Abstract:
Biogas generation is accomplished by anaerobic digestion of biodegradable materials in a
biogas digester. Anaerobic digestion being a quasi steady state process is amenable to
modelling for predicting process performance. Mathematical models for substrate
utilization and biogas production from anaerobic digesters described in this study were
used to predict biogas generation using experimental data.Two laboratory -scale digesters
of 0.01 and 0.005m3 capacities specifically developed for this study were monitored for
periods of about 60days. Samples were collected from these biodigesters weekly and
analysed in the laboratory for pH, Temperature (T), Biological Oxygen Demand (BOD),
Chemical Oxygen Demand (COD), Total Solids (TS), Volatile Solids (VS), Pressure and
viable counts. In addition, the biogas production rate was measured daily. Cow dung and
poultry droppings were used to assess the comparative performance of substrates and
digester sizes on biogas yield. Mathematical models for the prediction of biomass
degradation and biogas production in batch reactors were developed, calibrated and then
verified using four sets of experiments where cow dung and poultry dropping were
substrates. The predicted values of the substrate and biomass were close to the measured
values with coefficient of correlation, R = 0.926. Also, a comparative study was
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performed on the existing models for the prediction of gas yield. A modified version of
the time lag model was found to yield results closer the measured values than the rest of
the models. A mimeograph for sizing digesters for optimization of biogas production was
developed.
