The Characteristic Research On Treatment Of Xiangjiang Micro-polluted Source Water By Biofiltration

In recent ten years,the middle and lower reaches of Xiangjiang River has been polluted by various organic matter, NH4+-N, Fe and Mn.The water quality of these reaches usually couldn't be up to the standard of the third grade of source water quality standard which the current surface water environmental quality standards had prescribed.A majority of water plant which use the Xiangjing River water as the water source are disable to remove the most pollutant because of using the conventional filtration,thus the effluent water of these plants couldn't attain the biological stability. This research examined the results of the treatment of micro-polluted Xiangjiang River source water by biofiltration.The results show that the removal rate of TOC can be reached 25~32% , the removal rate of BDOC can be reached 41.3~65% , and the removal rate of AOC can be reached 59.2-84.2% respectively.The removal rate of CODMn can be reached 40.4-49.4%, the removal rate of UV254 can be reached 60.6-66.5%,the removal rate of NH4+-N can be reached 67~90%,the removal rate of Fe can be reached 88~95%, and the removal rate of Mn can be reached 36~87% respectively.For the efficient removal of organic matter, NH4 + -N, Fe and Mn,the biofilter has the ability to enhance the biological stability of drinking water.The removal of dissolved organic matters is strongly related to the molecular weight of the organic matters.The GAC-sand biofilter is capable of removing the organic matters with small molecular weight (<1000) and with molecular weight of 3000~6000.The removal rate of organic matter with small molecular weight (<1000) and with molecular weight of 3000~6000 is 54.46% and 54.57% respectively, and these organic matter mainly consist of synthetical compound(keto compound, hydroxybenzene and phenyl acid ester)and humic acid. The biofiltration has superior characteristic of turbidity removal,when the influent turbidity is bellow 5 NTU,the effluent turbiduty of the biofilters can maintain less than 0.1NTU for acceptable long time.The mechanism of turbidity removal is mainly attribute to the combined action of traditional adsorption and biosorption. The biomass in the biofilters decrease gradually from the top layer to the bottom layer along the water flow.The biofilm on the media surface mainly presented in zoogloea form.The dominant bacterial genusand sub-dominant bacterial genus were Pseudomonas and Bacillus respectively.We found that the species that made up the biofilm were comparatively complete by means of the microscope. It included bacteria, filamentous fungus,mold, vorticella and metazoan etc., which formed a stable microbial ecosystem jointly. The increase of EBCT and water temperature can improve the effect of biofiltration.Backwash with nonchlorinated water has less impact on bifiltration.Shutdown of the biofilters has minor impact on biofiltration performance,the biofilters can return to normal operation quickly after restart.