Hui Yun

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.

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.

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.

Electrode-Respiring Microbiomes Associated with the Enhanced Bioelectrodegradation Function

Microbial electrode-respiration process has been proved to significantly enhance the microbial oxidation or microbial reduction of various hazardous organic contaminants in bioelectrochemical systems (BESs). The microbial ecology and physiology of the involved electrode-associated multispecies biofilms are essential for the catalytic function of BESs. In this chapter, we summarize the advances of the electrode-respiring biofilm microbiomes involved in the catalysis of various hazardous organic contaminants at both the cathode and the anode sides. We also highlight the challenges and outlook for the electrode-respiring biofim microbiomes research from the microbial ecology perspective. Understanding the comprehensive information of the electrode-respiring microbiomes, including biofilm structure, composition, dynamics, activity, diversity, potential functional microbes, and interaction, is potentially feasible for regulating and scaling-up the microbial electrode-respiration-based engineering systems as well as the management of bioremediation applications.