Methane digesters that collect and burn methane from manure can provide numerous benefits to livestock producers and the environment. Still, digesters have not been adopted widely, mainly because the costs of constructing and maintaining these systems have exceeded the benefits accruing to operators. Currently, there are 157 methane digesters operating in the U.S., of which 126 are on dairies and 24 are on hog operations.

Methane is a potent greenhouse gas (GHG), and burning 1 ton of methane is equivalent to eliminating about 24 tons of carbon dioxide. There are a number of policies that could encourage farmers to use a digester to reduce methane emissions, either by providing financial inducements for those who install a digester or by penalizing those who do not.

A carbon offset market is one mechanism currently used for valuing methane emissions reductions. An offset market allows livestock producers who reduce methane emissions to sell these reductions, or “carbon offsets,” to other greenhouse gas emitters who face emissions caps or who voluntarily wish to offset their own emissions. Currently, only a few U.S. livestock operators sell offsets in regional or voluntary carbon offset markets. This is partly because the carbon prices in these markets have been low. However, future efforts to reduce greenhouse gas emissions could result in substantially higher carbon prices.

If farmers could earn a higher price for their methane emissions reductions, then digesters could become profitable on many more operations. However, there is likely to be wide variation in the scale, location, and characteristics of the operations that would benefit. The main beneficiaries would be producers whose operations emit substantial quantities of methane—particularly, dairy and hog operations with lagoon or pit manure storage facilities. Among these, larger scale operations will likely profit more from higher carbon prices because it is generally more cost effective to construct and operate larger digesters than smaller ones. Consequently, in the long run, valuing emissions reductions could encourage further concentration in the dairy and swine industries unless ways are found to promote the adoption of digesters on small-scale operations.

Digester profitability and adoption

Methane digesters, also known as “anaerobic digesters,” “biodigesters,” or “biogas recovery systems,” can be used to capture and burn methane from lagoon or pit-type manure storage facilities. With lagoons (earthen storage ponds), covers are installed to capture the methane. With pit systems (concrete or metal tanks located above or below ground), manure can be heated to encourage methane production. Digesters collect manure, optimize it for the production of methane by adjusting temperature and water content, capture the biogas, and burn it for heat or electricity generation. Burning methane reduces its global warming potential, which corresponds to a reduction in greenhouse gas emissions that could be marketed as a carbon offset.

Several factors influence the profitability of methane digesters and consequently determine which types of producers are likely to adopt the technology. These factors include an operation’s manure management method, startup and ongoing costs of a digester, buying and selling price of electricity, onfarm electricity expenditures, and carbon offset price. Many of these factors vary with farm size and location.

Only operations that generate a significant quantity of methane are viable candidates for biogas recovery systems. When manure is kept in oxygen-free (anaerobic) conditions that exist in lagoons, ponds, tanks, or pits, it decomposes to produce a biogas containing about 60 percent methane. When manure is in oxygen-rich environments, such as when it is deposited on fields, it generally produces little methane. Many dairy and swine operations employ anaerobic manure management facilities. Dairy cattle and swine are each responsible for 43 percent of U.S. methane emissions from livestock manure. Other livestock sectors predominantly using aerobic manure management methods, including beef cattle, sheep, poultry, and horses, are collectively the source of only 13 percent of emissions.

Anaerobic manure management methods are generally more common on large-scale operations. For example, only 38 percent of dairy operations with fewer than 250 head use anaerobic manure management systems, compared with 56-73 percent of larger operations. Consequently, larger operations produce a disproportionate share of methane emissions; dairies with more than 2,500 head accounted for 19.7 percent of total emissions in 2005, though they only produced 13 percent of dairy output.

There is substantial variation across regions in manure management methods and, consequently, methane emissions. Dairies in the West and South are much more likely to have lagoon systems than those in the Midwest and Northeast. Dairies in the West produce 43 percent of all emissions from the dairy sector, reflecting that region’s large share of output and the prevalence of lagoon systems.

The costs of building, maintaining, and repairing manure storage facilities and electricity generators generally decline on a per head basis with the size of the operation, which makes digesters more cost effective for larger scale operations. In addition, there can be substantial transactions costs associated with selling electricity or certifying and marketing carbon offsets. Larger operations can spread these costs over a larger revenue base.

Digester profitability depends on the value of the electricity generated, which varies by farm size (electricity use per head declines, on average, as herd size increases) and by region (electricity is most expensive in the Northeast and least expensive in the West). In most States, operations that generate more electricity than they use can sell their surplus electricity to the grid. However, the selling price of electricity varies widely and depends, in part, on whether local utilities are required to purchase renewable energy. Renewable energy mandates can substantially raise the selling price for digester-generated electricity and make adopting a digester more profitable. Whether an operation has surplus electricity depends on its generating capacity relative to its demand. On average, dairies in the West and South use substantially less electricity per head than farms in the Midwest or Northeast, and so have more electricity to sell.

Carbon revenues would accrue to Western dairies

ERS researchers used data from USDA’s Agricultural Resource Management Survey (ARMS) and a model of digester profitability to estimate the number, size, and location of dairy and hog operations that might adopt a methane digester at different carbon offset prices. ARMS is conducted by ERS and USDA’s National Agricultural Statistics Service (NASS). The researchers also estimated the distribution of the discounted stream of revenues over the life of the digester from emission reductions, the value of electricity generated, and total profits.

Research results indicate that even with moderate carbon offset prices, offset sales could substantially increase revenues for farms with digesters. At $13 per ton for carbon, the revenues from offset sales for dairies would exceed the value of digester-generated electricity by almost 30 percent. The revenues from digesters would accrue mainly to large-scale operations. Over 15 years, digesters would be worth $419 million to dairy operations with at least 2,500 head, or about 46 percent of the total value of dairy digesters.

Profits per farm and per head increase with farm size, which could give larger operations a substantial competitive advantage. At $13 per ton, it would not be profitable for operations with fewer than 250 head to adopt a digester. Regionally, dairies in the West would receive almost 60 percent of total digester profits, reflecting the prevalence of large-scale dairies in the region.

As carbon offset prices increase, more small-scale operations would find it profitable to adopt a digester. When there is no offset market (a price of zero), only operations with at least 1,000 head earn profits from operating a digester. However, if the offset price increases to $13 per ton, 15 percent of farms with 250-499 head and 45 percent of farms with 500-999 head would earn profits. If the price increases to $26 per ton, 3 percent of farms with fewer than 250 head and 39 percent of farms with 250-499 head would find it profitable to adopt a digester.

The substantial share of dairy operations without anaerobic manure management systems likely could not sell carbon offsets even if they were to install digesters. Farms that replace an aerobic manure management system (such as depositing manure on fields) with a pit or lagoon system would actually increase methane emissions. Even if the same farms then added digesters and reduced emissions to prior levels, these reductions likely would not qualify as carbon offsets. To be eligible as carbon offsets, emissions reductions usually must be “additional” to “business as usual”; as the level of emissions with aerobic manure management would be about the same as with anaerobic manure management plus a digester, there would be no additional reductions in methane emissions.

Higher offset prices would increase the profits that the livestock sector could earn from digesters. Over 15 years, the value of digesters to dairies is about $11 million with no offset market, about $908 million with a carbon price of $13 per ton, and $2.6 billion with a price of $26 per ton. Digester profits accrue mostly to large farms regardless of the carbon price. However, higher prices increase the number of smaller farms that could benefit from an offset program, which causes the distribution of benefits to become somewhat less skewed toward the largest operations. Dairies with at least 2,500 head earn 94 percent of digester profits with no offset market, compared with 48 percent at a price of $13 and 37 percent at a price of $26.

Policies and facility sharing

Depending on the price of carbon, the additional income from offset sales could substantially increase the number of livestock producers who would find it profitable to install methane digesters. In recent decades, the scale of production in the dairy and hog sectors has increased dramatically. Dairies with at least 1,000 head now produce almost a third of output, despite accounting for only about 2 percent of all operations. The additional profits that large farms could earn from digesters could enhance existing economies of scale in dairy and hog production and promote further consolidation of production over time.

One way for smaller scale livestock operations to achieve a more efficient scale is by supplementing manure with food waste from nearby crop or meat processing facilities, breweries, bakeries, and restaurants. When mixed with manure, food waste can provide an efficient feedstock for biogas production, and as an added incentive, livestock operators could collect waste disposal fees from the food facilities. However, the availability and suitability of food waste for use in methane digesters may restrict the feasibility of such mixtures to certain locations.

A centralized digester is another way that smaller scale operations could take advantage of a more efficient digester size. With several nearby farms using a single large digester, participating operations could share construction and maintenance costs; increase their leverage to negotiate electricity sales; improve access to financing, tax credits, or grants; and allow a manager to develop specialized skills in digester maintenance and operations. The main disadvantage to centralized digesters is the additional cost of transporting manure to and from the central facility.

If carbon offset prices are sufficiently high, a lower cost biogas system that flares methane rather than uses it to generate electricity may become profitable. This approach removes electricity generation from the biogas system, which eliminates the costs of the generator, electrical connections, and much of the maintenance. The lower cost biogas system might be economically viable for smaller scale operations that would find it difficult to finance or maintain an electricity generator. This option has the greatest potential for operations with lagoons, since lagoon covers can be installed relatively inexpensively, and offers other benefits to producers, such as reducing odor and increasing lagoon storage capacity by excluding rainwater.

Policies that raise returns to or lower costs of digesters can provide incentives for smaller scale operations to adopt the technology. Policies could include grants, such as USDA’s Rural Energy for America Program Grants, and incentive payments, such as the U.S. Department of Energy’s Renewable Energy Production Incentive. Other policy options include tax credits, such as the Renewable Electricity Production Tax Credit, accelerated depreciation (allowing construction costs to be written off faster for tax purposes), property and sales tax exemptions (usually at the state level), and other regulations, such as renewable energy mandates that raise the effective price of electricity sold to the grid. Many of these policies can be targeted toward smaller scale operations.