Sewage treatment has always been a dirty business, dating back to the frontier days when “waste management” meant the guy who followed after the horses with a bucket and shovel.
However, thanks to modern technology, there are ways to turn some of the treatment processes into clean energy that can power public infrastructure facilities.
The Hornsby Bend Biosolids Management Plant in Austin, Texas, located on 1,200 acres of land along the Colorado River, is a national model for innovative approaches to improve the environment, such as reducing waste, producing compost, and protecting ecosystems.
Each year, thousands of tons of biosolids, the nutrient-rich organic materials resulting from the treatment of sewage sludge, are anaerobically digested and composted with Austin’s yard trimmings into an EPA-certified soil conditioner called “Dillo Dirt” (as in armadillo). This popular product is sold to commercial vendors for sale and use in public landscaping projects across the city. Demand for “Dillo Dirt” often exceeds available supply.
During the 1980s, an initial effort to improve energy efficiency at the plant started when two 400 kW converted diesel generators were installed. The generators were fueled by a mixture of digester biogas from the site and diesel fuel. This worked fairly well, but after 20+ years the old generators are no longer serviceable or repairable, and in recent years the gas has had to be flared.
Austin decided to use $1.2 million of its Energy Efficiency and Conservation Block Grant from the American Recovery and Reinvestment Act to replace the old equipment with modern “biogas rated” generation equipment.
The new generator equipment will generate clean electricity by utilizing digester methane from the sludge treatment process without the use of fossil fuels. In short, the same anerobic digesting process used to create the Dillo Dirt will also make the biogas used to power the generators. The result will demonstrate distributed clean power generation, reduce the facility’s operating costs, and offset on-peak operation of the plant, thereby contributing to Austin’s effort to avoid building new conventional power generation plants.
The new equipment is on order and the city intends for the project to be fully operational by the middle of next year. This single generator should generate more energy than the entire Hornsby Bend facility uses, thereby offsetting the plant’s total energy use and generating a credit to the water utility.