| Bioelectrochemical system (BES) is a neoteric creation which has gained much attention due to its high versatility in the treatment of hardly degradable substance. Researchers have also come to appreciate the membrane-free technology and bio-cathode technology in the continually innovation of bioelectrochemical system technology. The realization of the combination with membrane-free technology and bio-cathode technology would adequately exert the technical advantage of them. Therefore, this study investigated the enhanced reduction of PNP under the membrane-free bio-contact coupled bioelectrochemical system (BC-BES). The the reduction of 2-nitrophenol (ONP),3-nitrophenol (MNP),4-nitrophenol (PNP), the formation of aminophenol correspondingly and the degree of mineralization under the same conditions were evaluated, and the bacterial community structure was also included.PAP formation efficiency always keep above 90% with the PNP loading rate gradually adjusted showed that the vast majority of PNP was reductively transformed to PAP in the biocathode of BC-BES. In order to confirm the key role of the electric frield in PNP reduction, the electric frield was removed at the 55th day and PNP removal and PAP formation efficiency sharply decrease under stable operation in 5 days. This phenomenon showed that the electric frield played a key role in both PNP reduction and PAP formation. PNP removal and PAP formation efficiency had no significant changed with the dosage of NaAc decreased from 14.6 to 3.66 mM, the concentration of PNP maintained at 2.52 mM in the meanwhile.As the dosage of NaAc further reduced, PNP removal and PAP formation efficiency had changed and the anode potential increased gradually. This phenomenon indicated that NaAc dosage of 3.66 mM is the minimum requirement with PNP influent concentration of 2.52 mM. PNP removal rate and PAP formation rate as high as 18.95±0.10 and 17.74±1.03 mol per m3 per day could be achieved at a cathode potential of-1000 mV vs. Ag/AgCl and hydraulic retention time (HRT) of 8.9 h, which were higher than other biological treatment methods. What’s more important, the energy consumption in the BC-BES was well below 0.02 kW h mol-1 PNP in the BC-BES. The low energy consumption in BC-BES was much lower than that in pure electrochemical system and dual bioelectrochemical system. High PNP removal rate, high PNP formation rate, low acetate dosage, low energy consumption, high system stability could be achieved in the BC-BES indicated that BC-BES has high value in PNP treatment.Compare with the reduction of PNP, MNP, ONP in BC-BES, the ONP removal efficiency was highest, meanwhile the PNP removal efficiency was lowest in the conditions of a cathode potential of-700 mV vs. Ag/AgCl, hydraulic retention time (HRT) of 5.8 h, influent pH of 6.0, NaAc dosage of 3.66 mM, and NP concentration of 0.72 mM. The order of NP removal efficiency in bio-cathode is ONP>MNP>PNP. The reason for low PNP removal efficiency has more to do with the low pH in influent. Correspondingly, the MAP formation efficiency was highest, and the OAP removal efficiency was lowest. The order of AP formation efficiency in anode is MNP>PNP>ONP. Furthermore, partial mineralization of PAP was observed in the anode of the BC-BES in the forst part experiment. For purpose of exploring the impact of different structure of AP on mineralization, the mineralization of the three kinds of AP in the anode were compared. The order of AP formation efficiency in anode is MNP>PNP>ONP. By comparing bacterial community that, we can discover that electrochemical activity microorganism of Geobacter was abundant in different stages. Desulfovibrio were capable of reducing nitroaromatics and the percentages in bio-cathode was ONP>MNP>PNP, which is consistent with the order of NP removal efficiency in bio-cathode. |
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