Deyong Kong

Accelerated Reduction of Chlorinated Nitroaromatic Antibiotic Chloramphenicol by Biocathode

Chlorinated nitroaromatic antibiotic chloramphenicol (CAP) is a priority pollutant in wastewaters. A fed-batch bioelectrochemical system (BES) with biocathode with applied voltage of 0.5 V (served as extracellular electron donor) and glucose as intracellular electron donor was applied to reduce CAP to amine product (AMCl2). The biocathode BES converted 87.1 ± 4.2% of 32 mg/L CAP in 4 h, and the removal efficiency reached 96.0 ± 0.9% within 24 h. Conversely, the removal efficiency of CAP in BES with an abiotic cathode was only 73.0 ± 3.2% after 24 h. When the biocathode was disconnected (no electrochemical reaction but in the presence of microbial activities), the CAP removal rate was dropped to 62.0% of that with biocathode BES. Acetylation of one hydroxyl of CAP was noted exclusive in the biocatalyzed process, while toxic intermediates, hydroxylamino (HOAM), and nitroso (NO), from CAP reduction were observed only in the abiotic cathode BES. Electrochemical hydrodechlorination and dehalogenase were responsible for dechlorination of AMCl2 to AMCl in abiotic and microbial cathode BES, respectively. The cyclic voltammetry (CV) highlighted higher peak currents and lower overpotentials for CAP reduction at the biocathode compared with abiotic cathode. With the biocathode BES, antibacterial activity of CAP was completely removed and nitro group reduction combined with dechlorination reaction enhanced detoxication efficiency of CAP. The CAP cathodic transformation pathway was proposed based on intermediates analysis. Bacterial community analysis indicated that the dominate bacteria on the biocathode were belonging to α, β, and γ-Proteobacteria. The biocathode BES could serve as a potential treatment process for CAP-containing wastewater.

Microbial community structure and function of Nitrobenzene reduction biocathode in response to carbon source switchover

The stress of poised cathode potential condition and carbon source switchover for functional biocathode microbial community influences is poorly understood. Using high-throughput functional gene array (GeoChip v4.2) and Illumina 16S rRNA gene MiSeq sequencing, we investigated the phylogenetic and functional microbial community of the initial inoculum and biocathode for bioelectrochemical reduction of nitrobenzene to less toxic aniline in response to carbon source switchover (from organic glucose to inorganic bicarbonate). Selective transformation of nitrobenzene to aniline maintained in the bicarbonate fed biocathode although nitrobenzene reduction rate and aniline formation rate were significantly decreased compared to those of the glucose-fed biocathode. When the electrical circuit of the glucose-fed biocathode was disconnected, both rates of nitrobenzene reduction and of aniline formation were markedly decreased, confirming the essential role of an applied electric field for the enhancement of nitrobenzene reduction. The stress of poised cathode potential condition led to clear succession of microbial communities from the initial inoculum to biocathode and the carbon source switchover obviously changed the microbial community structure of biocathode. Most of the dominant genera were capable of reducing nitroaromatics to the corresponding aromatic amines regardless of the performance mode. Heterotrophic Enterococcus was dominant in the glucose-fed biocathode while autotrophic Paracoccus and Variovorax were dominant in the bicarbonate-fed biocathode. Relatively higher intensity of diverse multi-heme cytochrome c (putatively involved in electrons transfer) and carbon fixation genes was observed in the biocarbonate-fed biocathode, likely met the requirement of the energy conservation and maintained the nitrobenzene selective reduction capability after carbon source switchover. Extracellular pilin, which are important for biofilm formation and potential conductivity, had a higher gene abundance in the glucose-fed biocathode might explain the enhancement of electro-catalysis activity for nitrobenzene reduction with glucose supply. Dominant nitroaromatics-reducing or electrochemically active bacteria and diverse functional genes related to electrons transfer and nitroaromatics reduction were associated with nitrobenzene reduction efficiency of biocathode communities in response to carbon source switchover.

Polarity inversion of bioanode for biocathodic reduction of aromatic pollutants

The enrichment of specific pollutant-reducing consortium is usually required prior to the startup of biocathode bioelectrochemical system (BES) and the whole process is time consuming. To rapidly establish a non-specific functional biocathode, direct polar inversion from bioanode to biocathode is proposed in this study. Based on the diverse reductases and electron transfer related proteins of anode-respiring bacteria (ARB), the acclimated electrochemically active biofilm (EAB) may catalyze reduction of different aromatic pollutants. Within approximately 12 d, the acclimated bioanodes were directly employed as biocathodes for nitroaromatic nitrobenzene (NB) and azo dye acid orange 7 (AO7) reduction. Our results indicated that the established biocathode significantly accelerated the reduction of NB to aniline (AN) and AO7 to discolored products compared with the abiotic cathode and open circuit controls. Several microbes possessing capabilities of nitroaromatic/azo dye reduction and bidirectional electron transfer were maintained or enriched in the biocathode communities. Cyclic voltammetry highlighted the decreased over-potentials and enhanced electron transfer of biocathode as well as demonstrated the ARB Geobacter containing cytochrome c involved in the backward electron transfer from electrode to NB. This study offers new insights into the rapid establishment and modularization of functional biocathodes for the potential treatment of complicated electron acceptors-coexisting wastewaters.

Effect of temperature switchover on the degradation of antibiotic chloramphenicol by biocathode bioelectrochemical system

Exposure to chloramphenicol (CAP), a chlorinated nitroaromatic antibiotic, can induce CAP-resistant bacteria/genes in diverse environments. A biocathode bioelectrochemical system (BES) was applied to reduce CAP under switched operational temperatures. When switching from 25 to 10°C, the CAP reduction rate (kCAP) and the maximum amount of the dechlorinated reduced amine product (AMCl, with no antibacterial activity) by the biocathode communities were both markedly decreased. The acetate and ethanol yield from cathodophilic microbial glucose fermentation (with release of electrons) was also reduced. Formation of the product AMCl was enhanced by the biocathode dechloridation reaction compared with that produced from pure electrochemical or microbial dechloridation processes. The electrochemical and morphological analyses of cathode biofilms demonstrated that some cathodophilic microbes could adapt to low temperature and play a key role in CAP degradation. The resilient biocathode BES has a potential for the treatment of CAP-containing wastewater in temperature fluctuating environments.

Accelerated azo dye removal by biocathode formation in single-chamber biocatalyzed electrolysis systems

Biocatalyzed electrolysis systems (BES) have been the topic of a great deal of research. However, the biocathodes formed in single-chamber BES without extra inocula have not previously been researched. Along with the formation of biocathodes, the polarization current increased to 1.76 mA from 0.35 mA of abio-cathodes at -1.2 V (vs. SCE). Electrochemical impedance spectroscopy (EIS) results also indicated that the charge transfer resistance (Rct) was decreased to 148.9 Ω, less than 1978 Ω of the abio-cathodes cleared. The performance of the biocathodes was tested for azo dye decolorization, and the dye removal efficiency was 13.3±3.2% higher than abio-cathodes with a 0.5 V direct current (DC) power supply. These aspects demonstrate that biocathode accelerates the rate of electrode reaction in BES and comparing with noble metal catalysts, biocathodes have low toxicity or non-toxic and reproducible properties, which can be widely applied in bioelectrochemical field in the future.

Response of anodic bacterial community to the polarity inversion for chloramphenicol reduction

Chloramphenicol (CAP) is a frequently detected environmental pollutant. In this study, an electroactive biofilm for CAP reduction was established by initially in the anode and then inverting to the cathode. The established biocathode could enhance the reduction of CAP to the nitro-group reduced CAP (AMCl2) and further dechlorinated form (AMCl), both had lost the antibacterial activity. The phylogenetic diversity of the acclimated biofilm was decreased after the polar inversion. Proportions of functional bacterial genera, including Geobacter, Desulfovibrio and Pseudomonas responsible for the bidirectional electron transfer and nitroaromatics reduction, had increased 28%, 104% and 43% in the cathode. The relatively high abundances (over 50%) of Geobacter in anode and cathode were rarely detected for the nitroaromatics reduction. This study provides new insights into the electroactive biofilm structure improvement by the polarity inversion strategy for refractory antibiotics degradation.

Spatial Abundance and Distribution of Potential Microbes and Functional Genes Associated with Anaerobic Mineralization of Pentachlorophenol in a Cylindrical Reactor

Functional interplays of microbial activity, genetic diversity and contaminant transformation are poorly understood in reactors for mineralizing halogenated aromatics anaerobically. Here, we investigated abundance and distribution of potential microbes and functional genes associated with pentachlorophenol (PCP) anaerobic mineralization in a continuous-flow cylindrical reactor (15 cm in length). PCP dechlorination and the metabolite (phenol) were observed at segments 0–8 cm from inlet, where key microbes, including potential reductive dechlorinators (Dehalobacter, Sulfurospirillum, Desulfitobacterium and Desulfovibrio spp.) and phenol degraders (Cryptanaerobacter and Syntrophus spp.), as well as putative functional genes, including putative chlorophenol reductive dehalogenase (cprA) and benzoyl-CoA reductase (bamB), were highly enriched simultaneously. Five types of putative cprAs, three types of putative bamBs and seven types of putative nitrogenase reductase (nifHs) were determined, with their copy numbers decreased gradually from inlet to outlet. Distribution of chemicals, bacteria and putative genes confirmed PCP dechlorination and phenol degradation accomplished in segments 0–5 cm and 0–8 cm, respectively, contributing to a high PCP mineralization rate of 3.86 μM d−1. Through long-term incubation, dechlorination, phenol degradation and nitrogen fixation bacteria coexisted and functioned simultaneously near inlet (0–8 cm), verified the feasibility of anaerobic mineralization of halogenated aromatics in the compact reactor containing multiple functional microbes.

Response of antimicrobial nitrofurazone-degrading biocathode communities to different cathode potentials

Bioelectrodegradation of various organic pollutants has been extensively studied. However, whether different cathode potentials could alter the antimicrobial-degrading biocathode community structure and composition remain poorly understood. Here, the microbial community structure and composition of the nitrofurans nitrofurazone (NFZ) degrading biocathode in response to different cathode potentials (-0.45±0.01, -0.65±0.01 and -0.86±0.05V vs standard hydrogen electrode, with applied cell voltages of 0.2, 0.5 and 0.8V, respectively) were investigated. The bioelectrodegradation efficiency and degree of NFZ were highly related to different cathode potentials. The 0.2 and 0.5V performed biocathode communities were similar but significantly differed from those of the 0.8V and open circuit biofilms. The bacteria possessing functions of nitroaromatics reduction and electrons transfer (e.g. Klebsiella, Enterococcus, Citrobacter and Desulfovibrio) were selectively enriched in different biocathode communities. This study offers new insights into the ecological response of antimicrobial-degrading biocathode communities to different cathode potentials.

Enhanced Biotransformation of Triclocarban by Ochrobactrum sp. TCC-1 Under Anoxic Nitrate Respiration Conditions.

Antimicrobial triclocarban (3,4,4′-trichlorocarbanilide, TCC) is frequently detected in soils and sediments for the widely reclaim of sewage sludge or biosolid in recent decades. This resulted from a weak removal of TCC during wastewater treatment, and most of it adsorbed onto sewage sludge. As the toxicity and persistence of TCC in the environment, the elimination of TCC from the source of output is of great importance, particularly in anoxic process. In this study, the biotransformation of TCC by a newly isolated TCC-degrading strain Ochrobactrum sp. TCC-1 under anoxic conditions was investigated. By testing different carbon nitrogen ratios (C/N), it showed that nitrate could support the growth of strain TCC-1 and enhance the hydrolysis of TCC to more biodegradable chloroanilines, especially with a higher C/N of 10 and under anaerobic conditions. In wastewater sewage sludge, strain TCC-1 colonized and maintained the TCC-hydrolyzing activity under the nitrate respiration mode. These results would lay a basic foundation for the potential bioremediation of TCC-contaminated anoxic sites with TCC-degrading strain.

Effects of surface charge, hydrophilicity and hydrophobicity on functional biocathode catalytic efficiency and community structure

The bioelectrotransformation efficiency of various organic matters and corresponding electrode biofilm community formation as well as electron transfer efficiency in bioelectrochemical systems (BESs) with different modified electrodes has been extensively studied on the anode side. However, the effects of cathode interface characteristics towards the BESs bioelectrotransformation performance remain poorly understood. In this study, the nitrobenzene-reducing biocathode catalytic efficiency and community structure in response to different modified electrodes (control: hydrophobic and no charge; -SH: hydrophobic and single negative charge; -NH2: hydrophilic and single positive charge -NH-NH2: hydrophilic and double positive charges) were investigated. The biocathode transformation efficiency of nitrobenzene (NB) to aniline (AN) (ENB-AN) was affected by the nature of electrode interface as well as the biocathode community formation and structure. Cathodes with hydrophilic surface and positive charges have performed well in the bioelectrotransformation experiments, and especially made an outstanding performance when inorganic NaHCO3 was supplied as carbon source and cathode as the sole electron donor. Importantly, the hydrophilic surfaces with positive charges were dominated by the electroactive nitroaromatic reducers (Enterococcus, Desulfovibrio and Klebsiella) with the relative abundance as high as 72.20 ± 1.87% and 74.86 ± 8.71% for -NH2 and -NH-NH2 groups respectively. This could explain the higher ENB-AN in the hydrophilic groups than that of the hydrophobic -SH modified group. This study provides new insights into the effects of electrode interface characteristics on the BESs biocathode performance and offers some suggestions for the future design for the improvement of bioelectroremediation performance.