Succeeding Anaerobically

Aug. 16, 2014

Most municipalities need to maximize their landfill diversion rates, whether in response to legislation, or as a result of spatial concerns, or to address the evolving view that organic waste is a resource. For non-landfill owners, it’s also a way to control their own destiny, says Dirk Dudgeon, senior vice president of business development at Zero Waste Energy LLC (ZWE).

The Lafayette, CA-based company designs, builds, and operates advanced solid waste processing facilities that optimize resource recovery and generate renewable energy in an environmentally sound way. Under a long-term agreement authorized in February 2012, the company partnered with the Monterey Regional Waste Management District (MRWMD) on a pilot demonstration project using Smartferm technology to design and build an anaerobic digestion plant for processing organic materials diverted from the wastestream.

Smartferm is a semimobile, small-scale, dry anaerobic digesting system designed to process and treat the organic portion of municipal solid waste. In addition to diverting waste from the landfill, the process recovers energy in the form of biogas that can be converted to electric power or CNG. The prefabricated modular system can process between 4,000 and 20,000 tons per year. “It’s the first system in California,” says William Merry, general manager at the MRWMD, “and the second in the US.” The other system is located in Oshkosh, WI.

The Monterey system includes four 40-foot dry AD modules, together capable of processing 5,000 tons of organic material per year, converting it into biogas to provide power and heat for the MRWMD’s use and to provide high-quality compost to local farms. Also part of the system are a below-grade, 95,000-gallon-capacity concrete percolate tank, a containerized 100-kW combined heat and power system, a packaged biofilter, a roof-mounted external biogas storage bladder, and a separate enclosed and negatively aerated receiving bay.

Inside the AD modules, the organic material undergoes aerobic composting, followed by anaerobic composting to release and capture methane gas. This gas will then be combusted to produce electricity in an engine generator mounted next to the digestion modules. ZWE estimates that it produces enough electricity to power 50 homes; however, the energy produced during this project will be supplied to the neighboring Monterey Regional Water Pollution Control Agency as part of a unique public-private partnership. The MRWMD sells enough of it to the wastewater treatment plant to meet 10% of its needs.

The plant became operational in March 2013. A 21-day batch process transforms waste into biogas and high-quality digestate for compost. “Anaerobic digestion is a very good process,” Merry says. “It captures methane in 21 days instead of 21 years; it’s a very accelerated process.”

In addition to extracting renewable energy from organics during the compost process, the benefits of the Smartferm system in Monterey County include reduced odor, reduction of fugitive methane emissions from the landfill, and the generation of a product that can be sold to county agriculture growers.

Smart Investment
“The byproducts of Smartferm-high-quality compost, electricity, CNG-are also attractive to customers,” Dudgeon expounds, adding that the system “can provide onsite generated renewable energy, cutting electricity costs and potentially becoming independent from the grid.” But perhaps one of the most important factors is that it has a solid return on investment, making it a good decision, both environmentally and financially.

However, he cautions, return on investment depends on a number of variables, such as state incentives and rebates, RIN and carbon credit costs, existing tipping fees, utility rates for putting electricity into the grid, and the cost of land. Nevertheless, he says, some projects have ROIs in excess of 20%.

The breakeven point for the MRWMD is $50 per ton, Merry says. “The all-in cost to run is $50 per ton.” So far, he says, the system “works at the cost proposed to us” and produces 60% methane around the clock.

Under the five-year pilot demo agreement, MRWMD gives ZWE the tipping fees for greenwaste and yardwaste (roughly 5,000 tons per year) and 12 cents per kilowatt-hour for the energy sold, but there is an option to purchase the system at the end of the test. “We’ll buy it shortly if we like it,” Merry indicates, hinting that it’s a strong possibility because “it’s working as promised.”

Landfill Options
Successfully operating for 63 years, the MRWMD has 150 years of remaining landfill capacity. “That’s a lot,” Merry notes. “Our back is not against the wall, yet we are putting in place a responsive array of programs because it’s the right thing to do at this time in this community. That’s the point. We’re on the leading edge of technology, not the bleeding edge.”

Years ago, the Monterey Regional Waste Management District developed one of the first landfill gas-to-electric energy plants in the nation. Presently, the project’s four generators provide approximately

5 megawatts of clean alternative power, meeting all of the district’s own power needs and providing electricity for nearly 4,000 homes.

Thirty years after the district began converting gas to energy, ZWE approached it with a plan to test a state-of-the-industry food scrap and organic material composting system. As the technology partner, Zero Waste Energy invested capital and provided the system. As the host, the MRWMD provided the land, permits, and material.

ZWE’s Dudgeon says permitting challenges are not as onerous as other waste processing facilities. “The largest obstacle is the perception that AD is still “˜unproven’ or too costly. Both of these beliefs are misplaced, and with more and more AD projects being developed, these misconceptions will prove to be just that.”

The MRWMD had 30 years of history in generating electricity from the landfill, Merry points out. “It’s familiar. [This project] is just building on what we do. We looked at the options. We had interest in doing it and the ability to get the project going immediately, so we acted quickly on ZWE’s offer.”

In a moment of self-deprecating reflection, Merry says, “They came to us because we already collect food scraps.” The MRWMD has been gathering food scraps from restaurants for four years and processing them by means of static pile composting. “We have the space, and it’s the most straightforward method.”

Even so, the district had been looking at the issue for 10 years, Merry reports. “For the past five to six years, we have focused on different means to process food scraps, which are regulated differently than other organic waste. Food-, yard-, and woodwaste are all organic, but food is different. It’s usually in a garbage can. Yardwaste is in a green bin. We can process it, compost it, use it for mulch; we have an established process. Processing food scraps is not the same. It’s regulated in California due to concern for rain and runoff-the leachate.”

Smartferm is a dry anaerobic digesting system designed to process and treat the organic portion of MSW.

Open-air composting has come under scrutiny due to emissions. “There are concerns, especially in the Central Valley, San Joaquin,” Merry indicates. Of course, the more composting the district does, they more it has to deal with odors.

Many composting operations have covered piles to control emissions. The MRWMD considered AD on top of the landfill to accept only food scraps, but it was determined that that option was too expensive, that it would take weeks or even months to process, and it was not as controlled as other methods. So the question remained: What to do about composting?

The cheapest option is landfilling, Merry says. “Our tip fee is the lowest in the region.”

Dudgeon acknowledges that in some areas of the country, landfill fees are indeed so low as to preclude economical options. “These areas will require legislation and regulation to improve the way organics are treated.”

Because California is reportedly considering legislation to divert organics, the MRWMD decided to investigate alternative means of processing organics-particularly food-outside of yard waste. “In California, there’s a huge push to divert organics,” Merry says. “Legislation, regulation, or ban-that’s what we’re faced with here.”

With California pushing for increased diversion of organics from the landfill, the state is also supportive of AD. It provides better environmental control than other options. The use of windrows in aerobic composting comes with problems such as birds and rain runoff. Anaerobic activity may be happening in the landfill and wastewater treatment plan, Merry acknowledges, but due to California’s water shortage, that raises additional concerns about solids in the pipes.

Projects like the one currently occurring in Monterey have a landfill diversion rate as high as 95%, based on the incoming organics stream, according to ZWE’s Dudgeon. “Results are relative, based on facility size and feedstock.”

Measuring Success
The ecologically minded business community of Monterey “wanted to do something better,” Merry recalls. “They wanted to recycle more.” Three years ago, a programmatic environmental impact report moved this project forward. “It was a huge step to promote the project, which fit with what we were already doing-food scraps were already coming here.”

It was an attractive package: ZWE brought the project and invested capital, including acquiring a 1603 federal grant. That was an important consideration for the regional recycling, processing and disposal facility serving Western Monterey County since 1951 because its annual operating budget of $18 million is self-generated (not from taxes). The MRWMD’s role was to collect and process food scraps and conduct testing.

Generating locally distributed energy added value to the plan, but Merry emphasized the importance of the role of markets to the success of the venture. A municipality that implements an AD diversion system will be flooded with compost and mulch. The MRWMD had a head start with this project because they already had a mercantile program in place that has led to 50% diversion of materials and brings in $700,000 per year. However, it takes time to develop markets…and quality is important in maintaining those relationships. For example, there is a concern regarding contaminants from post-consumer food that could impede development of markets.

Due to the MRWMD’s experience and established markets, the pilot has been a success, attaining the promised results. Thanks to the 5,000-TPY anaerobic digester’s 60- to 65-ton capacity, the MRWMD has achieved a 35%-40% reduction in volume. The system is producing approximately 44,000 kWh per month. In addition, the division is able to run a higher food-to-greenwaste ratio than expected: 70/30.

The pilot has been successful because the technology has been proved, Dudgeon believes. “There are facilities under operation where it has proved to provide the results organizations want.”

The amount of organics in the wastestream, coupled with government incentives and legislation calling for heightened landfill diversion rates, has further supported dry AD. Recycling of plastics, metals, and other materials has evolved, but until dry AD technology emerged, the processing of organic waste had not progressed much past basic composting; there was no energy recovery. Organic waste processing is now catching up with the technology that has evolved in other portions of waste processing.

Custom Designs
Approximately 60% of waste entering US landfills is organic.

Internationally, governments are starting to tackle the issue of waste, many of them by subsidizing energy prices to support projects. “Germany created an awareness,” Merry states. “Japan responds to a federal mandate. It’s an important element of progress.” In the US, he points out, there are subsidies for only solar and wind. “There’s not as much support for biogas.”

Some states, such as California, Mississippi, and Connecticut, are beginning to follow the European example by instituting regulations that support AD. Some are adding state regulations that mandate the community support AD by paying for it through taxes. “In our view, dry AD will soon be seen like other types of recycling,” Dudgeon says.

Subsidized or not, Merry cautions against blindly bringing in programs from other communities. “In California, we’re an advocate of installing programs for solid waste management that work in your community.”

ZWE specializes in providing solutions as unique as the client. “One of the most positive things about ZWE facilities is that they’re crafted to address the client’s specific needs and objectives,” Dudgeon confirms. Currently, the company has projects operating or in development throughout the US and has recently begun a project in Doha, Qatar.

Because the prefabricated Smartferm requires a minimal amount of space, can be constructed in as little as six months, and provides a solid ROI, it is widely accessible technology that has the ability to make a difference for individual organizations.

The potential benefits depend on the client’s situation and requirements: earning ROI and ongoing profit, hitting benchmarks for investors, demonstrating environmental sustainability, achieving legislatively mandated or guideline diversion rates, significantly extending the life of a landfill, or creating a convenient alternative to current fuel sources (compressed natural gas).

GreenWaste Recovery, ZWE, and Zanker Road Resource Management joined together to design and construct an innovative dry AD facility for the city of San Jose’s commercial organics processing services. Commercial operations began in November 2013.

As the largest dry AD project in the world, it processes an estimated 90,000 tons per yard of commercial organic waste per year. The waste that is diverted from the landfill is converted into high-quality compost. Additionally, the production of renewable biogas provides enough electricity for onsite operations, with excess power for sale locally. On-peak electricity is used to power Zanker’s stationary resource recovery equipment. Off-peak power is sold back to the utility.

Because of its size, the system was constructed with cast-in-place concrete digesters rather than shop-fabricated steel digesters, Dudgeon explains. This facility also features four in-vessel composting tunnels-a fully enclosed system that accelerates and accurately controls the natural aerobic break down of biodegradable waste to create a high-quality compost product.

The system meets the California AB 32 mandate by diverting almost 85% of organic waste from landfills. The 1.6 MW of renewable power it produces complies with California’s Renewable Portfolio Standards. An added benefit is the reduction of fugitive methane emissions from landfills.

The facility in San Jose produces 1.6 MW from 90,000 TPY and another produces up to 100 kW with only 5,000 TPY, Dudgeon elaborates. “We are also in the middle of construction on an 11,200 TPY facility in South San Francisco that will produce over 120,000 diesel gallon equivalents of low carbon CNG per year, which will be used to fuel the waste collection vehicles.”

Future Steps
Merry says the MRWMD is evaluating the possibility of converting to CNG for use in garbage trucks. “We’re planning a facility so we can fill the trucks overnight. It will close the loop if we can produce and use [energy] locally.”

Because the facility is next to the water treatment plant, it’s also conducting a study to evaluate other options. “We could expand the project as is,” Merry speculates. “The modular units are easy for adding onto. Or, we could do nothing. But we can’t keep putting organics in the landfill under the mandate, so that’s not really an option.”

Expansion to the residential sector is another consideration. “Residential is an opportunity to move to,” Merry says, although that would require updates in franchise agreements. “We’ll probably wait a couple years to see if it’s the right thing to do.” The commercial generators were behind the AD move, but he’s not sure residents feel the same way. “The restaurants wanted to do the right thing and were willing to put their money where their mouths are. They train staff, store food, pick up often, and use good containers and trucks.”

One of the hazards of adding a residential program is the risk of contamination. If residents don’t support composting, they are likely to be careless when separating foodwaste. “If we add food scraps to organics, there is contamination,” Merry conjectures. “It’s not organic anymore.” Contamination of the feedstock for organics also makes it difficult to gain the trust of the markets, jeopardizing the entire program.

Another aspect of residential composting revolves around collection. “The volume of residential food scraps is much smaller,” Merry explains. “How do we collect it?”

Just as important as collection is the need for a place that meets regulations for composting. If you don’t have the proper place, you have to take the waste elsewhere. Merry says the Sanitation Districts of Los Angeles spent a decade building a $430 million railway system to transport its waste 100 miles to a desert landfill when it was thought that landfill space was running out.

Instead, the high cost of transporting the trash, a reduction in the amount of trash due to increased recycling efforts and a down economy, and available space nearby at lower cost have resulted in an idle railway.

Due to changes in the economy, the amount of waste diminished significantly. According to district records, Los Angeles County’s disposal needs dropped 21% from 2008 to 2009. According to the Orange County Register, county records reveal that the average daily tonnage sent to landfills by Los Angeles County residents decreased 41% between 2005 and 2012. The district’s landfills received 46% to 67% less trash during the same period. Similarly, Merry says that Monterey “lost 35 percent of our waste in six to seven years due to a bad economy-and things are not back to normal yet.”

Disposal rates in Los Angeles County increased to pay for the rail system. When nearby landfills got permits to expand, lower-cost alternatives were suddenly available to trash haulers. Southern California has 2 billion cubic yards of remaining disposal capacity, which is estimated to last 100 years. The L.A. Districts entered into a two-year contract with Orange County to pay $15 million per year to dump 648,210 tons of trash in the O.C. landfills.

“The worst thing we can do is overbuild the system,” Merry comments. “I like the modular aspect of our system.” He maintains that flexibility is necessary in order to deal with the fluctuation of food scraps. “If you choose a modular system, you can dial it up or down as necessary. If you’re considering an AD system, take small steps. Keep flexibility in the system.”

About the Author

Lori Lovely

Winner of several Society of Professional Journalists awards, Lori Lovely writes about topics related to waste management and technology.

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