One wastewater treatment plant to rule them all, with solar power (photo courtesy of Engie).

Solar Power To Gild The Wastewater Treatment Lily

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The Intertubes have been buzzing with news about a soup-to-nuts sustainability makeover for a wastewater treatment plant in California, but why? The all-inclusive work features an on-site solar power plant of 1.1 megawatts, which sounds like small potatoes. Also, wastewater treatment is not particularly exciting compared to electric vehicles. However, the company behind the upgrade has many more solar gigawatts in the pipeline to help push the US energy transition into high gear, and it looks like no job is too small to catch its attention.

How Many Gigawatts Of Solar Power? This Many!

The company tasked with transforming the wastewater treatment plant from climate zero to climate hero is the diversified French energy firm ENGIE (see more coverage here). It has been active in the US renewable energy scene for several years now through the ENGIE North America branch, headquartered in Texas.

One recent highlight is a 200-megawatt solar farm under construction in South Dakota, which is helping to position the state as an exporter of clean power. The off-taker is the electric cooperative Basin Electric Power. When the solar farm revs up later this year, it will add to the grid mix used by Basin’s membership of 131 other electric coops spread among nine different states.

Two hundred megawatts is peanuts compared to ENGIE’s overall plans for the US energy market. Last December, the company announced that it sealed a deal for 2.7 gigawatts’ worth of solar projects from the Texas branch of the UK company Belltown Power. The deal provided ENGIE with instant claim over Belltown’s 33 different projects in various stages of development. In addition to 2.7 GW of solar, the total capacity includes 2.6 GW in standalone energy storage and another 0.7 GW in paired energy storage, for a total of 6 GW all together.

That’s a big leap over ENGIE’s total US investment in renewable energy capacity in the US to date, which stood at a mere 3.9 GW as of last summer.

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Why Sludge Matters

ENGIE’s wastewater treatment project involves the public utility West County Wastewater District of Richmond, California. It is anticipating a savings of more than $83 million over the life of the project, while cutting greenhouse gas emissions by 93%.

It’s worth noting that the wastewater treatment plant in question is no mere wastewater treatment plant. It goes under the name, “Water Quality and Resource Recovery Plant.”

While the solar power angle is an interesting angle, that thing about resource recovery is even more interesting. In the olden days, the leftover biosolids (aka sludge) from wastewater treatment plants were simply dumped in a landfill. Nowadays, there are opportunities to recover resources from biosolids. Generating biogas is a starting point. If the biosolids are “pure” enough — meaning primarily they consist primarily of digested foods and other organic matter — they can be further digested at the treatment plant, processed into an inert mass, and recycled as a soil enhancer, similar to the use of livestock manure as fertilizer.

That has been a major sticking point for WCW’s treatment plant. To date, its biosolids have not qualified for recycling. Instead, WCW has been shouldering the cost of landfill disposal.

So, it’s no surprise that the 1.1 megawatts of onsite solar power is just one highlight of the upgrade. Another key element is an overhaul of the plant’s biosolids management system. The plan includes new digesters, along with new facilities for dewatering and drying the sludge, with the aim of approval for soil enhancement. In addition to saving on disposal costs, WCW will eliminate greenhouse gas emissions related to the decomposition of its biosolids at the landfill.

Let’s Hear It For Energy Efficiency-As-A-Service

ENGIE’s Managing Director at Engie North America, Stefaan Sercu, explained why the project is of particular interest in a press statement. Describing it as “one of the most impactful energy, infrastructure and process improvement programs in the United States,” he said that the project will “serve as a proof point for the benefits of the comprehensive energy collaboration approach.”

He’s not kidding around. If all goes according to plan, the upgrade will showcase how cash-strapped local utilities can upgrade their treatment plants without shelling out the big bucks up front, and even cut costs in the long run.

ENGIE is performing the work under an energy savings performance contract that aims to cut 4.2 million kilowatt-hours off the plant’s annual energy consumption. Along with solar power and other efficiency upgrades, the new biosolids management system will deploy biogas to run a 450-kilowatt cogeneration system. Engie anticipates that all together, the new systems will account for almost all of the electricity needed by the treatment plant and other WCW facilities.

Solar Power Is Just The Tip Of The Iceberg

ENGIE may be on to something. The overall wastewater treatment market in the US is enormous and never-ending. The US Environmental Protection Agency estimates that 34 billion gallons of wastewater from homes and businesses goes into a treatment plant every day, where it is subjected to a series of energy-sucking processes before clean water and biosolids come out the other side. The US Department of Energy estimates that municipal treatment plants account for 30 terawatt-hours per year of electricity.

CleanTechnica has dipped into the wastewater topic every now and then, and there is a lot to see in terms of solar power and other renewable energy resources. That’s because treatment plants tend to occupy large swaths of land, some of which could be repurposed for sustainable energy generation. CleanTechnica is reaching out to ENGIE for more details about solar power at the WCW facility, so stay tuned for more on that.

Another interesting example of onsite solar power is taking place under the oversight of the Energy Department. In 2021, the agency devoted a $3 million grant to help the firm Solar Dynamics get its solar-powered biosolids drying process off the ground.

The organization Solar Paces has been tracking the company’s progress, and it looks like a game-changer is in the works. Solar Dynamics is applying its technology to a treatment plant in New Mexico, with the aim of improving the biosolids dewatering system. The end result would be a dry, granular fertilizer instead of a partially dewatered mass.

“There is a value to up-cycling biosolids as granular fertilizer instead of land-disposing them,” Solar Paces reports. “Biosolids, which are 80% water, are hauled sometimes hundreds of miles away and dumped in landfills or plowed into the land. This disposal process is compliant with federal and most state environmental statutes, but it is not environmentally optimal.”

In an interesting twist, the Solar Dynamics project involves concentrating solar power. That’s interesting because concentrating solar power systems have yet to gain widespread traction in the US. In contrast to solar cells that generate electricity, concentrating solar systems collect sunlight from reflective surfaces to generate high heat. The heat can be transferred to molten salt or another liquid medium for use in heat-dependent industrial processes that would normally rely on fossil energy.

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Photo: Solar power plant courtesy of Engie.


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Tina Casey

Tina specializes in advanced energy technology, military sustainability, emerging materials, biofuels, ESG and related policy and political matters. Views expressed are her own. Follow her on LinkedIn, Threads, or Bluesky.

Tina Casey has 3329 posts and counting. See all posts by Tina Casey