Activated Sludge Dispersion And Extraction Of Extracellular Polymeric Substances By NaCl-mediated Method

Recently,municipal sewage treatment plants are confronting the policy requirements of improving the quality and efficiency.How to improve treatment efficiency on the basis of the original process increasingly become a hot topic in research and engineering practice.Nitrifying bacteria proliferate slowly and are sensitive to temperature and poisons.How to maintain a high proportion of this bacteria in sludge is the key to improve the denitrification efficiency of municipal sewage treatment plants,which can be realized through adding nitrifying bacteria,separated from sludge,to the treatment system.In this study,the sludge of urban sewage treatment plant?A²/O process,oxidation ditch process?was taken as the object to explore a sludge dispersion method with engineering value based on the layered coagulation mechanism of EPS.Firstly,the feasibility of conventional ultrasonic method for sludge dispersion and nitrification bacteria separation was discussed.Then,based on the principle of resin method,a new method of activated sludge dispersion mediated by sodium chloride was proposed,and its dispersion effect was evaluated.Ultimately,activated sludge EPS of mediated by sodium chloride extraction efficiency and the influence factors were investigated.The main findings are as follows:?1?Ultrasonic centrifugation can be used as a method for dispersing sludge flocs before the recovery of functional bacteria;the significant factors that affected the dispersion of sludge by ultrasonic centrifugation were ultrasonic intensity,sludge concentration and treatment time,and their significant influences increased successively and a certain interaction among them existed.In the third and fifth sewage plant sludge dispersion tests,the actual value of the fitting equation obtained from response surface analysis fitted well with the predicted value of the model.The optimal operating conditions were as follows:the ultrasonic time of 1.8 min,the ultrasonic power of 738.8W,the sludge concentration of 3000 mg/L;the solvent density required to separate the nitrifying bacteria micelles from residual sludge was 1.03 g/mL through simple batch test;besides,found that the effect of ultrasonic centrifugation on the separation and recovery of NOB was better than AOB.?2?The test proved that NaCl can be used as a mediator to disperse activated sludge flocs;the mediator concentration,mediating time,and sludge concentration were the main factors affecting the sludge dispersion.The actual value of the fitting equation obtained from response surface analysis fitted well with the predicted value of the model.The optimum operating conditions were:the NaCl concentration of 120 g/L,the treatment time of 2 min,the sludge concentration of 3000 mg/L;the results of particle size analysis and microscopic examination indicated that most nitrifying bacteria micelles were retained after NaCl treatment and separated from the flocs;heavy flocculation experiments demonstrated that Ca²⁺and extracted EPS were the key substances for flocculation of activated sludge.?3?NaCl-mediated method can quickly and effectively extract EPS from actual sewage and activated sludge cultivated in simulated wastewater;the actual value of the fitting equation obtained from the response surface analysis had a good fit with the predicted value of the model,and the optimum treatment conditions were:the treatment time of 5.4 min,the NaCl concentration of 111 g/L,the sludge concentration of 8000mg/L;NaCl-mediated method compared with cation exchange resin method?CER?,the protein component extraction effect of the two methods was equivalent,while the polysaccharide extraction amount was relatively low,and the NaCl-mediated method posed a lower cell damage rate;the EPS components of the activated sludge in the sewage plant and the laboratory activated sludge exhibited very little difference,and humic acid components both were detected.