Research On Enhanced Hydrolysis Of Excess Sludge And Application Of Hydrolysate

Volatile fatty acids (VFAs) are the main products of wastewater anaerobic fermentation process. As a kind of short-chain organic acids, VFAs are welcomed carbon sources by microorganisms. They were often used as an exogenous carbon source for the treatment of wastewater with low C/N ratio. They can also be used as substrates for the synthesis of poly-β-hydroxyalkanoates (PHA). The research focused on the release of internal carbon sources of the wasted sludge and the production of PHA using the hydrolyte of the wasted sludge. The wasted sludge was hydrolyzed after the ultrasonic pre-treatment, the optimum operation parameters of the pretreatment and hydrolysis was investigated. The consequent method for ammonia nitrogen and orthophosphate removal from the hydrolysate was studied, as well as the settleability of the mixture after hydrolysis. Finally, the treated hydrolysate was used for PHA production.A set of orthogonal tests were designed to investigate the variation of the sludge acidification ratio, the protein solubility and the polysaccharide solubility under different sludge moisture content,ultrasonic pre-treatment time, energy density, hydrolysis time, pH and pulse ratio. The results showed that sludge moisture content, energy density and pulse ratio are the most influential factors on sludge acidification ratio. Other factors are less influential on sludge acidification ratio. Sludge moisture content, energy density and pulse ratio were determined respectively. After the process operation optimization, the process of sludge hydrolysis was studied on the basis of the analysis of extracellular polymeric substance (EPS). The results showed that sludge floc and EPS were hydrolyzed with in 36h, while the microorganisms cells were hydrolyzed evidently after 36h. The maximum acidification ratio of 64.61% was achieved at 48h during the hydrolysis. The hydrolysis effect with ultrasonic pre-treatment and lysozyme pre-treatment was compared in this research. The results showed that the ultrasonic pre-treatment was more effective.The hydrolysate contains high concentration of ammonia nitrogen and orthophosphate, and the sludge after hydrolysis showed poor settleability, therefore, efforts had to be done before it can be used. The methods of struvite (MgNH₄PO₄·6H₂O) sedimentation and ammonia stripping was combined to make sure the ammonia and orthophosphate concentration has little effect on the consequent usage. An interesting experiment that use fresh activated sludg to improved the settleability of the sludge after hydrolysis was carried out. The results showed that by mixing the fresh activated sludge, the settleability could be improved.The treated hydrolysate was used to synthesize PHA. The effect of ammonia and pH to the synthesis performance was investigated. The results showed that ammonia will not inhibit the PHA production, and the hydrolysate can be used as the substrate for PHA production without any special treatment.