Whether in response to a state mandate, a local policy, economic incentives or constituent support, communities and waste districts in North America have increasingly identified the organics fraction of their municipal solid waste (MSW) stream as a means by which their overall landfill diversion rates can be lifted.
To meet this demand, technology providers have come forward with a number of ways to use anaerobic digestion (AD) and other methods to divert these materials and produce energy from them.
But before AD and other waste-to-energy methods began attracting investments and attention, composting had long been seen as a way to capture value from organics while diverting these materials from the landfill or from an incinerator, where their high moisture levels are generally unwelcome.Three waste management entities were recognized by the Silver Spring, Maryland-based Solid Waste Association of North America (SWANA) with 2017 Excellence Awards for composting programs deemed to be leading the way in organics diversion.
Comprehensive composting in the Empire State
The Onondaga County Resource Recovery Agency (OCRRA), a SWANA 2017 Excellence Award Winner, describes itself as running the largest municipal food recovery program in the state of New York. North Syracuse, New York-based OCRRA also claims it is “the only one producing compost certified by the United States Composting Council’s Seal of Testing Assurance.”
In terms of scale, OCRRA in its SWANA award application states that since 2013, it has composted more than 15,000 tons of food scraps—and an even larger amount of yard waste—to create more than 30,000 cubic yards of the Seal of Testing Assurance (STA)-certified compost.
This volume has helped Onondaga County, which includes Syracuse as its largest city, achieve a 57 percent recycling rate, a percentage not easily reached by a district with some 450,000 residents to serve.
OCRRA has devoted 13 acres of land in Camillus, New York, to its composting operations. The site hosts eight 100-foot-long concrete bunkers that hold the material and are equipped with the aeration pipes that allow OCRRA to produce its 30,000 cubic yards of compost annually.
According to its SWANA award submission, the 90-day OCRRA composting process at the Camillus site in New York is completed in five stages:
- Incoming food waste is mixed in a 1-3 ratio with yard waste and wood chips (which act as a bulking agent); this mixture is then placed on top of in-ground aeration pipes in the eight bunkers.
- The food waste mixture is covered with already finished compost that helps control odors and helps maintain optimal moisture and temperature conditions.
- Eight 1.5-horsepower blowers are timed on cycles that typically run for seven minutes every 15 to 20 minutes, creating the ideal aerobic conditions for decomposition.
- After the food waste decomposes for 60 days and meets temperature and other monitored requirements, the finished compost is screened for use as a soil amendment.
- Another 20 to 30 days are required for final curing.
The aeration pipes have proven cost-effective on several fronts when compared with more traditional windrow composting methods, according to the agency. The OCRRA contends the system in Camillus reduces its energy and fuel costs by 50 percent compared with what would be needed in a windrow system. In the windrow process, a piece of gasoline- or diesel-fueled heavy equipment operated by an hourly worker would be needed to turn the rows of compost five times in every two-week period.
With the aeration pipe method, just a modest amount of electricity (estimated by OCRRA as “a few hundred dollars per month”) is required to run the eight blowers at their specified intervals.
On the collection side, where landfill diversion starts, OCRRA says it “engages in extensive and continuous public education campaigns and training [sessions] with the participating food waste generators to minimize potential contaminants.”
Equipment deployed at the 13-acre Camillus campus also plays a role in creating compost that can meet the STA standard. Inbound food scraps are blended in a vertical mixer. According to OCRRA, the device “serves as a blender for the food and yard waste that creates a homogeneous blend and also rips open any bagged material” that arrives at the facility.
Yard waste comes in many forms, and a slow-speed shredder provided by Denver-based Komptech Americas and two horizontal grinders made by Pella, Iowa-based Vermeer Corp. help reduce trees and branches, pallets and other wood waste to a size that belongs in a compost blend.In a final step, a trommel screen made by Ontario, Canada-based McCloskey International screens the compost before it is bagged or distributed in any other form.
Oregon trail leads to diversion
More than 2,000 miles west of Onondaga County, communities in the region of Benton County, Oregon, have worked with Phoenix-based Republic Services Inc. to create a composting system also honored by SWANA for its 2017 accomplishments.
The Pacific Region Compost (PRC) facility in Benton County, which includes the university town of Corvalis, is being managed by Republic to handle the food scraps increasingly mandated for landfill diversion by communities in the state.
The PRC site currently hosts comprehensive composting operations, and some of the material handled there may soon feed into an AD system. According to Republic, it is now “permitted to operate and build the first anaerobic digester in the Metro [Portland] region to process commercial food scraps.” The AD system is being designed and equipped to turn commercial food waste into fuel for collection vehicles, generate electricity to reach the grid and produce solid and liquid materials used for agricultural purposes. However, even after the AD system is up and running, composting will remain an essential part of the overall PRC operation, according to Republic.
The firm, in its SWANA Excellence Award nomination, indicates the PRC facility was designed to accept and process yard waste, but has evolved to include proper food scraps handling in its operations. As of 2018, the PRC facility can accept “proteins, dairy products and even bones” as inbound food scraps.
The windrow system is used for yard waste, with windrow turners used to rotate the rows to prepare material that can eventually be screened and tested until it is deemed ready for market. The food scraps are blended with composted yard waste in this process as well.
As in Onondaga County, aerated pipes are used at the PRC to process food scraps. In the Pacific Region Compost’s aeration process, air is pumped through each row for approximately one minute at roughly 30-minute intervals.
In addition to Corvalis, several other Oregon communities, including Salem, send organics to the PRC facility. According to Republic, more than 120,000 tons of organics are now being processed at PRC each year, and the company says it remains committed to working with communities in Oregon to provide “composting resources for generations to come.”
The company also touts cooperation between its management and Oregon communities as a means of proceeding without “cart before the horse” problems that can occur when collection programs are mandated before any processing or end market solutions exist.
Republic says via the PRC it was able to invest in and create “a stable processing option so cities could develop organics [collection] programs.”
Cooperation also has led to “a model organics collection system for MidValley Oregon communities” that means Republic and PRC managers can have a relatively consistent flow of materials and be properly equipped to handle them.
Finally, Republic states that cooperation also has led to the development of a rate structure designed so cities pay for new and existing programs in ways that reduce misunderstandings between local governments and Republic in its role as the facility manager.
For community solid waste planners and waste management company executives alike, the three SWANA 2017 Excellence Award winners are a model of what effective organics programs can achieve when waste diversion is made a priority by those involved.