Study On Removal Of Organic Matter From Raw Water By Three Kinds Of Aluminum Salt Coagulants

With the intensification of water pollution and improvement of drinking water qualitystandard, conventional water treatment processes in terms of performance fade inadequately.Coagulation is an important part of drinking water treatment process, and effective removalsof organic matters in water are achieved by effective control of coagulation in p hysical andchemical conditions. In the research, three kinds of coagulants, aluminum sulfate,polyaluminium chloride and polysulfide aluminium chloride were adopted as beaker tests incoagulation.With the city water plant for raw wate and removing organic matters as the goal,coagulant dosage and initial raw water pH changes on removal of organic matters coagulationeffect were studied.(1) The raw water in Suzhou xiangcheng district water plant contained mainlow-molecular-weight protein from dissolved organic matters and few large-molecular-weightorganic matters with molecular weight beyond30kDa which were mainly consisted ofpolysaccharides and proteins with low UV absorption of hydrophilic organic matters. Anotherpart contained medium molecular weight (10~2.5kDa) organic matters, mainly humic acidand aromatics with high UV absorption of hydrophobic organic matters. Humic substances inraw water was mainly terrigenous input, as well as, contained strong aromaticity with morebenzene rings. Raw water was heavily polluted by metabolites from algae and humanmodification.(2) Economic coagulant dosage of aluminum sulfate was4mg/L (Al2O3).When thedosage of4mg/L, aluminum sulfate to CODMn, UV254and DOC removals were27.77%,31.58and25.90%. Aluminum sulfate can effectively remove organic molecules (>30kDa), inhumus hydrophobic organic matter（10~2.5kDa）removal is better than that of hydrophilicorganic matter, the removals of Protein organic matters (2.5~0.5kDa) did not diminish butincreased, for hydrophilic organic small molecules (<0.5kDa) almost no removal efficiency.Optimum initial pH value was6for aluminum sulfate to remove organic matters. When pH=5and the dosage of4mg/L, the aluminum sulfate to CODMn, UV254and DOC removal rateswere37.8%,36.5%and41.1%. Lower pH can improve the overall removal efficiency oforganic matter, but did not improve the fluorescent organic matter removal efficiency.(3) Economic coagulant dosage of polyaluminium chloride was4mg/L (Al2O3).When thedosage of4mg/L, polyaluminium chloride to CODMn, UV254and DOC removals were33.77%,36.84%and29.71%. Polyaluminium chloride can effectively remove organic molecules(>30kDa), removing hydrophobic humic type organic matter (10~2.5kDa) was superior tohydrophilic organic matter. Compared with conventional aluminum sulphate, protein organicmatter (2.5~0.5kDa) removal efficiency is improved. Polyaluminium chloride can hardly to remove small organic molecules (<0.5kDa). Fluorescent organic matter removal is minimal.Optimum initial pH value was5for polyaluminium chloride to remove organic matters. WhenpH=5and the dosage of4mg/L, the polyaluminium chloride to CODMn, UV254and DOCremoval rates were44.63%,35.59%and36.78%. Molecular weight distribution analysisshowed that when pH=5, the removals of humic organic matters (10~2.5kDa) did notdiminish but increased, the removals of the protein (2.5~0.5kDa) has significant effect.Three-dimensional fluorescence spectroscopy showed that when the optimum pH,polyaluminium chloride can reduce the protein fluorescence of organic matter increased, butcannot have the effect of removing, humic type organic matter removal and no increasedsignificantly.(4) Economic coagulant dosage of polysulfide aluminium chloride was4mg/L(Al2O3).When the dosage of4mg/L, polysulfide aluminum chloride to CODMn, UV254andDOC removals were33.77%,36.84%and27.04%. Polysulfide aluminium chloride had thesame good removal effect on organic molecules; Specifically having certain removal effectson humic organic matters in molecular weight from10to2.5kDa,less removal effects onsmall molecule protein organic matters in molecular weight from2.5to0.5kDa, weakremoval effects on hydrophilic organic matters (<0.5kDa).Optimum initial pH value was5forpolysulfide aluminium chloride to remove organic matters.When pH=5and the dosage of4mg/L, the polysulfide aluminium chloride to CODMn, UV254and DOC removal rates were49.36%,37.29%and39.24%. Molecular weight distribution analysis showed that when pH=5,the removals of humic organic matters (10~2.5kDa) and protein organic matters (2.5~0.5kDa)had been improved obviously.Three-dimensional fluorescence spectroscopy showed thatwhen the optimum pH, the fluorescence intensity of Protein organic matter did not diminishbut increased, and removal of fulvic acid organic matters decreased, but removal of humicacid organic matters increased. The total fluorescence intensity in organics increased slightly.