Optimization Of The Advanced Treatment Process With Reverse Osmosis In Electronic Industry Wastewater

Currently, reverse osmosis has been widely used in electronic wastewater recycling.In the practice appilication, membrane fouling, short-life and other disadvantages havelimited its use. These shortcomings are not only related to materials and inherecharacteristics of reverse osmosis membrane, but related to operating conditions. Forexample, some ions and organic pollutants may result in membrane fouling, andresidual chlorine that is used to removal ammonia may cause irreversible damage toreverse osmosis membrane. In addition, some trace organic pollutants that exist inelectronic wastewater, such as Bisphonel A and Tetrabromobisphenol A, are usually ofgreat biological toxicity. In current study, removal of conventional pollutants has gainedconsiderable concern, while removal of these micropollutants is scarcely studied.Therefore, this thesis has studied effect of influent component on membrane fouling,damage of hypochlorine on polyamide reverse osmosis membrane and correspondingcontrolling measures through static small scale experiments. On this basis, removal ofconventional and trace pollutants has been studied as well as membrane fouling throughcontinuous dynamic experiment to give some advice for improvement in electronicwastewater recycling by reverse osmosis.Removal efficiencies of COD, UV254and TP are92.6%,98.0%and100%,respectively, while removal efficiencies of BPA and TBBPA are80%and100%.Removal efficiencies of nitrate, nitrite and ammonia range from40%to60%, andconductivity in effluent can decrease79.1%. With increase of filtration time and volume,membrane flux gradually decline. After one week continuous operation, membrane fluxdropped from100%to44.6%, which indicates reverse osmosis has been severelyfouled. Membrane flux can restored to83.0%by chemical cleaning of sodiumhypochlorite.Through a lab scale experiment, influence of metal ions, flocculants and organicpollutants in influent on membrane fouling has been analyzed. Results show that Cu2+has the most impact on membane fouling, followed by Al3+and Ni2+. Besides, thedegree of membrane fouling is proportion to concentration of metal ions. Comparedwith PAC, PAM plays a more important role in membrane fouling. Howere, organicpolltants is the main reason for reverse osmosis fouling.In addition, damage of hypochlorine to polyamide reverse osmosis membranes aswell as correspongding controlling measures has been studied. Results show that withincrease of soaking time, pH and concentration of hypochlorite, membrane fluxgradually increase, both salt rejection and contact angle gradually decrease. Activatedcarbon is useful for removal of hypochlorine. When concentration of hypochlorine is less than100mg/L, sodium hypochlorite can be totally removed as long as retentiontime exceed150s in activated carbon column.