چكيده لاتين :
Discharging wastewater effluent, while it includes nutrients, to surface water or groundwater is very dangerous to the environment. As phosphorus and nitrogen combination in aquatic environments have harmful impacts (mainly the poisonousness of ammonia, overgrowth of aquatic plants, groundwater pollution and diseases caused by drinking polluted water, and also eutrophication, resulting in frequent outbreaks of algal blooms and threatening the reliable supply of drinking water resources), some limitations were imposed on the consistency of these combinations in the waste inflow. Thus, nowadays the removal of these combinations must be considered in the design of treatment plants. Also, systems designed for treating the municipal wastewater must be able to remove nitrogen and phosphorus combinations to reach the standard limit. Therefore, in order for the aerobic-anaerobic-oxic (A2/O) method to perform well, in this research, a study in advanced treatment of municipal wastewater has been carried out, using the A2/O method to remove nitrogen and phosphorus in pilot scale in Ekbatan WWTP. In this research, firstly the principles of biological removal of nitrogen and phosphorus, and secondly the basis of designing biological treatment plants have been investigated. Thereafter, for laboratorial studies, an A2/O pilot has been made. This pilot consists of anaerobic, anoxic and aeration tanks and also a sedimentation tank. The volume of these 4 tanks are 40, 60, 170 and 120 L, respectively. In order to simulate the real condition, this pilot has been set up in Ekbatan plant and the experiments were carried out to observe the effect of hydraulic residence time on nitrate, ammonia and phosphorus removal, and also the effect of oxic mixed liquor recycling ratio on nitrate removal has been investigated. In order to observe the nitrate, ammonia and phosphorus removal processes efficiency, the experiments were carried out in a period of three months and in 5 aeration hydraulic residence times: 4, 6, 8, 10 and 12 h. In these experiments, the returned sludge was 25% and the oxic mixed liquor recycling ratio was 75%. After determining the best hydraulic residence time, experiments were continued in 5 different oxic mixed liquor recycling ratios, 75%, 150%, 225%, 300% and 375%. It was concluded that at aeration hydraulic residence time of 8 hours, 96% COD , 95% ammonia and 79% phosphorus (effluent: 9 mg/L COD, 0.87 mg/L ammonia, 2.1 mg/L phosphorus, 18.7 mg/L nitrate) removal were achieved, and that was the best HRT. Furthermore, according to the mixed liquor recycling ratio experiments, when the oxic mixed liquor recycling percentage was about 180 - 200%, the optimum nitrate removal has been occurred. Although the mixed liquor recycling ratio of 225-275% resulted in better efficiency for nitrate removal, it is not proposed, because effluent limitations in Iran for the nitrate is up to 10 mg/l which is resulted in the mixed liquor recycling ratio of 180-200%, and the other reason is that, by increasing the oxic mixed liquor recycling ratio, energy costs will increase, too.
