Study examines anaerobic digestion’s role in water, agriculture, and biofuels issues

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Courtesy of Fluence Corporation

According to a new analysis, working on both clean water and biofuels production in tandem may reap significant environmental and economic benefits. For example, using anaerobic digestion to treat manure could prevent nutrient-runoff pollution and create a renewable energy source, according to the study by EcoEngineers and Goss & Associates.

Looking at Iowa farming, the analysts estimated that a $17.6 million investment in one municipal anaerobic digester could yield roughly $158 million in benefits over a 20-year period. For an $8 million investment in an agricultural digester, roughly $70 million in benefits could be realized in a 20-year period, including $528,000 in subsidy payments to farmers growing miscanthus, a perennial energy crop.

This synergistic approach would involve producing high-quality biogas from municipal, industrial, and agricultural waste, coupled with the use of marginal land to grow energy crops such as miscanthus or switch grass, which can be added to organic waste before treatment with anaerobic digestion.

Benefits of Working in Tandem

These two efforts have been moving forward in parallel, but the study claims the benefits would be much greater if clean fuel and water quality challenges were tackled in tandem. The study looked at factors including the creation of jobs, the income derived from biomass fuel and fertilizer sales, and payments to farmers producing energy crops. Other potential benefits that were noted, but not calculated, include improved property values, income associated with the recreational use of public waters, and other environmental improvements.

There are now 63 anaerobic digestion facilities in Iowa; however, few of these, if any, reportedly produce high-quality fuels. There is enough organic waste volume in the state to accommodate another 1,140 digesters, according to the American Biogas Council.

Biogas production in the United States has been enhanced by national and state policies such as the Renewable Energy Standard and California’s Low Carbon Fuel Standard, which requires refineries to use more renewable fuels.

In addition to revenue from high-quality methane sales, farmers could derive additional income from nutrient-trading programs. For example, polluters could pay farmers to plant perennial crops that absorb extra nitrogen and phosphorous in the soil — thus, protecting water from excess nutrients — and also can be used to create biofuel. This might include planting miscanthus or switchgrass instead of corn or soybean.

Farmers could also participate in more than one tax-incentive program to stack the benefits.

Experimenting in Alternative Fuels

The University of Iowa has been experimenting with alternative fuels for use on the campus, including oat hulls and miscanthus.

The University of Iowa’s associate director of utilities and energy management, Ben Fish, told Iowa Public Radio:

[W]e’re renting land from Iowa farmers in order to grow our fuel so that we can stop buying our coal from out of state. […] In a single acre of this miscanthus grass, you can actually get enough energy to power the average home for a year. So actually, something that really drew us to this grass in the first place is the energy density. So it’s something we’re going with, and I think it has a really good potential.

The university is trying to meet a 40 percent renewable energy use target by 2020. The grass will be used in the campus power plant to produce power, heat, and cooling. Its largest field is 350 acres.

Investing in Anaerobic Digestion

These challenges are not the only water-related issues facing Iowa communities. Several cities and regions will need to upgrade existing wastewater treatment facilities.

Shashi Menon, a managing partner at EcoEngineers, said:

The reality is that Iowa has to spend over $2 billion to upgrade municipal wastewater treatment infrastructure. […] Simultaneously, we are also spending a billion dollars to reduce nutrient runoff. What we are recommending is that as we spend that money, we take into consideration the potential for anaerobic digesters to solve multiple problems in one investment.

The full report — “Anaerobic Digestion & The Water Energy Nexus 2016” — is available online.

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