Effect of Organic Loading Rate on Biogas Yields of Pig Slurry in a Continuously Stirred Tank Reactor at Mesophilic Temperature

Abstract

Renewable energy appears to be a way out of the associated challenges of the conventional sources of energy. One of these renewable sources is biogas. Biogas is the gas produced when anaerobic bacteria act on organic matters in the absence of oxygen. Anaerobic digestion has been considered as waste-to-energy technology. In this work, attempt was made to determine the effect of organic Loading Rate (OLR) on biogas production potential of pig slurry using a Continuously-Stirred Tank Reactor (CSTR) operated at mesophilic temperature (37oC). A 12-litre capacity CSTR was loaded with 8 litres pre-cultivated sludge as inoculum, leaving a free space for gas production. The loading of the calculated amount of pig manure into the reactor was commenced at a LR of 1.5goTS/l.d and was increased weekly by 0.5 goTS/l.d until an OLR of 5.0 goTS/l.d was reached. The biogas yields at OLR of 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 goTS/l.d were 0.255, 0.190, 0.170, 0.180, 0.170, 0.140, 0.120 and 0.140 m3/kgODM, respectively, with corresponding methane yields of 0.153, 0.12, 0.11, 0.11,0.11, 0.09, 0.08, and 0.09 lCH4/goDM. Biogas yield of 0.255m3/kgoDM was recorded as the highest at an OLR of 1.5 goTS/l.d. Summarily, pig manure was found to be best digested at OLR of 1.5 goTS/l.d in a CSTR at mesophilic temperature.