A Sequential ZVI-fixed Bed Reductive Transformation And Aerobic Biodegradation Treatment For Chloronitrobenzenes

Chloronitrobenzenes, as important building blocks for synthesis of industrial chemicals, are quite recalcitrant and toxic. They have been declared to be the priority persistent toxic substances(PTS) by the EPA of USA, EEC and China. Recently, ZVI reductive transformation as a new remediation technique for controlling water pollution, has been applied in important organic pollutants pretreatment, such as nitroaromatic compounds(NACs), azo dyes and RDX. ZVI is a strong reducing agent, can reductively transform the electron-withdrawing nitro groups to amido groups. But coupling biological/chemical oxidation or enzyme catalysis treatment proc essses is necessary, considering the further mineralization of the organic pollutants,. Based on the characteristics of CINBs and achievements by now, we investigated a sequential ZVI-fixed bed reductive transformation and aerobic biodegradation treatment for CINBs, to (1)gain insight into the reductive transformation kinetics of 4-CINBs in column, longevity of column, (2)analyse ZVI pretreatment for enhancing the biodegradability of CINBs, (3) understand the mineralization process of CINBs in ZVI-biological treatment system.The following results were achieved:1. In anaerobic, pH5, 4-CINB was reduced by ZVI to 4-CIA. Reductive reaction was follow ed by pseudo-first-order kinetics. The reductive transformation rate was related with the kinds and the specific surface area of ZVI, and the order was nanoscale ZVI>microscale ZVI>Iron po wder. The reductive rates were increased with increasing surface area of ZVI, but it is not a lin ear correlation. Reductive reaction in ZVI-fixed bed was also followed by pseudo-first-order kin etics. The reductive transformation rate constant k (88.68±3.90) h~-1.2. Anion effects on the longevity of ZVI-fixed bed was distinctly with low 4-CINB loading. There were difference in hydraulics and ZVI surface characteristic. Compare with HCO3-, high Cl- concentration enhanced its reductive activity within short time, by its corrosion on the surface of ZVI, but the performance was poor over the long term.Washing the column with 0.05M HCI, can dissolve mineral precipitation and Fe (hydro)ox ides on ZVI surface. Thus, resume ZVI reductive activity, and maintain the efficiency of ZVI reactor.3. ZVI-treated CINBs, render the recalcitrant compounds more amenable to subsequent aerobic biodegradation. Respiration rate and dehydrogenase data indicated that the aerobic culture existing ZVI treated solution exerted distinctly higher activity than untreated CINBs solution. After being incubated for 24h, the dehydrogenase activity and respiration rate of the aerobic culture existing ZVI treated solutionm were both over 2 times higher than untreated CINBs solution, and the highest reached up to 3.08 and 11.9 times, respectively. There were certain amount of Fe3+, Fe2+ in ZVI treated CINBs solution, meanwhile, and the total amount was 0.3 mg i-1, they can advance the activity of microorganism. According to the results, an integrated ZVI reduction-activated sludge process system may be a feasible option for mineralizing CINBs.4. Aerobic granules have the ability to biodegrade ZVI treated 4-CINB solution and mineralize it. Biodegradation is followed by first-order kinetics, the biodegradation rates were influenced by initial concentration. And the rate constant k was decreasing with increasing initial concentration.5. Integrated ZVI-SABR system was operated with influent COD loading 1.35-1.74 kg-m-3-d-1, and 4-CINB loading 250-340 g-m^-d-1. In effluent, COD concentration was lower to 65mg-L-1, and 4-CIA concentration was lower to 0.35 mg-L1. The results demonstrated that integrated ZVI-microorganism treatment system to mineralize CINBs is feasible.