Application Of Dual Membrane Process In Recycled Water Reuse Project

The rapid economic development in China is causing an increasing strain onwater resource. Reuse of recycled water, as a result, becomes increasingly popularnowadays. Recycled water is water that can be recycled after some sophisticatedtreatment. In selecting the proper way of processing recycled water, the membraneseparation technology, thanks to its low energy consumption and high efficiency, waswidely applied.This paper takes the waste water emitted by a chlor-alkali chemical plant as theraw water in an attempt to study the feasibility of ultrafiltration plus reverse osmosisprocess. The waste water contains contaminants such as benzene, sulphide andprussiate etc and has a high concentration of salt and chloride. As a result, a pilot scaletest was conducted to analyze the treatment effect of dual membrane process onindicators such as COD and turbidity and study if the processed water could meet therequirements for production and recycling purposes.The result of the test proved that ultrafiltration could get rid of certain amount ofCOD but the effect was not so good,10%-20%at the best. The ultrafiltration,however, could eliminate colloidal substance, macromolecules and particles. As aresult, the turbidity of the waste water was lowered. UF could get rid of70%of theturbidity in the waste water and the measured water turbidity value was below0.4NTU, meeting the requirements of less than1for reverse osmosis water turbidity.The reverse osmosis could eliminate more than90%of COD and had an apparenteffect on reducing the hardness of the water, higher than95%basically and ROhardness was near0, which demonstrated clearly that the membrane could effectivelyscreen Ca2+，Mg2+. The test confirmed that the waste water, after going throughultrafiltration and reverse osmosis process, met the water quality standards and therequirements set for recycled water and therefore could be reused for productionprocess and recycling purposes.According to a preliminary estimate, the water recycling project can recycle5.184million tons of waste water generated by the chemical plant. The expense offresh water and emission charges thus saved can offset the cost cause by the waterrecycling project. Moreover, a profit of690thousand yuan can be generated annually.Therefore, it’s worth a while to promote the dual membrane technology in thechlor-alkali industry.