Sewage Treatment With Solar Power

WSSC turns to solar power to cut sewage- treatment electricity costs

DC Water turns to digester to produce electricity

WSSC Headquarters

Nearly 8,500 solar panels covering 13 acres in Germantown began operating this month at a sewage-treatment plant in Montgomery County, one of the first in the Washington region to try solar power. The panels, also installed at a Washington Suburban Sanitary Commission facility in Upper Marlboro, began operating in October.
 

Solar panels are expected to provide up to one-fifth of the two plants’ electrical needs at rates 25 percent cheaper than traditional electricity.  For a utility, it’s a huge milestone, because very few have solar power.  The idea is catching on with water and sewer utilities across the country, in part because they guzzle electricity. Operating round-the-clock, the facilities run enormous pumps to deliver drinking water and then use huge blowers, centrifuges and other equipment to treat sewage and return the disinfected water to local rivers. Those energy costs can fluctuate dramatically, putting pressure on operating budgets.



Diagram of a typical wastewater treatment plant
using the Cambi thermal hydrolysis process
(courtesy of Cambi).

Sewage-treatment plants, in particular, are being looked at for solar power because vast parcels of land bought decades ago as buffers for nearby communities can accommodate acres of the panels.

Utility officials say they also are exploring ways to reduce their dependence on the electrical grid during and after severe storms, when power outages can wreak havoc on sewer systems and cause overflows into streams.
It’s also about saving money.

Blue Plains, Washington, DC

DC Water, the largest consumer of electricity in the District, is installing equipment similar to a giant pressure cooker at its Blue Plains Advanced Wastewater Treatment Plant in Southwest Washington. The equipment will “cook” and sterilize the brown, goopy sludge collected from treated sewage and turn it into food for methane-generating bacteria. The methane gas will then be burned to power steam turbines that produce electricity. DC Water officials expect the system to save the utility $10 million in electricity costs — and another $10 million in trucking costs because half as much sludge will need to be hauled away. The utility also is exploring selling the sterilized sludge as fertilizer.

The annual savings are expected to more than cover the debt service on the $470 

DC Digester Centrifuges

million borrowed for the project. That will free up money needed to repair and replace aging infrastructure, such as underground pipes that burst after too much decay.

The new process also is expected to cut the treatment plant’s greenhouse gas emissions by one-third. Blue Plains has less open land available for solar panels than some other treatment plants, he said. Still, DC Water is considering putting panels on some structures on the 150-acre campus.

The WSSC solar program is a public-private partnership. Washington Gas Energy Systems paid the $12 million to install the solar panels and will operate them for 20 years. The WSSC pays only for the solar power it uses. WSSC expect to save $3.5 million total in electricity costs over the 20 years and cut the two plants’ annual carbon dioxide emissions by 3,200 metric tons — described as the equivalent of taking 665 cars off the road.  

DC Water is the largest user of electricity in DC.  (Wash Post, 12/21/2013)