The methane-rich gas is so far burned to generate electricity for the plant in Delta, but could in the future be cleaned and sold into the natural gas distribution grid to heat local homes.
Waste grease from renderers arrives in tanker trucks at the plant and is added to digester tanks where bacteria treat sewage and burp out biogas as a byproduct.
The $2.6-million pilot project to add grease and fats to the process began in April.
It's so far yielding an extra 8,000 cubic metres of biogas per day and is expected to boost biogas production 20 per cent overall.
"It's working very smoothly," said Paul Lam, Metro's waste water treatment division manager.
Metro estimates the project will pay for itself within eight to 12 years, based on the value of the electricity or biogas produced and the tipping fees the region charges suppliers to dispose of the fat.
Engineers also plan to test out the use of brown grease from restaurants as another way to produce more biogas at Annacis.
Restaurant grease also goes to biodiesel makers and Lam acknowledge that could put Metro in "a little" competition with them.
But he said suppliers would ultimately go to the cheapest place for disposal.
Similar co-digestion projects exist in Europe and parts of the U.S. but Metro is one of the only operators using the technology in Canada.
The use of captured biogas – a powerful greenhouse biogas – helps Metro reduce its carbon emissions by offsetting the burning of fossil fuels.
"Selling the gas would generate more carbon credits than the electricity," Lam said, but added the power produced on site is an important backup source in case of outages.
Other treatment plants in the region, including Lions Gate on the North Shore, also capture biogas but Annacis is the first to supplement the feedstock with grease.
Metro is committed to recovering more energy from its sewage under its now-approved Liquid Waste and Resource Management Plan.
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