The circular economy in regional South Australia: The potential for making and using organic compost

This project builds on a previous study of biosolids and septage waste within Legatus Group councils which found that there was insufficient volume of this material to establish a composting plant. This study identifies additional sources and volumes of compostable organic waste from primary producers in the Mid North and potential users of locally produced compost within Legatus council region. It also discusses challenges and opportunities of combining compost feedstocks, potential contamination and stakeholder engagement. The main business obstacles within the scope of this study are feedstock contamination and industry standards, and availability of feedstock (Australian Organics Recycling Association 2021). Findings from this research suggest that sourcing a reliable supply of low-contaminant feedstock suitable for composting within the Legatus council region is likely to be a large obstacle that needs further investigation. Local government procurement of end products may also play a major role in the sustainability of a composting facility, particularly if the bulk of feedstock ends up being council collected organics. Utilising locally generated recycled organics within council projects such as landscaping would be a first step in implementing a circular economy within Legatus Group. Research outcomes and business recommendations are summarised below: 1. Sources of high-carbon organic feedstock need to be targeted within the Mid North to balance the high nitrogen content in biosolids and sewage sludge. The agriculture industry potentially has large volumes of source-separated organic waste. Contaminants present in this feedstock would likely be identified through existing testing and knowledge of their produce. While data from the South East agriculture industry show large volumes of organic material being generated, there is insufficient data about what types and volumes might be available within the Legatus region. Data of waste streams from Mid North and South East SA are estimates and note that much of it may already be allocated and unavailable or unsuitable for composting. Interviews with Legatus stakeholders indicate that primary producers are not reporting much waste and that they already have practices in place to manage what by-products are being generated. Farmers are using a combination of synthetic fertilisers, biosolids and manure to improve soil productivity. However, none of the three participants interviewed are using products that have been combined with other organic inputs. Primary producers would like to use more compost and manure for longer-term benefits, ideally products that are produced locally. However, year-to year finances can be an impediment to investing in these. • Further research is needed to identify potential sources of high-carbon compostable feedstock from the agriculture sector. • Recommend developing and distributing a stakeholder survey via a communication campaign that focuses on the advantages of blending feedstocks into a more refined, treated composted product. 2. If stables volumes of feedstocks cannot be sourced from the agriculture industry, Legatus council-managed organic waste and biosolids may be the primary inputs for a regional composting plant. Both of these inputs are known to be high in contaminants. End products would need further research and testing before use. Legatus councils may also need to establish or expand kerbside organics waste collection to ensure sufficient supply of material to achieve starting C:N of 25-30:1. • Recommend most likely application of these composted end products to be non food chain applications such as landscaping (dependent on testing). • Recommend implementing waste education plan for kerbside bin users to minimise contamination of materials. 3. While biosolids and sludge can be applied directly to agricultural land (as liquid slurry or dry pellets), it is the least ideal disposal option aside from landfill. Any soil conditioning benefits must be weighed against the risk of physical, chemical and biological contaminants that can make their way into the human food chain. Composting can help to mitigate these risks through heat pasteurisation and contaminant dilution. However, care must be taken when selecting organic inputs for combination as these can, and often do, contain contaminants as well. As contamination is large risk, input sources that maintain records of feedstocks need to be prioritised. While the Australian standards for compost are voluntary, any composted material produced by a regional composting facility should be tested for compliance with the AS 4454:2012. Testing is needed to ensure quality and safety for end users, particularly if agriculture and horticulture are the main likely consumer markets. Established commercial composting facilities were not contacted for this study, however they may be able to offer industry insight into sourcing appropriate feedstock, managing contaminants, technologies and additional markets for finished products. They should also be considered as potential outsourced operators and mutually beneficial partners with the Legatus Group. • Recommend that compliance with AS 4454:2012 be considered best practice. • Recommended future engagement with currently established commercial composters in South Australia.