Biogas

The process of anaerobic digestion benefits agricultural and dairy operations by providing a method for them to recycle animal waste and waste water into energy producing gases and quality fertilizer. In addition to serving as a waste management tool, it can be a profitable alternative for using an unending resource.

The best-known method of anaerobic digestion is the lagoon — a lined earthen pit where waste and used water from the operation are collected and digested. Bacteria digest the waste and produce gases, but may generate unpleasant odors that can permeate the air nearby.

Another type of facility is the enclosed waste management system or mechanical digester. These digesters manage organic waste by recycling nutrients, treating waste and providing odor control. They require less space than traditional lagoons and use the organic resources more efficiently. Enclosed anaerobic digesters include heated tanks or enclosed lagoons that exclude oxygen from the process, which enables bacteria to break down waste at an accelerated rate. The digester traps gases, which can later be burned to produce heat and electricity use or sale.

Anaerobic digestion affords many benefits:

  • Generation of electricity
  • Excess heat for dairy use
  • Odor control
  • Proven technology
  • Weed seed destruction
  • Low operation cost

Anaerobic Digestion Initiative

Idaho is the second largest milk-producing state in the west and ranks fifth nationally. Over half the dairy farm operations in the state are in the Magic Valley. Many Idaho dairy farms are large; a 5,000-head or larger dairy is not uncommon. The State requires dairies to manage wastes, but they remain largely untreated and land-applied. The result is concern for health, odors and flies.

A 5-year effort began in 2000 to educate the dairy and livestock industries on anaerobic digestion processes and help them incorporate these technologies into their operations. These processes reduce input waste volume and mass as well as the volume of landfill gas emitted into the atmosphere, while producing a methane- and carbon-dioxide-rich biogas suitable for energy production. The U.S. Department of Energy's Regional Biomass Energy Program (RBEP) provides a wealth of bioenergy resources and has been closely involved with anaerobic digestion research for years.

With RBEP support, a relatively new anaerobic digestion process, anoxic gas flotation, developed by Cyclus Envirosystems, Inc., has revolutionized anaerobic digestion for daily use. It works with flush, scrap or vacuum systems, so dairymen do not need to invest in new infrastructure. It also retains bacteria, significantly reducing retention time, and maximizes fuel production.

The Idaho Governor's Office of Energy Resources has a two-phase system to assist dairymen in treating wastes and converting them to profit. A grant from the Department of Energy provides outreach and education on anaerobic digestion and design and feasibility analysis tools for a typical dairy installation. A partnership of federal, state and local agencies, technology providers and utility and dairy industry representatives worked together, and an Advisory Committee provided expertise on optimizing benefits to dairymen and the community and obtaining funding. Additional DOE funding for the second phase of the project supports installation of the technology into dairies.

Phase I identified barriers to implementing the technology including markets for generated power and direct project funding. The most promising avenue for sales is through the Public Utilities Regulatory Policy Act of 1978, which requires utilities to purchase electric power from qualified facilities (QF) at the "avoided cost." An Independent Power Producers group brought about changes to Idaho Public Utilities Commission rules so that the maximum length of a power sales contract is now 20 years, with an avoided cost of approximately 6.1¢ per kWh. Although some problems remain, the process is workable, and avoided cost rates make many projects financially attractive. Direct state funding enabled some Idaho dairymen transition to anaerobic digestion technology, but overall program success was limited. The results of the Anaerobic Digestion Initiative indicated that dairymen are not likely to incorporate the process into their operations unless renewable energy production has a greater value in the state, they are forced to treat their wastes appropriately, or both. Another potential solution is to have separate entities not associated with dairies build and operate anaerobic digesters. Under such an arrangement, the Idaho Falls-based engineering company Intrepid Technologies built and now operates an installation near Whitesides Dairy near Rupert. Some of the methane is used to heat the dairy, and the remainder will be processed to commercial grade and sold to Intermountain Gas. With a similar business plan, Beranna Dairy near Caldwell is teaming with Sot Chimanos, an Eagle company, to install a $4 million digester that will produce about 3.2 megawatts beginning in 2008.

Anaerobic digestion is a superior waste treatment method that offers profitable co-products. The question is no longer if, but when it will become common in Idaho diaries.

Last Modified: Friday, February 28, 2014