| Municipal wastewater mixed with high concentration of industrial wastewater contains high COD hard to be degraded, resulting in the low biodegradability. It also contains hazardous materials. These properties bring difficulties in stable operation with standardized discharge and low energy consumption at current stage. At present, the most commonly used biological treatment process is the two-stage activated sludge process, including the stage of hydrolysis acidification- aerobic process and the stage of AB process. The sludge recycle in the process is to pump the concentrated sludge from secondary sedimentation tank back to biochemical tank, and the other excess sludge are discharged and treated. Our research introduced a new sludge control enhancement technology, with the return of excess sludge from secondary sedimentation tank of the second stage back to the biochemical tank of the first stage. The impacts of sludge control technologies on the two-stage activated sludge process operation were studied. The application prospect of the process was analyzed.Three wastewater treatment plants treating municipal wastewater mixed with high concentration of industrial wastewater were studied, with the industrial wastewater from printing and dyeing, electroplating, chemical engineering and pharmacy, separately. Based on the test and analysis during long-term operation in the plant, the main problems of the treatment processes, including hydrolytic acidification – A2 O, hydrolytic acidification – Ap O, and AB process, were recognized. Anaerobic hydrolysis tank worked not well with effluents of high suspended solids. Besides, its treatment capacity could not match the designed capacity. The shock load of hazardous materials resulted in the damage of nitration, leading to the ammonia nitrogen in the effluent exceeding standard. When the concentration of COD hard to be degraded increased, the effluent control risked the COD concentration exceeding standard.The application of endogenous sludge control technology in the two-stage series process was studied, with the return of excess sludge from secondary sedimentation tank of the second stage back to the anaerobic hydrolysis tank or A-tank of the first stage. Results indicated that the sludge control had low impacts on the concentration of COD, SS, and TP in the effluent. However, it removed NH4+-N significantly, which successfully made the final effluent quality meet discharge standard. Moreover, it reduced the SS concentration in anaerobic tank effluent efficiently, thus enhancing the treatment capacity and the stable operation in the plant. A modest increase of SS after A-stage treatment could ensure the efficient and stale operation in the next stage. The endogenous sludge control technology led to the increase of sludge settle-ability(SVI). The good settle ability of sludge increased the ratio of MLVSS/MLSS in anaerobic hydrolysis tank by 10%~63%. Besides, it improved the SVI in the secondary sedimentation tank signicantly, which increased the MLVSS/MLSS in the secondary sedimentation tank by 9%~22%.The application of exogenous sludge control technology in the two-stage parallel process was studied, with the return of excess sludge from secondary sedimentation tank of the second stage back to the biochemical tank of the first stage. Results indicated that sludge control increased the removal of NH4+-N, SS and TN in the beginning sections. It also enhanced the sludge flocculation performance and nitration ability. However, it had low impacts on the ratio of MLVSS/MLSS. When the shock of hazardous materials damaged the nitration in biological tank, the exogenous sludge could help recover the nitration effect in 5~10 days, with NH4+-N concentration lower than 1.0 mg/L in the effluent. Besides, the technology enhanced the removal ability of NH4+-N, sludge settle performance and nitration ability in the final sections, with the enrichment of nitrobacterium. |
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