Process Conditions Influence on Pig Slaughter House Compost Quality Under Forced Aeration

Abstract

The objective of this paper was to study the influence of process conditions (aeration rate, bulking agent (BA) particle size distribution, BA incorporation ratio and process duration) on the quality (moisture, stability, disinfection as per the temperature regime and nitrogen conservation) of mechanically aerated pig slaughterhouse sludge (PSS) compost. The waste and wood chips as BA were composted in 300 L mechanically aerated reactors. The range of process conditions tested were: aeration rate from 1.68 to 13.04 L/h/kg of wet sludge; BA particle size distribution of <10 mm, 10–20 mm and 20–30 mm, and; BA:PSS incorporation ratio of 0.55–1.11 (kg of wet wood chips/kg of wet sludge). The results showed that a high aeration rate and a high BA:PSS ratio produced a faster stabilization whereas BA of small particles size distribution increased the amount of biodegradable matter and slowed down stabilization. The composting temperature regime was positively correlated to O2 consumption with a high BA:PSS ratio and a small BA particles size. A low aeration rate, without being O2 limiting, optimized the composting process since too high or too low an aeration rate favored heat losses through respectively convection and water evaporation. Water loss was positively correlated with temperature regime and a higher BA:PSS ratio as opposed to a small BA particle size distribution. Similarly, medium to high aeration rates favored water removal. The composting process duration was reduced with a high aeration rates of 6.22 or 9.8 L/h/kg of wet sludge and a high BA:PSS ratio of 1.11. Finally, process condition had no influence on compost nitrogen conservation.