| With the acceleration of modernization process of small towns, the environmental problems arose. According to statistics, over90%of all small towns water environment pollution and deterioration appeared to varying degrees in the country. If we do not take timely and effective measures to curb water environment pollution in small towns, the damage will worsen in the future. So it is of great significance to focus on small towns sewage treatment. Based on the existing research, the combined process of flocculation magnetic separation-biological trickling filter was constructed. The combined process can achieve complementarity of the former technology, and also with good efficiency, strong shock resistance, simple process, convenient management and etc. The relevant research results can provide a technical reference for the development of small towns sewage treatment business. This study takes the technical and economic analysis of combined process as the key line, including inspection of the performance of the magnetic separation system, and analysis of the operating results of the biological trickling filter. In addition, compared with the traditional process, it has a simple economy analysis of the combination process.By means of Design-Expert, coagulant dosage flocculation, pH, magnetic seed (Fe3O4), PAM were analyzed, and the results confirmed that the effect of different parameters on the coagulation showing: coagulant dosage> magnetic species dosage> pH> PAM. The COD removal efficiency can reach as high as69.9%and TP removal rate can achieve98.9%, when the optimal parameters were best. In addition, the observation of magnetic floc structure show that magnetic seed dosing the can be used as condensation nuclei, enhanced coagulation removal effect during the flocculation process.The biological trickling filter supplied oxygen with the method of natural ventilation, which could save energy consumption extremely. It needed about25days to start the filter. Dissolved oxygen (DO) was important for the nitrification process. When the biological trickling filter was under stable operation, the path of DO in the filter presented the trend of high at both end and low in the middle, range of1.0~2.3mg/L. Under the hydraulic load were1.5,3.0,4.0,5.0m3/(m2d), the removal rate of COD and NH4+-N changed. The results show that the best hydraulic load was3.0m3/(m2d). Oxidation reduction potential (ORP) could reflect the comprehensive change degree of biochemical oxidation or reduction. DO and ORP changed with hydraulic load of systerm, but the trends were not quite the same. In order to further improve the effect of biological trickling filter on TN, the retrofit optimization was carried out. When the nitrifying liquid reflux ratio were150%, the TN removal rate reached75.8%, and the COD and NH4+-N removal rate were maintained around85%. In addition, the highest MLSS could reached up to4200mg/L. For the combined system, the main pollutant such as COD, NH4+-N, TN and TP removal rates were above90%,87%,76%and95%respectively. For the effluent of system: COD <50mg/L, NH4+-N <5mg/L, TN <15mg/L, TP <0.5mg/L, which met GB18918-2002IA.The sludge of system included chemical sludge and biological sludge, chemical sludge accounted for most, production rate of which was0.25~0.29kg/m3, and also its moisture content was only95.5%~97.5%. For the filter, when the COD was around150~220mg/L, the rate of sludge production remained about0.0005kg/kgCOD, and the sludge production had periodic sharp increase during the period of running. In addition, the engineering economic analysis of the combined process confirmed that it accounted for only16%to29%of the energy consumption, compared with the traditional sewage treatment process. |
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