Optimization Of Ultrafiltration Treatment Process For Washing Wastewater In Student Apartments

Washing wastewater is a kind of domestic sewage with less pollution.It accounts for 30% of the total domestic water,water quality is stable,large,and easy to collect.Therefore,the reuse of washing wastewater after treatment can realize the recycling of sewage and relieve the pressure of urban water use.In this paper,the ultrafiltration treatment system of rinse water in a college student apartment was studied to investigate the treatment efficiency of the ultrafiltration on the pollutants in rinse water.In view of the actual problems such as the deterioration of raw water quality in the treatment process,the optimization of the ultrafiltration treatment process was carried out.compared the direct ultra-filtration,coagulation-sedimentation-ultrafiltration,coagulation-ultrafiltration three ultrafiltration process,to find the most suitable ultrafiltration process parameters for wash wastewater,under the requirement of the removal rate of COD,ammonia nitrogen and turbidity in the process,the membrane speed is delayed as much as possible,and the membrane life cycle and effluent flux are increased.The main conclusions drawn are as follows:(1)In the initial stage of operation,the ultrafiltration treatment system has a good effect on washing water.In addition to the anionic surfactant slightly exceeding the standard,the water quality indicators such as COD,turbidity,total phosphorus and ammonia nitrogen can meet the standards of " The reuse of urban recycling water-Water quality standard for urban miscellaneous water consumption"(GB/ T 18920-2002).(2)The effects of physical cleaning and online chemical cleaning on ultrafiltration membrane fouling were studied.The results show that backwashing has better recovery effect than surface fast washing.Compared with physical cleaning,online chemical cleaning has a great effect on the improvement of membrane flux recovery rate,but The flux after each cleaning will decrease from the previous one,which indicates that the membrane is irreversibly contaminated.During the operation of the treatment system,students often wash tableware and even pour non-washing water such as soup and tea into the regulating pool,resulting in serious deterioration of water quality.In addition,the lack of effective mud discharge measures in the regulating tank makes the system run worse,resulting in serious membrane pollution.(3)In view of the problem of water quality deterioration,the paper used coagulation as the ultrafiltration pretreatment unit.The coagulant type(aluminum sulfate,polyaluminum chloride,ferric chloride),medium speed mixing time(2min,4min,6min)and slow mixing time(10min,15 min,20min)were investigated.There are three main factors,each of which has three levels of orthogonality.In the test,the dosage of fixed coagulant was 50mg/L,and the specific coagulant was polyaluminium chloride with the specific flux and COD removal rate.The stirring intensity and time were: medium speed 180r/min,4min;slow speed 80r/min,10 min.Under the above coagulation conditions,the effects of different dosages on the removal rate of each pollutant were further studied,and the optimal dosage of coagulant was optimized to be 60 mg/L.(4)The effects of direct ultrafiltration,coagulation-precipitation-ultrafiltration and coagulation-ultrafiltration on the washing water were investigated.It was found that the coagulation-ultrafiltration process had the largest flux and stable anti-pollution when the flux was stable.When the raw water is directly ultrafiltered,the flux decreases the fastest and the stable flux is low,and the anti-pollution performance is the worst.The removal rates of turbidity by the three ultrafiltration processes were all above 94%,indicating that the removal of turbidity by ultrafiltration was not affected by pretreatment;for the removal rate of total phosphorus,coagulation-ultrafiltration and coagulation-precipitation-Ultrafiltration is very high,the removal rate is above 91%,its removal is mainly due to coagulation pretreatment,and the ultrafiltration effect is not obvious.For ammonia nitrogen removal,the three processes are not high,but coagulation-ultrafiltration and coagulation-precipitation-ultrafiltration are slightly higher than direct ultrafiltration.Coagulation-ultrafiltration has the best removal effect on COD,and the direct ultrafiltration removal effect is the worst.It is comprehensively known that the coagulation-ultrafiltration process has a good advantage.(5)By analyzing the composition of membrane fouling resistance in different ultrafiltration treatment processes,the fouling resistance generated by coagulation-ultrafiltration is the smallest,among which the resistance of filter cake layer is the largest and the resistance of membrane hole obstruction is the smallest.In the test cycle,the blocking rate of the membrane hole of direct ultrafiltration is as high as 45.3%.Although the membrane flux can be restored by chemical cleaning,the dosage of agents is increased,and frequent chemical cleaning will also have an impact on the life of the membrane.Although the resistance of cake layer generated by coagulation-ultrafiltration accounts for a higher proportion,the resistance of cake layer is reversible pollution,and the membrane flux can be recovered by physical backwashing,and 80% is the highest recovery rate among the three processes.