Study On The Treatment Of Backwash Wastewater From The Method Of Coagulation And Membrane Filtration

In the water works a large percentage of in self-using water is the backwash wastewater from sand filter pool and activated carbon filter pool,which is collectively named as filter backwash wastewater.The backwash water contains a huge amount of particles from raw water and floe remained in coagulation.Based on different flushing methods adopted,the percentage of filter backwash water accounts for water works’ water withdrawals various,1.5%～5%commonly.Ordinary,water works direct discharge the filter backwash wastewater.However,if the filter backwash wastewater could be purified and reused,it would alleviate the water shortage problem and benefit environment protection.An experiment combining coagulant and flat membrane in backwash wastewater treatment is presented in this dissertation.Coagulants selected are three common kinds:PAC,PFS and PDM.Flat membranes chosen are PVDF flat membranes.The experiment tested the quality of water works’ influent water,filter backwash wastewater,effluent water purified by coagulants and effluent water purified by coagulant with flat membrane combined.The experiment also tested optimum dosage value,optimum reaction time and optimum pH of three kinds of coagulants.Afterwards,the optimum effective coagulant is picked by comparison.After purified by the picked coagulant,water flowed into PVDF flat membrane device to test the optimum aeration quantity,critical flux,and permeability of the membrane.At last,experiment effect was given by comparing the quality of effluent water purified by optimum effective coagulant and flat membrane with the quality of influent water.The experiment results show that the optimum dosage value of PAC is 10mg/L,optimum reaction time is 25 min and optimum pH is 6.Under optimum conditions,the removal rate of CODMn,Fe,Mn and turbidity were 53.2%,98.3%,92.9%and 96.5%separately;the optimum dosage value of PFS is 10mg/L,optimum reaction time is 20 min and optimum pH is 9.Under optimum conditions,the removal rate of CODMn,Fe,Mn and turbidity were 65.7%,99.1%,97.5%and 96.3%separately;the optimum dosage value of PAC is 8mg/L,optimum reaction time is 20 min and optimum pH is 8.Also under optimum conditions,the removal rate of CODMn,Fe,Mn and turbidity were 89.2%,99.6%,95.6%and 98.9%separately.Comprehensive comparison of the data above,PDM is the optimum coagulant for the next step.After purified by the picked coagulant,water flowed into PVDF flat membrane device directly.The experiment results show that the optimum aeration quantity was 0.4L/min and optimum critical flux was 10L/(m2·h).The quality of effluent water purified by coagulant and flat membrane sequential is shown as:the removal rate of CODMn,Fe,Mn and turbidity were 91.9%,99.6%,95.6%and 98.9%separately.By comparison,the water purified by combine method has roughly same quality to influent water of water works.The filter backwash wastewater can be applied to reuse by using coagulant and flat membrane combined purifying method.