Chemical Hydrolysis For Protein Extraction From Thickened Sludge And Its Dewatering Profile

Recently,more and more concern about sludge disposal was caused with the continuous development of urbanization and the resultant increasing of sludge production.Improper treatment and disposal of sludge would cause secondary pollution to the environment and endanger human health.According to the guiding ideology of green economy and circular economy,a new idea of recycling reclamation of sludge was proposed.In this paper,the thermo-alkaline,the thermo-acid and the ultrasonic-alkali coupling method were studied,respectively to expolore the the effect of protein extraction form excess sludge and the influence on the sludge dewatering performance.Meanwhile,the optimal conditions of protein extraction was obtained,and the application prospect of the this technology was analyzed correspondingly.The results are as follows:(1)In using the thermo-alkaline method,the influence of initial pH,temperature,hydrolysis time and sludge moisture content were first studied.The impact degree was as follows: initial pH > temperature > sludge moisture content > hydrolysis time,and the optimum operating conditions were pH = 12,T = 120 ?,W = 92% and t = 4h.Under this condition,the protein concentration in the supernatant was about 22019.4mg/L,which was 45.1 times higher than that of the control,and the protein extraction ratio was 88.3%.Meanwhile,the dehydration performance was increased by more than 90% with the sluge specific resistance being about 1.4×109S2/g.The test of forming performance of resulting sludge protein solution revealed that forming performance is correlated to the protein content,especialy the peptide content in the protein solution.Under the optimized conditions,the 450% of foaming degree and 85% of form stability was observed with the polypeptide concentration about 6600mg/L,and it could meet the commercial standard of the foam extinguishing agent and the concrete foaming agent.(2)In using the thermo-acid method,the influence of initial pH,temperature,hydrolysis time and sludge moisture content were first studied.The impact degree was as follows: initial pH > temperature > sludge moisture content > hydrolysis time,and the optimum operating conditions were pH = 0.5,T = 130 ?,W = 92% and t = 4h.Under this condition,the protein concentration in the supernatant was about 30432.6mg/L,which was 62.8 times higher than that of the control,and the protein extraction ratio was 92.15%.Meanwhile,the dehydration performance was increased by more than 99% with the sluge specific resistance being about 0.66×108S2/g.The test of forming performance of resulting sludge protein solution revealed that forming performance is correlated to the protein content,especialy the peptide content in the protein solution.Under the optimized conditions,the 650% of foaming degree and 88% of form stability was observed with the polypeptide concentration about 13800mg/L,and it could meet the commercial standard of the foam extinguishing agent and the concrete foaming agent.(3)In using the ultrasonic-alkali coupling method,the influence of initial pH,power density,ultrasonic time and sludge moisture content were first studied.The impact degree was as follows: initial pH > power density > sludge moisture content > ultrasonic time,and the optimum operating conditions were pH = 12,power density = 1.67W/mL,sludge moisture content = 92% and ultrasonic time = 4h.Under this condition,the protein concentration in the supernatant was about 10857.7mg/L,which was 19.4 times higher than that of the control,and the protein extraction ratio was 57.2%.Meanwhile,the dehydration performance was increased by more than 93% with the sluge specific resistance being about 1.2×109S2/g.The test of forming performance of resulting sludge protein solution revealed that forming performance is correlated to the protein content,especialy the peptide content in the protein solution.Under the optimized conditions,the 350% of foaming degree and 80% of form stability was observed with the polypeptide concentration about 3280mg/L,and it could meet the commercial standard of the foam extinguishing agent and the concrete foaming agent.(4)Based on the comprehensive analysis of the extraction effects and economic costs of the thermo-alkaline,the thermo-acid and the ultrasonic-alkali coupling method on protein extraction,it was concluded the thermo-alkaline is more practical in engineering.In comparison with the living example,this technology has a broader application prospects for it further improved the protein extraction and demonstrated the impact on the sludge dewatering performance.