Charging of Digesters
The two variants were charged into the 50L metal prototype digesters as originally weighed out. The wastes were charged up to ¾ of the digester leaving ¼ head space for collection of gas. The digester contents were stirred adequately and on a daily basis to ensure homogenous dispersion of the constituents of the mixture. Gas production measured in dm3/kg of slurry (35kg) was obtained by downward displacement of water by the gas.
Analyses of Wastes
Physicochemical analyses
Ash, moisture and fiber contents were determined using AOAC (1990) method [20]. Fat, crude nitrogen and protein contents were determined using Soxhlet extraction and micro-Kjedhal methods described in Pearson (1976) method [21]. Carbon content was carried out using Walkey and Black (1934) method [22], Energy content was carried out using the AOAC method described by Onwuka [23] while Total and Volatile solids were determined using Renewable Technologies (2005) method [24].
Biochemical analysis
The pH of the paper soaked in water was taken before charging of the waste while the ambient and influent temperatures of all the wastes were monitored daily throughout the retention period.
Microbial analysis
Total viable counts (TVC) for the wastes slurries were carried out to determine the microbial load of the samples using the modified Miles and Misra method described by Okore [25]. This was carried out at four different periods during the digestion; at the point of charging, at the point of flammability, at the peak of production and at the end of the retention period.
Statistical Analysis
The standard deviation was carried out using SPSS 15.0 version.