The Key to Water Security Could Be Lurking in a New Mexico Sewage Farm

by Mark Harris (The Guardian) In Las Cruces, New Mexico, a pilot project is using heat-loving algae to clean wastewater and generate energy --- ... “Galdieria sulphuraria is one of the most interesting microorganisms on the planet,” says Peter Lammers, a professor in algal bioenergy at Arizona State University. “It grows in a witches brew, can degrade over 50 organic molecules and even photosynthesise like a plant.” That makes it ideal, Lammers says, to use somewhere even more unpleasant than Yellowstone’s volcanic springs: urban sewage farms.

At a pilot site in Las Cruces, New Mexico, Lammers and researchers at New Mexico State University are diverting effluent from the city’s wastewater treatment plant into row upon row of long plastic bags primed with Galdieria sulphuraria. Air enriched with carbon dioxide is pumped gently through the tubes, while plastic wing-like foils move slowly up and down to mix the concoction.

The aim? To build an energy-positive wastewater treatment that helps preserve rivers, lakes and estuaries, reclaims the chemical energy in sewage, utilises sunlight to expand that energy footprint and ultimately pays for itself.

“The line where we traditionally differentiated wastewater utilities from energy utilities is becoming more permeable,” says Sharlene Leurig of Ceres, a nonprofit organisation helping institutional investors integrate sustainability into US capital markets. “Alexandria Sanitation District in Virginia rebranded itself to Alexandria Renew Enterprises, creating a revenue stream from nutrients collected at their facilities, selling reclaimed water and generating electricity from their digesters.”

But existing digesters still leave behind a nasty residue packed with nitrogen and phosphorus.

At the Las Cruces pilot project, the algae use sunlight and carbon dioxide to grow, breaking down over 95% of the nitrogen and phosphates in a couple of days. The high temperatures and acid conditions are also tough on bacteria, viruses and parasites. Sewage treated like this should require 10 times less chemical disinfectant than usual.

Thanks to the algae’s photosynthetic growth, the system also creates around four times as much rich organic sludge as traditional sewage treatment. That sludge can then be turned into biofuel oil using processes called hydrothermal liquefaction and catalytic hydrothermal gasification, both well established in the biofuels industry.

“If we’re talking about commercialisation, then harvesting [the algal sludge] becomes a very big problem,” says Meenakshi Bhattacharjee, executive director of Rice University’s Center for Applied Algal Research in Texas, where she is using wastewater and algae to produce biodiesel. Even after algae has been growing for days, it still makes up only a few grams in every litre of water. “We have chemical and electric ways to harvest it but we need to design something that is much less expensive,” says Bhattacharjee.

Space is likely to be another issue. Lammers calculates that a farm big enough to handle the sewage of a million people would need around 15,000 acres of plastic bags, as well as plenty of sunlight to keep the photosynthesis ticking along. “That wouldn’t work in the most of the US,” he admits, “but it will work beautifully here in the desert southwest.”

Given the problems in scaling algal technologies in the past, with many startups struggling to produce biofuels at competitive prices, a focus on tackling farm waste might make sense, says Leurig: “So much of the discharge is coming from agricultural producers, so the cost of implementing technologies in the agricultural context might be more economically efficient than doing it at the city scale.” READ MORE