Study On Reusing Of Electroplating Wastewater By Membrane (RO-NF)

Membrane reusing technology has been widely used in electroplating wastewater treatment for its high efficiency and low power. Electroplating wastewater treated with physical chemistry went through sand filter, UF and RO, removal of ion comes up to more than 99%. Because of the featuer that electroplating wastewater contains high salinity, when the salinity of wastewater goes higher and higher, quality of water conducting would be worse and Permeate flow would be lower, efficiency of the RO would be unfavorable. Strong sewage from RO being concentrated by NF, salt rejection would be lower than by RO, but nanofiltration membrane has higher membrane flux and stronger antifouling ability than reverse osmosis membrane, so nanofiltration membrane can be used as concentrating strong sewage of RO. The result was recovery of the system would be higher. This paper showed that using reverse osmosis(RO) and nanofiltration(NF) to concentrating electroplating wastewater, optimized the running condition by contrasting the experimental parameters. This paper also showed a pilotscale experiment that concluded the correctness of test in a electroplating enterprise.This thesis studied separation characteristics and treatment effect of BW30-365 reverse osmosis membrane and NF270-400 nanofiltration membrane in different water inlet condition.According to systemic experiment research, it is concluded that higher water flux and better water quality would be gotten by BW30-365 reverse osmosis membrane in electroplating wastewater treatment. NF270-400 nanofiltration membrane can be used to concentrated the strong sewage from RO system, the rate of desalination of NF was less than RO, but the conductivity of producing water met the requirement of inlet water of RO, the flux of producing water was large enough to achieve the design requirement.BW30-365 reverse osmosis membrane works properly and the rate of desalination is over 95% when the conductivity of water inlet is below 30000μs/cm. when it is over 30000μs/cm,it would result in salt scaling, at the same time the rate of desalination would change a lot and it would be reduced the producing water flux to decrease to zero. This paper studies when the pressure of water inlet arrived 1.6MPa, RO works in the best operatng condition.The rate of desalination of NF90-400 nanofiltration membrane is about 50% when the conductivity of water inlet is below 35000μs/cm. when it is over 35000μs/cm, it would result in salt scaling, at the same time the rate of desalination would change a lot. Research shows that when the pressure of water inlet arrived from 1.6MPa to 1.8MPa nanofiltration membrane works in the best operatng condition. The pressure be increased and decreased it would be reduced the producing water flux and conductivity to decrease. It is concluded that the best pressure is 1.6MPa-1.8MPa. Considering the economic cost,1.6MPa is a reasonable pressure.Experiments for RO pollution was done in different SDI and turbidity water inlet condition. Membrane flux droped different ratio in a month because of different SDI and turbidity. Chemical cleaning used HC1 and NaOH mixed with scale inhibitor. When SDI was below 1 the membrane does not need to carry on cleans. When SDI is 5, after chemical cleaning membrane flux recovered 94.5% of new membrane flux. It is concluded that SDI and turbidity is the key factor to affect membrane fouling and it would result in permanent pollution to difficult to clean. When chemical clean was operated, the higher the temperature, the better the effect. Considering the extreme temperature and the condition of clean, the reasonable temperature of RO is 40℃and the appropriate temperature of NF is 30℃. Pilot test on electroplating water was operated at the condition of RO and NF water inlet pressure 1.6MPa. When pH was controlled about 7 and conductivity of RO water inlet was about 4800μs/cm, the conductivity of the system was below 200μs/cm and the COD was below 20 mg/L. In front of the system the recovery of RO membrane can reach 82.2% and the recovery of NF as rear segment can arrive 65% at the most. The synthetical recovery of RO+NF system can be about 95%. It is approved that this system meet the precision requirements of the project.