Study On Treatment Of Wastewater From Electronic And Electroplating Industry By Loading Flocculation And Multi-membrane

As the important pillar of the national economy electronic and electroplating industry is irreplaceable, yet its production process produces plenty of toxic harmful waste water containing heavy metal ions, which is difficult to deal with and recycle. Among the existing wastewater treating methods, the traditional method called coagulating sedimentation is most common ly used. However, with the state of heavy metal wastewater discharge standards continu ing to improve, and due to the inherent disadvantages of this method such as poor resistance to impact load, unstable water quality and high sludge yield, this method gradually fails to meet the requirement of daily production. Ultra-filtration as a new wastewater treating technology, has the advantages such as low energy consumption, good separation effect and so on. Reverse osmosis as one of the most effective separation technology, has a great potential in wastewater reuse. So developing a new method in treatment and reuse of wastewater combining ultra-filtration and reverse osmosis is of practical significance.The treating process for rinsing wastewater from a PCB factory in this experiment has three sections. In the first section, loading flocculation is used as a pretreatment; ultra-filtration(ceramic membranes/hollow fiber membrane) is used for secondary processing; in the end, reverse osmosis is used as a recycling process. Further more, based on this process, we put forward a new type of treating process called the short process. Loading flocculation experiment examines the effects on the flocculation caused by these factors including the two pH— pH1 and pH2, the dosage of coagulant, the dosage of coagulant aid, the backflow sludge quantity, dosage of chelate-breaking agent. The experiments of ultra-filtration figure out the composition of pollutants and how the conditions of backwash influence the trans-membrane pressure(TMP). The experiments of reverse osmosis investigate how the loading flocculation + ultra-filtration as a pretreatment influences the effect of reverse osmosis and how operation mode(in series or in parallel) influences the effect of the reverse osmosis treatment.Results of the coagulation test show that either a pH1 too high or too low reduces the flocculation effect and the flocculation effect is the best when pH1 = 10.5. Removal of total nickel mainly related to pH2, and the flocculation effect is the best when pH2 = 9.5 considering all other indexes. Either dosages too high or too low of PAM and PAC reduce the flocculation effect, and the flocculation effect is the best when PAC =10 mg/L, PAM = 1 mg/L. As a loading agent, the backflow sludge can make full use of the surplus agents, but it may reduce the effect of flocculation when the reflux ratio is low. And the flocculation effect is the best when reflux ratio = 20%. In order to deal with chelating heavy metal, Na 2S, the chelate-breaking agent is necessary,but too much Na2 S reduces the flocculation effect.Results of ultra-filtration experiment show that the ceramic membrane makes a better removal of copper than the hollow fiber membrane as well as a lower TMP. The major pollutants of ceramic membrane and hollow fiber membrane are organic rinsing agent, PAM, PAC, Cu(OH)2, Cu S and surplus Ca(OH)2. To ceramic membrane the best combination of backwash conditions is a intensity of 37.5L/h, a last of 30 s and a backwash cycle of 60 min. To hollow fiber membrane the best combination of backwash conditions is a intensity of 30 L/h, a last of 60 s and a backwash cycle of 30 min.The effluent turbidity of ultra-filtration is between 0.1~0.2NTU while the total copper and total nickel both are less than 0.1mg/L. The effluent turbidity of short process is under 0.2NTU, and the total copper is less than 0.15mg/L while the total nickel is less than 0.1mg/L. Continuous aeration is necessary to short process to alleviate the membrane pollution so as to make the system steadily running. The sludge concentration of ceramic membrane pool affect both the filtration effect and the membrane pollution, so level of sludge concentration must be proper, and for the best, not higher than 30000 mg/L.Results of reverse osmosis experiments show that load flocculation+ ultra-filtration as pretreatment of reverse osmosis, makes a good performance in wastewater reuse. Using hollow fiber ultra-filtration membrane can reduce organic pollution of reverse osmosis, but the treating stability is lower than ceramic membranes. The desalting rate reverse osmosis is mainly related to the recovery rate. the decline of desalination rate and the rise of TMP is faster when the reverse osmosis are operated in series other than in parallel because one phrase of reverse osmosis in series is easier to be polluted.