Clean water and clean energy sound like they should work in tandem. But at the Blue Plains Advanced Wastewater Treatment Plant — the largest such facility in the world, located on the banks of the Potomac River — it’s not always that simple.
Wastewater treatment requires a lot of energy. Some smaller facilities have been able to generate all of their electricity onsite or acquire it from carbon-neutral sources. But the greater level of treatment required by wastewater plants in the Chesapeake Bay watershed requires more power, making it harder to reach sustainability goals.
Blue Plains covers 175 acres at the southern tip of the District of Columbia. Operated by DC Water, the plant removes pollutants from wastewater to meet some of the strictest federal limits in the country before discharging it to the Potomac River, which flows into the Bay.
Much of that process requires electricity, making Blue Plains by far the largest consumer of energy in the DC region.
Nitrogen removal, in particular, takes a lot of energy.
“Those bubbles are our largest electricity consumers,” said Ryu Suzuki, a process engineer for DC Water, as he passed vast, bubbling pools of water during a recent tour of the plant.
The aeration process helps “create the right biology for the microorganisms to do the work for us,” Suzuki said. “We give [them] plenty of air, and the food is what we flush down the toilet.”
But Blue Plains is working toward both cleaner water and cleaner energy.
Radhika Fox, assistant administrator for the US Environmental Protection Agency’s Office of Water, participated in the tour of the facility and said she wished she could “bottle up” the progress made there, then spread those to others.
Fox said one of her priorities for the $50 billion in federal infrastructure funds flowing through her office is to help water utilities become “net-zero” in its carbon emissions. That invovles generating their own energy or accquiring it from renewable sources.
A wastewater treatment plant in Oakland, CA, was among the first to achieve the net-zero goal and even brings in outside waste products to produce more biogas fuel than the facility needs, allowing them to sell the excess. But the plant doesn’t have to clean its wastewater to the same degree as plants in the Chesapeake watershed.
Blue Plains purchases most of its power from the grid. But in 2015 it became the first plant in North America to use thermal hydrolysis to meet about 30% of its energy needs. The process uses heat and pressure to “cook” the solids left behind after water treatment. That produces methane, which then runs the turbines that produce electricity. The remaining, sterilized solid product is sold as a compost-like material to local farmers and gardeners.
“It’s incredibly energy efficient, and we are making use of what was once a liability and now recover it as an asset,” said Chris Peot, director of resource recovery at DC Water.
In 2020, the utility began erecting solar panels over its parking lots and other locations as part of a 20-year purchase agreement with a solar provider. The arrangement should save DC Water $4 million in operating costs over 20 years and make the facility more resilient in the face of a power grid outage.
A new headquarters located off the Anacostia River in the District’s Navy Yard, which opened in 2019, uses heat recovered from sewage to provide energy to the building.
Suzuki said the low-hanging fruit of that effort is finding efficiencies, or ways to “do more with less.” With energy and chemical costs skyrocketing for the plant, there’s no time like the present.
But the utility’s research and development team is exploring more innovative solutions. During the tour, Haydee De Clippeleir, director of water quality and technology, explained some of their pilot projects. In one, they “starve” the microorganisms that consume nutrients by withholding fresh nutrients for a period of time and then reintroducing them, which speeds up and improves the pollution removal process. “Imagine you’re starved for a week, and you go to a buffet,” she said.
The team also is working with a bacteria called anammox that, while finnicky, can remove nitrogen without additional energy inputs. That could reduce methanol costs and aeration by 50%.
Many energy-saving strategies are fueled by a desire to reduce costs — a necessity for public utilities, which often pass new infrastructure expenses on to ratepayers.
That’s a concern for Blue Plains, as it faces other costly regulatory requirements. DC Water, under a consent decree with the EPA, is partway through a $2.7 billion project to curb polluted stormwater overflows into Chesapeake tributaries. That entails building miles of underground tunnels to store sewage-mingled stormwater until it can be treated at Blue Plains.
Matt Ries, director of strategic leadership and sustainability at DC Water, said the utility’s energy initiatives are informed by “that push and pull of trying to continue to be good environmental stewards and protect resources for the District and the Bay — and keep things affordable for ratepayers.”