Co-composting of sewage sludge:fats mixtures and characteristics of the lipases involved

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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. © 2006 Elsevier B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)275-283
    JournalBiochemical Engineering Journal
    Volume33
    Issue number3
    DOIs
    Publication statusPublished - 1 Mar 2007

    Keywords

    • Aerobic processes
    • Biodegradation
    • Fat
    • Lipase
    • Respiration index
    • Waste treatment

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