Research On Sludge Hydrolysis Using Immobilized Enzyme Technology

With the development of urbanization process and the continuous improvement of people's living standards,the demand for water has also been an upward trend.The workload of sewage treatment plant is growing,resulting in more and more excess sludge.The treatment of sludge is a huge problem at home and abroad.If it is handled improperly,the sludge will cause secondary pollution to the environment.The current widely-used physical and chemical methods have the defect of high cost and low efficiency.The residual sludge has a high moisture content,which sometimes reaches 99%.So sludge dewatering is an important part of sludge treatment.How to quickly and effectively reduce the sludge moisture content has been a key issue at home and abroad research.EPS is the polymer organic compounds secreted by the microbial organism in the sludge under certain conditions.The main component is protein and polysaccharide.EPS is the main cause of sludge loose floc structure.Water will be tightly adsorbed by protein and polysaccharide in EPS,leading to dehydration performance decline.Therefore,reducing the EPS content in the sludge,destroying its floc structure and releasing the water in it will play a positive role in improving the sludge dewatering performance.The use of enzyme on residual sludge hydrolysis has the advantages of high catalytic efficiency,low pollution,low energy consumption and simple operation.But there are some defects that free enzyme cannot be recovered and the cost is high.In order to solve these defects in the use of enzymes,academics began to try a variety of reusable enzymes technologies and increase the applicability of the enzyme.Among these,enzyme immobilization has the best application scenarios and prospects for industrialization.The immobilized enzyme has many advantages:?1?The efficiency is high,the cost is low and the specificity is strong;?2?The substrate is easy to be separated from the enzyme.Product quality and recovery rate is improved,which increase the yield of the product;?3?The enzyme can be used repeatedly;?4?In most cases,the stability of enzyme is improved.Its shelf life is also extended;?5?Immobilized enzyme has a certain mechanical strength.Substrate solution can be stirred or packed to facilitate the continuous and automation operation,easy to catalyze the reaction of the continuous and automated operation.Therefore,the current academic research on immobilized enzyme technology is more and more.A variety of carrier production technology and enzyme immobilization technology is arising from this.In this study,cellulose-based nano-Fe₃O₄ is chosen as carrier,alkaline protease and ?-amylase is chosen as catalyst,and glutaraldehyde is chosen as cross-linking agent.The production of magnetic recyclable immobilized enzyme can greatly reduce the cost of sludge hydrolysis.The aldehyde group in glutaraldehyde and the amino group in protein can be stably crosslinked by coupling.The immobilization effect of nanometer Fe₃O₄ was investigated by investigating the enzyme activity and enzyme recovery rate of immobilized enzyme under different conditions.Then,the effect of sludge hydrolysis is determined by COD,NH₄⁺-N,reducing sugar and VSS.The details are as follows:?1?100 mL of 0.3 mol / L FeSO₄ solution and 0.15 mol / L Fe2?SO4?3 solution were mixed into a 500 mL beaker at a molar ratio of 1: 1 and placed in a 65 ° C water bath,uniformly stirred.NaOH solution was used to adjust the pH of the solution to about 6.5.An appropriate amount of surfactant sodium oleate and sodium dodecyl benzene sulfonate was added and fully stirred after being reacted for 30 min.Then the product was transferred into water heat reaction vessel.The reaction temperature was set at 160 ° C and the reaction time was 6 h.The reaction was carried out by heating the reaction vessel.After the reaction is completed,the product is taken out,mechanically stirred for 30 min and ultrasonically dispersed for 30 min.Then it was washed with distilled water and acetone for several times.The supernatant was inverted.This process was repeated until the pH of supernatant reached 7.Then the solution should be mechanically stirred for 30 min,ultrasonically dispersed for 30 min,and finally collected with a magnet.?2?In order to ensure the dispersion of the carrier,preventing the agglomeration and oxidation of magnetic nanoparticles during immobilization process,the Fe₃O₄ should be modified.The production process is as follows:?1?Cellulose is dissolved in sodium hydroxide / thiourea / urea system under low temperature to produce 3% cellulose solution.300 ml of liquid paraffin and 20 ml of Span 80 were added to a three-necked flask and stirred at 20 ° C for 45 min.?2?1g of Fe₃O₄ was added into 15 ml deionized water for 15 minutes.Then 40 ml cellulose solution was added to it and mechanically stirred.When it was ended,the suspension was added to the three-necked flask with a burette in one hour.Then the emulsification was continued for 5 hours.?3?After the end of emulsification,the pH of system was adjusted to 7with dilute hydrochloric acid.And then it was stratified.The supernatant liquid was poured out.The remaining solid was repeatedly washed with acetone,ethanol and deionized water.?3?Glutaraldehyde is used as cross-linking agent.Alkaline protease and ?-amylase was respectively immobilized under 25?.The immobilization effect of two enzymes was investigated under different enzyme concentrations,glutaraldehyde concentration,crosslinking time,enzyme adsorption time,temperature and pH.The activity of alkaline protease was determined by Folin-phenol method.The enzymatic activity of amylase was determined by DNS method.The enzyme recovery rate was calculated by the difference method after the amount of residual enzyme was determined by Coomassie brilliant blue method.?4?The immobilized enzyme was put into the sludge for oscillation reaction.after 4 hours,the sludge supernatant was taken to detect each indicators.COD was determined by potassium dichromate precipitation method.NH₄⁺-N was determined by Nessler 's reagent spectrophotometry.Polysaccharides were determined by anthrone-sulfuric acid method.The hydrolysis effect was determined by comparing the indexes before and after the hydrolysis of the sludge.