There are many different waste managementoptions for litter including land application of litter as an organic fertiliser. Overseas broiler industries have had restrictions placed upon them regarding this practice due to over application of litter leading to pollution. Fortunately in Australia there are greater agricultural lands that can responsibly utilise litter and growers are generally less concentrated compared to overseas. Therefore, poultry waste managers can rely on land application of litter as a sustainable disposal method for the foreseeable future. That being said, the industry considers all other waste management options and their ability to value add to the litter resource.
An important concept for a waste manager is a closed-loop system where outputs from one industry become inputs for another. Therefore pollution could be defined as a resource or raw product that has an adverse effect on the environment, which has not been transformed into another useful product. Land application satisfies this requirement as litter is transformed into plants while soil structure is improved by increasing soil organic matter. Composting litter before applying to land can enhance both pant growth and soil structure.
Composting is the aerobic microbial breakdown of organic matter, usually incorporating a thermophilic phase. The adoption of composting systems for poultry waste has received attention due to its ability to reduce litter volume, dispose of carcases, stabilise nutrients and trace elements and reduce pathogens. Agronomic benefits of composted litter include increased plant available nutrients and humic residues and is known for its pleasant ‘earthy’ odour. The immobilisation of nitrogen and phosphorus during composting reduces the risk of soluble N and P entering aquatic systems via surface flow and leaching. Composting could also offer both on-site and off-site solutions to litter utilisation and potentially enhance a closed-loop system for the Australian poultry industry.
Direct combustion or incineration are recognised as an efficient option for generating renewable energy and fertiliser grade ash from litter and could potentially close the nutrient loop for the poultry industry. There are currently successful large scale off-site electricity utilities operating in the UK that primarily use litter as a fuel. For on-site electricity and heat generation smaller direct combustion systems are being researched and developed, and if commercialised could supply Australian broiler growers with both environmentally sustainable waste disposal and energy.
Anaerobic digestion could also promote a closed-loop system for the poultry industry, as the process could degrade and stabilise a wide range of organic poultry wastes including litter, producing potentially saleable methane and digestate. Methane could be captured after digestion, the gas then cleaned and then used as renewable energy, while the digestate could be utilised as a soil improving agent with potentially good fertiliser attributes.
It is also likely that poultry litter could be suitable for lignocelluosic alcohol production. If this technology is viable, this waste could supply biofuels to Australia and potentially reduce the demand for grain destined for ethanol production.
The use of specially selected earthworm species to degrade waste is known as vermiculture and has be widely adopted by home gardeners to utilize green waste and vegetable scraps. Vermiculture has the potential to produce both humic rich vermi-compost (vermicast) and meat meal (vermimeal) from litter. Traditionally, the vermiculture process has primarily been adopted to produce vermicast, a recognised valuable organic fertiliser. However, the production and processing of earthworms into vermimeal has been becoming an increasingly viable component. Both of these outputs potentially render vermiculture as a value-adding opportunity for the Australian poultry industry, while providing an alternative disposal option for litter (promoting a closed-loop system). Research is currently underway at the University of New England to determine the role vermiculture has in poultry waste management.
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