Experimental Study On Low Temperature And Low-turbidity Water Treatment By Enhanced Coagulation Of Recycling Sludge

Low temperature and low turbidity source water is widespread in the most regions ofnorth-east, north China and the northwest of ours. During the coagulation of lowtemperature and low turbidity water, the pollutants removal ability was greatlyaffected due to slower hydrolyzing process, higher aggregation shear and slowersettling velocity, less particulate concentration, small particulate diameter, moresignificant hydrophilicity, as well as lower probability of collision and aggregation. Toimprove water quality and ensure the safety of the effluent, the focuse on coagulationtreatment of low temperature and low turbidity water is significantly meaningful.Enhanced coagulation of recycling sludge put forward in recent years is an effectivemethod to improve coagulation performance in low temperature and low turbiditywater treatment.In this research, firstly, the optimization of traditional coagulation treatmentspecifically the selecting of optimum coagultants was conducted, Moreover, thecoagulation aids, such as calcined lime (CaO), anion polyacrylamide (APAM) andactivated silica acid (AS) solely, as well as potassium permanganate (KMnO4),powdered activated carbon (PAC) respective or combined effects were studied.Secondly, the coagulation efficiency of recycling chemical precipitates sludge derivedfrom poly-aluminum chloride (PACl) in terms of turbidity, organic matter removaland residual dissolved alum concentration was investigated as compared to mixedsludge mainly contains hydrolyzing precipitant and PAC (referred to as PAS).Theflocs characteristic analysis using optical microscopy and Image J software, and theinfluence of raw water properties on recycling process was analyzed as compared toconditional coagulation. Thirdly, the coagulation performance as well as residualaluminum species with respect to total alum (AlT), dissolved alum (AlD) andparticulate alum (AlP) through combined effects of AS, PAC and recycling sludge wasinvestigated by continuous bench-scale tests. The coagulation mechanism involved inenhcaning contaminates removal by recycling sludge process were discussed.The results indicated that PACl was the best coagulation for removing turbidity andorganics among alum-based coagulants.The highest turbidity removal efficiency couldbe attained when AS as coagulation aid, whereas the maximum organics eliminationoccurred by combination technique of KMnO4and PAC.Recycling sludge contains PACl hydrolyzing precipitant was less efficient thananother contains PAC and residual hydrolyzing products of PACl. It is also discovered that the flocs morphology by recycling process was more irregular than conventionalprocess, and PAC incooperated in flocs played a positive role on flocs formation andimproved organic removal. Recycling PAS was able to enhanced turbidity andorganics removal in case of relatively low initial turbidity and organic concentrationsin raw water, and to make sure the Al contents in settled water is less than0.2mg/L.Recycling sludge incooperates with AS exhibited excellent potential for turbidity andparticulates removal during the low turbidity water treatment. Organics eliminationwas improved when PAC was introduced, but the attribution of PAC on turbidity andparticulates enhanced removal was less influenced.The moderated combined dosingmodel of these three compoments could achieve the highest organics removal.However, the residual AlTor AlDin the effluent exceeded0.2mg/L, demonstrating thesubsequent treatment should be further carried out to limit the content undercontrol.The results may be ascribed to the higher background in raw water andaddition of sludge in recycling process, as well as the phenomenon of dissolved outalum.When recycling sludge was applied, the dosing parameters of chemicals and recyclingsludge in operation or debugging should be feasibly selected and evaluated based ondefined conditions of daily practices or managements. As a result, the mosteconomical benefits in drinking water treatment plant can be complished and thehigher water quality be obtained. The excessive sludge should be priodicallydischarged and the harmless treatment of recycling sludge be conducted in wideapplications of recycle designs.