| Chlorinated nitroaromatic compounds, which are important building blocks for synthesis of industrial chemicals, are serious environmental pollutants present in industrial wastes. The EPA of USA, EEC and Chinese have declared that chloronitrobenzenes are the priority pollutants. Therefore, waste management and detoxification of these kinds of compounds are important for protecting the environment and human health. In this paper, the acclimation of anaerobic and aerobic sludge, mechanism of chloronitrobenzenes biodegradation and the performances of anaerobic-aerobic process for removing chloronitrobenzenes in wastewater were studied. The following results were achieved:(1) The 2-CNB.4-CNB and 3,4-DCN-degrading anaerobic granular sludge was acclimated and enriched when a mixture of these three chloronitrobenzenes was employed as influent of anaerobic bioreactor. The anaerobic bioreactor was operated under COD 1.46~4.16kg.(m3.d)-1, chloronitrobenzenes 5 ~ 60mgl-1 and HRT 24~48h, more than 95% of chloronitrobenzenes and COD were removed. HPLC analytic results indicated that three chloronitrobenzenes were all transformated to 2-chloroaniline, 4-chloroaniline, 3,4-dichloroaniline and aniline.(2) The results of batch experiments showed that the anaerobic biodegradation kinetics of 2-CNB and 4-CNB by granular sludge were follwed by first-order reaction. The nitro groups of 2-CNB and 4-CNB were more easily attacked by electron than chlorines and they were reductively biotransformed to amino groups under anaerobic conditions. The acclimated anaerobic granular sludge, which could dechlorinate 4-chloroanline to aniline, showed that it had the ability of para-dechlorinating. The anaerobic biodegradating on pathway of 2-CNB and 4-CNB were suggested as follows:AbstractIn ZVI(zero-valent iron, Fe0)-reduction system, the nitro groups of 2-CNB and 4-CNB were reductively transformed to amino groups. The enhancement of transformation of chloronitrobenzenes was observed in ZVI-sludge-reduction system.(3) SBR system was employed to treat wastewater containing chloronitrobenzenes. In CK run with non-sludge aeration, approximately 50% of 2-CNB.4-CNB and 3,4-DCN were blowed off from liquid phase to atmosphere, the blow-off rate of them were 0.0587 -0.1 242h-1 for 2-CNB, 0.0682 ~ 0.1446h-1 for 4-CNB, and 0.0337 ~ 0.1568rr1 for 3,4-DCN. It was found that 4-CNB and 3,4-DCN were biodegradated in SBR by acclimated aerobic sludge, but it was poor for 2-CNB.(4) An aerobic culture utilizing 4-CNB as the sole source of carbon, nitrogen, and energy, named as A1 has been isolated from the acclimated aerobic sludge, it was Grame positive, the optimal condition for 4-CNB degradation were pH 7.5, the maximum specific substrate degradation rate of 4-CNB was 0.505mg.(g.H)-1, Ks 41.98mg.l_-1. This isolated aerobic culture was not efficient for degradation of 2-chloroaniline, 4-chloroaniline, 3,4-dichloroaniline , ailine, 2-chloronitrobenzene and 3,4-dichloronitrobenzene indicating biodegradating activity of the isolated bacteria was special.(5) The sequential anaerobic-aerobic system was set up to treat synthetical wastewater containing a mixture of three chloronitrobenzenes, the combined system was operated with influent COD 4011 -421 Img-L-i, chloronitrobenzenes (2-CNB.4-CNB and 3,4-DCN) 50mg-L-i, HRT 18~24h (anaerobic process)and HRT 24h(aerobic process). In the anaerobic phase, three chloronitrobenzenes were mostly biotransformed to chloroanilines and aniline, in the following aerobic phase, chloroanilines and aniline could be eliminated by aerobic sludge within 8~24h. COD concentration in effluent from A/0 system was lower to 50 mg-L1, and chloronitrobenzenes were undetected. One unkown product, which was more likely to be catechol, was decteded in enffluent. All of these results demonstrated that A/0 system was efficient for detoxification and also provided with the therotical foundation for application of sequential A/0 system to treatment of industrial wastewater containing chloronitrobenzenes. |
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