The higher volume gas produced by Digester A may be due to higher nitrogen content in poultry droppings as compared to other feedstocks (Ojolo et al., 2007b). Also, the higher biogas production from poultry droppings could also be attributed to large amount of available nutrients presented
in the droppings. According to Hill and Brath (1997) substrates should contain adequate amount of carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorous, potassium, calcium, magnesium and a number of trace elements. Average biogas production from digesters A, B and C were 3.84, 3.55 and 3.19 mL/day. Analysis of variance and test of significance were carried out to test for significant differences in biogas production in digester. Thus, any of the three designs may have been appropriate for the experiment. The cumulative biogas yield from 450 g (1:0.5 waste to water ratio) slurry of poultry and cattle dung digested over a period of seven days at room temperature was found to be 26.86, 24.86 and 22.30 mL at thermophillic temperature (370C). Mixing or shaking the digester is very important as it prevents scum formation within the digester. The main disadvantage of
poultry manure is that it produces a proportion of hydrogen sulphide, which even when present in only
small proportions, corrodes metal fittings.