Experimental Procedure
The yam peels, plantain peels and orange rind were chopped into smaller sizes (< 4 mm sieve size) to facilitate digestion. Each of the food waste was measured and poured into the mixing tank which contained cow dung (about 60% of the digester volume) and then stirred to ensure homogeneity.The homogenous mixture of food waste and cow dung slurry was then introduced into the digesters and hermetically sealed. Manual agitation was performed on the digester on a daily basis in order to ensure intimate contact between the micro-organisms and the substrate for effective biogas production. The schematic diagram of the set-up is as shown in Figure 1. The water tank was filled with water to its brim. The gas produced by the substrates inside the anaerobic digester was channeled to the water tank on which two separate holes were drilled at the top, two rubber hoses were inserted in the holes, the first one (1000 mm in length and 7 mm in diameter) was used to connect the digester while the second (800 mm in length and 7 mm in diameter) was used to connect the water collector. The weight of gas produced was equivalent to the amount of water displaced in the water chamber (Archimedes’ principle of floatation). The displaced water was collected in the water collector. The volume of water displaced in the water collector was measured daily (between 2 pm and 3 pm) using a measuring cylinder. A hole was bored at the bottom of the digester where the thermometer probe was fitted tightly with a rubber cork. The temperature reading was taken between 2 pm and 4 pm daily throughout the period of the experiment. The pH was measured weekly using a digital pH meter. The sample analyzed was collected in a dry bottle from the digester and then analyzed. The probe of the pH meter was immersed into the sample to be analyzed and the meter was allowed to stabilize before the reading was taken. Each treatment was replicated three times. Figure 2 shows a cross-section of the experimental set-up.