Livestock wastes cause both odour and land and water pollution problems but can instead be treated, via anaerobic digestion, to produce methane à¢€” a valuable fuel for the local production and use of heat, power or both. Erin Birgfeld and Mark Schlagenhauf report on international efforts from the US to promote the use of methane as a fuel.
Methane is both the primary constituent of natural gas and a potent greenhouse gas when released to the atmosphere. Reducing methane emissions can yield substantial economic, environmental and energy benefits. In the agricultural sector, the implementation of anaerobic digestion technology can lead to improved air and water quality, odour control, improved nutrient management, a reduction in greenhouse gas emissions, and the capture and use of biogas à¢€” a source of clean, renewable energy.
Figure 1. Estimated global methane emissions from livestock manure management, 2005
Methane is a potent greenhouse gas when released to the atmosphere with a global warming potential over 20 times higher than carbon dioxide. However, methane is also a clean burning fuel that can be captured and used for renewable energy generation and to replace fossil fuels.
The liquid manure management systems found in large livestock operations promote anaerobic (i.e. oxygen-free) environments, these lead to methane emissions from the decomposition of organics in the waste. Anaerobic digester systems (AD) are designed to capture methane released from liquid manure and allow the recovered biogas to be flared or used as a clean energy source to produce electricity, heat, or combined heat and power (CHP) à¢€” in gas-fired equipment such as engines, boilers, or chillers. Biogas produced from AD systems is typically 60%à¢€”80% methane, with an energy content of 600 to 800 Btu per standard cubic foot.
Figure 3. US EPA AgSTAR database summary map, showing the 2008 number of operating manure digesters
Project development in this sector can help to reduce greenhouse gas emissions and provide alternative energy sources. In addition, AD systems offer other environmental benefits, including significantly reduced odour and improved water quality protection, while also providing opportunities for agricultural diversification. In the US, odour control is often a major driver for implementing AD systems. The benefits of controlling odour can lead to a better and more productive relationship with neighbours, an easier time getting appropriate permits, and being viewed as a good environmental steward.
EMISSIONS FROM MANURE MANAGEMENT SYSTEMS
Each day millions of tons of livestock wastes are disposed of in lagoons, tanks and other structures that result in emissions of methane into the atmosphere. Total emissions from manure management systems in the US livestock industry were 41.4 million metric tons of carbon dioxide equivalent (MMTCO2E) in 2006 à¢€” accounting for about 7% of total anthropogenic methane emissions in the US. Globally, livestock manure management contributes more than 230 million metric tons of carbon dioxide equivalent of methane emissions, roughly 4% of total anthropogenic (human-induced) methane emissions.
Three groups of animals account for more than 80% of total emissions: swine (40%); non-dairy cattle (20%); and dairy cattle (20%). Figure 1 identifies the countries with significant methane emissions from livestock manure management.
Globally, livestock wastes are handled and disposed of in a myriad of systems. In many countries where there is no regulation or enforcement, wastes are directly discharged (point sources) or indirectly discharged (non-point sources) into surface waters which can cause eutrophic conditions, kill fish, and cause poor water quality. These types of discharges are one of the major causes of measurable nutrient loadings in the Gulf of Thailand, South China and Black Seas. In countries where wastes are regulated, they are typically land-applied to crops and other vegetation as a means of fertilization and reducing/eliminating discharges to surface water. Wastes that are improperly managed or handled are known to cause disease and gastro-intestinal disorders.
AD SYSTEMS FOR LIVESTOCK WASTE MANAGEMENT
AD systems are typically used in the primary treatment of high strength organic materials, such as livestock and food processing wastes à¢€” handled as either liquids, slurries, or semi-solids à¢€” where biogas is recovered and combusted for energy use, process heating, or flared as an odour control or greenhouse gas management method. In many cases the value of the gas as an energy source can pay for these benefits and add to a farm’s revenue where utility markets are favourable. Anaerobic digestion also results in a number of environmental and human health benefits such as reductions in biological oxygen demand (BOD), pathogen reduction, and improved odour control.
An AD system consists of the following components: a digester, a gas-handling system, a gas-use device, and a manure storage tank (or pond) to hold the treated effluent prior to land application. Biogas digester systems can generally accommodate manure handled as liquid, slurry, or semi-solid. The total solids content of the manure à¢€” a measure of manure thickness à¢€” determines these classifications. Facilities best suited for biogas digester systems typically have stable year-round manure production, and collect at least 50% of the manure daily. Several gas-use options are available, ranging from simple flaring, to engines, chillers, boilers, and cogeneration power systems.
AD systems, when properly utilized, can reduce methane emissions and yield significant energy, economic and environmental benefits. Internationally, significant opportunities exist for expanding AD, and an increasing number of conventional and emerging technology applications are becoming commercially viable to target this market. These systems can vary in operational complexity and cost à¢€” depending on scale, climate, and type of energy use.
AD is currently used in a variety of energy applications worldwide, such as: generation of electricity, use in thermal applications, use as cook fuels and lighting to replace biomass in poorer regions, creating pipeline quality gas, and use as fuel for vehicles.
TYPES OF AD PROJECT
The following are descriptions of conventional AD technologies:
- covered anaerobic lagoons are constant volume reactors that are operated at ambient temperatures. Manure is treated under anaerobic conditions producing methane, which is recovered by using impermeable floating lagoon covers.
- complete mix digesters are heated digesters constructed of concrete or steel designed to enhance anaerobic decomposition and maximize methane recovery.
- plug flow digesters are heated systems for semi-solid dairy manure that operate at a constant temperature year round, producing gas at a stable rate.
Table 1 lists the types of AD projects that have been or are being implemented. Projects that produce a beneficial product such as electricity or process heat, have two greenhouse gas reduction components. Firstly, the project directly reduces methane emissions from the manure management system, and secondly, the project produces renewable energy that offsets greenhouse gas emissions from the combustion of fossil fuels and biomass.
OPPORTUNITIES AND CHALLENGES IN DEVELOPING AD PROJECTS
The US EPA, Department of Energy, and Department of Agriculture, implement a voluntary partnership program called AgSTAR that aims to promote the use of AD systems and to reduce the environmental impact of livestock waste and fossil fuel power generation. In the past ten years, the AgSTAR program has helped develop over 120 AD projects in the US. These projects contribute more than 250,000 MWh per year equivalent (output estimate includes generation from electricity projects as well as equivalent output for non-electricity producing projects).
AD projects operating in the US typically range in size from 50 kW to 400 kW and are most often implemented on either dairies or hog farming operations. About 12% of the existing projects are listed as cogeneration projects. These AD projects are located across 26 states, in addition, there are 56 projects that are either planned or under construction. Many of the newer digesters can co-mingle wastes and introduce additional substrates to the digester to increase gas production and energy generation. These additives can be a wide variety of materials, including wastes such as fats, oils and grease, or cheese whey from cheese-processing plants.
AD projects that include cogeneration can create additional environmental benefits by offsetting fossil fuel-based electricity and heating demands with a renewable fuel. In addition, using the waste heat from biogas-fired cogeneration engines can improve a return on investment by offsetting the costs of conventional fuels. Reciprocating engines using biogas have similar heat conversion efficiencies, as small natural gas generators and are approximately 28% to 33% efficient. In comparison, engines with cogeneration systems have been found to have an effective energy efficiency of 69% to 84%.
Although AD projects often make good economic and environmental sense, financing can pose a barrier due to high upfront capital costs and/or low electricity prices in some markets. Many countries and states have different policy strategies and incentives to help overcome these financial barriers to implementation. In the United States, the Department of Agriculture offers loans, loan guarantees, and grants, to farmers, ranchers, and rural small businesses to purchase renewable energy systems and implement energy efficiency projects. In addition, states themselves may provide various types of funding opportunities or incentives to improve financing. A listing of state and federal funding opportunities in the US is available on the AgSTAR website at: https://epa.gov/agstar/resources.html.
Another potential source of funding for AD projects is through the sale of carbon credits on a carbon market. These credits are generated as a direct result of the collection and destruction of methane, and as offsets from using a renewable energy source to generate electricity. A number of AD projects have taken advantage of both carbon credits.
In developing countries, AD projects can take advantage of the Clean Development Mechanism which allows emission-reduction projects in developing countries to earn certified emission reduction credits à¢€” these can be traded and sold and used by industrialized countries to meet a part of their emission reduction targets under the Kyoto Protocol. In the US there are a variety of voluntary markets where carbon credits may be sold, including the Chicago Climate Exchange which is a voluntary, legally binding, pilot greenhouse gas reduction and trading program for emission sources and offset projects in North America. AD projects are also often eligible to sell ‘renewable energy credits’ as well.
One important issue for projects in many developing countries is that direct discharge to water is often the predominant disposal option. This type of management causes a host of environmental problems, including surface water contamination, dispersal of disease, fish kills, etc. These sites can realize significant environmental benefits from improved sanitation and reduced odour, by installing AD systems and implementing improved manure handling practices. In the parts of the world where warm climates predominate, farms or AD projects may be limited in the amount of waste heat that can be utilized via cogeneration.
Another important issue for AD energy project viability in both developing and developed countries is energy price structure. Government policies on energy can promote or hinder the beneficial use of AD. An uncertain regulatory environment is often a concern among potential investors. For example, project developers can be subject to different and sometimes conflicting laws at the local, regional and national levels. Moreover, a lack of regulations governing manure handling and discharge (i.e. no requirement or incentive to manage manure in an environmentally sustainable manner) in some countries can inhibit project development.
As countries begin to implement laws, regulations, and policies to improve manure management practices, promote alternative energy, and address greenhouse gas emissions, the economic viability of AD projects à¢€” including those that utilize cogeneration à¢€” is expected to improve. Moreover, creating an atmosphere where potential investors (private sector, international development banks, and financiers) are secure in the technical and policy framework that supports AD energy projects, will be essential to project development.
The Methane to Markets Partnership brings together the collective resources and expertise of the international community to address technical and policy issues and facilitate AD projects. Early initiatives include:
- assessing opportunities for AD projects
- performing initial feasibility studies including the potential for CHP applications
- demonstration projects
- capacity building within a country to allow for replication of demonstration projects.
ACTIVITIES TO PROMOTE Anaerobic digestion INTERNATIONALLY
Through the Methane to Markets Partnership, the US EPA and US AID are working to support a variety of activities to promote acceptance and use of AD projects internationally. As an example, USAID and EPA are working with Mexico’s SEMARNAT to demonstrate appropriate AD systems in medium- to large-scale farms in the Lerma-Chapala region of Mexico. These and other biodigesters will create a basis for national standards and certification à¢€” used to reduce risk and improve product reliability à¢€” that will promote the benefits of technology and project replication in the region.
In India, US EPA is working with the International Institute for Energy Conservation to develop an AgSTAR India programme, initially targeted at the dairy industry and expanding to other relevant industries. The programme will develop a nationwide institutional system that promotes capture of methane from livestock and food processing wastes in the Indian milk producing and processing sector through anaerobic digestion technology and various gas uses.
US AID/India launched an AD programme in October 2006 to explore the potential for using cattle waste to produce methane-powered energy services for rural economic development. In Uttar Pradesh, USAID is working with community-run ‘gaushalas’ (old-age homes for non-productive, scrub cattle) to construct biogas plants for the conversion of cattle waste to thermal and electrical energy. This energy will be provided to the community on a user-fee basis to run micro-enterprises à¢€” such as a milk-chilling plant and flour mill à¢€” and to power irrigation systems and the delivery of drinking water. The waste slurry will be used as high quality organic compost.
Three gaushalas have been selected, beneficiary groups identified for energy off-take, blueprints for the plants developed through a multi-stakeholder participatory process, and an application for a subsidy made to the Ministry of New and Renewable Energy. Challenges remain though, including the development of a larger market for organic compost, leveraging additional funds to support energy-utilizing entrepreneurial activities, and handling the seasonal demand for energy.
The programme also targets the dairy industry for the capture and use of methane gas. Three dairies located in the state of Maharashtra, with diverse management structures, have been identified for piloting anaerobic digestion. They are the Warana Milk Cooperative near Kolhapur, Bharat Agro Industries Federation near Pune and Chitale Dairy near Sangli. They represent the co-operative, research and development, and private sector dairies, respectively.
Methane to Markets Partnership
In the area of anaerobic digestion, the Methane to Markets Partnership centres on identifying opportunities for AD projects and on promoting cost-effective electricity generation or direct use of the resulting biogas. Efforts include: the identification of barriers to project development; the improvement of enabling legal, regulatory, and institutional conditions; and the creation of efficient energy markets. The active involvement by private sector entities, financial institutions, and other non-governmental organizations is considered essential to build capacity, transfer technology, and promote private investment that will ensure the Partnership’s success.
For more information on Methane to Markets visit the website at: www.methanetomarkets.org.
The AgSTAR Program
AgSTAR, a collaborative effort of EPA, US Department of Agriculture, and US Department of Energy, is an outreach program designed to reduce methane emissions from livestock waste management operations by promoting the use of biogas recovery systems. This program helps to reduce methane emissions by encouraging livestock owners and operators to install AD systems and use the collected biogas as an energy resource. AgSTAR was launched to encourage productive use of this resource as part of the United States’ commitment to reduce greenhouse gas emissions under the United Nations Framework Convention on Climate Change. AgSTAR provides an array of information and tools designed to assist producers in developing projects, including:
- conducting farm digester extension events and conferences
- providing ‘how-to’ project development tools and industry listings
- conducting performance characterizations for digesters and conventional waste management systems
- operating a free hotline
- providing farm recognition for voluntary environmental initiatives
- collaborating with federal and state renewable energy, agricultural, and environmental programs.
For more information go to the AgSTAR website: www.epa.gov/agstar
Erin Birgfeld is with the US Environmental Protection Agency AgSTAR Program, Washington DC.e-mail: firstname.lastname@example.org
Mark Schlagenhauf is the global oil and gas advisor with the EGAT Bureau (Economic Growth, Agriculture, and Trade) within the US Agency for International Development, Washington DC.e-mail: email@example.com
Patterson Farms, New York
Patterson Farms is two miles from Cayuga Lake à¢€” a popular recreational facility. Its close proximity to this area was one reason that the farm constructed a digester to control odour and improve manure management. A 250 kW cogeneration system was installed to provide heat (to maintain the digester temperature) and supply electricity to the facility.
Food waste (whey) from a nearby Kraft Foods Inc. cream cheese factory is combined with dairy manure and fed into a complete mix digester which increases biogas production. Kraft Foods Inc. pays a tipping fee to the farm, which substantially improves the economics of the system. Biogas is produced daily and approximately one-third is fed to the engine to generate electricity, and the remainder is flared on site. Carbon credits from all the combusted gas may provide additional revenue to the farm.
Patterson Farm’s digester project has also resulted in odour and pathogen reduction from the manure, reduced risk of run-off and leaching of nutrient, and revenue from the sale of excess energy, food waste tipping fees, and carbon credit sales.
Mason Dixon Farms, Maryland
In 1979, Mason Dixon Farms began operating the first plug flow digester at a commercial farm. For over 25 years, the farm has produced enough electricity for the farm, with excess sold on to the grid. Today, a total of three digesters produce biogas that fuels up to five cogeneration sets that reliably produce electricity in excess of 95% of the time. Hot air recovered from the engines heats the water that is circulated through the digester to maintain constant biogas production, which is estimated to be 120,000 ft3 (3400m3)per day.
The project has increased farm revenue from the sale of electricity to grid, reduced heating costs, reduced animal bedding costs, and provided an additional revenue stream for the farm from the sale of these composted solids for use as a soil amendment.
Haubenschild Farms Dairy, Minnesota
Haubenschild Farms has 850 milk cows which generate enough electricity to meet the farm’s needs, plus the farm sells enough excess electricity to power the equivalent of 70 homes. Waste heat from the engine-generator set is captured and used to maintain digester temperature, building heat, and hot water.
With a mission to be a sustainable, environmentally friendly farm, Haubenschild has become a leader in agricultural sustainability in the United States. The farm recently became one of first dairies in the country to sell carbon credits on the Chicago Climate Exchange. Built in 1999 as an AgSTAR Charter Farm, the 350,000 gallon (1.3 million litres) plug-flow digester generates biogas from manure and newspaper that is used as animal bedding. Bedding and manure are scraped to the digester, where the biogas produced is then used to fuel a 150 kW engine-generator set. The engine-generator has greater than 96% operating availability.