Anaerobic Digestion Yields High Returns in Waste Reduction

Anaerobic Digestion

With landfill options becoming increasingly scarce, many cities are seeking other options for waste diversion. Anaerobic digestion can play an important role in meeting targets.

More cities around the world are embracing zero waste goals. But, a lack of waste-to-energy facilities is causing some to question why adoption of the technology is not more widespread. Only 13 percent of municipal solid wastes were processed thermally in 2013, according to the United States Environmental Protection Agency.

A recent discussion of waste-to-energy in Waste Dive focuses solely on thermal combustion or burning waste. But, cities may be reluctant to adopt incineration. Jack Macy, commercial zero waste senior coordinator for SF Environment, explained:

Incineration is not the highest and best use of discarded resources, recovering only a small fraction of the embedded energy and less than if it was recycled. […] Highest and best use is a principle of our zero waste policy.

Composting trumps combustion, he said. San Francisco will be one of the first in the United States to reach its 2020 targets.

Anaerobic Digestion

Where is anaerobic digestion in these conversations? It might be mentioned first if more lawmakers knew of its significant return on investment.

The need to dispose of organic waste is imperative. It makes up roughly 30 percent of the waste sent to landfills. Anaerobic digestion uses microorganisms to break down biodegradable material in the absence of oxygen. A wide range of waste can be treated, from food waste and waste paper to yard clippings and animal waste. The process yields methane and carbon dioxide biogas, which can be converted into electrical and thermal energy.

After digestion is complete, a liquid sludge remains. The liquid can either undergo aerobic treatment or be recirculated through the digestion process. Remaining solids can be used as fertilizer or landfilled.

In the U.S., municipal and state governments may have specific environmental targets in place, and in the European Union, members must meet the European Commission’s 20-20-20 climate and energy targets. Biogas production can help meet these goals since it not only meets renewable energy standards, but it also actively helps fight environmental pollution.

Embracing anaerobic digestion along with other environmental goals (such as clean water and renewable fuel production) can help a broad swath of people, from farmers to governments, according to Smithsonian.

Synergistic Approach

A group of researchers from EcoEngineers and Goss & Associates decided to quantify the benefits associated with “a synergistic approach to both producing high-quality biogas from municipal, industrial and agricultural waste and using marginal land to grow an energy crop such as miscanthus,” a bamboo-like plant that can be treated anaerobically to produce biofuel.

They concluded that a $17.6 million investment in an anaerobic digestion facility that can accept and process both municipal and industrial waste can, over a 20-year period, return roughly $158 million in benefits. With an $8 million investment in technology to process agricultural wastes, roughly $70 million in benefits could be accrued in a 20-year span.

Anaerobic digestion, they conclude, can “solve multiple problems in one investment.”

Image by Serg Grigorenko/123RF.