After anaerobic digestion of excess sludge, dissolved organic matter is absorbed and used, but the treatment of refractory sludge is a headache. Oxidative acid (performic acid and hydrochloric acid) hydrolysis process can effectively prepare amino acids from refractory sludge. During the preparation process, insoluble proteins in sludge were turned into soluble proteins and peptides. All of them eventually hydrolyze into amino acids. The optimum conditions in the single factor experiment were as follows: the temperature of 110 掳C, the reaction time of 24 h, and hydrochloric acid (HCl) concentration of 6 M. The results showed that the maximum total yield of amino acids from refractory sludge was 94.76%. In the orthogonal experiment, the maximum total yield of amino acids was 97.20% under the optimum conditions of temperature of 113.45 掳C, the reaction time of 26.79 h, and 5.92 M HCl. The recovery rate of purity amino acids was 17.16 g per 100 g of dry sludge. The recovery rate of the hydrochloric acid was approximately 70%. There were 17 kinds of amino acids in the hydrolysate, which could be used as deodorants, food additives, preservatives and corrosion inhibitors. This new technology is expected to be very effective in the treatment of refractory sludge.
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