Experimental Investigation Of Upflow Bioreactors With Central Substrate Dispenser

ABSTRACT

Experimental investigation of anaerobic digestion of the organic fraction of municipal solid waste (MSW) in an upflow bioreactor with central substrate dispenser (UBCSD) is presented. The UBCSD consists of two similar size bioreactors joined by a central substrate dispenser (CSD). The UBCSD is a component of an integrated system of bioreactors also containing the upflow anaerobic sludge blanket (UASB) reactor and the continuous stirred tank reactor (CSTR), assembled systematically to achieve desired results. The UASB has an internal volume of 76litres, the UBCSD, 64.8litres and the CSTR, 76litres, respectively. The UBCSD utilized a CSD as its inherent feature to help generate an up-flow, down-flow and cross-flow pattern of the working substrate during its operation with a view to enhancing substrate mixing effectiveness. These reactors were fed with the slurry and allowed to run without interruption for a period of 10-days hydraulic retention time (HRT) at a mesophilic temperature of 370 C. Biogas production for each reactor was recorded every six (6) hours while the chemical oxygen demand reduction was measured daily. The UBCSD generated the highest level of cumulative biogas production with the value of 52915 ml, while the UASB and CSTR yielded 23550 ml and 28980 ml, respectively. UBCSD also yielded the highest percentage COD removal of 95.2%, followed by the CSTR with a value of 80.8%; while the UASB yielded the lowest percentage COD removal of 79.0%. The values for the first order kinetic constant (k) of COD which is a measure of the rate at which the substrate COD is reduced for UBCSD, UASB and CSTR were obtained as 0.2857, 0.147 and 0.1708, respectively, based on the modified Fenton’s first order model. With these results, it is deducible that the UBCSD is the most effective reactor amongst the three in terms of substrate stabilization and biogas production capacity. This is easily attributable to the central substrate dispenser for effective mixing of substrate during digestion.