Study On Iron Dosage For Enhancing The Operation Stability Of Large Scale Wastewater Treatment Plants

During recent years, with the gradual improvement of urban drainage network and the gradual implementation of rain and sewage separation systems, the load of pollutants in wastewater increased significantly. Some of the existing wastewater treatment plant which ran at higher load conditions than its designed capacity, could not operate stably and the effluent was not able to meet the standard. After continuous monitoring and investigation in one typical large scale wastewater treatment plant in Jinan, the operation sustainability and treatment effects were analyzed based on the study of influent quality, operation process conditions and treatment results in each units. The process of activated sludge with iron dosage was studied and applied in the plant to acclimate the traditional activated sludge, treat high-loading wastewater and enhance the efficiency of nitrogen and phosphorus removal.The influent quality and operation results in the plant during recent years were analyzed. COD, ammonia nitrogen and SS were higher than designed capacity in winter season, with the phenomenon of smelly black influent. In the condition of drastic fluctuation of influent quality, the influent quantity was reduced and th operation parameters in the plant were adjusted, in order to control the concentration of COD, TN, Ammonia-N and TP in the range of 8.0~39.0 mg/L, 5.0~15.0 mg/L, 0.20~7.20 mg/L and 0.10~0.43 mg/L, separately. However, the process equipment were overloaded with high sludge loading in the long-term operation, due to the high influent concentration and the mixture of illegal wastewater discharges. The operational costs were thus increased and some equipment and facilities were faced with serious problems.Based on the batch experiment, the impact of iron dosage on activated sludge process operation was studied. When the iron content reached 5% in the activated sludge, the optimal removal of COD, TN and TP was achieved, with removal efficiency increased by 5.9%, 10.1% and 4.5% compared with control. At the same time, nitrification and denitrification activity were increased by 17.9% and 15.7%, while the impact of iron dosage on sludge settling property was neglectable. Iron dosage also improved COD removal ability of activated sludge when wastewater containing heavy metals(Zn2+/Cu2+ concentration?20mg/L, Oil concentration?120mg/L) was treated.The process of activated sludge with iron dosage to acclimate the traditional activated sludge ensured the stable effluent quality to meet the discharge standard, when the influent load was relatively high, achieving the average COD/TN/TP/ NH3-N/SS removal efficiency of 94.0%, 77.3%, 95.5%, 96.5%and 98.4%, separately. When 30% FeCl3 was applid as added agent, the cost of dosage per ton of treated wastewater was reduced significantly, with the average cost of 0.0170 yuan/ton, lower than 0.0210 yuan/ton in the last year.