| The complicated process of printed circuit board(PCB) manufacturing makes its wastewater bears complex constituents. The removal of the complexed copper, ammonia nitrogen, total nitrogen and other pollutants is more difficult. This study used a combined process, “Na2S complexation-breaking pretreatment + anoxic activated sludge(AAS)-biological aerated filter(BAF)” to treat PCB wastewater. The key step in complexationbreaking pretreatment is precise control of Na2 S dosing. In this study, the controlling methods of using ORP and Ag+/S2- electrode monitoring in complexation-breaking pretreatment were compared, the feasibility of using the methods was analyzed, and the performance of continuously running this combined process to treat PCB wastewater was examined.The controlling methods of using ORP and Ag+/S2- electrode monitoring in complexation-breaking pretreatment were compared in this study. The results showed that when use ORP to monitor the complexation-breaking process the longer response time and co-present ions interfering would lead to the limitation in practical application. The sulfur/silver electrode monitoring demonstrated its advantages of having higher accuracy and precise, shorter response time, and less interference by co-present ions, and can be applied for controlling the complexation-breaking pretreatment process. When copper concentration in wastewater varied in 25~150 mg/L and the controlling potential value is set at-750 m V, copper in the water can be removed completely and sulfide concentration in water ranged in 2.6~39.6 mg/L.The effects of residual sulfide in pretreated wastewater on AAS treatment were studied. Results showed that the denitrification rate in AAS was suppressed when encountering the impact of residual sulfide. Increasing sludge concentration can diminish such suppression. In a long run, the presence of sulfide decreased denitrification rate by 32.3%, whereas the specific sludge denitrification rate was not significantly inhibited. In the presence of sulfide, sludge concentration was decreased and sludge dehydrogenase activity showed being inhibited. In practical application, the impact of residual sulfide in pretreated wastewater can be coped with by increasing sludge concentration to improve the treatment efficiency.Finally, the “Na2S complexation-breaking pretreatment +AAS-BAF” combined process was used to treat real PCB wastewater for examining its long-term pollutants treatment performance. Results showed that when the electrode potential of Ag+/S2-electrode was set at-617 m V, the fluctuation of the influent copper can be rapidly monitored. After receiving the electrode feedback, copper can be completely removed through increasing Na2 S dosage. When the AAS-BAF HRT was 4h, the sludge returning ratio was 50%, and the nitrification liquid returning ratio was 200%, total nitrogen, ammonia nitrogen, and COD concentrations in effluent can be treated to below 15 mg/L, 5 mg/L, and 80mg/L, respectively. The effluent copper was below 0.5 mg/L, SS was below 30 mg/L, and p H ranged between 7.0~8.5. The effluent water quality met the discharge requirements. |
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