Study On The Transformation Characteristics Of Organic Pollutants From An A~2/O Sewage Treatment Process

Focusing on the A2/O sewage treatment in Xi’an City, the changing of organicsduring sewage disposal process was discussed with the perspective of paricle anddissolved COD, polar and nonpolar state of dissolved organics and its molecular weightdistribution, rapid and slow biodegraded organics, which provides a theoretical basis fororganics pollutants transformation in sewage.The results show: COD in raw water is360±120mg/L, COD(SCOD) takes aproportion of39%while the remains composed of particle COD. Analysis on particlesize distribution shows: with smaller size and bigger specific area,the suspended solidsin raw water could adsorb more organics which makes more difficult for biologicalremovement.In raw water, polar organics accounted for about50%, the proportion fornon polar and weak polarity organics are25%~35%，10%~20%respectively whichindicates most of the soluble organics in raw water is polar organics. The polarity oforganics in secondary effluent shares the same regulation with the inflow. Themolecular distribution of raw water organics shows: the proportion for organics morethan10kDa molecular weight accounts for36.9%while the50%organics in secondaryeffluent with a molecular weight lower than1kDa. The excitation-emission matrixspectroscopy shows the fulvic acid organic matter and protein-like organics are rich inraw water, the peak of protein-like disappeared in effluent while polar humic organicswith small molecule weight increased.From the perspective of biological availability，slow biodegraded organics inexitence of particle takes50%of the inflow in raw water while soluble rapidbiodegraded organics only accounted for15.8%. In raw water, volatile fatty acids(VFA)is composed of acetic acid with a amount of15~30mg and2~6mg/L valeric acid aswell as a small amount of propionic acid. After anaerobic and anoxic periods, the amount and composition varation of VFA are increased in comparation with primarytreatment. The proportion of VFA in soluble COD increased rapidly which indicatesthe hydrolysis and acidification fermentation process of slow degraded organics washappened during anaerobic and anoxic period.