Melbourne Water is currently investigating the feasibility of adding organic waste into the anaerobic section of the sewage treatment process at its Western Treatment Plant.

011Melbourne Water treats in excess of 800 million litres of wastewater per day at its two metropolitan wastewater treatment facilities, which treat more than 90 per cent of Melbourne’s domestic, commercial and industrial wastewater.

Located in Werribee, the 10,500 hectare Western Treatment Plant (WTP) is a world leader in technical and environmental innovation. It processes around half of Melbourne’s sewage and produces almost 40 billion litres of recycled water a year.

The options for disposal of high-strength organic wastes (that cannot be accepted into the centralised sewer system) have been declining over recent years, and so there is a need to support industry through providing an alternative, cost-effective outlet for high-strength organic wastes.

Melbourne Water has been collaborating with both City West Water and South East Water and their customers to identify opportunities to use existing infrastructure and resources to help deliver more sustainable practices around waste treatment, reuse and disposal.

A co-digestion trial at WTP was commissioned to provide more qualitative and quantitative data on the organics waste market, leading to more informed decisions on Melbourne Water’s future role in these markets.

Exploring the possibilities

Melbourne Water undertook an extensive expression of interest process to canvas the organic waste transport industry and major businesses for the supply of high-strength organic wastes. Safety and risk were a high priority. Shortlisted transport companies and businesses then responded to a more detailed Request for Proposal.

Ultimately contracts were signed with Veolia and Stows Waste Management, recently followed by J&M Zammitt. There are other interested parties, with whom Melbourne Water is currently in negotiation with.

As part of the trial, high-strength organic liquid materials which are unable to be sent down the sewer – due to their potential to corrode and increase odour from the network – are transported to the WTP trial site and pumped into the main inlet.

The material mixes with the incoming wastewater from the sewer, then travels directly into the covered anaerobic lagoon where the biogas is collected to generate electricity for operating the wastewater treatment plant.

This trial was implemented to determine the market need for, and interest in, this new treatment service, and is the first step to help Melbourne Water build the business case for augmenting existing infrastructure or to construct a separate anaerobic digestion facility.

Through the trial Melbourne Water is seeking to build meaningful customer relationships and to gather information related to:

  • Market volumes of high strength organic wastes
  • Value of service to industry
  • Market interest in long term contracts and stability
  • Controlling and managing potential contamination of wastes received
  • Tracking and billing systems for waste deliveries

Improved environmental outcomes

The trial is the stepping stone to a service that provides a competitive choice to the manufacturing sector for high strength organic waste outlets.

Depending on the waste delivered, it is likely that there will also be improved environmental outcomes including:

  • Avoiding landfill and methane emission to atmosphere
  • Capture and use of biogas to produce electricity
  • Avoiding 100km+ of transporting
  • Use of recycled water for truck washing
  • Transparency of the sustainability of waste treatment at a publicly scrutinised, EPA-licensed facility

Melbourne Water charges a gate fee for the acceptance and management of the high-strength organic wastes.

This gate fee will cover the costs associated with the service and generate non-regulated revenue. Melbourne Water needs to comply with commercial neutrality requirements and does this by creating a commercially priced service.

Any profit generated through the waste-to-energy process will provide greater community value through offsetting wastewater treatment costs and/or enhancing outcomes including liveability.

010Generating; not just treating

Through the co-digestion process, Melbourne Water’s WTP has the chance to not only treat the wastewater that is sent to it, but to also generate clean energy for use at the plant – and to potentially be exported to the grid.

Energy generation isn’t new to Melbourne Water – the utility has been generating electricity from sewage since the 1970s and has been a leader in resource recovery in the water industry. Melbourne Water has kept a watching brief in the waste-to-energy space for a long time, periodically assessing new technologies, products and markets.

Anaerobic digestion of high-strength organic wastes from the commercial food industry is a new service that seamlessly fits with existing capabilities and service levels, and has the potential to provide additional benefits in the following areas:

  • Through avoidance of waste to landfill, such facilities can be registered as carbon offset schemes
  • Further generation of renewable energy, from a source not dependent on the sun shining or the wind blowing
  • The ability to blend the organic digestate with other Melbourne Water wastes to produce saleable soil products and fertilisers

The organic waste currently being supplied to the WTP is not suitable for disposal via sewage, and hence it often ends up in landfill after processing, potentially releasing methane gas into the atmosphere.

Co-digestion into the sewage offers an alternative treatment option for this waste.

Co-digestion has successfully been demonstrated to deliver multiple benefits at international sewage treatment plants.

If the co-digestion trial proves to be a success, the benefits of providing this service at a larger scale include:

  • An increase in renewable energy from biogas that can be used on site for treatment plant operations or supplied to the grid
  • An alternative revenue source, the benefits of which will be passed on to customers
  • Reduced waste to landfill
  • Reduced travelling distance for waste transporters.
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