| In this study, to settle the main problems existing in the field of current domestic sewage treatment in power plant, a method of low-concentration domestic sewage treatment which uses biological aerated filter(BAF) was discussed for the first time. In this technics , spherical expanded clay is used as biologic media. Based on the lab-scale experiment, systemic trial was processed and considering the water quality demand of circulating cooling water, pilot scale BAF experiment was conducted,the treated object is domestic sewage comes from power plant. According to the experiment datum and theoretical analysis , a new process of low-strength domestic sewage treatment in power plant was provided with the merits such as low investment low operation cost and simple management.In lab-scale experiment, the performance of BAF is studied. The main objects studied here are the disposal efficiencies of COD BOD5 SS and other factors which can influence the efficiency. The experiment reaches a conclusion that: When using spherical expanded clay as the media , the factors that can influence the performance of BAF are: the media height the ratio of gas to liquid hydraulic load and organic load . For the upflow BAF, when the media height is 2m ,the best media height for the remove of COD, NH4+-N and SS is at 80cm, 60cm~120cm,and 40cm from the bottom respectively. When the ratio of gas to liquid is 3:1 and the hydraulic load is 1.13m3/(m2.h), the most ammonia load of influent water for BAF reactor is about 0.5 kgNH4+-N/ m3.d, in order to ensure the concentration of NH4+-N in effluent water is less than10mg/1. The relation of hydraulic load and remove efficiency of COD is not linear,there is a optimum hydraulic load for the remove of COD. When the average concentration of COD in influent is 71.8~126.6mg/L, and the ratio of gas to liquid is 3:1,then the best hydraulic load is 1.69~2.82m3/m2.h, average remove rate of COD is 86.3%,and the average concentration of COD in effluent is 13.4mg/L; When hydraulic load is 2.82m3/m2.h,the most organic load that reactor can bear is 4.5kgCOD/m3 (filtration media) ,d in order to ensure the concentration of COD in effluent less than 30mg/L; When hydraulic load is constant, COD of effluent will increase as the organic load rises, but remove efficiency is steady, this shows that BAF has a best ability to resist the great change of organic load.The method, intensity, and period of backwash are all studied in experiment, results show that: the method of using air scouring firstly, then air-water backwashing, and adopting water-wash finally has many advantages over other methods. Backwash parameters summarized are: air scouring intensity is 12~14L/(m2.s), duration is 3min; air intensity, water intensity and duration of air-water backwashing is 12~14L/(m2.s), 7 L/(m2.s) and 6min respectively ,at the end of the process, single water-washing intensity is 9 L/(m2.s), duration is 6min;The results of pilot-scale BAF experiment shows: at the current characteristic condition of water, optimum operating parameters are shown as follows: hydraulic load is 3m3/m2.h, ratio of gas to liquid is (1.5~2) :1,DO of effluent is more than 5mg/L,the average remove rate of COD, BOD5 NH4+-N, SS, CODMn is 78.21%, 82.53%, 86.97%, 85.82%, 69.58% respectively, and corresponding concentration of effluent is 14.17mg/L, 3.72 mg/L, 0.4mg/L 3.67 mg/L, 2.61mg/L, it meets the criterion of water quality for reclamation in the circulating cooling system which condenser tubes are made of alloy-copper.Comparing BAF with SBR in the fields of technology and economic, if using BAF process to treat domestic sewage, it can be concluded that unit investment is 1046 yuan/m3.d, net cost for treatment is 0.257 yuan/m3, net economic benefit is 469.5 thousand yuan /a . The calculation is based on actual volume of domestic sewage in one power plant which is 4800m3/d. BAF has advantages such as low one-off investment, low operation cost, high annual economic benefit, etc. So BAF has good technic and economic effect.
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