DC finds clean energy in its dirtiest water

Fri, 2015-10-09 06:00 -- SCC Staff


You might imagine that anything that can “turn poop into power” might generate a lot of juvenile headlines, and Washington, D.C.’s newly upgraded wastewater treatment plant has certainly done that. But it’s also dramatically cutting costs, carbon emissions and solid waste, making it worthy of a serious look from other utilities.

D.C. Water’s Blue Plains Advanced Wastewater Treatment Plant began generating electricity last month, the first in North America to use a new purification process that was developed in Norway. It is a major milestone, turning the city’s largest electrical customer into a producer.

How it works
The treatment process begins just like at any other wastewater facility. The unique part is at the end: the addition of a pressure cooking process to treat solid waste that would normally be trucked to a landfill. (A Washington Post infographic explains the process in detail and you can watch a video below.)

The new step is called thermal hydrolysis. In short, exposing that waste to heat and pressure sanitizes it and makes it easier for microbes to digest. Those microbes turn the organic matter into methane, which is then burned, driving turbines that generate clean power. In D.C. Water's case, it's generating enough power to run one-third of the plant, equivalent to the energy needs of 10,000 homes.

Reducing the carbon footprint
There is still some solid waste left over, but even it is cleaner. The process reduces the amount of waste from 1,200 tons of biosolids a day to about 600. That means fewer trucks on the road. It had trucked 60 loads daily to farms that were 75 miles away. With the waste cut in half, the truck trips will be reduced as well.

And while the final biosolids don’t come out smelling quite like a rose, it is a dramatic improvement. D.C. Water describes the leftovers as mulch-like. People may be able to buy them next year for use in their home gardens.

Delivers dramatic savings
The upgrades cost $470 million, but D.C. Water says they will end up paying for themselves. In addition to sharply reducing the energy it has to buy, the utility says it’s saving about $11 million a year on trucking and $2 million on treatment chemicals. And overall, the plant’s carbon footprint has been reduced by a third.

D.C. Water says it’s hearing from other utilities wanting to know more about the process and how well it works. Its deployment of the new process is the largest in the world, but the equipment needed to do it takes up relatively little space, making it an option for many urban wastewater treatment facilities.

The federal government is encouraging more to explore it. Water and sewer utilities use about 4% of the nation’s power, making them the largest consumers in most places, according to the Environmental Protection Agency and Energy Department. Reducing that consumption would ease the pressure on those communities.

Comments

Submitted by Joshua Grusing on
I wonder how close other plants are to this technology? Would other plants need a complete overhaul or can this process be integrated with existing equipment?