Pilot Study On Electroplating Wastewater Treatment By Loading Flocculation-Ultrafiltration-reverse Osmosis

Printed circuit board(PCB)wastewater contains high concentrations of heavy metal ions and lower concentrations of COD,NH4+-N.The use of a loading flocculation-ultrafiltration-reverse osmosis process to treat PCB waste water enables it to meet discharge standards.The small-scale pretreatment process was optimized and applied to the pilot system study.In order to prolong the life cycle of the membrane system and improve the stability of the system,the membrane fouling and its control methods were studied.First,a pilot flocculation pretreatment optimization study was performed.The process parameters were as follows:precipitation pH1=10.5,coagulation pH2=9.5,PAC=10 mg/L,PAM=1.0 mg/L,return sludge amounting to 47%of the treated water,and tertiary mixing strengths were 250 r/min,150 r/min,50 r/min,respectively.The third-level stirring times were 6 min,8 min,and 4 min,respectively;the corresponding speed gradients G were 144.0,72.4,16.5 s-1,respectively;and the GT values were 51840,36192,and 3960,respectively.The pre-treatment effluent water quality is stable.Compared with the sludge without returning sludge,the turbidity was reduced by 9.8 NTU,the Cu2+concentration was reduced by 0.72 mg/L,and the Ni2+ concentration was reduced by approximately 0.53 mg/L.95%of the particles in the effluent had an average particle diameter of 2.09 ?m,indicating that 95%of the particles can be filtered out by the ultrafiltration membrane.Then the pretreated effluent entered the ultrafiltration-reverse osmosis system and compared the operation conditions of the two ultrafiltration membranes(flat ceramic membranes and hollow fiber membranes)with the effluent quality and the desalination rate of the reverse osmosis membrane series and parallel mode.After treatment with plate ceramic membrane,the concentrations of Cu2+ and Ni2+ in the effluent were 0.034 and 0.029 mg/L,respectively.The removal rates were 87.2%and 86.9%,respectively.The concentrations of Cu2+ and Ni2+ in the effluent of hollow fiber membranes were 0.025 and 0.022 mg/L,respectively.The rates were 90.7%and 90.1%,respectively.The removal effects of COD and NH4+-N were similar.The effluent concentrations were 46 and 7.55 mg/L,respectively.Both outlets were up to standard,and hollow fiber membranes had better removal of pollutants.When the reverse osmosis membrane series and parallel recovery rates were 64%and 80%respectively,the desalination rate in the series mode was 97.6%,and the desalination rate in the parallel mode was 97.06%.The desalination effect in the series mode was better than the parallel mode,but the tandem membrane had a larger amount of water,and the stability was worse than that of the parallel mode.The optimized PCB waste water treatment system operated stably.Finaly,for the stable operation of the membrane system,scanning electron microscopy and energy spectrum analysis of the membrane were performed.It was found that organic matter caused irreversible contamination of the flat ceramic membrane,and inorganic substances caused irreversible contamination of the hollow fiber membrane.The chemical cleaning methods of the membranes had found that the optimal chemical cleaning methods for flat ceramic membranes and hollow fiber membranes were:first alkali washing(NaOH + NaCIO,0.20%(W/V)),and then pickling(HCl + EDTA,0.25%(W/V)),transmembrane pressure differential recovery rates were 97%and 98%,respectively.After five chemical cleanings,the TMP recovery rate of the flat ceramic membrane changed from 96.6%to 73.8%,and the running time was shortened from 108 h to 76.8 h.The total running time in this process was 571 h;the TMP recovery rate of the hollow fiber membrane was 97.7%changed to 81%,the running time reduced from 122 h to 86 h,and the total running time was 609 h.From the analysis of membrane fouling model,it was found that both the middle plugging model and the filter cake plugging model were suitable for the flat ceramic membrane,and only the middle plugging model was suitable for the hollow fiber membrane,but the filter cake layer had not yet formed at the beginning of the flat membrane operation,and the model fitting results did not fully accord with the actual situation.From the model of series resistance,it could be seen that the plugging and adsorption resistance of the membrane pores of the plate ceramic membrane was the largest,accounting for 60.28%of the total resistance,followed by the filter cake resistance,which accounted for about 20.67%.