THE EFFECTS OF INDIGENOUS CATALYTIC ADDITIVES ON QUANTITY AND QUALITY OF BIOGAS AND BIO-SLURRY PRODUCED FROM UNCOOKED KITCHEN WASTES

Abstract

Biogas production in third world countries is still un-optimized and produce very minimal outputs. Optimization of biogas quality by increasing the temperature of the bio-digester is quite technical. On the other hand, commercial enzymes used to increase biogas quantity are also expensive and substrate-specific. T. brownii and Acanthaceae spp. extracts were successfully used to hasten saccharification and fermentation of cellulose during the preparation of traditional alcohols. This study aimed at exploiting the potentials of these indigenous extracts in catalyzing biogas yields, methane levels, and bio-slurry plant nutrients. The additives and kitchen waste substrate were characterized for possible biocatalytic and anaerobic digestion properties. A 28-day retention period was used. The Acanthaceae spp. extracts had more bio-metal concentration while the T. brownii extracts exhibited more organic compounds. The order of biogas output was T. brownii (15861.4ml/gVS); Acanthaceae spp. (13219.6ml/gVS) and the control (7444.8ml/gVS) at an average temperature of 19.5±0.5°C over the 28-day retention period. Methane levels were in the order of T. brownii (43.375±0.922%), control (41.750±1.401%) and Acanthaceae spp. (39.275±0.263%) on retention day-28. The Inferior Calorific Power (ICP) of the biogas systems increased over the retention time. The ICP values on retentionday 28 were 3538.86 Kcal/Kgbiogas (T. brownii), 3196.98 Kcal/Kgbiogas (Acanthaceae spp.) and 3398.45 Kcal/Kgbiogas (control). T. brownii bio-slurry had more lime content, total Kjehdahls nitrogen, total sulfur, total phosphorus, total phosphoric acid and soluble silicic acid. The Acanthaceae spp. bio-slurry had more calcium, potassium, nitrates, total ammoniacal nitrogen, sulfates and phosphates. The additives were proven to increase biogas yields, methane levels and available plant nutrients showing their viability to optimize biogas systems.