Cogeneration and solar power have brought big sustainability gains in Albuquerque — now operators are looking for more advances.
As the Southside Water Reclamation Plant taps biogas and solar resources, operators are looking for ways to make it even more sustainable.
The plant, New Mexico’s largest, treats an average of 50 mgd (76 mgd design) for some 650,000 customers of the Albuquerque Bernalillo County Water Utility Authority. Only 7 percent of the plant’s daily 5 MW electrical demand comes from the local utility, Public Service Company of New Mexico. The remainder comes from a pair of cogeneration units and a solar photovoltaic array.
Built in 1962 as a trickling filter plant, the facility was expanded and converted to an activated sludge process. It has 14 anaerobic digesters for creating biogas, according to Jeffrey Romanowski, chief engineer. Its South cogeneration system, built in 1985, is powered by a pair of 1.1 MW Cooper Superior (Eaton) engine-generators burning biogas. The North unit, built in 2002, uses mainly natural gas in two 2.2 MW Caterpillar generator sets. Both systems can burn either fuel or a blend.
“It wasn’t really done as a money-saving measure,” says Romanowski. “The point was to beneficially use the biogas and provide a reliable secondary power source. We also have an engine heat recovery system that generates hot water for some of the process buildings and for heating the digesters. That’s a cost savings over burning natural gas in a boiler.”
Across the plant, 63 percent of the energy comes from natural gas, and biogas provides 24 percent. The 1 MW solar installation, built in 2014, provides 6 percent of the energy under a 20-year power purchase agreement with SunEdison.
“We have to either buy power from our local utility or make it ourselves,” Romanowski says. “When you run the numbers, you get into upwards of $400,000 in savings. Looking at the relative costs, grid power is 10 cents per kilowatt-hour on peak, natural gas-generated electricity is about 6 cents, solar is 5.4 cents, and biogas-generated electricity is about 1.7 cents.”
Most of the effluent from the Southside plant goes to the Rio Grande. About 1 to 1.5 mgd is reused, half in the plant and half for landscape irrigation in the community. Biosolids are sent to the authority’s Soil Amendment Facility, where 75 percent is land-applied and 25 percent is turned into compost.
There’s more to the Southside plant’s drive for sustainability than cogeneration and solar power. All metal halide and sodium vapor lamps are being changed over to LEDs to save energy and money. There have been discussions about replacing the cogeneration sets with high-efficiency gas turbines.
“We had a consultant do a study on our blowers,” adds Romanowski. “We have these old 500 hp blowers and we’ve talked about going to the new high-efficiency turbo blowers. We’ve done some preliminary studies on transitioning, but there’s obviously a huge capital cost, so that’s on the horizon.
“When we first looked at it, they were pretty expensive. We hope that over time those prices will come down. The reality is that our blowers are getting old and at some point will have to be replaced. We’ve replaced a couple over the years. Even though turbo blowers are a big outlay, they’re more efficient and that plays into the decision.”
Romanowski is also following industry research into the de-ammonification process, which uses anammox bacteria and ammonia-oxidizing bacteria to produce nitrogen gas. It makes it easier to remove nitrogen and requires much less energy for aeration.
“By doing that, you reduce your air requirement considerably, and if you can do that you can save a ton of energy,” says Romanowski. “We’re always looking at industry trends, and they seem to be migrating that way in Europe. Our plant would be a good candidate to switch over to use that process, but it’s in the five- to 10-year horizon.”
All told, the water authority has spent about $20 million on renewable energy projects over the years and saves about $2 million a year over buying electricity. Annual savings are about $1.34 million by using natural gas, $400,000 from using biogas, and $113,000 from solar energy. More solar power is under consideration.