Research And Application Of Integrated Membrane Technology In Reclaimed Water Recycling

Reclaimed water is one of water resources that can not be discharged directly. Membrane separation technology is widely used in reclaimed water recycling for its characteristics of high efficiency, low energy consumption, excellent water quality. Based on secondary effluent of XinHeCheng biochemical pharmaceutical Co., Ltd, ShanDong, the paper carried out a integrated membrane route of Sand filtration-Ultrafiltration (UF)-Resin Softening-Reverse osmosis(RO)-Disc tube reverse osmosis/Nanofiltration (DTRO/NF) for advanced treatment. For five months pilot test, we investigated the feasibility and stability of the process mainly from separation capability of membrane units, water quality, membrane fouling and cleaning so as to optimize the process operation parameters and provide the basis for industrialized production. Furthermore, a economic analysis had been conducted to evaluate the value of the route. Through the integrated membrane process98%of reclaimed water will be recycled, the remaining waserwater can be treated by multi-effect evaporation. After membrane treatment the reclaimed water became limpid, conductivity and CODcr decend from5050-6760μs/cm and126.2mg/L～420.1mg/L to147.3～282.1μs/cm and1.8～19.5mg/L removal rate of turbidity, BOD, SS and NH4-N reached to100%closely, the discharged water quality reached not only first-class A standard of 《Water Pollutant Discharge Standard in Shandong Peninsula Basin》(DB37/676-2007), but also 《Circulating Cooling Water with Reclaimed Water Quality Standard》(HG-T3923-2007), the water can be used in workshop directly.From pilot test we optimized the polyaluminium chloride (PAC) as coagulant, sodium macroporous weak acid cation resin was used to remove hardness; Meanwhile, the condition of85%recovery rate and25℃operating temperature was more favorable for UF membrane operation; Furthermore, the operating pressure of RO could be as low as1.13～1.55MPa under the recovery rate of73.7%; Lastly, setting the three-level DTS system operating pressure on6.5MPa、9.5Mpa and5.5MPa, the water flux and concentrated water production could meet predetermined requirements.Membrane cleaning is extremely important for membrane units running, through cleaning experiments we established UF membrane chemical cleaning solution of "citric acid (3%) pickling+NaClO (3000ppm) caustic"; Meanwhile, for DTRO/NF membrane fouling characteristics, a chemical cleaning solutions of "C555(2000ppm) sterilization+C531(2%, pH≈11.5) caustic+HCl (pH≈2.4) pickling" had been explored; the chemical cleaning cycle of UF and DTRO/NF membrane were about30days and a week.The treatment cost of reclaimed water was4.36yuan/ton, if the permeated water is used as cooling sater supply, the cost will be low to1.85yuan/ton, the process has a promising economic prospect.