Turning Wastewater Into Clean Energy

Oct. 5, 2004 -- — One day, when you flush a toilet or rinse those dirty dinner dishes, you could be doing more than just washing waste down the drain. Soon you could be helping to produce watts of energy for your home and those in your neighborhood.

With fuel costs rising, many cities and local municipalities are increasingly looking for cheaper ways of producing electricity — including recovering energy from waste material such as sewage.

For now, many municipal water-treatment plants produce enough "biogas" — a methane-rich fuel derived from decomposing organic waste — to energize the plant's operation. But some researchers say there's a lot more potential power in wastewater that's being, well, wasted.

David Bagley, an engineering professor at the University of Toronto, along with graduate student Ioannis Shizas recently studied the waste from three local water-treatment plants. They determined that there was enough organic material in the wastewater to possibly produce up 113 megawatts of electricity — enough to power a small town for a year.

"Most [treatment] plants are not recovering the energy from biogas completely," said Bagley. "They use it to heat the water that aids in the waste-treatment process and maybe to heat the building, but that's about it."

From his research, Bagley believes wastewater could contain nine times the energy that typically is captured and used in a water-treatment plants. And to capture all that wasted potential energy, Bagley and other researchers believe new treatment processes will have to be used.

Flushing Out More Potential Power

For now, most treatment plants use a so-called aerobic process. Tiny microbes use oxygen and heat to break down the wastewater's organic material into carbon dioxide, other tiny microorganisms, and biogas. While the gas is siphoned off and used to create electricity and heat through a furnace or even a fuel cell, the organic byproducts are dumped with the rest of the effluent.

But Bagley believes that by implementing an "anaerobic" process — one that doesn't require oxygen — first, plants can recover a greater percentage of the organic material can be recovered before the effluent is discharged from the treatment plant.

Bagley isn't alone in his research or his quest to squeeze the most out of dirty water. Reza Iranpour, chair of the engineering and research committee at the California Water Environment Association in Oakland, says anaerobic processes are one of the many ideas being pursued by municipal water treatment facilities around the world.

Dollars Down the Drain?

"Many [wastewater treatment] plants in Europe and the U.S. are looking into this," said Iranpour. "When you can recapture this gas efficiently, you can burn it for energy … you can get lower [operating] costs. Bottom line: it becomes a resource."

But he notes that the number of plants using anaerobic processes is still probably very low because adding new equipment means additional costs for municipalities interested in keeping costs low. Still, he says some regions, such as California and Sweden, have begun to aggressively pursue these projects as part of larger alternative and environment-friendly energy programs.

Whether or not anaerobic treatment processes will become more widely adopted remains uncertain. And even Bagley admits the processes he used in his research were very much limited to laboratory conditions. The "technical challenge," he said, would be to design the process so they are "economically useful" to municipalities.

Bagley believes that with further research being conducted globally now, researchers will come up with a cost-effective answer within a few more years. And the payoff will be well worth it.

"There's a lot of energy in wastewater," said Bagley. "If we become clever enough, we'll find a way to recapture it."