Towards Zero Waste: Opportunities for Bio-based Fertilisers (Digestate & Biochar) in Mining, Forestry, Municipal, NRM and Landcare

30th March was Zero Waste Day! So I thought it would be appropriate to post this article outlining the methodology we used to assess opportunities to use wastewater derived bio-based soil conditioners and fertiliser by mining, forestry, municipal, NRM and Landcare in the vicinity of 127 red meat processors across Australia.

Background

As outlined in a previous blog, we were sub-contracted by Tessele Consultants as part of a larger R&D project Tessele are undertaking for the Australian Meat Processors Corporation (AMPC) to help them transition to Net Zero by 2030 using a Circular Economy approach (Figure 1).

Figure 1 - The Australian Meat Processors Corporation (AMPC) are advocating a Circular Economy approach to help its members transition to Net Zero.

Substantial progress can be achieved by red meat processors replacing open pond wastewater treatment systems with anaerobic digestor (AD) tanks or covered ponds where gases (e.g. methane) can be captured and used to generate energy for facilities, thereby significantly reducing greenhouse gas emissions (GHGs). The liquid will form a recycled water source while the solids (Figure 2), which are normally disposed of to landfill or composters, could be processed into stabilised bio-based fertilisers such as dried digestate pellets (DDP) and biochar pellets (BCP).  This is more preferable to existing methods of disposal or reuse which result in the ongoing emission of greenhouse gases (GHGs) and nutrient leaching.

Figure 2 - Dewatered wastewater solids can be processed into valuable bio-based soil conditioners and fertilisers such as dried digestate and/or biochar.

Using wastewater solids in an optimised commercial manner and as a base for bio-based soil conditioner and fertiliser can help reduce the costs associated with waste management. It can also assist adjacent industries that AMPC does not currently collaborate with, specifically mining, forestry, municipal, natural resource management (NRM) and Landcare, to increase their level of sustainability. Potentially this could enable overall positive environmental outcomes, improved resource recovery rates and establishment of a Circular Economy. Land Use Futures analysed opportunities for use of bio-based soil conditioners and fertilisers by the target industries located in the proximity of red meat processing establishments across Australia.

Supply Side Analysis

A mass balance study was undertaken by Tessele to estimate the supply of resource (quantity and quality) available for use as bio-based fertiliser following processing. Tessele Consultants provided Land Use Futures with data for each of the 127 red meat processing establishments which identified the maximum potential production of treated wastewater and solids. Solids composition were broken down into 5% (liquid solids), 22% (spadable solids), 90% (dried digestate) and 98% (biochar). We then matched this to the location of each establishment and categorised each as small, medium or large based on their maximum production capacity (Figure 3).

Figure 3 - Potential mass volumes of bio-based soil conditioner and fertiliser were calculated and mapped to each establishment.

Tessele undertook a comparative assessment of the likely qualities of dried digestate and biochar which might be produced through the dehydration and the pyrolysis process. This considered composition of carbon (C), phosphorus (P), nitrogen (N), potassium (K), dryness and porosity.  Land Use Futures then undertook a comparative assessment of the advantages and disadvantages of using DDP versus BCP, especially as they related to soil chemical, physical and biological qualities. Positive impacts included adding carbon (labile and/or resistant forms), improving water holding capacity, neutralising pH ( ‘liming effect’), and providing nutrients such as N, P and K. Disadvantages assessed included volatisation of N (i.e. generating nitrous oxide gas) and leaching risk of N and P. While BCP provided significant advantages over DDP, it would also take more energy to produce.

Demand Side Analysis

The project brief required us to evaluate the potential use of bio-based fertiliser and soil conditioners by five target industries. The potential range of applications within these industry sectors was quite extensive so we focused on soil-based applications. Twelve (12) applications or demand segments were identified and then related to land uses aligned to the target industries.

List of target industries and demand segments

• Mining

  • Mine and quarry rehabilitation

• Forestry

  • Plantation forestry (softwood and hardwood)

  • Environmental forestry including carbon forestry

• Municipal

  • Urban forestry including street trees

  • Sporting and playing fields i.e. turf

  • Civil works rehabilitation and landscaping

• NRM

  • Salinity

  • Erosion

  • Soil acidity

• Landcare

  • Landcare/Carbon farming

• Production nurseries

• Composters

Using the Australian Land Use dataset (see previous blog article) analysis was undertaken of the land use types within a 50 kilometre radius around each establishment (the ‘demand catchment’) to determine the incidence and area of each target land use in each catchment. For each land use type and demand segment, an indicative DDP and BCP application rate per hectare was determined then applied to the area.

Figure 4 - Land use analysis was conducted around 127 red meat processors across Australia.

Supply:Demand Ratio

The primary aim of the project was to determine the proof of concept for the idea of using bio-based soil conditioners and fertilisers in the target industries, and whether this would be feasible for red meat processors at various scales to pursue. Supply:demand ratios in relation to DDP and BCP and demand segments were undertaken for each establishment (Figure 5). Most establishments had at least one demand segment which could potentially take up all supply and all had multiple demand segments which when combined would be able to take all supply.

Figure 5 - Bio-based soil conditioner supply:demand ratios were determined for each establishment.

Conclusion

The analysis provides the AMPC with confidence there are a range of potential opportunities to use bio-based soil conditioners and fertilisers in the vicinity of red meat processors across Australia. Bio-based soil conditioners such as dried digestate and particularly biochar can increase the levels of sustainability of surrounding land users, thereby enabling overall positive environmental outcomes, improved resource recovery rates, and establishment of place-based Circular Economies.