| During the process of rapid urbanization and industrialization in our country,sewage plants and sewage treatment facilities have been popularized in cities and towns,huge amount of sludge is produced in municipal sewage treatment.The Eighteenth and Nineteenth National Congress of the CPC,it was proposed that ecological civilization should be built while economy is developed.Therefore,the problem of sludge treatment and disposal has been gradually taken seriously.As the rate-limiting step of anaerobic digestion of sludge,how to accelerate the rate of hydrolysis is the core content of this paper.There are a number of researches on sludge pretreatment at home and abroad,the classifications are as follows: the first one is Physical treatment method,such as thermal hydrolysis and Ultrasonic,the second one is chemical treatment,such as adding acid,alkali or potassium ferrate,the third one is Biological treatment,such as adding surfactants and using biological predation,which have been proved effective.However,adding biological enzymes can not only promote the hydrolysis,improve the anaerobic digestion performance of sludge,improve the dehydration,but also produce the biodegradable organic matter with high solubility,which enhances the effect of anaerobic fermentation.Besides,the product Short-chain fatty acids(SCFA)can be used as a carbon source to remove nitrogen and phosphorus.What'more,this method realizes the reduction of sludge,and the utilization resource,whose product will not cause secondary pollution to the environment.Comparing the hydrolysis rates after adding protease,cellulase and lipase(dosing were 0,30,60,90,120,150 mg / gTS),it is indicated that the catalytic effect of protease is the best because the properties of protease is closer to the protein whose content is dominant in the sludgeIn this experiment,the optimum dosage is 90 mg/gTS.In this condition,the concentration of SCOD solution reaches 1711.6mg/L.VSS removal rate is 9.2%.The concentration of protein,sugar,ammonia and phosphate reaches 752.6mg/L,93.1mg/L,120.8mg/L and 52.9mg/L,whose concentration is 617.9%,513.3%,700.6%,859.8%,284.6% and 487.7% higher than those without adding enzymes respectively.Under the catalysis of protease,the hydrolases in the sludge begin to dissolve,dissolving the sludge solids together with the added enzymes,and the macromolecules are hydrolyzed into small molecules such as proteins andpolysaccharides.Then the proteins can be hydrolyzed into amino acids and peptides.After determining the optimum dosage of protease,the influence of different temperature on the pretreatment effect of sludge was compared.The result shows that the hydrolysis rate can be greatly promoted by raising the room temperature to the optimum temperature for protease.The combination of Biological enzyme and heat treatment not only can maximize the activity of the enzyme,but also can change the structure of the sludge cells which effectively reduces the protective effect of extracellular polymers(EPS)and cell wall,accelerating degradation rate of sludge,driving organic matter in solid phase into the liquid phase more easily and increasing the index in solution.In the experiment,the optimum reaction temperature is 50 ?.Under this condition,the concentration of SCOD solution can reach 2366.4mg/L.VSS removal rate is 13.98%.the concentration of protein,sugar,ammonia,phosphate is 924.5mg/L,144.3mg/L 251.1mg/L,50.7mg/L,whose concentration is892.6%,832%,926.7%,1387%,602.4% and 496.5% higher than those without pretreatment.The concentration of SCOD,protein,sugar and ammonia nitrogen and the removal rate of VSS increased rapidly in the first four hours of hydrolysis,which accorded with the first order kinetic response relationship.This paper also studied the effect of anaerobic fermentation of sludge and direct anaerobic fermentation by physical method(ultrasonic)and chemical method(adding alkali,EDTA-2Na or the potassium ferrate),biological(enzymatic),physical and chemical method(adding alkali / ultrasonic method)and biochemical methods(adding proteinase /EDTA-2Na).The result shows that the dissolution by physical and chemical methods of sludge cells may be better than biological method,while the SCOD produced by biological hydrolysis is more biodegradable,so the anaerobic fermentation can have higher degree of utilization.The utilization ratio of protease/EDTA-2Na pretreatment was 0.58 mgVFAs/mgSCOD,and the SCOD utilization rate of protease pretreated sludge was up to 0.70mgVFAs/mgSCOD.The highest concentration of SCOD pretreated by proteinase/EDTA-2Na is 4133.5mg/L,which is less than the concentration SCOD produced by alkali/ ultrasonic,4239.6mg/L,while the anaerobic fermentation can produce acid 2371.4mg/L,far higher than the alkali /acid producing group 1665.3mg/L ultrasonic anaerobic fermentation,which indicated that the quality and quantity of SCOD produced by pretreatment is very important to the efficiency of anaerobic fermentation and acid production.Protease hydrolysis and EDTA-2Na hydrolysis have little effect on the size of sludge floc.synergistic effect of protease and EDTA-2Na is more conducive to sludge hydrolysis and broken.The ability to strip EPS from sludge cells and depolymerize microbial micelles is stronger than protease hydrolysis and EDTA-2Na hydrolysis respectively.After being hydrolyzed by protease / EDTA-2Na,the diameter of the sludge less than 13?m accounts for 10%,while that ranks between 13~148?m accounts for 80%.The sludge becomes loose with the porosity increasing which improve the biodegradability.The amount of SCOD released by adding protease and EDTA-2Na was far more than the sum of SCOD released by protease hydrolysis and EDTA-2Na hydrolysis respectively,so was the acid produced during anaerobic fermentation which suggests that there is a synergistic effect between protease and EDTA-2Na during protease /EDTA-2Na hydrolysis.During the proteolytic process,the remaining polymer in the sludge can be decomposed.However,protease may be retained and wrapped by EPS,resulting in low efficiency of SCOD release.EDTA-2Na can prevent protease from being trapped on the surface of sludge flocs,which enhanced dissolution of SCOD... |
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