Livestock producers are seeking new ways to deal with manure from their operations in a safe, efficient and sustainable way, especially in these times of nutrient management concerns. Among the options being considered is the use of an anaerobic digester.
Henk Huizenga of Ottawa Valley Harvestore in Kemptville is working with two large Ontario operations on the installation of two such systems developed by Engineered Storage Products Company, parent of both Harvestore and Slurrystore, and points out the benefits to large dairy operations - those with a minimum of 125 to 150 cows - in reduced fertilizer and Hydro costs, odour reduction and composted biosolids for re-sale.
An anaerobic digester is a completely closed (oxygen free) system that receives and biologically treats manure with naturally occurring organisms.
A successful system should be easy to operate, cost effective and characterized by consistent and significant reduction in volatile solids, production of methane rich biogas, and discharge an effluent with less odour, pathogenic organisms and weed seeds than was present in the incoming waste. In a successful system, no additives or additional organisms are required.
Biogas production is best suited for farms that handle large amounts of manure as a liquid, slurry, or semi-solid with little or no bedding added. Biogas systems require a financial investment and management responsibility. The system must be designed by an experienced consultant, who is well versed with the requirements associated with biogas production.
A typical digester system will have a retention time of 20 days. To size a digester, take the daily manure production in your operation and multiply by 20. Research has shown that an above ground mixed reactor similar to tanks designed by Engineered Storage Products Company (ESPC), is going to be more efficient than a plug flow system.The largest component of a digester system is the digester tank. ESPC has been manufacturing and installing glass to steel structures since 1949. They have been designing tanks used in digester systems for more than 25 years. Most ESPC dealers can also supply reception pit pumps, manure storage structures, manure spreader tanks, and solids separators. An Engineered Storage Products dealer can also complete the installation of many of the digester components. With these partners in mind, a farm owner can determine his or her desired role in the project development process. The selection of an engineering consultant or developer is a critical decision. The farm owner often relies on the consultant or developer to manage the process of transforming a feasible idea into a functional facility. In addition to a consultant that designs the digester system, the owner may need to team with other equipment vendors.
Have your engineering consultant call your local authorized ESPC dealer today for a price quotation for a digester tank.
• Engineering Consultant
• Engineered Storage Products Company
• Authorized ESPC dealers
• Additional Vendors
Biogas is approximately 60 percent methane and 40% carbon dioxide, with a heating value of approximately 600 Btu/ft3.
Gas of this quality can be used to generate electricity, as fuel for a boiler, space heater, or refrigeration equipment; or it may be directly combusted as a cooking and lighting fuel. Most equipment that uses natural gas, propane, or butane fuels can be modified to operate on biogas.
Digester systems offer potential economic and non-economic benefits.
Actual benefits will vary from farm-to-farm. Recovered biogas can be utilized in a variety of ways.
Research has shown that anaerobic digestion does not lower the total amount of nitrogen, phosphorous and potassium in the manure but does increase the amount of ammonia nitrogen. The manure effluent will have a higher nutrient availability and plant uptake may be improved with digestion. Fertilizer purchases are expected to be reduced and crop yields possibly improved.
Perhaps the greatest potential indirect economic benefit comes from the reduction in risk of legal action and forced outright closure. Farm employees as well as neighbors would prefer not to deal with odours associated with manure management.
After digestion, compounds, which usually produce odours, are greatly reduced.
Digester systems, properly designed and operated, significantly reduce the odours associated with manure storage and distribution.
Also depending on the operating conditions, pathogenic organisms may be reduced by as much as 90%.
Electricity can be generated for on-farm use or for sale back into the power grid.
The most common technology for generating electricity is an internal combustion engine with an induction generator. The predicted biogas production rate and the operating plan are used to size the electricity generating equipment.
For some dairies, this may be the most cost effective option for biogas utilization.
Other energy use options may exist. For example, a nearby greenhouse could be heated with the bio-gas, and carbon dioxide from the heater exhaust could be used to enhance plant growth. These options need to be evaluated on a case-by-case basis.
For more information an anaerobic digesters, poit yoru browser to www.slurrystore.com or call Huizenga at 1-800-267-7940.
From the Archives:
Construction, February 2003
