Reducing gaseous emissions during sludge composting: influence of the physical structure of the mixture

According to industrial Sludge composting fast and recent development in France and to increasing sensitivity addressed to odour and GHG emissions, one of the three tasks of the ANR labelled ESPACE R&D program has been focused on the study and reduction of gaseous emissions during sludge and refuse composting. This paper describes the protocol and main results of 300 l pilot reactor composting trials comparing odorous and GHG emissions of different and more or less humid mixtures of one slaughter house sludge feedstock with different sizes of pre-screened bulking agents (recycled rejects and fresh shredded wood pallets). 2 odorous compounds specific emissions : dimethyl disulfide (DMDS) and ammonia are considered and commented. It is shown that 20-40 mm bulking agents and initial moisture of about 50% lead to better composting behaviour and to lowest emissions. GHG emissions (CH4, N2O) only occur with mixtures using bulking agents < 20 mm and presenting initial too high moisture and density.