| Nitrobenzene is a typical organic contaminant in industrial wastewater. It is widely used in the production of different types of products such as dyes, explosives, and pesticides. Many countries have listed it as a priority pollutant because of its mutagenicity, recalcitrance, and tendency to accumulate in the environment. Nitrobenzene has a serious threat to environment and human health. It is traditionally to remove nitrobenzene from wastewater by anaerobic treatment processes. However, this anaerobic reductive process is usually very slow and requires an electron donor to create the necessary reductive conditions, and sometimes the intermediate products are more harmful. Therefore, it is necessary to develop methods with high efficiency to remove nitrobenzene when it occurs as a pollutant.Attributable to the strong electron affinity of the nitro group, the oxidatin of NB is difficult to achieve by traditional aerobic methods. However, under anaerobic conditions, nitrobenzene can be used as the electron acceptor and be reduced to aniline. the toxicity of aniline is much lower than nitrobenzene and can be biodegradable easily. Therefore, the reduction of nitrobenzene to aniliene is the key step.In this study, an innovative up-flow bio-electrochemical reactor (UBER) was developed. Graphite granular and carbon brush were used as cathode and anode respectively. Cathode was placed under anode. Wastewater flowed into the reactor from the bottom and flowed from cathode zone to anode zone. Nitrobenzene was mainly reducted at cathode. UBER can be scaled up because of its membranless design and the cost was greatly reduced. In addition, the cathode played a role of protecting anode and avoiding the the formation of pH gradient.Nitrobenzene loading rates were changed by raising the nitrobenzene concentration of influent. The efficiencies for nitrobenzene removal and anilian formation were ananlysis, as well as the nitrobenzene removal rate which presents the maximum capability of UBER. The results showed that effective removal of nitrobenzene at rates up to 3.5 mol/m~3 TV·d(TV: total volume) was achieved with the efficiencies for nitrobenzene removal and aniline formantion of 99%±0.05 and 85%±0.08, respectively. Current density was up to 22 A/m~3 TCV (TVC: total cathode volume) at HRT of 7.2h.In order to improve the efficiency of nitrobenzene reduction, the key factors affecting UBER were analysis. The results showed that a high nitrobenzene removal rate can be achieved when power supplied for UBER was as low as 0.3±0.02V. The concentration of sodium acetate can be decreased to 0.3g/L for UBER. Nitrobenzene can be efficiently removed when buffer concentration decreased to 10mM. In order to make UBER more practical, glucose was used as carbon souse instead of sodium acetate. It revealed that biological effects had taken an important role for nitrobenzene removal when nitrobenzene concentration was lower, which leading to the Coulombic efficiency based on nitrobenzene reduction was higher than 100%. When nitrobenzene loading rate was higher, eletrochemical reaction played a major role and the Coulombic efficiency was close to 100%. It also showed that bio-cathode was formed when glucose was used as substrate, which made the capability of UBER for nitrobenzene removal was higher. |
