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

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 O 2 consumed per g organic matter and hour) 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 38.3ºC 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.

The use of composting for the treatment of animal by-products: Experiments at lab scale

“…Gea et al [25] observed that fat degradation has an important role in the preservation of high temperatures in the reactor with higher fat contents resulting in longer processes. However, in this case a more stable product was obtained in a shorter time from an initial material with higher fat content indicating thus that the control strategy used effectively improved the process despite the higher fat content.…”

Enzyme Dynamic in Plant Nutrition Uptake and Plant Nutrition

“…They focused in particular to phosphatase and dehydrogenase activity [121]. Focusing more on the fats mixtures and the effect of lipase on co-composting sludges, Gea et al [122] reported 85% reduction in fat content, with an initial fat content of 30%. The authors note that due to hydrophobic nature of the fats, the moisture content needs to be maintained above 40%.…”

Immobilization of Enterobacter aerogenes E13 strain culture medium, distinguished by its lipase activity, in the ethylcellulose microcapsules

“…The preparations with lipasic activity can be used for the treatment of oil waste [8][9]. By using immobilized lipa sic preparations it's possible not only to degrade oil waste, but also to recycle it into biofuel [10,11], biooil and other compounds [12,13].…”