Best practice litter management manual for Australian meat chicken farms

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Other options to utilise and treat spent litter – energy recover

Spent litter is potentially a valuable source of energy, however recovery of this additional value has generally not been adopted by the Australian chicken meat industry. Energy recovery from biomass is not a new concept and public interest and research attention has grown in the past 20–30 years due to increasing energy costs and the GHG emissions generated from the combustion of fossil fuels. Spent litter has a relatively high energy value and low moisture content compared with many other organic by-products, making energy recovery a potentially viable option.

Energy recovery has the benefit of depleting the carbon content (energy value) of the spent litter, which results in a more concentrated fertiliser product. This reduction in carbon does, however, reduce the soil amelioration properties of spent litter.

Research has been conducted to investigate energy recovery options for poultry litter by McGahan et al. (2010) and Playsted et al. (2011). These reports included details on energy recovery technologies applicable to poultry litter, including pyrolysis (and biochar production), combustion, gasification, anaerobic digestion and others. Many of these technologies are in the development phase, particularly with regard to their use of poultry litter.

Carbon is the energy provider in poultry litter and usually comprises 28–40% (Playsted et al. 2011). Total carbon in poultry litter is comprised of carbon originating from the bedding portion and carbon from manure. Carbon from these two sources have quite different properties, particularly with respect to energy recovery. Carbon content is especially important for understanding different energy recovery systems, and substantial errors can be made when researchers and designers do not understand the differences between the manure and bedding components.

When discussing the energy content of a substance, the organic materials within the litter are described using the term volatile solids (VS) content. A simple theoretical mass balance by Playsted et al. (2011) for a single batch of poultry litter (10.5% ash) estimated that the proportion of VS derived from manure was 55%, while 45% came from the litter. This is important, for example, when investigating potential energy recovery using anaerobic digestion. In this process, most of the litter component will not be readily digested and hence little energy will be derived from it.

The heating value or energy value of a substance is the amount of heat released during the combustion of a specific amount of that substance. The energy content of spent litter is reported in terms of megajoules (MJ) per kilogram of material on a dry basis. The higher heating value (HHV) is usually reported. The energy content of single batch poultry litter in Australia is estimated to be 17.5MJ/kg (HHV) (Playsted et al., 2011).

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