Study On Extraction Of Protein From Sludge By Thermal Pre- Treatment-assisted Enzymatic Hydrolysis

With the acceleration of urbanization,the number and scale of sewage treat-ment plants are increasing,and the amount of excess sludge is increasing day by day,so treatment of sludge is an urgent problem to be solved.The residual sludge con-tains a large amount of organic matter,and its protein content can reach30%⁶0%?relative to dry sludge?,extracting protein from the residual sludge has became a new way of sludge resource utilization.Compared with acid thermal method and alkaline thermal method for protein extraction,the enzymatic hydrolysis method not only has mild reaction conditions,but also has no secondary pollution to the environment,but its extraction efficiency of protein is low.Therefore,thermal pretreatment-assisted alkaline protease hydrolysis sludge by for protein extraction was studied,and the sludge dewatering performance and sludge composition after hydrolysis were analyzed,the main conclusions are as follows:?1?The protein extraction rate and specific resistance to filtration?SRF?after sludge hydrolysis were taken as analysis indexes,and the optimal conditions of thermal pretreatment-assisted alkaline protease hydrolysis sludge for protein extrac-tion which were obtained through single factor and response surface methodolo-gy?RSM?were as follows:thermal pretreatment temperature 105?,time 3h;initial pH 10.5,enzyme reaction temperature 55?,reaction time 3h,enzyme dosage3000U/g dry sludge,and sludge moisture content 95.5%.Under these conditions,the protein concentration was 11277mg/L,the protein extraction rate was 56.48%;and the solubility of chemical oxygen demand?SCOD?concentration and dissolution rate were 16800mg/L and 52.57%respectively;and SRF was 3.387×10⁹s²/g,the de-watering performance of sludge was 62.73%higher than that of raw sludge.Mean-while,compared with the sludge hydrolysis by enzyme alone,the protein concentra-tion in sludge supernatant was increased by 43.6%,and SRF was reduced by 22.5%.?2?Under the optimal conditions,the changes of protein concentration during the hydrolysis of sludge catalyzed by thermal pretreatment-assisted enzyme were analyzed and compared with that of sludge hydrolyzed by enzyme alone.The results showed that the first 3h reaction of sludge hydrolysis catalyzed by thermal pretreat-ment-assisted enzyme accorded with the first-order reaction kinetics,whose equation is:=₀0)^-0.179,and its hydrolysis rate constant?k_h=0.179?was more than 2 times higher than that of the single enzyme method?k_h=0.048?,indicating that thermal pre-treatment could effectively improve the rate of sludge hydrolysis.?3?The thermal pretreatment-assisted enzymatic method was compared with acid thermal method,alkaline thermal method,enzyme method,ultrasonic-assisted enzymatic method from three aspects:sludge hydrolysis efficience,drug consump-tion and energy consumption in hydrolysis process,changes of sludge composition after hydrolysis.In terms of extraction efficiency,the chemical hydrolysis meth-od?acid thermal method and alkaline thermal method?had the highest protein ex-traction rate,but its energy consumption was 50%higher than that of biological hy-drolysis method?enzyme method,thermal pretreatment-assisted enzymatic method and ultrasonic-assisted enzymatic method?.Compared with the enzyme method,the protein extraction efficiency of thermal pretreatment-assisted enzymatic method and ultrasonic-assisted enzymatic method could be improved by more than 30%,and their protein extraction rates were similar.Considering that the thermal treatment equipment is relatively mature and has more engineering application prospect,the thermal pretreatment-assisted enzymatic method can be used as one of the effective methods for sludge protein extraction.?4?Further comparing the components of sludge supernatant and residue ob-tained by different hydrolysis methods,it could be seen that the chemical method was more thorough in the hydrolysis of sludge.The content of amino acids and pep-tides was analyed and it was found that amino acids content of enzymatic hydrolysis produced by enzymatic and ultrasonic-assisted enzymatic was higher and their pro-tein products were suitable for animal feed and liquid fertilizer;the peptide content of thermal pretreatment-assisted enzyme method is higher,and its protein product was more suitable for protein foaming agent.