EFFECT OF CO-DIGESTING PRETREATED CHICKEN - GOAT AND UNTREATED COW MANURE ON BIOGAS PRODUCTION IN FIXED DOME LABORATORY DIGESTER

Abstract

The effect of hydro, mechanical and thermal pretreatment of chicken and goat manure on biogas production was
done using a 0.15m3 laboratory scale batch digester. The feedstocks were subjected to 6, 12 and 18 hours of
soaking, 2 mm, 3 mm and 4 mm of mechanical mincing, and 60 ̊C, 80 ̊C and 100 ̊C of heating. Pretreated feed
stocks were co-digested with untreated cow manure from an extensive dairy rearing system. Experiments were
done at 8 % substrate total solids and a constant temperature of 35°C. Averagely, mechanical pretreatment
resulted in the highest increase in mean biogas production rate with 11.11%, over the co-digestion control (0.54
m3/m3d), followed by thermal and hydro by 5.56% and1.85%. Maximal increase in production for each
pretreatment was at 6 hour soaking time (9.30%), 3 mm effective feed stock particle sizes (18.52%) and 80 ̊C of
heating (14.81%). Co-digestion increased mean biogas production rate over mono-digestion by 68.97%
(chicken), 81.84% (goat) and 8.8% (cow manure). Superior outer cell wall and cover disruption of feed stocks
for easy hydrolysis advantaged mechanical pretreatment.