Membrane Fouling Control In Immersed Ultrafiltration And Reverse Osmosis Process For Municipal Wastewater Reclamation

This thesis studied the immersed Ultrafiltration(UF) and Reverse Osmosis(RO)process of Zibo water reclamation plant owned by Everbright Water Service Company.Aiming at the existing problems of the initial operation, according to three years’ detection and analysis, the thesis investigated the control effectiveness of online operation and chemical cleaning on UF and RO membrane fouling, the pollutant removal and slat interception, and evaluated the main operational cost such as energy and chemical consumption.Organic matter, salt, iron, manganese, silicon and calcium of raw water are high.Immersed UF, as pretreatment unit of RO unit, could eliminate turbidity and colloidal particles remarkably with their effluent value low than 0.5 and 3 for most of the time.The average removal efficiency of CODCr was 19.95%. Appropriate coagulant dosing before UF, could delay the UF membrane fouling, lower CODCr of the UF effluent. But the aluminum can increase the risk of aluminum silicate pollution of RO membrane.Heating the raw water by steam in winter was favorable to ease membrane fouling, but the cost of steam is too higher(0.075 yuan/m3) to be used in practice. Addition of Na Cl O in UF influent making the residual chlorine in its effluent to above 0.3 mg/L could delay UF membrane fouling. Setting 15 min backwash cycle, 37.9 L/m2·h washing intensity and 220 m3 /h aeration volume, could effectively control membrane fouling during the UF performance. The chemical cleaning can effectively remove UF membrane fouling, making the membrane flux close to that of the new membrane.Pollutants of RO membrane fouling are mainly organic matter, soluble microbial products, humic acid and humic substances. Main elements of surface membrane fouling are C, O, Si, Al, Ca, Fe, S and so on. There were pollutants of silicate,carboxylic acids, amino acids etc. on both membrane surfaces of the two RO sections.Sulfate was found on the membrane located at the end of the second section. The Na OH plus chelating agent could effectively remove the organic pollutants on the surface of RO membrane. The citric acid cleaning after alkali washing could improve the RO desalination rate. Cleaning of RO with Na OH solution regularly could effectively mitigate membrane fouling and increase membrane flux.After three years’ continuous operation, the UF flux was stable. Detection resultsof RO membrane unit showed that water production rate of the first element of the first section and the last one of the second section declined 6.5% and 19.3% respectively.The desalination rate of the first element of the first section declined 0.5%, while which of the last one of the second section did not decline, revealing the overall performance was good.Electricity cost and membrane depreciation expense occupied the largest part of the operation cost. Applying the energy saving and membrane fouling controlling measurements proposed by the research, the electricity cost of the process dropped year by year.