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The automotive industry continues to see increased growth and demand for parts and accessories (P&A), especially online.

The concept of anaerobic digestion is capturing the attention of more and more recycling companies as the industry learns about the inherent benefits that anaerobic digestion offers the environment, while providing another revenue generating option within the recycling industry.

At Its Core

Anaerobic digestion is a process carried out by a consortium of diverse microbial organisms including hydrolytic, fermentative and methane-forming bacteria. In the absence of molecular oxygen, the synergistic action of these organisms transforms biodegradable organics into a methane-rich gas and a stable fertile residue.

According to Dr. Agamemnon Koutsospyros, Ph.D., professor and graduate coordinator of environmental engineering at Connecticut’s University of New Haven, anaerobic digestion systems, at a minimum, include an air-tight vessel that sustains a favorable environment for biological activity upon organic feedstock.

“Reactor performance can be enhanced by integrating provisions for mixing, heating, pH, and temperature control,” Koutsospyros said. “Engineered systems also include a variety of pre- and post-treatment subsystems.” These subsystems may include organic feedstock pretreatment; a gas collection/purification system to improve energy recovery and marketability; and digested material withdrawal/treatment to enhance the potential for beneficial applications.

Merrill Kramer, a renewable energy lawyer at Sullivan and Worcester in Washington D.C., who is working with a consortium of Boston area colleges and universities to develop anaerobic digesters to manage excessive food waste, explained that a biodigester is basically a large, fully enclosed collection tank for organic waste.

“Anaerobic means the absence of oxygen,” Kramer said. “If you lock anaerobic microbial organisms in a sealed environment without oxygen, but with plenty of food and other organic waste, the microbes produce methane-rich gas through their digestive process.”

Essentially, it’s the natural process of decomposition technologically revved up to optimal speed and efficiency. The trapped methane gas is then cleaned and used to generate electricity and steam for heating and cooling via a combined heating and power (CHP) or cogeneration system.

“The biogas also can be directly used to produce steam in boilers for hot water and heating,” Kramer said. “Leftover organic solid waste can be used as fertilizer, a soil enhancer or be further composted.”

Biodigesters are used by municipalities and counties in connection with wastewater treatment facilities and municipal trash disposal. They are also used in the food service and agricultural industries for disposal of organic waste, and by universities to dispose of cafeteria and other organic waste products.

Bill Camarillo, chief executive officer of Agromin, a composter for over 50 California cities, further explained that anaerobic digestion is a process under zero oxygen conditions using bacteria to digest food waste materials for a minimum of 21 days. The result is production of methane gas that can be used to produce electricity or low carbon fuels.

“Agromin uses natural biological processes and other technologies to convert organic waste streams into electrical power, heat, fertility products and low carbon fuel for private customers and public utilities,” Camarillo said. “Through the composting process Agromin’s waste-to-energy program incorporates anaerobic digestion, gasification and renewable hydrogen.”

Agromin also receives more than 30,000 tons of organic material including food waste each month and then uses a safe, natural and sustainable process to transform the material into soil products. Agromin has pioneered the business of organic waste management through sustainable processing, industry leading technology, compliant recycling and a marketing model that allows the company to provide a loop solution to the largest waste haulers in the country.

“The foundation for Agromin’s solutions are based on using natural and biological processes to support sustainable agriculture including the conversion of organic waste streams into non-chemical fertility, renewable energy, water saving and erosion control products,” Camarillo said. “The high solid and high liquid digestion resulting from anaerobic digestion adds another option for the recycling industry when determining the best value for the customers they serve.”

Since the company’s founding, Agromin has been responsible for diverting more than five million tons of organic waste from landfills. A growing portion of the green materials that Agromin converts is food waste collected from grocery stores, restaurants and government facilities – amounting to over 400,000 tons a year.

Today, according to the American Biogas Council, it is estimated that in the U.S. there are about 2,100 sites producing biogas: most of which are operated by municipal wastewater treatment facilities (1,241). About 247 anaerobic digesters are operated by farms, 38 are non-agriculture/non-wastewater, and the balance (645) is represented by landfill gas collection projects.

“Based on the same source, there is huge potential for U.S growth with an estimated 11,000 sites considered to be ripe for development today,” Koutsospyros said. “It is hard to know the number of anaerobic digesters in the world however, it is estimated to be over a million. A recent study, inventoried 111,000 small-scale tubular anaerobic digesters treating livestock waste in the developing world.”

The Use of Anaerobic Digestion in the Recycling Environment

Anaerobic digester systems are a form of recycling. Digesters, particularly when the trapped gas is used to generate electricity and steam for heating and cooling, provide a means of recycling organic waste while satisfying multiple goals of reducing its carbon footprint, lowering energy costs, reducing use of fossil fuels, and capturing an important source of renewable energy – methane.

As Kramer explained, anaerobic digesters are a supplement to other forms of recycling. “Food waste in particular is one of the least recovered recyclable materials in the U.S. Unfortunately, too many companies dispose of their organic waste in landfills,” Kramer said. “Other programs such as composting or delivering uneaten food to feed the needy, only begins to solve the problem.”

According to the EPA, food waste is the second largest category of municipal solid waste sent to landfills, accounting for 18 percent of their waste stream. “Left to decompose in landfills, food waste creates methane gas, a lethal greenhouse gas that is the single largest short term contributor to climate change and global warming,” Kramer said. “The EPA has found that, pound for pound, the comparative impact of methane gas on climate change is more than 25 times greater than carbon dioxide.”

The good news is that in today’s recycling environment, a wide variety of organic feedstock and waste streams are amenable to anaerobic treatment including agricultural residues and waste streams, municipal wastewater and wastewater treatment residuals, industrial byproducts and waste streams, municipal solid wastes.

“In recent years, the biofuel and biomethane potential of algal biomass is being explored,” Koutsospyros said. “Thus, anaerobic digesters cover a wide spectrum of applications across the municipal, agricultural and industrial sectors.”

For example, the agricultural sector uses anaerobic digesters for the agro-veterinary wastes including crop residues and animal wastes or a combination of both. Municipalities operate anaerobic digesters for the treatment of municipal wastewater residuals, the organic fraction of solid wastes and food waste residues generated in institutional or commercial dining establishments.

“Although most municipal anaerobic digesters treat wastewater residuals, co-digestion units treating a combination of sludge, solid and food wastes are a relatively recent trend,” Koutsospyros said. “Industries often operate anaerobic digesters to treat wastes produced by alcohol production, bakery, brewery/winery, petrochemical, pulp and paper, slaughterhouse, sugar processing, textile starch and desizing, dairy, food and beverage plants.”

But in its simplest form anaerobic digestion can be done in a large tank or fully sealed tent – anywhere where microbial organisms can be locked in a sealed environment without oxygen, but with plenty of food and other organic waste. The biogas can then be directly used to produce steam in boilers for hot water and heating.

“Many college campuses do this right now,” Kramer said.

According to Camarillo, the recycling industry should pay close attention to anaerobic digestion technologies. “As always with all technology, the more companies that focus on it as a recycling solution, the sooner anaerobic digestion technology will get better, faster and cheaper.”

Kramer added that the disposal of organic waste is a small fraction of the business of the recycling industry, and often is a wasted by-product of other recycling efforts with metals, paper and glass. However, by converting organic trash into electricity, the recycling industry can take advantage of some very attractive governmental incentives such as green energy credits, renewable energy credits, carbon set aside credits and investment tax

“These credits can cover more than 50 percent of the costs of installing a biodigester,” Kramer said. “In addition, the project economics of converting organic trash into electricity and steam include revenues received for the sale of electricity and steam, in addition to renewable energy credits, plus tip fees for  waste disposal. Assuming the appropriate economies of scale, anaerobic digestion can be very economically attractive while at the same time solving a pressing social and environmental problem – greenhouse gas emissions and global warming.”

Published in the January 2017 Edition of American Recycler News