Comparative Study on Ignition Time of Biogas from Cattle Dung and Mixtures of Cattle Dung with Cassava Peels

This paper investigated the ignition time of biogas from cattle dung and mixtures of cattle dung with cassava peels. The cattle dung was sourced from FUTA agricultural farm and cassava peels from a gari processing farm in Akure. The cassava peels was mashed before mixing with the cattle dung. The substrates were charged to four digesters each with a radius 0.173 m, 0.66 m high and 2 mm thick. 8 kg of cattle dung was mixed with equal mass of water and charged to the first digester; the second digester was charged with 1 kg cassava peels and 7 kg cattle dung; the third with 2 kg cassava peels and 6 kg cattle dung while the fourth digester was filled with 4 kg each of cassava peels and cattle dung. The substrates with water were made to two-third the volume of each digester before they were closed gas tight and then subjected to anaerobic digestion for 55 days in an open workshop in FUTA. Biogas from each digester was daily tested for combustion. The pH of the substrates was measured with digital pH meter before they charged to the digesters for incubation. That of the effluent was determined after the biogas was tested for ignition and the volume measured. Biogas from each digester was measured by water displacement method. Ambient and digester temperatures were also daily monitored at 10 a.m. and 4 p.m. using mercury-in-glass thermometer already installed on top surfaces of the digesters. The biogas from the first digester ignited with a blue flame on day 14, while the one obtained from digester 2 ignited on the 27th day of incubation. Biogas from the 3rd digester ignited on day 48 as that from 4th digester got ignited on the 55th day of incubation. The ambient and digester temperatures in the mornings were generally lower than those for the evenings for the days of incubation. On cold days, as a result of rainfall or cloud formation, the morning ambient and digester temperatures fell below even morning environmental temperatures. It showed that cattle dung produced biogas earlier than the mixture of the two wastes and the combustion time increases with increase in the mass of cassava peels in the mixture. The PH for cattle dung slurry and those of the mixtures in order of increasing mass of cassava peels were respectively 6.9, 6.6, 6.4 and 6.3 while the pH of the effluents are 7.12, 7.16, 7.14 and 7.21. The volume of biogas in the same order were 4500 ml, 5200 ml, 5400 ml and 6500 ml.Keywords: Ignition time, cattle dung, mixture, cassava peels, biogas