Co-composting of sewage sludge:fats mixtures and characteristics of the lipases involved |
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| Institution: | 1. School of Food Technology, Institute of Agricultural Technology, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand;2. Department of Food Science and Chemistry, College of Science and Mathematics, University of the Philippines Mindanao, Barangay Mintal, Davao City 8022, Philippines;1. College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi Province 712100, PR China;2. Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, PR China;1. Chinese Academy of Agricultural Engineering Planning and Design, No. 41, Maizidian Street, Chaoyang District, Beijing 100125, China;2. Key Laboratory of Technologies and Models for Cyclic Utilization from Agricultural Resources, Ministry of Agriculture, Beijing 100125, China;3. Key Laboratory of Energy Resource Utilization from Agricultural Residues, Chinese Academy of Agricultural Engineering, Beijing 100125, China;1. College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, PR China;2. College of the Environment & Ecology, Xiamen University, Xiamen 361102, PR China;1. College of Life Science, Northeast Agricultural University, Harbin 150030, China;2. Heihe Branch of Heilongjiang Academy of Agricultural Sciences, Heihe 164300, China;1. School of Municipal and Environmental Engineering, State Key Laboratory of Urban Water Resource and Environment (SKLUWER), Harbin Institute of Technology, 73 Huanghe Road, Harbin, Heilongjiang 150090, China;2. Residues and Resource Reclamation Centre, Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore 637141, Singapore;3. Polymer Materials Research Center, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China |
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| Abstract: | Co-composting of sewage sludge and animal fat mixtures was studied in order to determine the possibility of using this technology to recycle fat-enriched wastes. A maximum fat content of 30% in fat:sludge mixtures is recommended to achieve the international sanitation requirements on compost quality and to avoid an excessive thermophilic composting time. Under these conditions a fat content reduction of 85% was achieved. Biological activity was highly dependent on the moisture content as shown by the respiratory quotient values. Moisture content is a critical control factor because of the hydrophobic nature of fats and should be maintained above 40% in the composting of fats. Biological indices of the compost obtained after 69 days of process (maturity grade: IV; respiration index: 1.1 mg O2 g OM?1 h?1) indicated a high stability and maturity degree of the material. Lipases responsible for fat hydrolysis were monitored during the composting process and a sample from the thermophilic period was characterized in terms of stability in front of pH and temperature. Optimal conditions for lipase stability were found at 38.3 °C and pH 7.97, however, the maximum lipolytic activity was observed at thermophilic temperatures. Lipases from the thermophilic period were purified by anion exchange chromatography and visualised by SDS-PAGE. Two major bands were observed at molecular weights of 29 and 62 kDa. These bands could not be identified precisely by N-terminal sequence analysis. |
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