Enhancement of municipal wastewater treatment plants by chemical application

Abstract

The enhancement of municipal wastewater treatment plant was investigated at the two model plants by full scale and semi-pilot scale experiments. The simple application of 20 0 60p1/1 of Hi-PAX(Po1y Aluminum Chloride Silicate, A1203 17%) to the inlet of the influent pump of the primary sewage treatment plant(250,OOO m3/day) showed enhanced removal eficiencies in all contaminants. The removal rate of SS increased from 40% to 81%, while that of BOD and COD from 30% to 71% and 29% to 57%, respectively. In addition, the removal rate of total nitrogen and phosphorous also increased from 3% and 29% to 27% and 96%, respectively. The effect of chemical pre-precipitation on the biological treatment was evaluated by semi-pilot plant with and without pre-precipitation step, The addition of 15pVl of Hi-PAX to the preprecipitation step could enhance the removal efficiencies of S S , organic matters, nitrogen and phosphorus. In addition, the increased removal of organic matters in the primary sedimentation could reduce the F/M ratio of the following biological step by about 30% and reduce the oxygen requirement in the aeration tank by about 50%. Introduction As the end of 1997, there were 93 sewage treatment facilities in Korea with the total capacity of 15.04 million tons/day, and the sewage treatment ratio was 60.9%. However the standard activated sludge process(90%) is the most widely used, except for a number of places where extended aeration(2%), rotating biological contactor(3%) and only primary sedimentation(5%) are used(Korea MOE, 1996). The implications of the 1996 Amendments to the Water Quality Protection Act reflected the desire of the public for the clean water environment. The effluent standards for BOD, COD and SS were tightened from 30 mg/l , 50mg/l and 70mg/l to 20 mg/l, 40mg/l and 20mg/l, respectively, and two new pollutants total nitrogen(T-N, 60mg/l) and total phosphorus(T-P, 8mg/l)-were added to the effluent standards. Due to the strengthening effluent standards for BOD, COD, S S , T-N and T-P, interest in the improvement and expansion of the existing treatment plants and new processes for the anticipated more stringent effluent standards are increasingly growing up. Chemical application(0degaard. H. and Karlson. I. 1994) has been used in various ways to improve the wastewater treatment such as the only treatment process(Primary precipitation or direct precipitation) and in combination with biological treatment in terms of pre-, simultaneousand postprecipitation. However, many factors, such as the variation in composition and degree of pollution, the type of technologies in use, the type and mix of industrial and domestic sewage, and the amount of surface water, must be fully considered before applying the chemical upgrading technologies. Thus two model plants are selected for the feasibility study of chemical upgrading of municipal 0-7803-5729-9/99/$10.00