Studies On Sewage Treatment And Recycle Reclaimed Water In Residential Areas

With the development of high education, many cities have taken on centralized distribution of academies, and the increasing students have brought on more sewage drainage. It is very difficult for water treatment plant to dispose of all sewage due to dispersive layout of residential areas. The wastewater of schoolyard areas have some characteristics, such as: low contamination, single component, strong space-time of using and displacement, and so on. In addition, sanitation washing and campus virescence which occupied a large scale of school total demanding keep rasing the burden of urban water supply, resulting in the crisis of water resource. In order to relax the crisis of water resources, sewage treatment station can be set up to treat the sewage as mixed water reusing campus. It is an effective instrument to solve schoolyard domestic wastewater polluting and water shortage.Aiming at sewage quality and the criterion of mixed water, SBR, SBBR and biological contact oxidation system were adopted to treat schoolyard domestic wastewater. The treatment performance, effective factors and technical parameter of each technics have been studied. The following results were obtained:1. Using SBR treating schoolyard domestic wastewater, the influencing degree of aeration rate, aeration time, MLSS and settling time on COD, NH₃-N and PO₄^3- were determined by orthogonal experiment. When the optimum parameter is: aeration time 4.0h, aeration rate 0.200m3/h, settling time of 0.5h and MLSS around 1000mg/L, the COD, NH₃-N, PO₄^3- and BOD₅ can be effectively removed by the rate of 88.14%, 98.78%, 94.14% and 96.83%, and the discharge of COD,NH₃-N,PO₄^3- and BOD₅ were 4～32mg/L,0.01～0.4mg/L,0.01～0.2mg/L and 0.48～8.75mg/L ,respectively. The main indexes of discharge like COD, NH₃-N, PO₄^3-, BOD₅, smell, colour and pH can meet the Criterion of Living Mixed Water (or Standard of Middle Water in Beijing). The higher concention of SS can be removed by sand filtration.2. When SBBR was brought to treat wastewater, anoxic time, aeration time, aeration rate and settling time were chosen as the main factors and the influencing degree was determined by orthogonal experiment. The optimal reaction conditions were acquired by single factor tests: anoxic time 1.0h, aeration time 4.0h, aeration rate 0.200m3/h and settling time of 1.0h. Under these conditions, the removal rate of COD, NH₃-N, PO₄^3- and BOD₅ in wastewater can be achieved about 89.63%, 77.40%, 99.38% and 95.48%, and the discharge of COD was 14～45mg/L, BOD₅ was about 4mg/L, NH₃-N and PO₄^3- were less than 10mg/L and 0.2 mg/L, respectively. At the same time, other indexes excepting SS also can meet the reclaimed standards.3. Biological contact oxidation treats schoolyard domestic wastewater taking artificial inoculation. It needs about 10 days to start-up well and has a high removal rate on COD and NH₃-N during this time. The research results indicated that when the influent wastewater COD was about 150mg/L, NH₃-N was 10mg/L, aeration rate 0.040m3/h, HRT=4.0h and Vg/VL12～25:1, COD and NH₃-N can be removed by the rate of 80% and 90%, respectively. After treatment, COD can be decreased to 30mg/L, NH₃-N was less than 2.5mg/L in the effluent. During in the stable running and some organic load range, the reactor can resist a lot of shock load, still having good effect on COD and NH₃-N.4. By the comparison of SBR, SBBR and Biological Contact Oxidation on the treatment of schoolyard domestic wastewater, they have no obvious difference on effect. Under the condition of having similar treatment effects, SBR does not need fillings compared with SBBR, so it can save some expenditure; If SBR is compared with Biological Contact Oxidation, it also does not have fillings, moreover, it does not require continuous aeration, saving energy consumption and consistent with the intermittent discharge characteristics of schoolyard domestic wastewater. So after general consideration, SBR process is more economical and reasonable.The innovation of this study is disscussing three different technicses to treat schoolyard domestic wastewater, and choosing SBR method as the best for the treatment of sewage in Northwest A&F University (Northern area). The indexes in study except SS can be reached the Criterion of Living Mixed Water (or Standard of Middle Water in Beijing). These parameters have high reference value for the middle water reuse project design and management in the future.