Composition And Function Of Extracellular Polymeric Substances In The Activated Sludge

Extracellular polymeric substances（EPS）is the product in the process of microbialmetabolism and play a crucial role in the formation of activated sludge. This studyfirstly discussed in activated sludge flocs formed in the process, dissolved organicmatter and particle state of activated sludge characteristics and its effect on the substrateremoval rate. And then puts forward the concept of classified according to the functionof EPS, EPS can be divided into floc EPS (Extra-Microcolony Polymers, EMPS) andmicrocolony EPS (Extra-Cellular Polymers, ECPS). Based on the granulometricdistribution evaluation of activated sludge, using the cation exchange resin(CER)method as the step1extraction method,and using the heating method,formaldehyde-alkaline method and ultrasonication-high speed centrifugation method asthe step2extraction to separate the EMPS and ECPS and analyse the composition,function and flocculation character. The results are as follows:（1）The activated sludge concentration with sweet potato starch as the organicsubstrate cultivation is lower than the activated sludge with glucose. The activatedsludge with sweet potato starch grows the small amounts of filamentous bacteria andcaused a certain influence to the settling performance. And the dewatering performanceof activated sludge with glucose is superior to the activated sludge with sweet potatostarch. About the removal of the substrate, the activated sludge nitrification withglucose is more completely, and the activated sludge nitrozation with sweet potatostarch is completely, nitrification is incompletely. The activated sludge phosphorusremoval effect with glucose is better than the activated sludge with sweet potato starch,the removal rate of organic matter of two are both high. （2）Based on the granulometric distribution evaluation of activated sludge, cationexchange resin treatment is efficient to disintegrate the flocs for EMPS extraction,however, inefficient to disaggregate the microcolonies for ECPS harvesting. However,ultrasonication-high speed centrifugation method is efficient to disintegrate themicrocolonies for ECPS extraction. It suggested that cation Ca2+, Mg2+bridginginteractions are more crucial in floc level flocculation.（3）Composition analysis was showed that more exopolymers were found insidethe microcolonies. The content of protein and polysaccharide of ECPS is almost2timesof EMPS, the protein/polysaccharides ration of ECPS was higher than that of EMPS.The results indicated that protein content in the microcolonies more than the out.Protein amino groups with positive charge could neutralize the carboxylic acid groupwith negative charge in the EPS, can reduce the negative charge on the surface of thesludge, make the sludge internal combined more closely, so the microcolonies is moredifficult to separate than flocs.（4）Based on the electrophoresis of the molecular weight of protein, proteinmolecular weight of ECPS is larger than EMPS, the larger protein molecular weight hasthe longer protein chain, the entanglement function is stronger, so the entanglementfunction of macromolecular protein could be a kind of important microcolony internalcohesion.（5）There are three obvious peak in the three dimensional fluorescence spectrumof EMPS and EPS, but there are two obvious peak without the humic substances peak inthe three dimensional fluorescence spectrum of ECPS. The humic substances of EMPSand EPS may come from the test of water used in the natural water bodies. So the humicsubstances mainly gathered in the outer EMPS to adsorb, and can’t enter themicrocolonies internal ECPS.（6）The contents of hydrophobic substances in ECPS were also found to be higherthan that of EMPS. The content of hydrophobic neutral substances in ECPS was almost15times of that in EMPS. It means that the hydrophobic interactions are more importantin microcolony level cohesion.Both types of EPS were found to be much negativelycharged. However, the isoelectric points of EMPS （pH=1.1） and ECPS （pH=2.3）were different. It showed that EMPS has more negative charges than ECPS.