Study On Enzymatic Hydrolysis Of Sludge Enhanced By Ultrasound

In recent years,with a large number of sewage treatment plants established,the water pollution has been effectively controlled.But a large number of sludge production is coming.If we can’t have the reasonable and effective treatment,it will hurt the ecological environment and human health.Commonly,30-60% of protein exists in the excess sludge.It will be an effective methods of sludge stabilization,reclamation and reduction to extract and utilize it in a reasonable way.In this paper,the excess sludge from a city sewage treatment plant in Zhengzhou was used as the research object.First,the excess sludge was hydrolyzed by single ultrasound and single enzyme,respectively,by which the main factors affecting the protein extraction were studied.on this basis,the enhancement effect of enzymolysis with ultrasonic pretreatment was explored.The main results are as follows:(1)The single ultrasound was adopted to extract protein from excess sludge.With the optimal condition of the power density being 2W/mL,the water centent being94% and the irradiation time being 20 min,the protein extraction ratio was 15.3%,and the sludge specific resistance reduced to 2.419 × 109S2 / g which increased about83%;(2)The alkaline protease was used to hydrolyze the sludge.With the optimal condition of water content being 94%,the pH being 8,enzyme dosage being 2%(w/w),the temperature being 55 ℃and the hydrolysis time being 4h,the protein extraction ratio was 58%,and the sludge specific resistance was 1.382 × 109S2/g,which improved about 90%;(3)The optimal conditions of enzymolysis with ultrasonic pretreatment was consistent with that of enzymolysis of single alkaline protease.However,the protein extraction ratio was improved to 69%,which was 19% higher than that of single enzymolysis.Besides,The specific resistance of sludge of 0.62 × 109S2/g was obtained which was 55% higher than that of single enzymolysis.Thus,the ultrasound pretreatment effectively enhanced the enzymolysis of the excess sludge;(4)Although the extraction ratio of enzymolysis with ultrasound pretreatment was 21% lower than alkaline heat method,the sludge dehydration performance was56% higher than alkaline heat method.In addition,the protein extracted is suitable for fluid fertilizer,animal feed etc.for more amino acid was obtained by enzymolysiswith ultrasound pretreatment method than alkaline heat method.It worth noting that the reaction conditions of enzymolysis with ultrasound pretreatment method was mild and produce no secondary pollution,so it has a broad application prospects.