Statewide Composting: Can it be Done in R.I.?

By GREG GERRITT/ecoRI News contributor

JOHNSTON — The Central Landfill has only a limited amount of space, and is filling fast. Replacing that capacity will be expensive, so reducing the amount of waste tossed into the state landfill is the best way to extend its life.

Plants need nutrients in order to grow into the food we eat. As fertilizers made from natural gas become more expensive, it seems logical to consider recycling the nutrients in food scraps back into our food growing system.

There is a conjunction of interest in these two issues. Rhode Island would like to reduce what goes into the landfill, and one of the things we toss away in great quantities, food scraps, would provide greater benefits to the community if we recycled it.

In 2009, Rhode Island municipalities generated 514,811 tons of material, according to Krystal Noiseux of the Rhode Island Resource Recovery Corporation (RIRRC). The last waste characterization study completed by RIRRC, in 1990, classified 23.2 percent of the entire stream as “other organics,” including food scraps. More recent data from the Environmental Protection Agency (12.7 percent) and neighboring states such as Connecticut (13.7 percent) and Vermont (21 percent) would make 20 percent a more reasonable R.I. estimate.

Under this 20 percent assumption, 102,962 tons of state municipal waste stream, in 2009, would have been food scraps, and 100 percent of these food scraps went to the landfill as refuse.

Municipalities are charged $32 a ton to dispose of refuse, up to an allotted cap, and an over-the-cap rate of the lower between $75 a ton or the current, lowest commercial contract rate. In fiscal 2010, state municipalities delivered 318,835 tons of refuse at $32 a ton, 13,933 tons at $54 a ton, 9,823 tons at $58 a ton and 146 tons at $75 a ton.

If Rhode Island municipalities had been able to capture 100 percent of the potential 102,962 tons of food scraps through a compost collection system, the total savings on landfill tips fees would have amounted to $3,862,986. At a 75 percent capture rate, this cost savings would have been $3,039,306, and at the more likely 50 percent capture rate, the savings would have been $2,215,594.

Of course, to put a municipal composting system into place, there would be additional costs to provide composting bins for every household, expanded collection services and to pay tip fees at another compost facility.

The state goal for the rate at which municipal materials should be diverted from the landfill is presently 50 percent for each municipality. Diversion rates for municipalities are calculated on the calendar year, but if we assumed the same 102,962 tons of food scraps over the calendar year, keeping these food scraps out of the municipal stream would have also boosted the state average diversion rate from 28.1 percent in 2009, to 48 percent (at 100 percent capture), 43 percent (at 75 percent capture) or, more likely, to 38 percent (at 50 percent capture).

In fiscal 2010, state municipalities delivered 29,548 tons of leaf and yard waste to the Central Landfill and generated another 32,617 tons in 2009 that they either composted at their own municipal sites or sent to another facility. At RIRRC, municipalities are charged nothing to dispose of leaf/yard waste up to their allotted cap, and an over-the-cap rate of $25 a ton.

A new policy allowing for municipalities to gift their excess cap went into effect in fiscal 2010, but 11 municipalities still went over by a total of 9,000 tons. If we assume a municipal composting facility would have kept 100 percent of this overage away from the state landfill through a competitive tip fee, the total municipal savings on RIRRC leaf/yard waste tipping fees in fiscal 2010 would have amounted to $225,000.

This would have made total municipal tip fee savings from organics collection — food scraps and leaf/yard waste — at $4,087,986 for 100 percent capture, $3,264,306 for 75 percent capture, or more likely, $2,440,594 for 50 percent capture.

It’s worth noting, however, that the municipal under-the-cap tip fees of $32 a ton for refuse and nothing for leaf/yard waste have proven to be barriers for private companies looking to develop a composting operation in Rhode Island.

Also, unlike municipal waste, which is obligated to come to the Central Landfill by state law, commercial waste can go here or be brought elsewhere.

Growing practice
Around the country and the world more and more communities are adding up the numbers for the total cost of their trash systems and opting for composting their organic materials. The cost of disposing of food scrap in landfills or incinerators varies. As Noiseux noted, tipping fees in Rhode Island are on the low side, despite the severe lack of long-term disposal capacity and that has probably slowed the development of our compost industry compared to other places.

Even so, it’s likely that communities and businesses throughout the state, in cooperation with RIRRC, will eventually find that the separation and collection of organic compostable materials makes sense once you consider the costs of burying this waste and the benefits of recycling it.

A properly operated compost facility ensures that the gases that create offensive odors are not produced in appreciable quantities. Still, special care must be taken in locating compost facilities. In windrow facilities, food scrap and leaves are shredded, mixed at approximately a one to three ratio, piled in long windrows, and turned every three days or aerated through pipes. The piles reach at least 160 degrees Fahrenheit to kill off pathogens and weed seeds early in the process and eventually transform into a nearly uniform brown mass with an earthy aroma and incredible fertility. Compost can be stored for months before sale without losing its qualities, but not indefinitely.

A facility that could handle all of the collectable food scrap in Rhode Island — mixed with an appropriate amount of brown material such as leaves and/or wood chips — would cover about 9 acres. Such a facility or even a much smaller one would have to adhere to Department of Environmental Management permitting requirements. There are rules for runoff, odor, setbacks, wetlands, etc. A facility would operate on an engineered pad, with a leachate collection and treatment pond, and truck traffic will have to be accounted for.

A site within the perimeter of the RIRRC operations and related businesses seems a logical choice for a large composting facility, while smaller facilities might be created in other favorable locations throughout the state.

Commercial composting facilities require water, sewage, electricity, an engineered pad, proper drainage, a grinder, large equipment for moving and turning compost, space for large equipment to maneuver, and loading docks for compostables being dropped off and finished compost being shipped out.

Built and equipped from scratch, a 2-acre aerobic compost facility capable of handling the commercial food scrap from the food industries — about 60 tons a day — would cost about $500,000 to set up and several hundred thousand dollars a year to operate. It could generate $500,000 or more in annual sales. A 9-acre facility would cost more than $1 million to set up.

Landfill gas
Landfills are the No. 1 source of methane emissions in the United States, and food scraps produce much of that methane. Methane is a potent greenhouse gas, reflecting at least 21 times as much heat energy back to the earth as the same amount of carbon dioxide. Composting and putting the compost back into the food system dramatically reduces the amount of greenhouse gases emitted.

Landfilling food scraps also causes us to lose the soil-building capacity of this material, burying it underground instead of returning to the topsoil to grow more food. One of the fastest-growing industries in Rhode Island is agriculture for local consumption. Not returning all the food scrap to the soil definitely will impede future growth in this industry, as farmers will struggle to sustain their soil fertility.

Collecting organics and composting also would create jobs in the compost industry, in the food industries and possibly in the renewable energy sector.

There are costs in transforming from a landfilled food waste system to a composting one. These costs include developing and implementing the proper separation and collection system, and the development of compost facilities. The usual place to find the money to implement the various aspects of a compost system is in reduced tipping costs. Rhode Island’s low municipal tipping fees mean that model might not work as well here, as there is likely to be little in the way of savings in tipping fees available to offset the expanded collection costs. We may have to look at this issue a bit more broadly to understand our savings.

There are the types of compost facilities needed if we are to capture and compost the majority of compostables created in Rhode Island:
• Home composting, including vermiculture
• Community garden composting
• School composting
• Farm composting
• Commercial composting operations
• Municipal composting operations
• Centralized large-scale composting operation
• Food scrap-fueled anaerobic digester/clean-energy facility
• Sewage treatment plant composting and digesting

Composting begins at home, and thousands of Rhode Islanders currently compost. Community gardens also compost, on a scale not much different than home composting, and most farms compost. Many Rhode Island schools also compost, with elementary, middle and high schools having tumblers in the yard and worms in the classroom, and several state universities/colleges are researching their options and starting to compost food service scrap.

A willingness to compost
Currently, several Rhode Island municipalities compost leaves and yard waste, and the RIRRC composts leaves and yard waste for communities without their own composting facility. Several private companies also compost leaves and yard waste disposed of by landscaping industries.

A few businesses also have the necessary permits that allow them to compost other people’s food scrap in large quantities, but only Earth Care Farm in Charlestown is regularly composting commercial food scrap and selling high-grade compost.

Currently, no Rhode Island municipality collects and composts food scrap, though Bristol has the capacity and willingness to work with potential partners using the facility that composts the town’s sewage sludge.

However, food-scrap collection is the wave of the future and food-scrap-focused digesters are being built, often by businesses that believe there is a profit to be made in the electricity business, with compost an additional value center. Large-scale digesters will only be built with power-purchase agreements in hand from electricity utilities or if a community has a need for the power generated at a digester facility, such as powering a sewage treatment plant.

It has been suggested that with the price of oceanic wind power in Rhode Island coming in so high, digesters working food scrap could come in with cheaper green power that is more reliable. As long as people eat and are processing uneaten food, the digester has fuel. In fact, densely populated places such as Rhode Island have more food scrap per square mile than other places, making the state an efficient place to set up a digester.

The proposed size for a commercially viable anaerobic digester/electricity production facility is one capable of digesting 150 tons of food scrap a day.

When a digester is finished, what is left over is a sludge-like material called digestate.  This digestate can be composted with leaves, creating nutrient-rich compost. Another alternative, one suggested to me by several different people in the digester business, is that the waste heat from the electricity production could be used to dry the digestate, and that dried digestate can be pelletized into commercial nutrient-rich organic fertilizer with some properties similar to compost.

An anaerobic digester and its associated power plants sized to digest 150 tons a day of food scrap would cost in the range of $10 million to $20 million. This can be justified by the selling of electricity or natural gas to the grid. No one will build a freestanding commercially operated anaerobic digester/energy facility unless they have a power purchase agreement in place with an electric utility and can contract for sufficient food scrap.

Electricity generated by burning the methane produced in digesters is more expensive than electricity from old coal-fired power plants, but appears to be significantly less expensive than what some of the oceanic wind power projects say they need to be paid to be profitable.