Colorado State University Professor Developing Anaerobic Digester to Reduce Cost of Waste Disposal, Particularly in Western States

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 mixing of the waste in addition to stimulation of the growth of microorganisms that convert waste into methane.

“In the arid West, you pay for water rights, so water use is very controlled and there’s a financial motivation for producers to conserve water, which is why management practices are different,” Sharvelle said.

Sharvelle and her graduate student, Luke Loetscher, are collaborating with Fort Collins, Colo.-based Stewart Environmental Consultants Inc. and the university’s Agricultural Experiment Stations to evaluate the feasibility of anaerobic digestion at Colorado feeding operations. She has an Extension appointment 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 underserved 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 and, at the same time, provide the operations with stable and predictable energy costs for multiple years in advance.”

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 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.

“Feedlots are huge and they produce a lot of manure, and the compost they produce is usually more than the area around them has demand for,” Sharvelle said. “Feedlots are often located in areas where there is not a lot of fertile farmland, so they’re ending up with this extra waste material that there’s nothing to do with.”

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.

Sharvelle is based in the College of Engineering. Her research interests include biological waste processing, water reuse and sustainable water and waste management. She also contributes to the CSU Institute for Livestock and Environment with the goal of finding practical, economical solutions to minimize environmental impacts from the livestock industry.