A New Way To Renew Biosolids

In one of the most significant nods to date toward the future of renewable wastewater biosolids, the U.S. Department of Energy (DOE) awarded Southern California Gas Co. (SoCalGas) $1.2 million for its part in a pilot project that produces natural gas and liquid fuel.

The DOE is paying for about half of the design and planning of the pilot plant, which is to be located at a municipal wastewater treatment facility near Oakland. SoCalGas is responsible for overseeing the design and obtaining necessary regulatory approvals.

“Wastewater treatment operations have had to move past the days when they could simply move their solid wastes to landfills,” said a representative of SoCalGas. “Landfills are filling up and there are increasing restrictions on, and costs for, landfill use. At the same time, more challenging renewable fuel goals are being set by many states. So, it makes sense instead to turn that waste into renewable energy.”

The plant will utilize a high-temperature and pressure technology provided by Genifuel Corporation, which combines pressure and heat to break down waste material extracted during the treatment process, a technique known as “hydrothermal processing.” It breaks this material up into its primary constituents of water, carbon monoxide, and hydrogen. The hydrogen and carbon monoxide are converted into renewable methane, which can be injected into natural gas pipelines. The system can also produce a liquid bio-crude that can be sold to refineries, replacing fossil oil and serving as a green fuel with zero net carbon emissions.

“This technology was originally developed by Pacific Northwest National Laboratory over a number of years and has been observed to be effective at lab scale,” said the representative. “We see promise in the technology due to its relative simplicity, which generally indicates a lower cost for the ultimate technology.”

As vital as the technology is, it is not the only breakthrough that has enabled this high-profile renewables program. Operations that are interested in implementing something similar will also be curious about how it secured its robust funding.

That process started with the Water Environment & Reuse Foundation (WE&RF) and its research mission to recover beneficial materials from wastewater. The organization contacted SoCalGas about helping it put together a proposal that would respond to a DOE solicitation for such projects.

“The process was led by WE&RF, which gathered a team that included Genifuel Corporation, which holds the license to the hydrothermal processing technology, SoCalGas, and several other participants,” the representative said. “The team responded to a competitive funding opportunity announcement issued by the DOE. Each of the submissions to the announcement is reviewed by a panel of energy experts and the best are selected.”

As part of the funding arrangement, the design of the project, which started in March, is scheduled to be completed in two years. It will then be eligible for “phase two” funding, which would lead to a full-scale commercial project. It won’t be until then that SoCalGas has a real handle on how much fuel it can produce, but there is reason for optimism.

“Wastewater treatment plants produce over eight million tons of dry weight of solids in the U.S. annually,” said the representative. “Estimates show that converting the wastewater solids produced by treatment plants in the U.S. with hydrothermal processing could produce about 128 billion cubic feet of natural gas per year and save treatment utilities $2.2 billion in solids disposal costs. A city of one million people could produce more than 600 million cubic feet of natural gas per year, save more than $7 million per year in disposal costs, and power nearly 7,000 vehicles per day.”

It’s also too early to forecast a return on investment, but SoCalGas expects “attractive returns” from sellable fuel and reduced disposal costs. If the technology is proven effective, there could also be benefits at wastewater treatment operations around the world in the form of wider adoption.

“This technology provides a new approach to dealing with waste material and other forms of wet biomass,” said the representative. “Typical approaches today involve anaerobic digestion. Hydrothermal processing technology does not use microbes to digest the waste material and because of that, it dramatically increases the amount of energy produced and significantly reduces the amount of CO2 produced. For this reason, it has the potential to significantly improve on the existing approach’s overall economics.”