ABSTRACT
Solid waste management and energy crisis are two of the major problems facing Nigeria. Nigeria’s high population generates large quantities of solid wastes. Nigeria with an estimated population of 186, 987,563 at present is the most populated country in Africa and 6th in the world. This population is expected to increase to 398,507,704 by the year 2050. With this increase, more solid waste will be generated and demand for energy will be high. Therefore, there is a need to develop a technology that can help to manage the generated solid waste in Nigeria and the same time produce green energy that is sustainable, thus, this study. An experimental design and preliminary tests using co-digestion of non-uniform multiple feedstocks typically available in Nigeria were conducted with operation and process parameters (i.e., organic loading rate, seeding, pH, carbon/nitrogen ratio, temperature, particle sizes, hydraulic retention time, stirring, percentage total solid and volatile solid) utilized in this study. An experimental three stage anaerobic digestion plant and a single stage fixed dome anaerobic digestion pilot plant were used. The fabricated anaerobic digestion plant was evaluated for performance using a known mass (i.e., 40 kg, 48 kg, 60 kg, 65 kg, 75 kg, 87 kg, and 95 kg) of substrate composition. The actual quantity of biogas yield and cumulative biogas yield were compared to the biogas yield and cumulative biogas yield predicted by artificial neural networks and modified Gompertz kinetic model. The results obtained reveal that unlike the single stage fixed dome anaerobic digestion plant, the three-stage continuous anaerobic digestion plant enables continuous production of biogas. Besides, optimum conditions of neutral pH range, mesophilic temperature range of 360C-370C, C/N ratio of 20≤CN≤30, %TS of 91.10%, and %TS of 10.16% that favoured optimum biogas yield were established. Also, for 40 kg, 48 kg, 60 kg, 65 kg, 75 kg, 87 kg, and 95 kg, the respective cumulative biogas yields were 3.40 kg, 3.550 kg, 5.00 kg, 5.370 kg, 6.510 kg, and 7.100 kg. The performance of the developed ANNs models was validated and the results obtained reveal the effectiveness of the model to predict biogas yield with a mean squared error (MSE) of best validation performance of 5.115e-004. Also, the R2 values of the training set, the testing set, the validation set, and the all data set were found to be high and close to 1, the values being 0.97193, 0.96510, 0.98378 and 0.97229 respectively. The results of modified Gompertz kinetic model showed high coefficient of determination (R2 ) (0.9630-0.9993) for each substrate composition (i.e., SC1, SC2, SC3, SC4, SC5, SC6, and SC7) used. The high values of coefficient of determination (R2 ), demonstrates the appropriateness of the modified Gompertz kinetic model for accurate estimation of anaerobic digestion of the substrate.
