Application Research On Biological Contact Oxidation—Ultrafiltration Membrane System For Community Intermediate Water Reuse

This issue is mainly on biological contact oxidation-ultrafiltration membrane water reuse project application. By the tracking test of the operation period, investigated and determined the system optimum operating parameters of hydraulic retention time (HRT) and dissolved oxygen (DO), besides the operation mode of the membrane. Furthermore, the organic matter and ammonia nitrogen removal of the system were analyzed emphatically, under stable operation condition, and the economic and environmental benefits of the water reuse project was evaluated.Employing the natural start-up, which making the wastewater flow through the packing only, without inoculation sludge, after46days, biofilm culturing was succeeded, and behaved that CODcr removal of the biological contact oxidation zone had stabilized at70%above.In addition, to ensure the good performance on filtration of the membrane, and taking into account the maximum possible reduction in energy consumption, the suction pressure of pump was controlled at0.1MPa, aeration volume maintained from400m3/h to600m3/h, and using operation mode of the membrane as suction for13min, then stopping for2min. A reasonable HRT for biological contact oxidation zone was determined to be3h, and the dissolved oxygen concentration from2.2mg/L to3.7mg/L should be ensured. To increase oxygen transfer efficiency and reduce the rate of membrane fouling, microporous aerators should be utilized.Studying on organic matter and ammonia nitrogen removal of the biological contact oxidation-ultrafiltration membrane system during stable operation period, it was found that CODcr of membrane effluent was at range of14mg/L to41mg/L, with an average of25.42mg/L, which has reached domestic miscellaneous water quality standard. And CODcr removal was from87.42%to95.51%, with an average of92.37%. Biological contact oxidation-ultrafiltration membrane system for the removal of CODcr was stable and efficient. Ammonia nitrogen of membrane effluent was from1.60mg/L to4.10mg/L, with an average of2.74mg/L, meeting the miscellaneous water quality standards also. Ammonia nitrogen removal of system maintained from80.44%to94.32%, with an average removal rate of89.40%.For the removal of CODcr, regulation pool accounted for about11%, and biological contact oxidation zone occupied73%, while the membrane accounted for16%. The above distribution of CODcr removal rate was quite meaningful for system running effect. Microbial nitrification in the biological contact oxidation zone played a major role in ammonia nitrogen removal, while the contribution of membrane was only1.82mg/L or so, about6%.The investment in fixed assets of this water reuse project, including three aspects, which were acquisition costs of membrane and filler, construction costs of processing structures, and equipment purchase costs, totally was295,000yuan. Total annual operating cost was276,300yuan, and unit cost of water treatment was2.05yuan/m3, which was lower, compared to conventional activated sludge for water reuse of2.43/m3, and three stage biochemical process of2.15yuan/m3.The system each year may treat and reuse135,100tons of wastewater, representing an increase of the same amount of water. And every year, the CODcr, SS, NH4+-N, and animal and vegetable oils emissions were reduced up to38.10tons,25.80tons,2.85tons and4.05tons, respectively. For river water quality improvement and raising the level of health of people, this project will play a positive role.