California Dreamin': Dealing with Biosolids
California, as we all know, is the quintessential center of clean energy and environmentally sound practice. It's also the setting for one of the Rolling Stone's 500 greatest songs of all time by the Mamas & the Papas-California Dreamin'. So when the hauling of hundreds of truckloads of biosolids (type of sewage sludge) from Ventura, Calif., to a central California landfill (150 miles) became too problematic, the Ventura Regional Sanitation District decided to deal with the problem. Their solution: process the biosolids into a more benign fodder at a closer facility-using very little if any fossil fuel to accomplish the task. That's dreaming.
The solution involved four major elements: a closer existing landfill, two 80-ton per day batch dryers, nine microturbines, and $19 million. Sounds simple doesn't it?
It was determined that an old landfill closer to Ventura than the other "long-haul" landfill had enough inherent gas to sustain gas burners on the two batch dryers plus power nine 250-kilowatt microturbines for a total of 2.32 megawatts of electricity. Within two years, the gas extraction pipes, gas treatment systems (to remove water, sulfur and siloxane), blower/compressor units (to fire the burners and the turbines), batch dryers, and receiving hoppers were all installed. Southern California Edison and other entities provided incentives and a million-dollar grant, and the project was installed with likely payoff in about 10 years.
The process seems fairly efficient. Biosolids are hauled to this closer facility and dumped into receiving hoppers where they are dried to a dirt-like material consisting of 70 percent solids and no pathogens. The U.S. EPA Class A recyclable solids are currently used as daily cover for garbage material entering the landfill. In the future, these solids may also serve as fertilizer or biomass fuel. Water that is extracted is used as dust suppressant. About one-third of the electricity produced by the microturbines is used to power the facility.
This project has taken a problematic biosolids waste and turned it into a fuel for a money-making, renewable-energy-producing power plant. Greenhouse gases have been substantially reduced by converting biosolids- and landfill material-derived methane to carbon dioxide and by reducing transportation fuel consumption.
Advances at the Energy & Environmental Research Center give this project an opportunity to push the economics even more into the black, especially for regions that don't have southern California incentives. One way to improve on the cost return for this model might be to improve on the landfill gas cleanup technology. EERC has performed extensive research in gas cleanup systems and sees that technology as a developmental area.
In short, this particular situation with the proximity of the existing landfill, southern California incentives, and financial backing may not be the same in other regions of the U.S. But the simple concept of using renewable energy to drive off moisture from wet "biomass-like" material is not only a concept worth dreamin' about, it's worth repeating.
Chris Zygarlicke is a senior research manager at the EERC. Reach him at firstname.lastname@example.org or (701) 777-5123.
NEPCon, NSF International, Westervelt Renewable Energy recognized by Sustainable Biomass Partnership