**2.2. Waste from livestock**

Livestock raised in very large confined animal feeding operations generate an enormous amount of manure, which can be used for bioenergy, but also frequently pollute water supplies in many locations. Fortunately, on the smaller end of the livestock production scale, farmers convert manure into biogas with the aid of anaerobic digesters resulting in both economic and environmental paybacks. The biogas can be employed to provide heat and power on the farm, or it can be further purified and sold as renewable natural gas for use elsewhere. Prospect of anaerobic digesters for biogas production from manure can enhance water quality, reduce obnoxious greenhouse gas from manure, and assist farmers to fixate nutrients to the soil. In the United States, reports show that almost 60 million tons of manure can be adopted to produce bioenergy in 2030 [8].

This resource is best used close to where livestock produces it, and would ideally be integrated with crop production. Crop residues do not usually appear in official statistics hence an estimate of the amount of crop residues produced are usually deduced based on production data [19, 20]. Available data for processing residues is generally poor, due to a wide variety of processing techniques producing an array of different stocks of residues [21, 22]. The ratio between main product and residue vary depending on a set of factors including variety, moisture content, nutrient supply, and use of chemical growth regulators among others. In reality, there are factors which limit the use of certain residues for bioenergy production such as scattered abundance, technical constraints, ecosystem functions, and other demands such as animal fodders, fertilizer, domestic heating, and cooking for which the application of the resource is being explored for.

Bentsen et al., presented a report relative to the production data of some crops which were combined with the residue-to-product ratios (RPR) of the different crops to obtain the amount of residues for each annual crop and from perennial plantation crops. The analysis showed that the estimated total amount of crop residue that is potentially available for energy was 150 million tonnes. Using 30% conversion that is typically obtained in biomass to energy conversion systems efficiency and the heating value data, these residues can generate about 0.60 EJ, which is equivalent to 34% of the current energy consumed in Nigeria.
