Methane production using rabbit residues

At the rabbit farms of Tlaxcala, Mexico two residues are produced: a mixture of sawdust with rabbit manure and urine (R₁) from the hatchery area, and the viscera (R₂) from the slaughter process. In this work, the anaerobic digestion (AD) process of such residues was evaluated to define the conditions at which they can be used to produce an alternative energy source. Methane content of the biogas produced was assessed in four stages. The first stage was the co-digestion of R₁ and R₂ inoculated with different manures: cow (A), pig (B) and goat (C), in order to select the residue-manure pair to be used. At stage two, the treatment which performed better at the previous stage was selected to evaluate the effect of pH adjustment to 7.2 and/or a C/N ratio to 23/1; during the third stage, it was evaluated the impact of internal temperature (ambient temperature and 37°C) and the addition of two carbon sources (oat straw and sawdust) on the methane content of the biogas produced; and finally, at stage four, the addition of micronutrients (step 4) over methane production was assessed. It was found that anaerobic digestion of rabbit entrails inoculated with 10% of goat manure generated the highest production of biogas with a 71% methane content; which was achieved by adjusting the process parameters (pH 7.2, C/N ratio to 23/1, internal temperature to 37°C and addition of micronutrients). Statistical analyses showed that temperature was the parameter that had the greatest effect on the methane content of the produced biogas; adding micronutrients reduced the lag-phase and helped to achieve 45% of methane in the biogas (minimal value required to be flammable); and, replacing sawdust by oat straw had no significant effect on the production of biogas or methane content.