Improvement in the efficiency of hydrolysis of anaerobic digestion in sewage sludge by the use of enzymes
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The effects of enzymatic pre-treatment on a mixture of sludge (primary, secondary, digested) collected from different municipal wastewater-treatment plants was investigated by Batch experiments in the laboratory to enhance the hydrolysis of sludge. The experiments were carried out at mesophilic (37 degrees C) temperature. Six commercially available enzymes, supplied by Novo Industries, were used which ware Alcalase, Caresyme, Celluclast, Lipolase, Termamyl and Viscosyme. The experiment showed that with 50% digested sludge and 0.1% enzyme dosage of Carezyme and the mixed enzymes there was 11.5% and 10.6% decrease in volatile solids (VS), whereas with 25% digested sludge and 0.1% Viscosyme enzyme was very much effective for VS reduction compared with the blank (it shows 16.3% higher than blank). In another set of experiments, which differed in sludge characteristics with 25% digested sludge and 0.5% enzyme dosage the culture containing the mixed enzymes presents the highest percentage of VS reduction among all the samples (13.6% higher than blank), where with 25% digested sludge and 0.5% enzyme dosage of Termamyl and mixed enzymes show 13.5% and 12.8% greater VS reduction respectively compared with the blank. The experimental work showed that enzymatic pre-treatment can be successfully used as a pre-treatment step for treating sludge mixture produced from municipal wastewater treatment plant and the performance of individual enzymes largely depends on the characteristics of sludge.