Xian Cao

Simultaneous degradation of toxic refractory organic pesticide and bioelectricity generation using a soil microbial fuel cell.

In this study, the soil microbial fuel cells (MFCs) were constructed in the topsoil contaminated with toxic refractory organic pesticide, hexachlorobenzene (HCB). The performance of electricity generation and HCB degradation in the soil-MFCs were investigated. The HCB degradation pathway was analyzed based on the determination of degradation products and intermediates. Experimental results showed that the HCB removal efficiencies in the three groups (soil MFCs group, open circuit control group and no adding anaerobic sludge blank group) were 71.15%, 52.49% and 38.92%, respectively. The highest detected power density was 77.5 mW/m(2) at the external resistance of 1000 Ω. HCB was degraded via the reductive dechlorination pathway in the soil MFC under anaerobic condition. The existence of the anode promoted electrogenic bacteria to provide more electrons to increase the metabolic reactions rates of anaerobic bacteria was the main way which could promote the removal efficiencies of HCB in soil MFC.

Enhanced degradation of azo dye by a stacked microbial fuel cell-biofilm electrode reactor coupled system

In this study, a microbial fuel cell (MFC)-biofilm electrode reactor (BER) coupled system was established for degradation of the azo dye Reactive Brilliant Red X-3B. In this system, electrical energy generated by the MFC degrades the azo dye in the BER without the need for an external power supply, and the effluent from the BER was used as the inflow for the MFC, with further degradation. The results indicated that the X-3B removal efficiency was 29.87% higher using this coupled system than in a control group. Moreover, a method was developed to prevent voltage reversal in stacked MFCs. Current was the key factor influencing removal efficiency in the BER. The X-3B degradation pathway and the types and transfer processes of intermediate products were further explored in our system coupled with gas chromatography-mass spectrometry.

Reductive dechlorination of hexachlorobenzene subjected to several conditions in a bioelectrochemical system

A microbial fuel cell (MFC) is a very promising way to remove organic pollutants. Hexachlorobenzene (HCB) is a widely used agricultural pesticide. In this study, single-chamber and membrane-less soil MFCs were constructed. The HCB was degraded to pentachlorobenzene (PeCB), tetrachlorobenzene (TeCB), and trichlorobenzene (TCB) in sequence by a reductive dechlorination process in soil MFCs. The influences of the external resistance, concentration of phosphate buffer, and electrode spacing in soil MFCs on the degradation rate and removal efficiency of HCB were analyzed. The results showed that the degradation rate and removal efficiency of HCB were increased when the external resistance decreased from 2000 to 20Ω, and also when the concentration of phosphate buffer increased. The anode area played a significant role in dechlorination of HCB. Altering the spacing of the reducing electrode resulted in a lower ohmic resistance in the soil MFCs. The ohmic resistance was negatively correlated with the removal efficiency and degradation rate (P<0.05). In conclusion, HCB removal efficiency could be enhanced by soil MFCs, the performance of which was improved by a decrease in external resistance and internal resistance, and an increase in phosphate buffer concentration, rather than just by shortening the electrode spacing.

Electrode and azo dye decolorization performance in microbial-fuel-cell-coupled constructed wetlands with different electrode size during long-term wastewater treatment

Microbial-fuel-cell-coupled constructed wetlands (CW-MFCs) with various cathode layers were used for long-term azo dye wastewater treatment. Their performance was assessed using cathode diameters ranging from 20 to 27.5cm and the influence of plants at the cathode was also examined. Bioelectricity generation, ABRX3 decolorization, and chemical oxygen demand (COD) removal performances first increased and then decreased with increasing cathode diameter. The CW-MFCs with larger cathodes had an anoxic region at the cathode where ABRX3 was decolorized. This phenomenon has not been reported in previous research on MFCs using traditional air cathodes. Anode performance was influenced by the cathode. The CW-MFC with a cathode diameter of 25cm showed the best electrode performance, and the highest voltage and power density were 560mV and 0.88W/m3, respectively. The highest ABRX3 decolorization and COD removal volumes were 271.53mg/L and 312.17mg/L, respectively.

The performance of the microbial fuel cell-coupled constructed wetland system and the influence of the anode bacterial community

ABSTRACT In order to analyse the influences of substrate and electrode on the performance of microbial fuel cell-coupled constructed wetland (CW-MFC), the electrical generation efficiencies, the decolourization mechanism of reactive brilliant red X-3B, and the microbial communities in the anode were investigated. The closed circuit reactor fed with a mixture of X-3B and glucose (166.7 mg/L X-3B and 140 mg/L glucose) (the mixture CC reactor) got a decolourization rate of 92.79%, which was higher than the open circuit reactor (the mixture OC reactor) and the reactor fed with X-3B (the X-3B reactor). The mixture CC reactor got a maximum power density of 0.200 W/m3, which was much higher than the X-3B reactor. The intermediates produced by X-3B decolourization were further degraded in CW-MCs. The PCR-denatured gradient gel electrophoresis analysis indicated the dominance of Proteobacteria-like 16S rRNA gnen sequences. The brightest band was detected to be dominant by a Lactobacillus kefiranofaciens-like sequence. The electrogenic bacteria-associated sequences, such as Geobacter metallireducens and Desulfobulbaceae, both existed in the closed circuit and the open circuit reactors, accompanied with Desulfobacterium sp., Klebsiella sp., Aminobacter sp., Flavobacterium sp., Thauera aromatic, and Sphingomonas sp. The abundances of Geobacter sulfurreducens and Betaproteobacteria in the mixture CC reactor were 32.2% and 7.2%, respectively, and were higher than those in the mixture OC reactor. In summary, substrate and electrode can promote the performance of the CW-MFC and have effects on the microbial community in the anode of the CW-MFC.

Effects of electrode gap and wastewater condition on the performance of microbial fuel cell coupled constructed wetland.

ABSTRACT The effects of electrode gap, PB solution concentration and azo dye on the wastewater treatment and electricity generation of microbial fuel cell coupled constructed wetland (CW-MFC) were studied. The electrode gap had obvious influence on the decolorization, while the influence of PB concentration on the decolorization was not obvious. The best decolorization efficiency was 91.05% and was gained when the electrode gap was 13.2 cm. The smaller the electrode gap, the smaller the ohmic resistance. However, a too small electrode gap would reduce the electricity generation. The best PB concentration in this study was 50 mM. In the glucose group, when the PB concentration was 50 mM, the power density was enhanced to 0.38 W/m3, while the PB concentration was 5 mM, the power density was only 0.14 W/m3. In the ABRX3 group, when the PB concentration was 50 mM, the power density was 0.18 W/m3, while when the PB concentration was 5 mM, the power density was 0.12 W/m3. The electricity generation performance of the CW-MFC was enhanced with an increase in running time. Long-time running CW-MFC got a higher cathode potential and a smaller internal resistance.

Augmenting atrazine and hexachlorobenzene degradation under different soil redox conditions in a bioelectrochemistry system and an analysis of the relevant microorganisms

Soil microbial fuel cells (MFCs) are a sustainable technology that degrades organic pollutants while generating electricity. However, there have been no detailed studies of the mechanisms of pollutant degradation in soil MFCs. In this study, the effects of external resistance and electrode effectiveness on atrazine and hexachlorobenzene (HCB) degradation were evaluated, the performance of soil MFCs in the degradation of these pollutants under different soil redox conditions was assessed, and the associated microorganisms in the anode were investigated. With an external resistance of 20Ω, the degradation efficiencies of atrazine and HCB were 95% and 78%, respectively. The degradation efficiency, degradation rate increased with decreasing external resistance, while the half-life decreased. There were different degradation trends for different pollutants under different soil redox conditions. The fastest degradation rate of atrazine was in the upper MFC section (aerobic), whereas that of HCB was in the lower MFC section (anaerobic). The results showed that electrode effectiveness played a significant role in pollution degradation. In addition, the microbial community analysis demonstrated that Proteobacteria, especially Deltaproteobacteria involved in current generation was extremely abundant (27.49%) on soil MFC anodes, although the percentage abundances of atrazine degrading Rhodocyclaceae (8.77%), Desulfitobacterium (0.64%), and HCB degrading Desulfuromonas (0.73%), were considerably lower. The results of the study suggested that soil MFCs can enhance the degradation of atrazine and HCB, and bioelectrochemical reduction was the main mechanism for the pollutants degradation.

The degradation of azo dye with different cathode and anode structures in biofilm electrode reactors

In this study, biofilm electrode reactors (BERs) were constructed to degrade the azo dye Reactive Brilliant Red (RBR) X-3B. Three different BERs, namely, cathodes with differently structured reactors, cathodes filled with a granular activated carbon (GAC) reactor, and a dimensionally stable anode (DSA) electrode anode reactor, were individually studied to investigate their influence on the removal of both X-3B and chemical oxygen demand (COD). Experimental results showed that it was the internal resistance rather than the total surface area of the cathode that influenced the X-3B removal efficiency in the different cathode reactors. The smaller the internal resistance, the larger the current in the reactor. The larger the current in the whole system, the more electrons that could be utilized for the reduction of X-3B, resulting in higher removal efficiency. The cathode filled with a GAC-BER did not improve the COD removal efficiency, while the X-3B removal efficiency actually declined. Using the DSA electrode as an anode increased the current in the system and improved the removal efficiency. Scanning electron microscopy results showed that the DSA electrode anode had a longer service life than a graphite anode. UV-vis spectral analysis determined that the conjugate system in X-3B was destroyed.

Simultaneous degradation of refractory organic pesticide and bioelectricity generation in a soil microbial fuel cell with different conditions

ABSTRACT In this study, the soil microbial fuel cells (MFCs) were constructed based on sandy soil to remove the refractory organic pesticide hexachlorobenzene (HCB) in topsoil by a simple method. The construction of membraneless single-chamber soil MFCs by setting up the cathode- and the anode-activated carbon, inoculating the sludge and adding the co-substrates can promote HCB removal significantly. The results showed that HCB removal efficiencies in the soils contaminated with 40, 80  and 200 mg/kg were 71.14%, 62.15% and 50.06%, respectively, which were 18.65%, 18.46% and 19.17% higher than the control, respectively. The electricity generation of soil MFCs in different HCB concentrations was analyzed. The highest power density reached was 70.8 mW/m2, and an internal resistance of approximately 960 Ω was obtained when an external resistance loading of 1000 Ω was connected. Meanwhile, the influences of temperature, substrate species and substrate concentrations on soil MFCs initial electricity production were investigated. The addition of the anionic surfactant sodium dodecyl sulfate (SDS) into the soil MFCs system contributed to the improvement in HCB removal efficiency.

Azo dye degradation pathway and bacterial community structure in biofilm electrode reactors

In this study, the degradation pathway of the azo dye X-3B was explored in biofilm electrode reactors (BERs). The X-3B and chemical oxygen demand (COD) removal efficiencies were evaluated under different voltages, salinities, and temperatures. The removal efficiencies increased with increasing voltage. Additionally, the BER achieved maximum X-3B removal efficiencies of 66.26% and 75.27% at a NaCl concentration of 0.33 g L-1 and temperature of 32 °C, respectively; it achieved a COD removal efficiency of 75.64% at a NaCl concentration of 0.330 g L-1. Fourier transform infrared spectrometry and gas chromatography-mass spectrometry analysis indicated that the X-3B biodegradation process first involved the interruption of the conjugated double-bond, resulting in aniline, benzodiazepine substance, triazine, and naphthalene ring formation. These compounds were further degraded into lower-molecular-weight products. From this, the degradation pathway of the azo dye X-3B was proposed in BERs. The relative abundances of the microbial community at the phylum and genus levels were affected by temperature, the presence of electrons, and an anaerobic environment in the BERs. To achieve better removal efficiencies, further studies on the functions of the microorganisms are needed.