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26 Jun 2014

On Front Lines of Recycling, Turning Food Waste into Biogas

An increasing number of sewage treatment plants in the U.S. and Europe are processing food waste in anaerobic biodigesters, keeping more garbage out of landfills, reducing methane emissions, and producing energy to defray their operating costs.
By rachel cernansky

In February, trucks from Waste Management, Inc. started working new routes in Los Angeles County, California. Waste Management collects food scraps from restaurants, grocery stores, hotels, and food processing plants, takes them to a company facility in Carson City, and grinds them into a slurry. That liquid is taken to a Los Angeles County wastewater treatment plant, where it is mixed in with sewage — one part food waste to nine parts human waste — and processed in an anaerobic digester.

The end result? Biogas that can be burned as fuel — a benefit that may encourage the Los Angeles County Sanitation District to expand the
More cities are trying new ways to harvest energy from food that otherwise would rot in landfills.
initiative into a full-scale program after two years.

The facility is hardly the first sewage treatment plant to take in food waste, and it certainly won’t be the last. Efforts to recycle food waste are growing nationwide, and many are doing it the traditional way, by collecting and composting food scraps. But there is increasing interest in sending food waste, particularly from commercial sources, to facilities that use anaerobic digesters to convert the food into biogas.

About 15 wastewater treatment facilities in the U.S. are engaged in this practice — a small number, but that’s up from one or two about a decade ago, according to the American Biogas Council. Following the lead of Europe — which is increasingly either composting its food waste, incinerating it, or processing it in biodigesters — more U.S. cities are trying new ways to harvest energy from food that otherwise would have rotted in landfills and emitted methane, a powerful greenhouse gas.

"Whether the food waste is diverted to traditional composting sites or goes to an anaerobic digester, I think that's a good use of that resource,” said Mark Hutchinson, an agricultural extension professor at the University of Maine. “We no longer consider it to be a waste product — it's something we're trying to manage as a resource."

According to the American Biogas Council, about 860 sewage treatment plants in the U.S. produce biogas using anaerobic digestion, in which bacteria break down the organic matter in an oxygen-free environment and produce biogas composed primarily of methane. That gas is generally burned on site to help power the facilities. (Another 381 plants have
Food waste for biogas plant
Universal Images Group/Getty Images
Roughly 300 tons of food waste produces 42,000 cubic meters of biogas.
anaerobic digesters but are flaring the gas.)

Some facilities — including the Carson City plant and treatment plants in West Lafayette, Indiana and Des Moines, Iowa — have started taking in food waste to "co-digest" with sewage in tanks or large digester “eggs.” In addition to biogas, anaerobic digesters produce decomposed organic matter than can be used as fertilizer.

In 2002, California's East Bay Municipal Utility District (EBMUD), which serves Oakland and Berkeley, became the first sewage treatment plant in the U.S. to digest food waste with wastewater and produce biogas. And in 2012, the utility district became the first to generate, on-site, more energy than it needs through anaerobic co-digestion. In the last fiscal year, the facility produced about six megawatts of power and made about $1 million by selling surplus electricity to the Port of Oakland via the grid operated by Pacific Gas and Electric.

New York City, as part of an ongoing pilot program, sent tons of food waste from Brooklyn and Staten Island to a waste transfer station, where it was pulverized into a slurry. It was then sent to the Newtown Creek wastewater treatment plant in Brooklyn and processed in an anaerobic digester to produce biogas for the facility. The city — which is now scaling up the collection and composting of food scraps — is evaluating the effectiveness of the Newtown Creek project.

Bridget Anderson, the Department of Sanitation's acting deputy commissioner for recycling and sustainability, is hopeful the project will continue. "We want to keep the material as close to New York City as possible,” she said. “And obviously, creating renewable energy is another beneficial use that we wanted to explore besides composting."

Connecticut and Vermont have banned commercial food waste from landfills. In Massachusetts, new food waste disposal regulations will go
Anaerobic digestion provides an outlet for the growing amount of food waste cities want to keep out of landfills.
into effect in October, requiring any business that disposes of at least one ton of organic material a week to either donate the food, send it for composting or anaerobic digestion, or ship it to animal feed operations. State agencies awarded a $100,000 grant to a wastewater treatment plant in Boston Harbor to study the impact that co-digesting food waste will have on its operations.

The state also is talking with businesses about creating markets for the compost and digestion products. "Let's say you're a large college that produces a lot of this material — we want the college to be able to go out and say, 'Where can I best get rid of this stuff at the best price?'" said David Cash, commissioner of the Massachusetts Department of Environmental Protection. "Or maybe they want to figure out how to do it themselves on campus.”

Waste management companies and cities are interested in anaerobic digestion because it provides another outlet for the growing amounts of food waste they're trying to keep out of landfills. The addition of some food waste is beneficial to anaerobic digesters at sewage treatment plants because more organic matter means more energy production. Since food waste is richer in organic matter than manure or sewage, it generally produces several times more methane per unit of volume.

"It's been an evolution of having these digesters and flaring the gas, to putting that gas to good use, to now moving into, 'I want to actually generate more gas,'" said Chris Hornback, senior director of regulatory affairs for the National Association of Clean Water Agencies.

Recycling food waste may be relatively new in the U.S., but it's common in other countries, particularly in Europe. In Germany, residential food waste is mainly composted, with more than a quarter of it biodigested first, according to David Wilken, head of waste, fertilization, and hygiene at the German Biogas Association. Most industrial and commercial food waste is broken down in biodigesters.

The continent has roughly 14,000 municipally operated biogas digesters, with nearly 9,000 in Germany alone. In Denmark, most food waste is incinerated for energy recovery along with other household garbage, according to Ioannis Bakas, a waste expert at the Copenhagen Resource Institute.

Elsewhere in Europe, composting is common, but anaerobic digestion is on the rise. It's growing quickly in the U.K. as well as Sweden, which last year declared a lofty goal: At least 50 percent of organic waste should be recycled by 2018 — using either composting or anaerobic digestion — and 40 percent of the energy should be recovered. As a result, said Asa Stenmarck of the Swedish Environmental Research Institute, "There is a switch toward anaerobic digestion. It is, however, hard to get the
Government assistance has a lot to do with why anaerobic digestion has taken off in Europe.
economics to work, so this is also to some extent depending on subsidies from the government."

Government assistance has a lot to do with why anaerobic digestion has taken off in Europe. But as Patrick Serfass, executive director of the American Biogas Council, points out, it’s also meant that operators haven’t necessarily had to figure out the economics. “Projects get developed that are dependent on those incentives, and they’re not forced to innovate as much as the U.S. market has been,” he said. “That sort of innovation is what helps biogas projects in the U.S. to achieve profitability and helps make the market, even though it's smaller, more nimble.”

For example, New Hampshire-based Neo Energy is developing anaerobic digestion projects specifically for food waste in Massachusetts and Rhode Island. In Central Florida, a Harvest Power facility co-digests sewage and food waste from nearby businesses, including Disney World, and extracts phosphorus from the waste to form a crystal called struvite, which is sold as a fertilizer additive.

Recycling food waste is steadily growing in the U.S. A 2012 survey conducted by BioCycle Magazine identified 183 communities in 18 states offering curbside food waste collection.

Experts agree that anaerobic digestion is growing quickly, but not necessarily at the expense of composting. “You can't draw a box around these two and call them exclusive,” said Scott Beckner, an integrated waste management specialist at California’s Department of Resources, Recycling and Recovery. “We're seeing both increase at an even pace. Anaerobic digestion is really picking up right now. Composting facilities are figuring out new technologies to meet local needs.”

The cost of building an anaerobic digestion system ranges widely, depending on the size of the plant, the feedstock, types of end-products produced, and other variables. It’s not cheap. Last year, the Lewiston-Auburn Water Pollution Control Authority, a relatively small sewage treatment plant in Maine, finished installing a $14 million anaerobic digestion system. DC Water in the nation’s capitol, meanwhile, is spending an estimated $500 million on a new anaerobic digestion system modeled on Norwegian technology, but it also expects to recoup those costs. The utility expects to save $16 million a year in operational costs and $10

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million on its electricity bill. The new Lewiston-Auburn system is expected to save the plant $600,000 a year through reduced energy costs and lower volumes of solids to dispose of.

The anaerobic digesting process is more complex technically than composting, and digesters — especially pre-existing ones — can be easier to operate when the feedstock is predictable, which residential food waste is definitely not. The bacteria that break down the organic matter during digestion also prefer a moist environment, and it's hard to control the ratio of liquids to solids in residential food waste.

“Biosolids” remain after the anaerobic digestion process, and some are used as fertilizer. But detractors of sewage sludge recycling object to that practice and to adding food scraps to co-digestion tanks. "The residuals (biosolids) from sewage treatment plants should never be used as a soil amendment” because they contain a mixture of pathogenic and industrial pollutants, said Caroline Snyder, professor emeritus of the Rochester Institute of Technology and founder and chair of Citizens for Sludge-Free Land.

Despite such concerns, the wave of innovation in food recycling and anaerobic digestion is picking up speed globally. Said Serfass, “We're seeing Europeans looking to how we're innovating and creating new products in the U.S.”

Correction, June 27, 2014: Due to outdated statistics on the Web site of the American Biogas Council, the original version of this article misstated how many U.S. sewage treatment plants produce biogas in anaerobic digesters to generate electricity. Roughly 860 plants use biogas to produce electricity and 381 are flaring the gas.



ABOUT THE AUTHOR


Rachel Cernansky is a Denver-based freelance journalist who covers the environment and food issues. She has written for Matter, Grist, The New York Times, National Geographic News, and other publications.

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COMMENTS


Good stuff but we need to be re-purposing more food to keep as human food. If it is going to a digester or compost system we are losing too much money and not reducing the food product footprint as much as we might.
Posted by Andy Whitman on 26 Jun 2014


Is mixing food waste with sewage the best use? Or is it just creating more sewer water and contaminated solids? Wouldn't it be better to keep it clean and use it as an animal feed?
Posted by creg shaffer on 27 Jun 2014


Excellent article. The most important initial issue when considering the application of anaerobic digestion systems is the feedstock to the process. Almost any organic material can be processed with anaerobic digestion however, if biogas production is the aim, the level of putrescibility is the key factor in its successful application. The more putrescible (digestible) the material, the higher the gas yields possible from the system.

Feedstocks can include biodegradable waste materials, such as waste paper, grass clippings, leftover food, sewage, and animal waste. Woody wastes are the exception, because they are largely unaffected by digestion, as most anaerobes are unable to degrade lignin. Xylophalgeous anaerobes (lignin consumers) or using high temperature pretreatment, such as pyrolysis, can be used to break down the lignin. Anaerobic digesters can also be fed with specially grown energy crops, such as silage, for dedicated biogas production. In Germany and continental Europe, these facilities are referred to as "biogas" plants. A codigestion or cofermentation plant is typically an agricultural anaerobic digester that accepts two or more input materials for simultaneous digestion.

Anaerobes can break down material with varying degrees of success from readily, in the case of short-chain hydrocarbons such as sugars, to over longer periods of time, in the case of cellulose and hemicellulose. Anaerobic microorganisms are unable to break down long-chain woody molecules, such as lignin. Anaerobic digesters were originally designed for operation using sewage sludge and manures. Sewage and manure are not, however, the material with the most potential for anaerobic digestion, as the biodegradable material has already had much of the energy content taken out by the animals that produced it. Therefore, many digesters operate with codigestion of two or more types of feedstock. For example, in a farm-based digester that uses dairy manure as the primary feedstock, the gas production may be significantly increased by adding a second feedstock, e.g., grass and corn (typical on-farm feedstock), or various organic byproducts, such as slaughterhouse waste, fats, oils and grease from restaurants, organic household waste, etc. (typical off-site feedstock)

Digesters processing dedicated energy crops can achieve high levels of degradation and biogas production. Slurry-only systems are generally cheaper, but generate far less energy than those using crops, such as maize and grass silage by using a modest amount of crop material (30 %), an anaerobic digestion plant can increase energy output tenfold for only three times the capital cost, relative to a slurry-only system

For large scale biogas production the best option is to use Agave and Opuntia as input as both are care-free growth, regenerative CAM plants. These can be grown in waste lands. There are MW size Biogas power generation plants commercially available.
Dr.A.Jagadeesh Nellore(AP),India

Posted by Dr.A.Jagadeesh on 27 Jun 2014


A very encouraging article. It is so much more logical to recycle in this manner, to produce energy and fertilizer, than to dump the stuff into landfill or waterways. People who say the economics don't work are ignoring the environmental cost of the old practices. An agricultural scientist friend told me 30 years ago that in his opinion, piggeries could be self-sufficient for energy, by bio-gas production. It amazes me how slowly we move to rectify problems with pollution, that we have been well aware of for so long. No doubt the large energy producers see this type of operation as a "threat" and oppose it all the way.....which may be why these operations seem to be all at a local government level.
Posted by Steve Matthews on 28 Jun 2014


Thanks for this informative article.

I am wondering if such AD or 'biogas' production facilities could (and would) also accept (as a feedstock) invasive plant biomass collected as part of control efforts.

Many thousands of pounds of invasive water chestnuts (Trapa natans) are hand- or machine-harvested out of my state (Massachusetts)'s waterways each year, in an effort to reduce the adverse impact of those proliferating plants on the ecological and other beneficial functions of those waterways.

Many bags of hard-pulled garlic mustard (Alliaria petiolata) plants are collected each spring (see, e.g., http://www.wickedlocal.com/lincoln/news/x1780478677/Lincoln-conservation-groups-hold-Garlic-Mustard-Pull-Days). The contents of bags are typically not composted, because there's too great a risk that Garlic Mustard plant parts might remain viable after the composting process, and might infect areas where the compost is subsequently used. It seems to me that sending the garlic mustard to an AD facility is a better alternative.

There are many more species of invasive plants out there that would also provide good fodder for AD facilities: Asiatic Bittersweet, Phragmites, and Japanese Barberry come immediately to mind.

Have any of you heard about invasive plant biomass being used as a feedstock for an AD/'biogas' facility? Knowing that this is already happening somewhere might help me to convince folks in Massachusetts to give it a try here.

Posted by Russ Cohen on 02 Jul 2014


I agree with Creg. Mixing wasted food with sewage, whether down the garbage disposal, or collected and brought to a sludge (biosolids) anaerobic digester is a waste and transfers the environmental impact from one media to another. I feel these methods results in a loss of nutrients and organics that could have been returned to the soil, used as animal feed, or recovered for human consumption (donated). If wasted food is to be anaerobically digested, all source reduction and reuse efforts should be exhausted first, then brought to an AD facility that excludes sewage. In that way, the liquid and solid residuals are not contaminated with human waste and have a better chance of being clean enough for land application and other beneficial uses.

As for the question about using AD for the destruction of invasive plants, I'd be interested in this too. If it works, it would help solve a big problem that many states are facing. Perhaps there is a bench-scale AD at a university that can test this.
Posted by Kathy Alexander on 07 Jul 2014



 

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