Strengthen Of Waste Actived Sludge Anaerobic Digestion And Nitrogen And Phosphorous Removal Of Digestion Liquid

The issue of reduction and reuse about waste activated sludge (WAS) has been a problem in urban development. Since the short chain fatty acids (SCFAs) have been proved to be a carbon source for nitrogen and phosphorus removal, WAS anaerobic acidogenic has attracted much attention. The low sludge anaerobic digestion rate and a large amount of nitrogen and phosphorus released in digestion process hinder the development of WAS anaerobic acidogenic. This paper studied two methods to improve sludge anaerobic digestion rate and strengthen acidogenic effect:one is adding specific bacterium NJUST19. to construct thermophilic/mesophilic two-phase anaerobic digestion (TPAD) system; another is adding external surfactant.The thermophilic phase (TAR) with NJUST19. as the advantage flora and mesophilic phase (MAR) with sludge original bacterium as the advantage flora connected the TPAD system, microbial growth reached stable relatively after42d domestication and the system achieved stable acid production, the average SCFAs concentrations were3690.2mg/L in TAR and4637.1mg/L in MAR. Through the discussion of pH, temperature, sludge adding ratio and residence time effect on sludge hydrolysis and acidification of TAR and MAR, we determined the optimum operation parameters of TPAD system, namely, pH=9, T=65℃, adding ratio=12.5%and HRT=72h in TAR and pH=10, T=40℃, adding ratio=50%and HRT=72h in MAR.By comparing the effect of chemical surfactant sodium dodecyl sulfate (SDS) and biosurfactant alkylpolyglucoside (APG) on sludge hydrolysis and acidification, studies have shown that two kinds of surfactant strengthened sludge hydrolysis and promoted SCFAs accumulation, and there were linear relationships between soluble protein and soluble carbonhydrate concentrations and surfactant dosages. Considering the SCFAs production and economic cost, the optimal dosages of SDS and APG were0.1g/gTSS and0.2g/gTSS, and the maximum SCFAs concentrations appeared in the anaerobic digestion of48h and12h respectively. The presence of SDS and APG promoted acid production and resulted in more NH41+and PO43-releasing simultaneously. With the extension of digestion time, NH4+concentration increased while PO43-concentration increased first and then decreased. Mechanism of two surfactants promoting sludge hydrolysis and acid production have in common, namely, reducing sludge surface tension to promote the dissolution of organic matters, enchancing the hydrolytic activities and increasing the amount of acid accumulation ultimately. The differences are the variations of a-glucosidase activity and protease activity effected by SDS and APG dosages. In addition, sludge extracellular polymeric substances (EPS) agglomeration eased after adding surfactant and mass transfer channel substrate appeared in the presence of APG. Appropriate elevated temperature (≤35℃) and alkaline conditions are good to the effect of surfactants on sludge hydrolysis and acid production.Orthogonal experiments were employed to optimize the reaction conditions of caustic dross+zeolite combined to remove nitrogen and phosphorus. Considering experiment results, intuitive analysis and variance analysis, we determined the optimal conditions for the first step, nitrogen and phosphorus removal by caustic dross:orthophosphate/caustic dross was12mg/g, time of24h, pH of9, and the caustic dross after nitrogen and phosphorus removal can be used as agricultural fertilizer; the optimal conditions for the second step, nitrogen removal by molecular sieve:nitrogen/molecular sieve was100mg/g, time of30h, pH of7.