Composting : Applying systems thinking to the revision of the Australian Standard for Composts, Soil Conditioners and Mulches

The Australian Standard for Composts, Soil Conditioners and Mulches (AS 4454—2012) serves as the benchmark for recycled organic product quality in Australia. It outlines minimum processing requirements to eliminate pathogens and weeds, and mandates reporting on various analytical tests for products intended for unrestricted use across all market sectors.

However, AS 4454—2012 is based on factors established in the 1990s, many of which are now outdated, raising concerns around the standard’s current effectiveness. Consequently, only a limited number of organic recycling companies and products have achieved third-party accreditation under this standard, while compliance via self-declaration is widespread.

While the contaminant limits in AS 4454—2012 are comparable to those in similar international standards (Biala and Wilkinson, 2020), the approach of evaluating products against a small and fixed list of chemicals ‒ some long banned ‒ may not accurately reflect present-day risks.

This paper presents the findings from a comprehensive review of the Australian Standard AS 4454—2012 and the entire urban organics recycling supply chain, a pivotal element in the circular economy for organics[1]. By applying systems thinking methodology, we analysed the interconnections within the broader organics recycling framework and the standard's effectiveness within it. Our aim was to elucidate how the standard functions within this complex system and to propose enhancements within and outside the standard that align with contemporary industry practices and circular economy principles.

[1] Full project reports are available from www.as4454review.com.au

Recycling of urban organics could be the best example to showcase the benefits of a circular economy in Australia. Achieving this ideal necessitates a comprehensive, system-wide approach to quality management. Each stakeholder across the supply chain ‒ from waste producers to processors and end-users ‒ bears a critical responsibility in ensuring the efficacy of this cycle. For example, proper waste separation practices at the source, robust guidelines for collection and processing, and collaborative efforts among all stakeholders are imperative. Without these systemic measures, adherence to the standard alone cannot guarantee the desired outcomes in product quality and environmental sustainability, and places responsibility for product quality solely on the processing sector.

Recognising this complexity, a systems thinking approach was employed to identify critical control points. This involved examining the interdependencies of system components at various scales and mapping the main elements of the organics recycling supply chain. Emphasis was placed on process options that manage quality at these critical junctures. To validate and refine these insights, extensive stakeholder consultations ‒ including workshops and interviews ‒ were conducted, ensuring that proposed solutions were both practical and grounded in real-world experiences.

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First of all, project stakeholders highlighted the necessity of clarifying the purpose of AS 4454—2012, as its current objectives appear convoluted and ambiguous. To address this, we believed it essential to evaluate what the standard can realistically achieve within the entire organics recycling circular economy. As previously discussed, the effectiveness of AS 4454—2012 is compromised without concurrent systemic controls throughout the circular economy. 

In examining the circular economy as a whole, three broad areas of critical importance were identified for quality control:

• Feedstock quality, encompassing the physio-chemical characteristics of the feedstock itself as well as the levels of impurities in it
• End-product quality, which is measured by testing products against specifications. This is the specific domain of AS4454. End-product quality is determined by both feedstock quality and the controls placed on processing itself (“process control”) and
• Quality assurance, which is data collection, analysis and reporting against specifications or key performance criteria, usually associated with a “certificate of compliance” if the quality assurance process is audited by an independent third party.

Physical and chemical contamination of feedstock material supplied to organics processing facilities poses a major problem, possibly even an existential threat to the organics recycling industry in Australia, and therefore also to organics recycling activities overall. Government regulators in Australia are responsible for managing the public health and environmental risk associated with the application of waste and recycled organic products to land. Yet, feedstock quality controls at the point of collection, often managed by local government, tend to be neglected.

Stakeholders reinforced that, as a voluntary standard, AS4454 should not be used as a de-facto regulatory tool. Therefore, regulatory controls over municipal and commercial feedstock quality certainly need to be developed separately to AS4454 (see Table 1). With these in place, feedstock controls are more likely to be implemented by the feedstock supplier[2].

There has also been some confusion over whether the AS4454 is really a “minimum quality” or a “fit-for-purpose” standard, since AS4454-2012 currently tends to have a foot in both camps. Stakeholders argued that fit-for-purpose specifications are best determined by the supplier engaging directly with the market they service[3]. In fact, AS4454-2012 already states that it ‘does not attempt to classify products by suitability for any specific use’ and that product specifications outside the requirements of AS4454 do not ‘imply that the product is not fit for the intended purpose’ (see Section 3.1.2 of AS4454-2012).

With this in mind, we concluded that revisions to AS4454 should reflect its redefined purpose as a quality assurance framework specifying minimum physical, chemical and biological characteristics for beneficial use.

[2] In addition to regulation, other financial incentives may also be required. This is discussed in more detail in our research reports which can be downloaded from www.as4454review.com.au

[3] A standard cannot possibly specify physico-chemical requirements for every possible end-use scenario 

The current scope of the standard covers ‘composts, mulches and soil conditioners and related products that have been derived largely from compostable organic materials’ (quoted from Section 1.1 of AS4454). It excludes such things as home composting end-products, blood and bone, liquid organic wastes and seaweed products, non-organic or non-compostable materials and untreated garden organics.

The reference to “compostable materials” rather than “composted products” in the scope is probably a reflection of the original desire to accommodate the needs of many interested parties manufacturing a wide range of products through different processing methods. However, composting is by far the dominant technology for organics processing in Australia and is likely to continue to be so for the foreseeable future. AS4454, as a minimum-quality standard, cannot adequately consider and/or describe minimum-quality attributes associated with every type of recycled organic end-product, particularly in light of ever-changing technology and feedstocks.

For this reason, we proposed a tightening of the scope of AS4454 to be only for products derived from a controlled (or managed) aerobic, thermophilic composting process.

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AS4454-2012 currently differentiates products based on product maturity (pasteurised product – composted product – mature compost) and particle size distribution (soil conditioner – fine mulch – coarse mulch). In all, thirteen broad types of recycled organic products are defined in the standard. Stakeholders found this product classification system to be convoluted and difficult to follow. Furthermore, the particle size specification is quite prescriptive and is difficult to assess reliably in practice, resulting in some marketable products failing to meet these specifications.

Adopting the revised purpose of AS4454 to be any product derived from a controlled (or managed) aerobic, thermophilic composting process, while also taking a less prescriptive approach to particle size grading means that product classification could be simplified down to three types, viz.:

• Pasteurised product (i.e. a product derived from a controlled [or managed] aerobic, thermophilic composting process of short duration; often termed “fresh” compost)
• Composted product (i.e. a product of greater maturity and stability compared to the pasteurised product category) and
• Mature compost (i.e. a product of greater maturity and stability compared to the composted product categories).

In this way, all composted products, whether used as a soil conditioner or mulch (or for any other purpose) are covered in the revised standard. Reducing the number of product classifications gives greater scope for processors to meet fit-for-purpose specifications according to market requirements without compromising the need to also meet AS4454 specifications. This means that AS4454 products could be used a “base” stock for the development of products that meet specific market requirements.

Rationalising the number of product categories would simplify end-product testing requirements. Under our suggested model, there are two levels of specification for end-product quality ‒ the first being to specify minimum quality criteria for beneficial use (the principal domain of AS4454), and the second is associated with risk management (a domain of regulators).

In the first instance, the three product categories can be determined by maturity and stability testing using the existing suite of tests currently recommended in AS4454-2012, which are:

• Ammonium-nitrogen and nitrate-nitrogen levels
• Nitrogen drawdown index 
• Self-heating test
• Solvita 
• Plant growth test and
• Wettability.

Other testing requirements can then follow from maturity and stability testing. Some of the quality parameters may need hard limits to be defined for all products, while others may be “required reportables” for some or all products or fully optional (see Table 2). 

Instructions for use should be recommended for any product that is expected to make a contribution to plant nutrition. This is consistent with best practice, since end-users need to account for nutrients applied to soil based on crop requirements, especially when they are used in combination with fertilisers.

Chemical contaminants and their limits in AS4454 were established 25 years ago. Previous efforts to update them failed because the AS4454 technical committee that has broad representation and ultimately decides about any changes to the standards, couldn’t come to an agreement on any proposed changes. 

Our work clearly established the need, and support for, an evidenced-based national approach to the management of problem chemicals in recycled organic products[4]. This was beyond the scope of the current project as it will be resource-intensive and requires specialist scientific skills. While the prime responsibility for developing a national approach to the management of problem chemicals lies with the regulators, the project team was tasked with outlining how the evidence base for it could be developed.

Simply expanding the list of problem chemicals to be monitored in the standard is not going to be possible due to the likely continual addition of problem chemicals to watchlists. Current methods see individual chemical concentrations c0mpared to established thresholds, limits or criteria. But the chemistry of recycled organic products is extremely complex, so the risks of individual chemicals in these products can seldom be adequately determined. We proposed an alternative system using New Approach Methods (NAMs). NAMs measure the effects of the chemical mixtures as they occur in products. New approach methods are well developed in other fields and confidence in them is increasing worldwide (Ball et al., 2022). They are beginning to be deployed in some countries but their application to recycled organics hazard assessment will need investment in research and development.

[4] Australia is a federation of independent states; regulations can therefore vary greatly between jurisdictions. However, organics recycling companies often operate in multiple jurisdictions.

A systems thinking approach was used to analyse the Australian Standard AS 4454—2012’s effectiveness and its interconnections within the broader organics recycling framework. Technical aspects were accompanied by deep stakeholder consultation from all parties involved in the circular economy for organics recycling. 

To be successful, organics recycling demands an integrated, cross-jurisdictional approach. System mapping helped to clearly define the roles and responsibilities of each participant in the supply chain, and to pinpoint areas where stakeholders must collaborate to achieve shared objectives.

By embracing this collaborative model, Australia can enhance its recycled organics industry, reduce landfill reliance and promote sustainable agricultural practices.

Alloway, B.J., Graham, R.D., Stacey, S.P. (2008). Micronutrient Deficiencies in Australian Field Crops. In: Alloway, B.J. (eds) Micronutrient Deficiencies in Global Crop Production. Springer, Dordrecht.

Ball, N., Bars, R., Botham, P.A., Cuciureanu, A., Cronin, M.T., Doe, J.E., Dudzina, T., Gant, T.W., Leist, M. and van Ravenzwaay, B. (2022). A framework for chemical safety assessment incorporating new approach methodologies within REACH. Archives of Toxicology, 96(3), pp.743-766.

BGK, Bundesgütegemeinschat Kompost. (2023). Schwellenwerte und Grenzwerte (Limits and thresholds)  

Wilkinson, K., Price, J., Biala, J., McDonald, D. (2021). Review of regulations and standards for recycled organics in Australia. Report for Department of Agriculture, Water and Environment, Canberra, ACT

This work was funded by the Australian federal government of Department of Climate Change, Energy, the Environment and Water (DCCEEW) under its Food Waste for Healthy Soils Fund.