Municipal sewage sludge ranks high upon the list of things that are sure in life, right alongside death and taxes. The good news is that it can be dried and re-used as fertilizer, or upcycled into various forms of renewable energy. The bad news is that all these processes require energy, which can put you right back at square one in the fight against global warming. One way out of the energy-sludge matrix is solar power, and the US Department of Energy is betting $3 million that the sun can shine its sustainability light on wastewater treatment plants all across the nation

Sewage Sludge: Another Reason For Natural Gas Fans To Stress Out

To be clear, the Energy Department is not mapping out the solar powered sewage sludge revolution just yet. It is starting with a modest pilot project under the umbrella of the firm Solar Dynamics, but apparently hopes run high.

Earlier this week the Energy Department awarded a $3 million grant to Solar Dynamics as part of a new $45 million round of funding for solar energy manufacturing and grid technologies that “seamlessly integrate clean energy sources onto the grid.”

Solar Dynamics will add $21 million to its share of the pot, for a project under the title, “Solar-Thermal Biosolids-to-Fertilizer Demonstration.” Solar power is already beginning to ease itself into the sludge drying business, but typically these systems are based on latent solar energy and require drying beds with large footprints. The Energy Department has its eye on more compact, efficient systems.

“In partnership with a wastewater utility, this project will conduct pilot-scale testing and demonstration of solar process heat instead of natural gas to dry municipal sewage sludge and convert the dried granules into a high-value commercial fertilizer,” the Energy Department explained, adding that “This project will help decarbonize the agricultural, wastewater, and industrial sectors, as well as improve water quality and the economics of biosolids management.”

If you caught that thing about “instead of natural gas,” you’re on to something. Municipal wastewater treatment plants are gigantic energy-sucking operations. Transitioning them into renewables would cut fossil energy off from yet another major market.

What’s Cooking In Broomfield, Colorado?

The Energy Department doesn’t mention where the pilot project will take place, but Broomfield, Colorado is a good guess, because that is the location listed in the funding award, and Solar Dynamics is based in nearby Denver, and the company has previously won an Energy Department award for a solar power project in Broomfield.

In addition, Broomfield already has a leg up on the sewage sludge conversion game. It uses the familiar technology of bacterial digestion to convert raw sludge into reusable form.

“The treatment units are kept at 98 degrees F for approximately 20 days during which time the bacteria continue to break down the waste byproduct into a stable and beneficial organic material called biosolids,” Broomfield explains. “Biosolids are a nutrient-rich fertilizer and soil amendment that is used on farm ground.”

If you know your digesters, you know that renewable methane gas is another byproduct of the process. In the olden days it would have been flared, but in Broomfield they capture that gas and use it to keep the digester units at that optimal 98 degrees F.

“Wastewater treatment not a glamorous job by any standard, but it has its rewards. Knowing that future generations are being protected and the world they will inherit is a reward in itself,” Broomfield concludes.

Yes, it is.

Concentrating Solar Power To The Rescue

So, what is wrong with this picture? Nothing in particular, except that the stuff coming out of a digester is still heavy with water. Further processing and dewatering would lower the cost of transportation and potentially open up the range of commercial application.

If you are guessing that concentrating solar power is in play, run right out and buy yourself a cigar.

Solar Dynamics bills itself as a “a technology company leveraging practical experience, innovative designs, and state-of-the-art engineering tools to develop next-generation products and services for concentrating solar energy.”

The company’s previous solar power award was a $2,062,246 chunk of change to develop something called the DROP C (Drop-in, Ring-Of-Power Heliostat for COLLECTS, which refers to the company’s new “SunRing” design for heliostats, the specialized mirrors that collect solar power in a concentrating solar power plant.

“The new design allows the heliostats to be dropped into a location with drastic reduction of the preparation of the site location, which enables a reduction in costs and improves financing terms,” explains the Energy Department.

That project built on a previous award aimed at improving the technology used in the tower that receives all the solar power from a field of heliostats.

The company has also developed a new low cost, high efficiency parabolic trough-style concentrating solar design along two tracks, also with an assist from the Energy Department.

“The SunBeam is a conservative design leveraging bankable components, proven assembly approaches, and the support of a veteran team.  A second-generation, more technically-aggressive SunBeam variant is in parallel development,” Solar Dynamics hints.

Did they just say something about variants…?

Concentrating Solar To Haters: I’m Not Dead Yet!

So, which will it be for the sewage sludge project, the Sun Ring or the SunBeam? Our money is on SunBeam, but either way, Solar Dynamics pitches concentrating solar as a replacement for conventional fossil energy power plants, helping to keep the grid balanced no matter what the sun and wind are doing. That dovetails with the Energy Department’s plans for integrating more wind and solar power into the grid at the expense of fossil energy.

“Increasing contributions from wind and PV solar require US grid operators to address the challenge of steep ramps and multiple daily peaks to balance energy supply and demand,” Solar Dynamics explains, adding that its concentrating solar power plant design is “optimized for dispatch, capacity, and flexible operation.”

“This system provides a cost-competitive option to deliver on-demand solar capacity and ancillary services to the utility in much the same manner as current gas peaking plants,” the company concludes.

Concentrating solar power had plenty of doubters on its case back during the Obama administration. The Energy Department promoted concentrating solar as a showpiece for US renewable energy innovation, but critics argued that it was too complex and costly to compete with fossil energy on cost.

However, the technology has been catching on elsewhere around the globe big time, and the Energy Department seems determined not to be left behind in the dust. Even during the renewables-phobic tenure of former President and accused insurrectionist Donald Trump, the Energy Department kept plowing promoting the Obama administration’s SunShot initiative and plowing more R&D dollars into concentrating solar projects aimed at pushing coal, oil and gas out of the picture.

As for your friendly neighborhood sewage treatment plant, it looks like there is still plenty of room for renewable energy to help transform these massive energy-sucking systems into a more sustainable energy future.

Follow me on Twitter @TinaMCasey.

Image (screenshot): Parabolic trough concentrating solar power system courtesy of Solar Dynamics, LLC.