Experimental Study On The Filtration Performance Of Micro Flocculation Direct Filtration

Drinking water’s security has become a great concern in small towns and thecountryside.The dosage ofcoagulants is always high when treating low turbidityreservoir water by conventional treatment process, making the water production costincreased.Low economic development and irregular management are widespread inrural area. In that case,it is necessary to find a proper and economical treating processthat suitable forsmall towns.Micro flocculation direct filtration process is suitable for treating low turbidityreservoir water. This water disinfection techniques can reduce project investment andwater production cost by saving occupied area.It combines coagulation and filtrationprocess,needs no coagulation or sedimentation tank. Experimental study shows thatunder the conditions of turbidity between15NTU and20NTU, filtration rate10m/h, andthe dosage of aluminium sulfate14mg/L,the effluent turbidity can maintain less than1NTU for at least12hours.The average effluent turbidity in12hours is0.57NTU.Affects of four filter aid, anionic polyacrylamide(APAM),non-ionicpolyacrylamide(NPAM), poly dimethyl diallyl ammonium chloride(PDMDAAC) andchitosan(CTS),on performance of the filter were also studied. The results shows that theeffluent water quality may be further improved by adding filteraid.Comparing theperformance,the turbidity fromthefilterwithPDMDAACasfilteraidwasmuchlower thanthe other three. The turbidity emoval rates raisedwhen increased the dosage of filteraid.Micro flocculation direct filtration can romove humic acid by removing turbidity.Using aluminum coagulant may increase the aluminum in effluent. The resultsshow that the effluent aluminum was significantly raised when the dosage of coagulantis above the optimal dosage.the effluent aluminum is182μg/L when adding aluminumcoagulant18mg/L. particulate aluminum s is the most part of alumium removed byfiltrition, the concentration of alumium had good relevance with effluenttubidity.Adding the filter aid can reduce the effluent concentration of residual aluminumby improving the removal rate of turbidity. The reductionrate of residual aluminumfrom the filter with CTS as the filter aid was the hightest.Chitosan(CTS) is a natural polymer flocculant.It had got more attention in watertreatment areabeause of its advantage including natural harmless, nontoxicity andbiodegradable.Due to the abundant free amino and hydroxyl on chitosan molecules,chitosan has strong capability of coordination and adsorption of metal ions.Chelation can be taken between CTS and metal ions such as aluminum ion. Theexperimental results show that CTS not only can reduce particulate aluminum in waterby removing turbidity,but also can remove dissoluble aluminium. Effluent aluminumcan be controlledat a stable low level throngh addion of CTS0.1to0.2mg/L,it reducetheexcessive risk of effluent aluminum.