Treatment Of Small Towns Domestic Wastewater By Combined Cept-tf-uf Processes

Combined process of water treatment technology can effectively make up for the disadvantages of each individual process and play their respective advantages as much as possible. The application of the combined process in treatment of the small town wastewater treatment not only meet the features of small town wastewater that the water quality and quantity was changeable, but also can save investment, reduce cost. This paper focused on the “CEPT-TF-UF” combined process disposing small town wastewater, investigated the performance of the combined process and the efficiency of pollutants removal and the influence factors. The migration transformation of DOM which bring huge harm to small town’s environment and the utilization of sludge were paid especial attention.To save investment, fly ash from the local power plant was used as the raw material. Fly ash coagulant was prepared and applied in the coagulation unit. The dosing amount of 2.5 m L/L, the reaction p H value of 6~8, and the coagulant form of static sink after the upper turbid fluid were the optimum reaction condition for the fly ash coagulant. When the optimum surface hydraulic load was 4.00m3/(m2?d), the temperature was above 20 oC, The removal efficiency of COD、SS、TP and NH4+-N was 55%、92%、88% and 12%, respectively. The effluent of the CEPT-TF process could met the B standard of urban wastewater treatment plant pollutant discharge standard(GB18918-2002). When the temperature was under 20 oC, the removal efficiency was decreased a little, however, The effluent could meet the B standard of urban wastewater treatment plant pollutant discharge standard(GB18918-2002) if the appropriate ultrafiltration membrane was selected.According to comparison of the basic sewage water quality, DOC, molecular weight, ultraviolet spectrum characteristics and the three-dimensional fluorescence spectrum from the three different areas, the imitated water in the laboratory could be used to simulate the small town sewage. DOM was first divided into hydrophobic organic acids(HPO-A), transition of hydrophilic organic acids(TPI-A), hydrophobic neutral organic matter(HPO-N), transition hydrophilic neutral organic(TPI-N) and hydrophilic organic matter(HPI) according to XAD resin classification technology. DOM was consisted mainly of HPI and HPO-A, which accounted for 57.5% and 20.7% of the total DOC, respectively, HPO-A was the main aromatic substance(60.1% of total UV254). DOM in the small town’s domestic wastewater was removed about 79.3% through the CEPT-TF-UF process unit, the DOC removal effect in the TF process unit was the most obvious, reaching 54.2%. But the aromaticity material removal was limited in the CEPT-TF-UF process, with the largest removal rate of 30.8% in the CEPT process unit. The removal effect of HPO-A, HPO-N and TPI-N was good because of the biological function in the TF unit of the combined process, and the biological function given priority to the degradation of TPI-N.The different characteristics of the chemical sludge and biological sludge produced by the small town’s domestic wastewater was found through the comparison analysis of three small town’s chemical sludge produced by domestic wastewater and the primary settling tank sewage and excess sludge of wenchang waste water treatment plant in Harbin. The main composition of the chemical sludge was inorganic compound, containing a large number of fly ash coagulants adding to the primary reinforcement process, the various forms of polymer formed by hydrolysis of aluminum and iron ions, the network structure, and the network structure formed by the mixture of small amount of live or killed microorganisms’ extracellular polymer. The dissolution quantity of aluminum and iron during the recycling of sludge coagulant under the condition of 100 oC, Vacid/mchemical sludge=3, 30 min heat was 3462 mg/L and 1595 mg/L, respectively. The effluent could meet the B standard of urban wastewater treatment plant pollutant discharge standard(GB18918-2002) and the chemical sludge decreased by 30.8% because the dissolution of soluble and colloidal substances applying this recycling sludge coagulant of 2.4 ml/L to dispose small town’s domestic wastewater. The repeated application of recycling sludge coagulant can led to accumulation of heavy metals and organic material and decline of COD, ammonia nitrogen removal efficiency, therefore, the repeated use of recycling coagulants should be less than 4 times.