Study On Bioaugmentation For The Treatment Of K·D Initial Explosive Wastewater

The Wastewater from the factory producing K-D initial explosive contains low concentration of lead ion, high concentration of picric acid (2,4,6-trinitrophenol) and high concentration of nitrate-N. The wastewater is difficult to be treated because of the characteristic of high-salt, high organic concentration and poor biodegradability. In this study, a novel treatment process based on bioaugmentation was developed, in the aim of cost effective and innocuous treatment of K-D initial explosive wastewater.A picric acid-degrading bacterium, Rhodococcus sp.NJUST16, was isolated and applied into the biological aerated filter. A modified anoxic/oxic-membrane bioreactor (A/O-MBR) was adopted for the biological denitrification of high strength nitrate waste. The feasibility of the combined process, which was consisted of chemical precipitation, biological aerated filter and A/O-MBR, was tested for the remediation of K-D initial explosive wastewater at a technical-scale pilot plant, with the operational parameters optimized.A series of specially efficient bacteria capable of utilizing picric acid as the sole source of carbon, nitrogen and energy were isolated, with strain NJUST16 as the representative bacteria. The strain NJUST16 was identified as a member of Rhodococcus sp. based on 16S rRNA sequence, biochemistry experiment and morphological observation. The metabolites and mechanism of TNP degradation by NJUST16 was analyzed by FTIR, UV-vis spectrophotometry, MS/MS, combined with COD and nitrite tests. The results indicated that hydrogenation, elimination of nitro groups, cleavage of benzene ring occurred under the degradation by NJUST16, resulting into significant mineralization of TNP. For batch experiments, Haldane's model could be well fitted to the inhibitory growth kinetic data of Rhodococcus sp.NJUST16. TNP degradation kinetic data described by Haldane's model fitted well with experimental degradation profiles.The bioaugmentation system coupled specially efficient bacteria with biological aerated filter (BAF) was constructed through inoculating NJUST16 into BAF. After startup, the pollution load increased gradually. Finally, a maximum volumetric removal rate of 2.56 g TNP-L(-1)·d(-1) was reached, with low residual COD and TNP concentration. During the startup process, nitrite, which is one of the metabolites of TNP, was nitrified. Nitrite-oxidizing occurred spontaneously during TNP degradation in the BAF system, could have significant influence on TNP degradation. Overloading of TNP inhibited the nitrite-oxidizing activity, resulting in poor TNP degradation performance in the BAF systemThe COD concentration at different reactor height can be expressed as a function of influent COD concentration and hydraulic loading rate, In and , respectively. The microbial community was analyzed through PCR-DGGE The results indicated that one year after the startup process, the initially inoculated Rhodococcus did not loss their dominance after the system had stabilized.The combined process composed of chemical precipitation, biological aerated filter and anoxic/oxic-membrane bioreactor, was used to treat K-D initial explosive wastewater, showing it feasible in technique. The results of the technical-scale pilot plant indicated that under the optimal operational conditions, the lead ion, picric acid, COD, BOD and the color were removed effectively. The indexes of effluent were lower than the discharge standard for water pollutants from ordnance industry (GB 14470.2-2002). In addition, the concentrations of nitrate-N, nitrite-N and total bacterial counts in the effluent were rather low.In conclusion, the combined process consisted of chemical precipitation, biological aerated filter and anoxic/oxic-membrane bioreactor, which is based on the application of bioaugmentation, is promising for the economic, effective and innocuous remediation of K-D initial explosive wastewater.