Study On Thermal Alkali Hydrolysis Of Waste Activated Sludge Based On Protein Recovery

With the continuous expansion of scale of urban sewage treatment plant,the output of byproduct sludge has been increasing,which has become one of the main problems of sewage treatment plants.Excess sludge was riched in organic matter,such as proteins,polysaccharides,nucleic and so on.Among them,proteins accounted for about 50% of the dry weight of cells.If the protein in sludge can be recycled and used on the basis of hydrolysis,the waste can be realized in the real sense,and the excess sludge reduction,harmless and resource can be realized.In this paper,taking a sewage treatment plant in wuxi city binhu district after digestion and dewatering of sludge as treatment object,the protein dissolution rate of sludge as the index,In research the thermal acid and thermal alkali hydrolysis for the effects of the dissolution protein of excess sludge,on the basis of research of composite enzymatic hydrolysis of protein dissolution effect,getting the best technology of sludge dissolubility protein hydrolysate,using standard of sludge protein and polysaccharide(bovine serum albumin and cellulose),studying its during hot alkali hydrolysis of dissolution,transformation and degradation rule,provide technical support for excess sludge recycling.The main conclusions of the research are as follows:(1)When the sludge concentration was 30 g/L,at p H 1.0 and the temperature was 125oC under the condition of thermal acid hydrolysis for 6.0 h,rotein dissolution rate was the best effect,the supernatant protein concentration and the dissolution of protein was 1686 mg/L and 24.01%,respectively.Under the optimum hydrolysis condition of thermal acid,There were still 53.43% in sludge residue,at the same time proteins were broken down or converted to other small molecules,only 24.01% existed in the form of soluble protein,(2)When the sludge concentration was 30 g/L,at p H 12.5 and the temperature was 80oC under the condition of thermal acid hydrolysis for 3.0 h,rotein dissolution rate was the best effect,the supernatant protein concentration and the dissolution of protein was 2436 mg/L and 42.24%,respectively.Compared with thermal acid,the effect of thermal alkaline hydrolysis was better,and the rate of sludge proteins was higher,more than 18.23%.At the same time,the hydrolysis time of thermal alkaline hrdyolysis was shorter and less costs.(3)When the sludge concentration was 30 g/L,the composite enzyme(alkaline protease,papain = 1:12)dosage was 1%,at p H 7 and the temperature is 55oC under the condition of enzymatic hydrolysis for 2 h,and then at p H 12.5 and temperature was 90oC under the condition of alkaline thermal hydrolysis after 1.5 h the residual sludge,protein dissolution rate was the best effect,the supernatant protein concentration and the dissolution of protein was 6050 mg/L and 84.33%,respectively.(4)During the hydrolysis temperature rised from 80°C to 100°C,cellulose hydrolysis for the reaction of reducing sugar increased,cellulose caramelization reaction did not occur.When the hydrolysis temperature rise to 100°C,compared with 80°C,the maillard reaction occurred more easily,thus affect the purity of protein and the recovery of protein.And based on this condition,thermal alkaline hydrolysis of excess sludge protein dissolution rate was 67.59%.There are still 32.41% in sludge residue.36.64% exists in the form of soluble protein,30.95% proteins are broken down or converted to other small molecules,such as polypeptide,amino acid,ammonia nitrogen,nitrate nitrogen,volatile fatty acid,and an unknown substance,and be converted into small molecules of protein.