New anaerobic digester to reduce costs

Sep 3, 2010
by WLJ

A Colorado State University professor is developing an anaerobic digester that turns animal waste into methane using much less water than conventional technology, making it more economically feasible and easier for use by feedlots and dairies in western states. Anaerobic digesters are often applied at large animal feeding operations elsewhere in the country, largely in the Midwest or on the East Coast, because of the abundance of water resources, said Sybil Sharvelle, assistant professor of civil engineering. High liquid content waste is required by existing technology to enable pumping and mix- ing of the waste in addition to stimulation of the growth of microorganisms that con- vert waste into methane. Sharvelle and her gradu- ate student, Luke Loetscher, are collaborating with Fort Collins, CO-based Stewart Environmental Consultants Inc. and the university’s Agricultural Experiment Sta- tions to evaluate the feasibil- ity of anaerobic digestion at Colorado feeding operations. She has an Extension ap- pointment to help tackle issues related to agricultural waste throughout the state of Colorado.

Stewart Energy, a wholly owned subsidiary of Stewart Environmental Consults in Fort Collins, is working to commercialize the process and has an exclusive option to license the process from the Colorado State University Research Foundation, or CSURF.

Forbes Guthrie, CEO of Stewart Energy, said, “This process addresses a significant and under-served market of energy production from low-moisture biomass. In addition, the process will ultimately help the agricultural community to meet more stringent environmental regulations with regards to both air and water emissions.”

Sharvelle’s system is unique because it separates the digestion process into two major steps. How it works: Water is trickled over dry waste in a vessel to capture organic materials and convert nearly 60 percent of the solid material into liquid organic acids. The liquid is put into another reactor which is heated to incubate the bacteria living in the digester.

These bacteria then convert waste into methane.

That separation of processes also assists western farming and ranching operations that must contend with rocks and sand in the waste of the Held at KG Ranch, Three Forks, Montana

when they scrape it from their lots. These materials are detrimental to operation of conventional anaerobic digestion technology. With Sharvelle’s system, remaining solids from the first step—known as hydrolysis— are separated and can be composted.

The methane produced in the digester can then be used as a source of energy to run a generator and used in a natural gas pipeline once byproducts such as carbon dioxide are removed.

Biological processing through anaerobic digestion became common practice with wastewater treatment in the 1960s and 1970s, Sharvelle said. — WLJ