Biogas - from waste to resource

Written by Network member: Karin Harding of Goulburn Valley Water

Goulburn Valley Water (GVW) provides urban water and wastewater services to a population of over 121,000 people in 54 towns and cities from the northern outskirts of Melbourne to the Murray River in north-central Victoria.

GVW asset performance engineers Alan Tyson and Dave Southcombe in front of the Shepparton generation plant

Between 1999 and 2004, GVW upgraded its primary wastewater treatment processes at the Mooroopna, Tatura and Shepparton Wastewater Management Facilities to high rate anaerobic lagoons (HRAL). These facilities were upgraded because they receive large volumes of high organic strength trade waste from industrial customers, particularly food manufacturing sites, which the HRAL are particularly effective at treating.

A by-product of the HRAL process is the generation of large quantities of biogas (composed of 70% methane) which can be captured under flexible covers. Traditionally this biogas has been considered a waste and is flared to convert the methane into carbon dioxide as it has a lower global warming potential.

GVW has achieved a significant 69% reduction in its greenhouse gas emissions - from 94,457 t CO2-e in 2001-02 to 29,423 t CO2-e in 2007-08 – primarily through the installation of HRAL and flaring of biogas, and cleaner production partnerships with industrial customers to reduce both their organic loads and trade waste volumes.

As part of its ongoing commitment to sustainability and reducing its greenhouse footprint, GVW decided in 2003 to further investigate the potential to use biogas as a resource. These investigations resulted in the formation of a partnership between GVW and Diamond Energy to convert the biogas into electricity.

The GVW-Diamond Energy partnership operates with GVW selling the rights to its biogas output to Diamond Energy, who are responsible for the construction of each generation plant, ongoing operation of the plants and sale of the electricity generated. The partnership required the negotiation of innovative agreements between the parties, including a Heads of Agreement, Access Agreement, Gas Infrastructure and Supply Agreement and Memorandum of Understanding for green rights on flared gas.

At the beginning of the partnership it was estimated that the electricity generated from the biogas from the three sites each year would be about 14,000 MWh - equivalent to that required to power 2,600 homes - and result in the abatement of 17,500 tonnes of carbon dioxide by avoiding coal-fired electricity generation.

The first stage of the project was the installation of a biogas generation plant at the Tatura Wastewater Management Facility, which started operation in January 2007. A second generation plant was successfully commissioned at the Shepparton Wastewater Management Facility in December 2008. The Shepparton generation plant is able to be expanded to include a second generator if sufficient volumes of biogas are produced. A review of the electricity generation potential of the Mooroopna Wastewater Management Facility is planned for 2010.

Each generation plant incorporates a 1.1 MW generator. During 2007-08 the Tatura plant generated nearly 4,000 MWh of electricity. The Shepparton generator is also expected to generate 4,500 MWh of electricity each year. This electricity is fed into the local electricity grid as renewable energy, thus generating renewable energy certificates for Diamond Energy.

The financial models used to develop the project were based on GVW receiving an income from sales of biogas and lease of land and Diamond Energy, through its retail arm CommercialGreen, generating income by selling accredited renewable electricity (GreenPower) and renewable energy certificates to business customers across Victoria.

One of the key features of the project was the ability of the generation plants to generate and sell electricity into the grid during times of peak demand, thus receiving the highest price for the electricity generated. This is done using the flexible covers on the HRAL to store the biogas.

The partnership between GVW and Diamond Energy to establish the cogeneration plants at Tatura and Shepparton Wastewater Management Facilities has enabled biogas previously considered a waste to be converted into the resource electricity, and abated a significant amount of greenhouse gas emissions.