Effect of moisture content on the heating profile in composted broiler litter

Moisture content can affect the magnitude of heat generation during composting. Temperature was recorded every 2 min for 7 d at 10-cm increments throughout the vertical profile of broiler litter treated with five quantities of water addition. Water additions were applied to achieve litter moisture contents of 25, 30, 35, 40, and 45% MC w.b. Broiler litter moisture content between 30 and 35% was found to provide maximum heat generation during composting. Mean maximum temperature across all treatments was highest at the 10 and 20 cm litter depths. No moisture content treatment generated temperatures of required durations to meet all aspects of the EPA 503b rule for class B compost standards. Populations of total culturable aerobes, total culturable anaerobes and total culturable coliforms were enumerated in raw litter (time 1) and in treated litter after 84 h of composting (time 2) to determine if changes in population density were apparent. Over the 84 h composting period, a 4-log 10 reduction in aerobes and coliforms was found for litter samples where a temperature of 40°C was sustained for as little as 4 h. Populations of total culturable anaerobes were reduced from time 1 to time 2, though the reduction was not physiologically relevant. The results demonstrate that incorporation of water to achieve a litter moisture content between 30 and 35% provides for greater heating during litter composting. Published time-temperature goals for pathogen reduction may not be achievable even with the added moisture, though relevant reductions in total culturable aerobes and coliforms were demonstrated with 84 h of composting.