Optimization of C/N ratio for Mesophilic anaerobic digestion from food wastes found in Nairobi a lab-scale case study

Abstract

Extensive work has been done on Anaerobic digestion of single substrates and using codigestion. In a number of cultures around the world, the wastes that are discarded as household waste may not easily fit in the biogas models that have been developed so far. It is therefore necessary to analyse the biogas produced from food mixtures found in unique settings and compare them with literature values of individual substrates. In the current study, food mixture found at waste bin at a cafeteria used by StudentsofUniversity of Nairobiwas analysed. The purposes of this study were to investigate adjusted modes of substrate pretreatment (Mechanical, thermal and thermo-chemical) and their role in maximizing the process of anaerobic digestion through speeding up hydrolysis. The experiments were carried out on waste samples consisting of carbohydrate food waste (ugali+Rice),potato peels, banana peels and a mixture of the substrates mixed with rumen slurry in the ratio 3:1 under controlled mesophilic anaerobic conditionsin the lab scale digester. Thermo-chemical pre-treatment was the most effective for speeding up hydrolysis with the co digested substrates producing maximum biogas. The desired C:N ratio of 31 was obtained when all the four substrates were combined. Similarly, the biogas produced from the mixture of the four substrates was higher than from any of the substrates.