The local water utility here in the East Bay has achieved a remarkable feat: they are producing enough energy from their main wastewater treatment plant to sell power to the grid. I had hoped to report on this after viewing the plant myself, but I was turned away from the Grand Opening Dedication Ceremony of their new gas turbine on Tuesday. Turns out that I needed media credentials. Oh well.
Wastewater treatment is notoriously energy intense, if for no other reason than that water is heavy to move around. According to the East Bay Municipal Utility District (EBMUD), the average California power cost to deliver one million gallons of water is approximately 7000 kW-hrs. So a common move towards energy efficiency is to cap all tanks for water and sludge, then recover the methane (a.k.a. natural gas) to be burned for energy. This also alleviates a lot of odor issues with wastewater treatment plants — trust me, I used to work at one in East St. Louis. Well, EBMUD had already done that. They had 3 gas turbines running about 6.3 MW, which was nearly enough (90%) to power the wastewater treatment plant, and they had excess methane. So they just bought and installed a big, efficient gas turbine, 4.5 MW, to use the excess methane and generate energy in excess of their needs. That’s right, a wastewater treatment plant is producing enough power to sell some to the grid.
Now, the East Bay utility in general will still need to purchase energy from the grid occasionally for water treatment and delivery and maybe office building use. Their 2010 energy purchase amounts to 9.3 MW, more than the roughly 3.8 MW excess capacity that they just added. So they’re not exactly going to get rich. Yet.
The real secret behind the EBMUD strategy is the food wastes that they accept (for a fee) from regional restaurants, wineries, cheese producers, and chicken farms. They feed all this disgusting junk to a tank full of microbes, and end up with way more methane than standard sewage would provide. This stuff is too complex to toss in a standard wastewater treatment plant or even to travel through sewer pipes, but a bunch of trucks deliver it every day to the specialized bioreactors EBMUD has had since 1991. Considering that this junk would otherwise end up in a landfill, emitting methane (a greenhouse gas far more potent than carbon dioxide) unchecked, this economical decision also makes sense from an environmental perspective. It’s nice when we can all agree on something.