Comparison among three kinds of advanced water purifying processes: Prepositioned, medially positioned and post positioned biological treatment

On account of subtropical micro-polluted raw water, adopting biological treatment technology in water purification process is suitable. Through engineering projects and experiments comparison, this paper analyzes the characteristics and applicable conditions of three kinds of water advanced purification process: prepositioned, medially positioned and post positioned biological water treatment. Prepositioned biological treatment process purifies raw water directly, the preoxidation result was apparent, the rate of NH₃-N nitrification was high, with the aid of bio-enhanced action in coagulation sedimentation unit, total organic matter removal rate can reach the level of advanced treatment. But biological treatment unit has to stand adverse impact by high turbidity, sediment impurities, shellfish and algae in raw water, which increases its running maintenance cost. Medially positioned biological treatment unit is located between sedimentation tank and sand-filter, the vast majority of turbidity in raw water is removed through coagulating sedimentation, and with sand-filter behind, technology of high-efficiency biochemistry and absorption can be used to increase the rate of NH₃-N nitrification and organic matter biodegradability. Post positioned biological treatment process is aimed at residual light pollution in effluent of conventional process, the purification efficiency is high, but the problem of tiny creatures leak is evident, so it needs to be connected with ultrafiltration membrane.