Enhanced Treatment Of Nitrobenzene Wastewater In Membrane Bioreactor Bioaugmented With Electrochemically Active Bacteria

As an important chemical primary and intermediate substance, nitrobenzene is widely used in the production of aniline, dyes, pesticides and explosives. It has high biological toxicity and is considered as one of the priority pollutants in many countries. Anaerobic-aerobic process (A/O) is the most effective strategy for nitrobenzene wastewater treatment, which can enhance the biodegradability of the subsequent aerobic process. However, the slow metabolic rate of common anaerobic microorganisms were found to be the rate-limiting step of complete biodegradation of nitrobenzene wastewater.To solve this problem, the electrochemical bacteria (Shewanella sp. XB)/quinone modified polyurethane foam (Q-PUF) was added to the anaerobic membrane bioreactor in order to achieve high effective processing performance. The electrochemical bacteria and quinone-modified polyurethane foam (Q-PUF) could present double enhancement effect. The synergies of Shewanella sp. XB and Q-PUF can strengthen the anaerobic degradation of nitrobenzene wastewater. Meanwhile, the effective immobilization avoided the losses of the high-efficiency strain and exogenous mediator from MBR.Different strengthening methods were assayed in analog anaerobic MBR to treat nitrobenzene wastewater. The optimal conditions were as follows:pH7-8,30℃,2g MLSS/L, and10mM glucose. The experiment period was24h. It was demonstrated that the degradation of nitrobenzene in MBR process could be promoted by adding Shewanella/Q-PUF. After6rounds of simulation usage at optimal operating mode of MBR, the removal rate of nitrobenzene could stayed up to80%. The removal rate of nitrobenzene remained stable at85%when the nitrobenzene wastewater contained5%salinity.Through adding10%Shewanella sp. XB/Q-PUF (w/w) in the anaerobic membrane bioreactor, the biotreatment study was carried out on the simulated nitrobenzene wastewater, under the appropriate conditions:2g MLSS/L,10mM glucose concentration, HRT24h,15-3O℃, and200-800mg/L nitrobenzene. When the reactor was run for16days continuously, over90%nitrobenzene was degraded from the membrane effluent water. After a long period of stable operation, the sludge concentration was1.5g/L and the TTC-dehydrogenases activity was18mgTF/(L·h). Under the same operating conditions, in control activated sludge system without adding Shewanella sp. XB/Q-PUF, nearly30days of continuous operation was needed to reached about90%removal efficiency. Thus it can be seen that:the addition of Shewanella sp. XB/Q-PUF (w/w) could drive the MBR system quickly and make the operation stable, and the removal effect was better than that without Shewanella sp. XB/Q-PUF.Finally, DGGE in molecular ecology technology was used to analyse the microbial community structure variations in the bioaugmented membrane bioreactor. The results showed that the biodiversity of the system gradually reduced. Post-sequencing results showed that Shewanella might become the dominant species. The LC-MS analysis indicated that aniline was the end product and hydroxylamiobenzene was the intermediate product in the bioaugmented membrane bioreactor.