Aligning Australia’s organic waste management with circular economy principles is not only critical for reducing methane emissions and reaching net zero by 2050, it’s also an opportunity to transform waste into a valuable energy resource. Making this transition, however, will require cross-sectoral collaboration and a concerted effort to overcome existing barriers. In a recent Sydney-based study, stakeholders from the energy, water and waste sectors united to quantify and map urban organic waste layers, unveiling the potential of anaerobic digestion as a climate solution.

Generating biogas through the use of anaerobic digestion (AD) has the potential to make substantial contributions to Australia’s energy landscape, diversifying energy sources and reducing the environmental burden of landfilling.

Yet, obstacles to realising the full benefits of this sustainable approach persist, including a lack of knowledge around the feasibility of biogas technology and investments required in infrastructure and facilities.

Race for 2030’s June 2023 report, Mapping Organic Waste in Sydney: Advancing Anaerobic Co-Digestion, explores the opportunity for co-digestion of urban organic waste at three Sydney wastewater treatment plants (WWTP) to generate bioenergy while diverting these waste streams away from landfill.

The insights from this study offer valuable lessons and potential strategies that can be applied to other local government areas (LGAs) across Australia, supporting efforts for a more sustainable future.

By processing organic materials in AD systems alongside sewage, WWTPs can effectively harness the energy potential of these organic wastes while simultaneously preventing the release of greenhouse gas emissions that would occur if these materials were landfilled.

In a joint research project, Race for 2030 selected Malabar, St Mary’s and Riverstone Sydney Water WWTPs to illustrate diversion opportunities for urban organic waste generated in adjacent local government areas of Penrith, Blacktown, Randwick and Bayside.

Bringing circularity to WWTPs

AD not only generates bioenergy but also reduces waste emissions and optimises existing infrastructure, promising substantial cost savings and bolstering sustainability efforts. Additionally, the AD process generates byproducts like Bio-CO2 and digestate/biosolids, which can have various applications, including greenhouse horticulture and beverage manufacturing.

The three selected WWTPs could provide as much as 20 per cent of the identified AD infrastructure capacity gap needed for Sydney by 2030, which is over 50 kt/y capacity, equivalent to the capacity at EarthPower, the only commercial AD plant in Sydney.

Co-digestion of sewage utilising urban organic waste streams also benefits WWTPs, positioning them as central players in the circular economy space where they not only act as renewable energy sources but also serve as suppliers of soil conditioning agents to benefit the communities and businesses that contibute organic waste materials.

Possibilities for circular WWTPs are continuing to evolve across the globe, presenting a range of innovative opportunities. Among these is the potential to venture into the production of bio-based materials, including the manufacture of bioplastics using organic waste as a valuable resource.

Bioenergy potential

Race for 2030’s report outlines the hypothetical potential electricity generation from bioenergy in the study area for 2020/21, considering different organic feedstocks including food organics, garden organics, wastewater, fats, oils, and grease.

Its findings reveal the significant potential benefits of diversion from landfill. This process could yield an impressive 38 billion litres of biogas, possessing an energy value equivalent to over 1.371 billion megajoules.

Nearly half of this potential, approximately 49 per cent, arises from food organics, with an additional 38 per cent stemming from garden organics, while the remaining portion is derived from sewage and fats, oils, and greases. Wastewater contributes approximately 10-18 per cent to the bioenergy potential in different LGAs, with non-residential wastewater contributing only 2-3 per cent.

AD could result in the production of 9,600 tonnes of biosolids, enriching soil quality, and an annual reduction of 33,000 tonnes of carbon dioxide equivalent emissions. The total estimated bioenergy potential in the study area is approximately 126,000 MWh per year, with Blacktown LGA having the highest potential at around 52,600 MWh per year.

Cross-sectoral benefits

Co-digestion of urban organic waste at wastewater treatment plants (WWTPs) offers many benefits for the wastewater, waste and energy sectors. Accepting external urban organic waste streams for co-digestion boosts energy generation in the wastewater sector and contributes to the generation of renewable energy for the energy section.

At the same time, it provides an alternative pathway for processing urban organic waste and diversion from landfills for the waste sector.

This approach can adapt to the evolving needs of cites, providing short and long-term opportunities for AD capacity while harnessing the existing knowledge and expertise of the wastewater industry.

Additionally, it allows for the utilisation of energy and nutrients on a smaller, more local scale. This contribute to reducing emissions, avoiding waste and meeting landfill diversion goals across all three sectors.

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