Study On High Recovery Rate Process For Desalination Of Industrial Brine

Industrial salty wastewater is treated by membrane concentration (generally usingultrafiltration+reverse osmosis treatment technology) or heat concentration technology andproduces brine, which includes concentrated drainage, backwash drainage and chemicalcleaning drainage. Inner Mongolia Dalu industrial park is a coal chemical industry based oncoal. With the industrial enterprises entered, industrial water consumption has increaseddramatically, also industrial wastewater drainage has increased and discharged to theevaporation pond on southeast of the park, which is full of brine now, even some ofenterprises discharge brine into farmland directly. Therefore, it is imperative to protect theindustrial park farmland soil from pollution and the yellow river water, contribute to thedevelopment of regional economy, study brine high recovery rate desalination process.There are two conventional brine treatment methods including physical and chemicalmethod(including membrane, ion exchange and thermal evaporation) and biological method.Conventional membrane method has low water recovery rate, ion and thermal evaporationmethod treatment costs high, biological method has been studied at present and not taken intopractice yet. Therefore, the study puts forward to such a brine treatment process by usingdouble membrane, plus brine system can be treated by VSEP and brine RO, effluent cansatisfy industry process recycle water quality index. Meanwhile, the study analyses economiccost of this high recovery desalination process, finalizes the brine recovery process ofpopularization. According to each unit experiment during operation, the results are as follows:The experiment adopts double membrane (ultrafiltration+reverse osmosis) to deal withindustrial brine. RO pretreatment units include sand filter and ultrafiltration, which canguarantee RO feed SDI value less than3. RO unit brine and UF normal backwash enter tovibrate shear enhance process (VSEP), RO product enter to general product tank. VSEP unitproduct to brine RO unit and brine enter to evaporation pond. Brine RO unit product enterto general product tank.From the conclusion, sand filter unit operation pressure is3bar, feed capacity is30m~3/h,unit water recovery rate is99.8%. Sand filter will do the backwash on the condition that theinlet/outlet pressure difference is0.3bar or continous operation interval reaches72h.UF unit suitable working pressure is1~1.5bar, filtering cycle is50min. UF effluentturbidity and SDI value is better than RO feed requirement, which cannot effect RO operation,turbidity is in the range of0.3~1.2NTU, effluent SDI value is less than2.5, COD removal rateis10~18%, which meets effluent requirement already. UF unit chemical enhance backwash isconfirmed as10UF filtration cycle. UF chemical cleaning in place uses hydrochloric acid,sodium hypochlorite and sodium hydroxide. Reverse osmosis unit can remove all kinds of ions in the water effectively, RO adoptsthree stages, permeate water TDS average value is20mg/L, average desalination rate is higherthan99%. Chemical cleaning will be implemented on the condition that the permeate watercapacity reduce by10%of original value. Cleaning adopts hydrochloric acid(pH less than3)and circulate the membrane module, by this way, membrane fouling can be removed andmembrane flux can be recovered to the original value.Vibrate shear enhance nanofiltration process optimal operation pressure is12bar, feedtemperature is16.2℃, desalination rate is in the range of28~35%, unit recovery rate averagevalue is70%.Brine RO unit feed TDS concentration is about8000mg/L, permeate water TDSconcentration is100mg/L, desalination rate of this unit is about98.5%. feed capacity is about3m~3/h, permeate water is1.5m~3/h, unit water recovery rate is about50%.The whole system influent capacity is30m~3/h, and TDS is in the range of2000~2500mg/L, effluent capacity is27.2m~3/h, total system recovery rate average value is90.7%, and effluent TDS is in the range of500~700mg/L, and other water quality itemssatisfy industrial enterprises process water standard.The whole industrial brine high recovery rate process operation cost is in the scope of6~8RMB/t. This study has good economic and social benefit and better promotion value.