Poultry litter to biogas: adding more value to farm waste

The benefits of using chicken litter as fertiliser are well known. As the poultry industry grows, however, other uses for it must be found. Dr Idan Chiyanzu and Primrose Magama of the Agricultural Research Council’s Institute for Agricultural Engineering explain how energy can be generated from litter.

Smaller poultry businesses, comprising mainly broiler and egg producers and suppliers of day-old chicks, are helping address the need for job creation. But this growing industry has a problem: how to manage the environmental impact of ever-greater volumes of poultry litter.

The premise of our research is that the industry needs to shift away from the direct use of litter as a fertilizer, due to the high quantities of nitrogen, phosphorus, and potassium that accumulate in agricultural soil. Instead, individual farmers and entities, such as co-operatives, have a responsibility to utilize the litter produced by their businesses for deploying renewable energy-generation technologies for a more sustainable and efficient economy.

Biogas and electricity are the most commonly generated forms of energy by any of the waste-to-energy processes.

At this stage, anaerobic digestion is the technology of choice for the conversion of poultry litter and other wastes into bioenergy and other bioproducts such as biofertilizer. A challenge for the digestion of poultry litter, however, has been the need to add a large volume of water to digesters to adjust the litter to a total solids (TS) concentration of under 15% (as the TS concentration of poultry litter is about 70%).

The transition from the dumping of poultry litter to the repurposing of this waste is unescapable but will require careful selection of technology. All of the existing technologies require a certain amount of investment; should a farmer choose anaerobic digestion or thermochemical conversion option, the feasibility and justification would, therefore, need to be very strong.