major component of SOD was chemical SOD due to iron predominate. The ferrous SOD accounted for 21.6-78.9% of the total SOD and 33.26-96.79% of the chemical SOD. Biological SOD represented 41.13% of the overall SOD averagely. Sulfide SOD accounted for 1.78-45.71% of the total SOD and it was the secondary predominate of the chemical SOD. Manganous SOD accounted for 1.2-16.6% of the total SOD and it was insignificant at many sites. Only four kinds of benthos were collected in the Ziya River watershed, resulting from the low DO concentration in the sediment surface due to SOD. This study would be helpful for understanding and preventing the potential sediment oxygen depletion during river restoration.

Determination of Sediment Oxygen Demand in the Ziya River Watershed, China: Based on Laboratory Core Incubation and Microelectrode Measurements.

A study coupling sedimentcore incubation and microelectrode measurementwas performed to explore the sediment oxygen demand (SOD) at 16 stations in the Ziya River Watershed, a severely polluted and anoxic river system in the north of China. Total oxygen flux values in the range 0.19–1.41 g/(m2·d) with an average of 0.62 g/(m2·d) were obtained by core incubations, and diffusive oxygen flux values in the range 0.15–1.38 g/(m2·d) with an average of 0.51 g/(m2·d) were determined by microelectrodes. Total oxygen flux obviously correlated with diffusive oxygen flux (R2 = 0.842). The microelectrode method produced smaller results than the incubation method in 15 of 16 sites, and the diffusive oxygen flux was smaller than the total oxygen flux. Although the two sets of SOD values had significant difference accepted by the two methods via the Wilcoxon signed-rank test (p < 0.05), the microelectrode method was shown to produce results that were similar to those from the core incubation method. The microelectrode method, therefore, could be used as an alternative method for traditional core incubation method, or as a method to verify SOD rates measured by other methods. We consider that high potential sediment oxygen demand would occur in the Ziya River Watershed when the dissolved oxygen (DO) recovered in the overlying water.

Prospectivity and play analysis in the frontier Great Australian Bight: the benefits of a public domain data system and the application of traditional and new technologies

The deep water portion of the Great Australian Bight remains an untested basin with the Gnarlyknots–1A well drilled in 2003 not penetrating deep enough to test the well's targets within the Upper Cretaceous Ceduna Delta section. If an anoxic marine shale source system, that is an effective source in many parts of West Africa, is present beneath the delta, then this could supply a material oil charge into the numerous fault block structures identified on seismic data. With eight wells due to be drilled in the next few years, this area will be one of the most active exploration frontier settings in the region. Since Australia has an open file system for technical data, the regional Flinders 2000 2D Marine seismic Interpretation report containing five regional Time structure maps is now in the public domain, as is the Gnarlyknots–1A well data and the raw seismic data from the Ceduna 3D survey acquired in 2012. These data were used to evaluate the untested Coniacian play interval with the construction of Reservoir Presence and quality, seal and charge relative probability maps made from various proxies that were then stacked to show areas of relative prospectivity. This traditional approach was supplemented by the an example showing pre-interpretation surfaces from the pre-Cenomanian portion of the 3D volume to help develop a better understanding of the potential prospectivity of deeper intervals not captured on the submitted open file maps. The workflow presented here suggests some parts of the Ceduna Sub Basin are significantly more prospective than others. Moreover, we demonstrate that even in frontier settings with minimal well data, pre-interpretation processing and simple play analysis together can be a useful and efficient approach for delivering significant insights into prospectivity. This workflow will ultimately promote more exploration thinking and activity in the future.

A combined upflow anaerobic sludge bed, aerobic, and anoxic fixed-bed reactor system for removing tetramethylammonium hydroxide and nitrogen from light-emitting diode wastewater

ABSTRACTA laboratory study using a combined upflow anaerobic sludge bed (UASB) and aerobic and anoxic fixed-bed reactor system was undertaken to explore its capability for removing tetramethylammonium hydroxide (TMAH) and nitrogen from light-emitting diode wastewater. When the organic loading rate was maintained at 0.26–0.65 kg TMAH m−3 d−1, the UASB reactor removed 70–100% of TMAH through methanogenesis. When the -N loading rate was maintained at 0.73–1.4 kg -N m−3 d−1, the aerobic reactor oxidized 31–59% of -N to -N through nitritation. When the nitrogen loading rate was maintained at 0.42–0.75 kg N m−3 d−1, the anoxic reactor removed 27–63% of nitrogen through anammox. The performance data of the combined reactor system agreed well with the stoichiometric relationships of methanogenesis, nitritation, and anammox. The batch studies showed that a higher initial TMAH concentration of up to 2520 mg L−1 gave a higher methanogenic activity of up to 16 mL CH4 g−1 VSS d−1. An increase in the initial TMAH concentration of up to 500 mg L−1 gradually decreased the activity of ammonia-oxidizing bacteria; whereas an increase in the initial TMAH concentration of up to 47 mg L−1 imposed a marked inhibiting effect on the activity of anammox bacteria.

Vermistella arctica n. sp. Nominates the Genus Vermistella as a Candidate for Taxon with Bipolar Distribution.

A new amoebozoan species, Vermistella arctica n. sp., is described from marine habitats in the central part of Svalbard archipelago. This is the first report on Arctic amoebae belonging to the genus Vermistella Moran and Anderson, 2007, the type species of which was described from the opposite pole of the planet. Psychrophily proved in the new strains qualifies the genus Vermistella as a bipolar taxon. Molecular phylogenetic analyses based on 18S rDNA and actin sequences did not show any affinity of the genus Vermistella to Stygamoeba regulata ATCC(®) 50892(™) strain. A close phylogenetic relationship was found between Vermistella spp. and a sequence originating from an environmental sample from Cariaco basin, the largest marine permanently anoxic system in the world. Possible mechanisms of bipolar distribution are discussed.

Influence of an oxic settling anoxic system on biomass yield, protozoa and filamentous bacteria

An oxic settling anoxic system coupled with an activated sludge process has been studied to reduce sewage sludge production. The reduction of sludge yield, excess sludge production and active biomass yield were 51.7%, 52.9% and 67.1%, respectively, compared with the control system. The oxic reactor of the oxic settling anoxic system, even with a lower active biomass concentration than the oxic reactor of control system, showed a higher metabolic activity in their active biomass. Diversity and crawling ciliates group have been shown as promising bioindicators of active biomass yield reduction. The identification of floc-forming bacteria in the control system suggested that oxic settling anoxic system will improve settling properties compared to a Conventional Activated Sludge process.

Simultaneous in-situ sludge reduction and nutrient removal in an A2MO-M system: Performances, mechanisms, and modeling with an extended ASM2d model

Among the existing in-situ sludge reduction processes, the oxic-settling-anaerobic (OSA) process is of particular interest because it has shown significant sludge reduction with several advantages. However, an ideal process for practical application must simultaneously incorporate effluent quality with sludge reduction. In this study, an improved OSA system, the stage-aerated anaerobic, anoxic, micro-aerobic, and oxic system combining a micro-aerobic starvation tank (abbreviated as A2MO-M system) was developed. Compared with OSA3# (hydraulic retention time (HRT) of 12 h), the A2MO-M2# system with optimized HRT of 9 h yielded almost 16.3% less sludge. The average total nitrogen (87.3%) and total phosphorus (91.9%) removal efficiencies in A2MO-M2# were 20.6 and 42.2% higher than those in OSA3#. Investigation of the mechanisms of sludge reduction revealed that, except for the main factors of energy uncoupling metabolism (16.7%) and sludge decay (21.2%), enrichment of slow-growing bacteria and lysis-cryptic growth metabolism analyzed by high-throughput 454 pyrosequencing were shown to contribute to sludge reduction in the A2MO-M system. On the basis of effluent organic matters (EfOM) measurements, soluble microbial products (SMP) were the major components in EfOM; and different reduction-oxidation (redox) potentials controlled in the OSA and A2MO-M systems led to different SMP formation mechanisms. To explore the mechanism and kinetics of SMP formation under different redox potentials, three new components (SUAP, SBAP, and XEPS) were integrated in an extended ASM2d model. Experimental and modeling results revealed that biomass-associated products (BAP) supported a substantial population of SMP that were quite sensitive to different redox potentials. The extended ASM2d model further illustrated that more BAP produced in the alternating anaerobic and aerobic conditions in the OSA system adversely affected its effluent quality.

An Investigation on the Persistence of Uranium Hydride during Storage of Simulant Nuclear Waste Packages.

Synchrotron X-rays have been used to study the oxidation of uranium and uranium hydride when encapsulated in grout and stored in de-ionised water for 10 months. Periodic synchrotron X-ray tomography and X-ray powder diffraction have allowed measurement and identification of the arising corrosion products and the rates of corrosion. The oxidation rates of the uranium metal and uranium hydride were slower than empirically derived rates previously reported for each reactant in an anoxic water system, but without encapsulation in grout. This was attributed to the grout acting as a physical barrier limiting the access of oxidising species to the uranium surface. Uranium hydride was observed to persist throughout the 10 month storage period and industrial consequences of this observed persistence are discussed.

Enhanced pyridine biodegradation under anoxic condition: The key role of nitrate as the electron acceptor

Enhanced biodegradation of pyridine under anoxic condition was elucidated in this study through both batch and continuous experiments. The results of the batch experiment indicated that pyridine biodegradation was significantly enhanced in the anoxic condition, probably due to the presence of the electron acceptor, i.e., NO3−. Pyridine could be mineralized in the anoxic condition, accompanied by the release of ammonia. Pyridine could be degraded optimally at neutral to slightly alkaline pHs. High concentrations of nitrate or pyridine had inhibitory effects on the anoxic degradation of pyridine. The combined anoxic–aerobic process consisted of an anaerobic baffled reactor (ABR) and a moving-bed biofilm reactor (MBBR) was operated to investigate the performance of pyridine biodegradation and total-N (TN) removal in this integrated system. The NH4+ released from pyridine biodegradation in ABR was nitrified completely into NO3− in MBBR, which was then recirculated into ABR, serving as the electron acceptor for pyridine biodegradation. With the effluent recirculation rates increased from 0% to 400%, both pyridine biodegradation and TN removal were improved, probably due to the high availability of nitrate and the mitigation of the toxic effect over the biomass at relatively high recirculation rates. In addition, high-throughput sequencing analysis demonstrated that Paracoccus, Thiobacillus and Paludibacter were the dominant species in the anoxic degradation system.

Mechanisms for removal of p-nitrophenol from aqueous solution using zero-valent iron

Batch experiments were conducted to examine mechanisms for removal of p-nitrophenol (PNP) from aqueous solution using zero-valent iron (ZVI). Removal of PNP using ZVI was mainly attributed to three mechanisms: degradation, precipitation and adsorption. A complete removal of 30 mg L−1 PNP with ZVI dosage of 1000 mg L−1 achieved within 30 min at pH 3. The PNP removal rate in the acidic solutions was significantly suppressed at higher pH. The modified Langmuir–Hinshelwood kinetic model could successfully describe the PNP removal process using ZVI at different pH conditions. Total organic carbon (TOC) removal efficiencies were found to be almost independent of pH. While the TOC removal at lower pH was profoundly affected by the reductive and/or oxidative degradation, the adsorption was favorable at higher pH. The effect of dissolved oxygen on PNP removal was investigated at pH 3 where a maximum contribution of oxidative degradation could be expected. The PNP removal in the anoxic system purged with nitrogen gas was quick as well as that in the system being open to the air. However, the TOC removal under the anoxic condition was negligible as compared with that in the oxic system. The profiles of the intermediates formed during the PNP degradation indicated that the reductive degradation was predominant in the initial phase of the removal and subsequently the oxidative degradation occurred.

대용량 저산소 농도 살충 챔버 시스템을 이용한 박물관 해충의 살충력 및 운용성 평가

대용량 저산소 농도 살충 챔버 시스템을 이용한 박물관 해충의 살충력 및 운용성 평가

Anoxic gas recirculation system for fouling control in anoxic membrane reactor

Anoxic gas recirculation system was applied to control the membrane fouling in pilot-scale 4-stage anoxic membrane bioreactor (MBR). In the anaerobic-anoxic-anoxic-aerobic flow scheme, hydrophilic polytetrafluoroethylene (PTFE) membrane (0.2 μm, 7.2 m2/module) was submerged in the second anoxic zone. During 8 months operation, the average flux of the membrane was 21.3 L/(m2·hr). Chemical cleaning of the membrane was conducted only once with sodium hydroxide and sodium hypochlorite. Dissolved oxygen (DO) concentration in the second anoxic zone was maintained with an average of 0.19 ± 0.05 mg/L. Gas chromatography analysis showed that the headspace gas in the second anoxic reactor was mainly consisted of N2 (93.0% ± 2.5%), O2 (3.8% ± 0.6%), and CO2 (3.0% ± 0.5%), where the saturation DO concentration in liquid phase was 1.57 mg/L. Atmospheric O2 content (20.5% ± 0.8%) was significantly reduced in the anoxic gas. The average pH in the reactor was 7.2 ± 0.4. As a result, the recirculation of the anoxic gas was successfully applied to control the membrane fouling in the anoxic MBR.

Induction of anoxic microenvironment in multi-phase metabolic shift strategy during periodic discontinuous batch mode operation enhances treatment of azo dye wastewater

Variation in anoxic microenvironment (multi-phase (MP) metabolic shift strategy) during cycle operation of periodic discontinuous batch/sequencing batch (PDBR/SBR) mode operation showed enhanced degradation of recalcitrant azo dye (C.I. Acid Black 10B) at higher dye load (1250mg/l). The process performance was evaluated by varying anoxic phasing period during cycle operation. Before multiphase (BMP) operation with 2.1% of anoxic period showed color/COD removal efficiency of 41.9%/46.3%. Increment in anoxic period responded favorable in enhancing treatment efficiency [AMPI (16.2%), 49.4%/52.4%; AMPII (26.6%), 54.7%/57.2%; AMPIII (34.9%), 58.4%/61.5%]. Relatively higher bio-electrochemical activity, persistent reductive behavior (redox catalytic currents, 0.26/−0.72μA), prevalence of redox shuttlers (Fe–S proteins, cytochromes, quinones) facilitating enhanced electron transfer by minimization of associated losses and higher enzyme activities were observed with induction of anoxic phase. Anoxic condition shifts system microenvironment between oxidation and reduction assisting reduction of dye to its intermediates followed by their mineralization.