Eliminating sewage is an energy-intensive process that is a key component of our modern lifestyle — but rather than just processing it, groups and utilities are looking to make energy from what we flush down the toilet.
“There’s five times more energy in domestic wastewater than is needed for treatment,” said Lauren Fillmore, a senior program director at the Water Environment Research Foundation, speaking Wednesday at the Energy Department’s Biomass 2014 conference. “This is a renewable energy source,” she said. “As the population grows there is going to be more of this material available.”
A quarter of sewage treatment plants use anaerobic digestion to break down waste and a quarter of those harness the produced methane to run engines or boilers to produce electricity or combined heat and power, according to Todd Williams a wastewater engineer with CH2M HILL.
Using a process called swing adsorption, the gas can be upgraded to a natural gas equivalent that can be put into the pipeline system or compressed to run vehicles. William Eleazer, a supervising engineer with Brown and Caldwell is using the swing adsorption process at a sewage treatment plant in St. Petersburg, Fla., expected to be completed by 2017.
Fair Oaks Farms dairy in Indiana already uses the process to produce natural gas for its farm vehicles from cow manure.
Another technology, called hydrothermal processing, is twice as effective as anaerobic digestion and in a fraction of the time can produce biocrude oil to make biogasoline and other drop in fossil fuel equivalents, said James Oyler, president of Genifuel, which is deploying a pilot project next month to produce biocrude oil and methane gas from algae.
The process can use a variety of wet waste like sewage sludge, manure, wood pulp, potato peals or beer-making waste heated to more than 600 degrees Fahrenheit at 3,000 psi. His company has developed four pilot scales to figure out how to lower costs and hopes to scale up to a commercial system after completing its latest project.
“Wet waste could supply more than 15 percent of U.S. fuel supply,” he said. “Wet waste materials are all around us — we produce them every day and there are huge quantities of these things worldwide.”