Study On Coagulation-Ultrafiltration In Treating Urban Secondary Effluent To Reuse To Landscape Water

Along with the urbanization expediting and the sustainable development stratagem implementing, for satisfying people's request of the living environment, Xi'an renovate and resume some rivers and lakes. But the water resources of Xi'an is shortage, so how can we obtain the landscape water which is used to renovate and resume the rivers and lakes, is the whole problem we need to resolve. Water reuse is the necessary choice of society and economy sustainable development. Water reuse can increase water supply quantity, resist drought, lessen water pollution, improve public hygiene condition, and protect natural environment. Therefore, wastewater reuse to landscape water as a important part of urban recycled resource is widely deploying in the world.The research object of this paper is the secondary effluent of Xi'an Bei Shi Qiao Sewage Purification Center, the quality of the effluent is stable, the concentration of the pollutant is low, and is close to Urban Sewage Reuse to Landscape water Standard. Aim at the characteristic of the effluent, combining the present condition of the sewage reuse disposal, this research adopt coagulation-ultrafiltration process, and probe the feasibility of this technics dispose the secondary effluent reuse to landscape water.Coagulation pretreatment can remove the impurity in secondary effluent, especially turbidity. This research through a series of single text and orthogonal test conditions to confirm the operation condition and parameter of coagulation technics: the dosage of 931 is 30mg/L, PAM is 1mg/L, fast stirring velocity and time is 400r·min^-1 and 5min, slow stirring velocity and time is 60r·min^-1 and 30s, sedimentation time is 20min, on this condition, the turbidity can be decreased from 10NTU to below 3NTU; but the coagulation-ultrafiltration process is ineffective to ammonia-nitrogen disposal, this research choose NaClO oxidation method to dispose ammonia-nitrogen, the combination condition is: the dosage of 10%(volume ratio) NaClO is 28ml/L, pH is 6.0, reaction time is 20min, the result indicates that the removal rate of ammonia-nitrogen is above 80%, the concentration can be decreased from 15mg/L to 3mg/L, it can also make the total nitrogen concentration decrease to around 10 mg/L; the concentration of total phosphorus, turbidity, COD are respective below 0.4mg/L, 0.2NTU, 36mg/L; the removal rate of the total E. coli and the muck E. coli are over 3.71og, and the number of total E. coli and muck E. coli are respective below 130MPN/L and 80MPN/L. The final effluent water can satisfy the standard of urban wastewater reuse to landscape water.Through the non-parameter assumption examination analysis, we find that the concentration of muck E. coli in the secondary effluent is close to obeying logarithms normal school. The quantity ratio of muck E. coli and virus in urban sewage is about 10⁵:1, according to that comparison relation, and treating the entire virus as one kind of virus: rotavirus, making use of probability statistic calculation method to assess the health risk of pathogen of wastewater reuse. The result shows that, if the secondary effluent reuse without disposing virus or the removal rate is low, the health risk is high. Only the removal rate is above 60%, the reclamation water to landscape water is safe.Coagulation-ultrafiltration process dispose urban secondary effluent reuse to landscape water, the technics is reliable, technic is feasible, economy is reasonable. It is a comprehensive benefit with the resources of sewage and worth to generalize and apply.