Sewage as energy: An essentially unlimited renewable resource

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B.C. is leading the way in using one of mankind's most renewable resources to heat its buildings – sewage.

The trend started when both Vancouver and Whistler decided to create neighbourhood energy-generating plants (district-energy systems) for their Olympic villages. They became the first cities in North America to use sewer systems to provide heating and hot water.

The heat is extracted from liquid waste only – it is too difficult and expensive to use solid waste for this purpose.

Several developers and municipalities in the region, including Vancouver, North Vancouver and Richmond, are looking at jointly developing new sewage-powered, district-energy systems.

"There are different sources for district-energy systems, but sewage heat is sometimes the most attractive one," said Jeff Carmichael, Metro Vancouver's manager for utility research. "Especially if it's nearby, it's cheaper."

He has developed a draft policy, to be voted on Wednesday, that sets out the rules for allowing other entities to access its systems.

There's one enormous advantage to sewage as an energy source: it never stops. "The sewage just keeps on coming. It's essentially an unlimited resource," said Mike Homenuke, an engineer with Kerr Wood Leidal. That's the firm that designed the Whistler system, which runs on treated effluent, and is working on potential projects for Metro Vancouver and the Capital Regional District on Vancouver Island.

The company considered using the methane gas from a capped landfill as the energy source for Whistler's district plant. "But we realized it would only last about 20 to 25 years. Sewage is very renewable," said Mr. Homenuke.

Mr. Carmichael said B.C. is "ahead of the game in general" in using sewer heat as an energy source because of one factor – most of its power comes from hydroelectric generation, which is both cheaper and cleaner than power from coal, nuclear or natural gas. That power is needed to run the pumps that extract the heat from sewage and turn it into energy.

"In Alberta, [where power would be generated from coal] the carbon signature with that heat pump can be worse than burning natural gas," said Mr. Homenuke.

As a result, although there are about 80 sewage-powered energy plants in Europe, the two already in B.C. remain the only ones on this continent. Other jurisdictions in Canada and the U.S. are now looking at sewage for power, but Vancouver is the furthest ahead in developing concrete plans.

That's partly because of positive results from the local examples.

"The heating from our Neighbourhood Energy Utility [at the Olympic Village] has had good results," said Vancouver Councillor Raymond Louie. "We are seeing a 74-per-cent reduction in greenhouse-gas emissions in the first four months of 2012, compared to what they would have been otherwise."

Getting heat and power from sewage may seem mystifying to the average user of a toilet, but not to engineers. Human waste in the sewers is warmer than the ground it typically flows through. In winter, it is about 14-15 degrees; in summer, around 20.

Heat is extracted through a process that is "basically like a refrigerator in reverse," said Ayman Fahmy, another Kerr engineer.

The Metro Vancouver policy envisions allowing its member municipalities to tap into sewer pipes to create district-energy systems in the short term. The region is looking long term into whether it should develop its own energy plants.