Study On The Preparation Of Excess Sludge Compound Amino Acid By Enzymatic Hydrolysis And Compound Amino Acid Chelate Copper Derivatives

Excess sludge, produced in wastewater treatment plant, is an inevitable by-product of biological treatment process. An amount of the sludge has greatly increased due to more stringent environmental regulations. According to statistics, the annual production of excess sludge and dewatered sludge in China increased to64billion tons and11.2million tons, respectively. Furthermore, the treatment of excess sludge is reported as high as20%-45%of the total cost of wastewater treatment operation. For such a huge amount of sludge, the final disposal is harmless and resources treatment. It is not only turning the sludge into treasure, so that the environment is protected, but also conducive to social and economic development.According to reports, the crude protein content in the excess sludge is known to account for between30%and60%of the weight of dry sludge. For these rich resources of protein, some researchers have used methods to extract the sludge protein, such as physical, chemical and so on, but enzymatic extraction of sludge protein has been reported rarely. In this study, the digested and dewatered excess sludge of a wastewater treatment plant in Qingpu district of Shanghai was used as the main raw material. Firstly, the protein was extracted from excess sludge by enzyme hydrolysis, and the content of the protein was determined by Kjeldahl method to study the optimum conditions of protein extraction. Secondly, the extracted protein was further hydrolyzed by protease, and the optimum conditions were studied through the content of compound amino acid, which was determined by reversed phase high performance liguid chromatography (RP-HPLC) with precolumn derivatization. Finally, the synthetic condition of compound amino acid chelated copper from copper and compound amino acid were studied. The optimum conditions for the synthesis were found. The prepared compound amino acid chelated copper can be used as a third-generation feed additive, and has broad application prospects. The main conclusions of the experiments were as follows:(1) The pH and moisture content of the excess sludge were6.85and84.3%, respectively. There were six proteases including alkaline protease, papain, acid protease, neutral protease, pepsin and trypsin were used to extract the sludge protein in respective suitable hydrolysis conditions. The alkaline protease was selected as the optimal enzyme and the optimal hydrolysis conditions were studied. The results show that in the optimal condition of pH8, enzyme/substrate2%, hydrolysis temperature55℃, the ratio of liquid to solid4:1and hydrolysis time5.5h, the extraction rate of sludge protein was of52.4%.(2) There were five proteases including alkaline protease, papain, acid protease, neutral protease and pepsin were used to hydrolyze sludge protein in respective suitable hydrolysis conditions. The alkaline protease was selected as the optimal enzyme and the optimal hydrolysis conditions were studied. The results show that in the optimal condition of pH10, E/S9mg/mL, reaction time8h, and temperature55℃, the yield of compound amino acids was more than10g/100g dry sludge (DS). There were seven kinds of essential amino acids and ten non-essential amino acids in the hydrolyzate, and the yields were4.621and5.999g/100g DS, respectively. The concentrations of heavy metals in hydrolyzate were lower than standard of feed hygiene. So, it was concluded that extraction of amino acids from excess activated sludge by enzymatic hydrolysis proves to be high nutritional value and security.(3) The synthetic condition of compound amino acid chelated copper from copper and compound amino acid were studied. In the optimal condition of pH6, reaction time6h, hydrolysis temperature60℃and the molar ratio of ligand of compound amino acid to coppercation2:1, the chelation ratio was of35.96%. The chelating product, purified through alcohol wash, was testified by Na2S chemical method. The results show that the free amino acid did not exist in the purified chelating product, while it was appeared after adding an excess of Na2S in the chelate solution. In addition, the chelating product was analysed by IR. The results show that the absorption peaks of the amino group and carbonyl group of the composite amino acid appeared obvious redshift, from3441.27cm-1and1632.57cm-1move to3467.03cm-1and1638.08cm-1. So, it was concluded that the compound amino acid chelated copper was obtained.