The Research Of Optimizing The Hydrolysis The Excess Sludge By Compound Enzymes And The Rule Of Transportation And Transformation Of Heavy Metal

Sludge, as the byproduct of biological sewage treatment, is increasing rapidly. It isestimated that its annual output will break through30millions tons in2015. The composition ofsludge is quite complicated, it contains both available resources and heavy metal pollution. It willseriously effect the environment if the sludge management hasn’t been done properly. Resourcefultreatment of sludge is not only the future direction,but also the necessarily need of sustainabledevelopment of our country. The protein in activated sludge reaches60%-70%. It is a promisingmethod if we can extract and use the protein. The main methods of hydrolyzing the residualsludge is to be divided into alkaline process, acid process and enzymatic process. Besides, theresearch of alkaline process and acid process prolongs more. However, the enzymatic process ismore benefit to environment and with less energy consumption, the structure integrity of proteinwhich extract from the sludge is better and will be much easier to assimilate. Nonetheless, thedisadvantage of enzymatic process is its low extraction efficiency. The heavy metal in sludgeremains a obstacle of resource utilization. It has a great significance for working out the rule oftransportation and transformation of heavy metal in the enzymatic hydrolyzing process. Thisresearch is aiming at improving the extraction efficiency of enzymic hydrolysis for residual sludge,attempted to having bi-enzymic hydrolysis which based on the single enzymic hydrolysis. Thisexperiment proceeds by means of recombination of3enzymes with each two, testing theextraction efficiency of protein in hydrolyzing the excess sludge by compound enzymes and thedepletion rate of organic matter in residual compare to the sludge, the value of SCOD/TCOD toensure the best proportion of each two enzymes and optimizing the best condition of hydrolyzingthe excess sludge by compound enzymes. With the modified method of Tessier continuous extraction to extract the residual of hydrolysis the excess sludge by compound enzymes for1,2,3,4hours, then ensure the rule of transportation and transformation of heavy metal in the process ofhydrolysis such as Cd, Cr, Cu, Mn, Pb, Zn, Hg, As. Finally, research the curing protein by usingthe method of accumulative sedimentation to study the extracting solution of protein of hydrolysisof excess sludge of compound enzymes.Here’s the main conclusion:1. The efficiency of combination of alkaline proteinase and neutral proteinase is better. Thebest proportion is3:1(alkaline proteinase: neutral proteinase).2. Alkaline proteinase: neutral proteinase3:1, the best hydrolysis condition leads to ph9,reaction temperature:55℃; liquid-solid ratio:4:1; volume of enzyme:5%; reaction time:4h. Inthis condition, the extraction rate of protein is65.89%, the valus of SCOD/TCOD is61.43%, thedepletion rate of organic matter is78.05%. The extraction rate of modified enzymic process isclose to the extraction rate of chemical method.3. In the process of hydrolysis of excess sludge by compound enzymes, heavy metal transferto stable combined state from active one. This shows that hydrolyzing the sludge by enzymicprocess is helpful and decease the harm to environment. Add Zn in low concentration of ionicstate would increase the efficiency of hydrolysis and extraction rate of protein. Otherwise, the Znin high concentration of ionic state would inhibit the efficiency of hydrolysis, but with proceed ofhydrolysis, it would stabilize the Zn2+.4. For the extraction solution of protein by hydrolyzing the excess sludge of compoundenzymes, the non-ionic polymer precipitation works better than the isoelectric point method andorganic solvent precipitation. As experiment reagent, polyethylene glycol works best. Theproportion of polyethylene glycol and protein hydrolysate is17:12, the efficiency of precipitationof protein is63.75%.