Wastewater operators have spent many hours telling the public how their plants make two great products: Clean water and valuable fertilizer/soil conditioner.

Now there's a third: clean energy. Of course, making electricity and heat from digester methane (biogas) is not at all new. But these days the bar is being raised. It's no longer enough for plants to conserve energy and make some for themselves. Now the goal is to make plants energy self-sufficient or, better still, net producers of energy.

Indeed, that filthy water flowing into the headworks looks more like fuel every day.

Think of the potential impact tens of thousands of clean-water plants can have on the nation's energy picture. Cities and villages are major consumers of energy, and an Electric Power Research Institute study found that in midsize cities, 30 to 40 percent of electricity is used by water and wastewater utilities.

What if clean-water plants could achieve or surpass net zero energy? The demand on the nation's electrical grid would decline (or grow more slowly). Carbon emissions would decrease significantly. And the fuel used to produce this energy is clean — chemically the same (but for process impurities) as the natural gas that is becoming a preferred source for utility power generation.

Yes, digester methane belongs in the list of the nation's renewable energy sources, right there with wind, solar thermal, solar photovoltaic and geothermal.

More than conservation

Energy initiatives at clean-water plants began with conservation: doing the same work with less energy. Of course that's a worthy aim and is part of the pathway to net zero energy. (This issue of TPO reports on an excellent energy- and demand-reduction program in New Castle, Colo., enabled by energy reporting software).

Then came solar and wind energy — clean-water plants often have large properties, removed from central cities and residential areas, where it makes sense to install wind turbines and solar panels. This, too, contributes to self-sufficiency.

But the real engine lies mixed in with the influent stream — the organic matter that treatment plants are designed to remove. That wastewater contains significant energy, and most treatment plants have little things called anaerobic digesters to extract it in the form of methane. The more precious energy becomes, the more wasteful it looks to flare and thus waste that fuel.

And as long as those digesters are there, why not feed them more and produce more gas and more energy? Increasingly, treatment plants are doing just that. Suddenly, all sorts of organic materials we've called "wastes" are sources of fuel.

Model performers

East Bay Municipal Utility District in California (profiled in TPO last December) is one agency that has moved boldly into energy production. The plant adds food and process wastes to its digesters, and, as a result, already makes more energy than it can use and sells excess power to the local utility. By 2020, EBMUD expects to create twice as much electricity as it needs.

And digester methane can do more than just fuel combined heat and power systems. In New York City, the Newtown Creek Wastewater Treatment Plant (see August 2011 TPO) plans to sell its digester gas — cleaned and compressed — to a local utility for use as home heating fuel.

It's only a tiny step from there to using purified digester gas as fuel for compressed natural gas (CNG) cars, trucks and buses — potentially creating a new frontier in clean vehicle technology.

New outlook

There may not be "gold in that thar sewage," but there's lots of energy, and that's a commodity worth extracting and using.

Chances are that the day you came to work in a clean-water facility you never thought of yourself as operating a power plant. But, to the extent your facility made use of digester methane, you did. And if current trends continue, your own facility and thousands of others will look more like power plants every year. It's just another way the industry and the profession add significant value to our society.