Effects of Organic Loading Rate on Biogas Yield in a Continuously Stirred Tank Reactor Experiment at Mesophilic Temperature

In this work, an attempt was made to study the effect of organic loading rate (OLR) on biogas yield using cow slurry as a single substrate at mesophilic (37°C) temperature in a long time experiment with Continuously Stirred Tank Reactor (CSTR). The reactor was loaded at OLR of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 goTS/l.d. Each OLR was maintained two (2) weeks before increasing it by 0.5 goTS/l.d. The experiment was run continuously for 140 days. It was observed that the biogas and methane yields decreased with increase in the organic loading rate after the reactor had attained stability. Both biogas yield and CH4 in the biogas decreased with the increase in OLR. For OLR in the range of 2.0 g (oTSl-1d-1) – 5.0 g (oTSl-1d-)1, biogas and methane yields obtained varied between 0.435 lN/g - 0.300 l/g and 0.251 lNCH4/goS - 0.165lNCH4/goS, respectively at mesophilic temperature. The biogas produced by cow slurry was found to have an average methane (CH4) content of 58%. It was concluded that organic loading rate has a decreasing effect on the biogas and methane yields in a continuously tank reactor experiment at mesophilic temperature. The kinetic model developed could be used for dimensioning CSTR digesting organic wastes.