PRODUCTION AND PURIFICATION OF BIOGAS FROM COW-DUNG AND CASSAVA PEELS

This work investigated the anaerobic digestion of cow-dung and cassava peels, the effect of co digestion in biogas production and purification process for biogas upgrade. The biogas experiments were carried out in five different anaerobic digesters which contained cow-dung and cassava peels slurry in the (wt-wt%) ratios of (100:0), (75:25), (50:50), (25:75), (0:100) and were incubated for a 30-day period at ambient temperature. Combined absorption and adsorption process was used to purify and hence upgrade the biogas. Under batch conditions, the biogas was allowed to pass through aqueous solution of Ca(OH)2 to absorb CO2, activated carbon to adsorb H2S and silica gel to adsorb water vapor for a 20 – 240 minutes run time. The results showed that the (50:50) substrate produced the highest amount of biogas, 103.3-L cumulatively. Modified Gompertz, Logistic Growth and First-order kinetic models were used for the correlation studies of the experimental data obtained. The rate constants from each kinetic model show that the 50:50 substrate had the fastest production rate with 6.368 L/Kg/day, 0.2563/day and 0.03/day as the rates for the modified Gompertz, Logistic growth and first-order models respectively. The applicability of the kinetic models used was clearly revealed in the study with the high correlation coefficients obtained for each model, 0.99615, 0.9872 and 0.9501 being the correlation coefficients for the modified Gompertz model, logistic growth model and first-order model respectively. Test results proved that the purification process was time-dependent. CO2, H2S and H2O removal efficiencies increased from 31.9% to 93.1%, 21.7% to 94.9% and 45% to 96.7% for 20 minutes to 240 minutes batch time respectively. The high removal efficiencies prove the combined absorption and adsorption process as a very good method recommended for biogas purification.