Waste Power is Flush With Success

High natural-gas prices, along with the the growing interest in both water quality and renewable energy, are fueling continued efforts to turn animal and human waste into economically viable power sources. Two current utility projects on opposite sides of the U.S./Canada border are focusing on new ways to encourage the capture of manure-based methane (or "biogas") as a generating fuel. In addition, Pennsylvania researchers have succeeded in generating electricity directly from human waste-water through the use of a bacteria-powered "microbial fuel cell."

Central Vermont Public Service, based in Rutland, Vt., is counting on the support of environmentally conscious consumers in its application to sell a new renewable-energy product dubbed "Cow Power." Similar to other utilities' wind-power initiatives, the plan would allow utility customers to opt to obtain some or all of their electricity from farm-based methane sources, at a $0.04-per-kWh premium. The surcharge would be paid back to participating farmers, to counter the expense of generator installation and to provide an additional income stream.

Similarly, utility planners in the Canadian province of Saskatchewan have initiated a pilot program with area pig farmers. Engineers at Clear Green Biotechnologies Inc. partnered with utility SaskPower to install a methane-digestion project with a 125-kW generating capacity. The design incorporates four microturbines and accompanying heat exchangers. The heat exchangers both partially warm the facility's hog barns and keep the digester's microbes at a comfortable 37ºC.

Clear Green Biotechnologies is using this installation to model the manure-management services it plans to offer other area pig farmers.

Meanwhile, scientists at Penn State University are investigating the possibility of waste itself—rather than the methane it releases—as a viable power resource. Researchers have developed a small fuel cell that harnesses the energy released by bacteria as it breaks down organic waste. Bacteria release electrons as they do their work. With the microbial fuel cell, these electrons are passed to an anode and then travel through a wire to a cathode, producing an electrical current. Similar devices have been developed to work with water containing chemicals such as glucose, acetate and lactate, but this is the first to use wastewater skimmed directly from a water-treatment plant.

As presently designed, the fuel cell only produces between 10 and 50 milliwatts of electricity per square meter of electrode surface. However, researchers hope future designs, with greater surface areas and more efficient materials, could aid development of self-powered water-treatment plants.