Managing hefty organic waste streams and associated costs while reaching lofty sustainability goals are among urban jurisdictions’ toughest pursuits. Some municipal solid waste operators set up local compost sites to help achieve these ambitions. They are finding other benefits along the way—from new, valuable products with a strong, local market to a way to cut out multiple complex steps involved in sending compost out of town. They are regenerating depleted soils, and some are bringing their shuttered landfills back to life with another purpose: home to these new facilities.
But how do you make compost projects work with residential neighborhoods and businesses close by, limited space that’s at a premium, and other challenges of high-density urban and suburban communities?
An urban compost success story.
The answer varies depending on each jurisdiction’s special needs and characteristics. New York City is one example of a compelling metropolitan success story, with over 200 drop-off sites and seven community-scale compost programs or facilities across its five boroughs.
SCS Engineers’ Vice President Greg McCarron helped design two of that flourishing city’s facilities, including a layout and design overhaul of one of them, located near Manhattan. The project goal was multifold: keep pace with the growing demand for finished compost and food scraps management and do it within a compact facility footprint –one-third of an acre.
Known as the Queensbridge project, it operates under the Queensboro bridge, next to six-story residential towers, a hotel, and other commercial development. So, maintaining tight odor control is a paramount priority. It’s a job that takes technical skills mastery and a robust design; the facility can process up to 1,000 tons of rapidly decomposing food scraps a year, which are mixed with leaves and woodchips.
GORE cover for odor control and process control.
“The proximity to a dense residential neighborhood allows little tolerance for issues such as odors, pests, and dust, and we designed the site with this in mind.
One of our most important strategies was to install a second SG/GORE cover [there was already one in operation]. It’s an in-vessel system with a semipermeable membrane, so it traps odors and other emissions such as dust and volatile organic compounds (VOCs) and prevents pest issues by encapsulating all fresh food scraps,” McCarron says.
The technology also sheds rainwater as clean water and provides process control, enabling a higher throughput on a smaller footprint.
Designing an efficient stormwater management system is a critical part of the plan, entailing site grading and installing drainage pipes. The team ensures the collection of contact water that touches the initial compost piles via an in-ground trenching system, which also delivers air to the composting process. Contact water is recycled back into the composting process.
Stormwater control features prevent run-on to the facility site. And clean stormwater is routed away from the in-process compost material.
Another situation called for special attention: existing utilities nearby, including high-voltage electric lines and high-pressure natural gas lines.
“It required due diligence to ensure the facility’s infrastructure would not disrupt the utilities’ operations. We looked at site surveys, prepared design drawings, and dug construction test pits to make sure we would not run into these large lines during installation of the below-grade components of the aerated static pile system,” McCarron says.
Between these build and design strategies and other tweaks, Queensbridge has continued to grow its operations while melding with the active, surrounding community. The outcome? Doubled processing capacity and improvements to access and overall workflow while managing contact water and stormwater in a better manner.
SCS Senior Project Professional Ryan Duckett finds municipalities like the control they gain when they opt to run their own facilities rather than transfer their organic waste long distances. Some haul these heavy, wet loads more than an hour away, and common organic waste hauling methods can be inefficient on a pound-for-pound basis. Besides having tighter reins on monetary and time investments, their local governing authority can allow easier rezoning of parcels or other changes to permit new activity.
Aerated static piles for faster throughput.
For composters in more densely populated areas such as urban municipalities, Duckett typically suggests bunker aerated static piles (ASP), which involve mechanically pushing or pulling air through organic waste.
“Aerated static piles have faster throughput than some other methods because you run blowers, so you constantly inject air, which speeds decomposition. In urban areas with limited real estate, accelerating production in a controlled manner is important. It’s how you scale and produce a quality product with what land resources you have,” he says.
Though having small, narrowly spaced parcels can actually facilitate economies of scale when it comes to residential collections. With hundreds to thousands of households in close proximity, the process tends to be quicker per customer and more efficient.
Still, collections are typically the most expensive part of the compost equation, so Duckett does feasibility studies to model the costs and benefits of different approaches to recover organic waste.
“If you include food scraps, you have to consider whether you want curbside or front door collections or if you prefer drop-off sites, keeping in mind that a third bin at each home will add expense. Some municipalities add a fee,” he says.
Space can be an issue; not all urban and suburban communities feel that they have enough room for another bin. Sometimes the answer is to collect food scraps from porches in buckets, though it can be more time-consuming and labor-intensive than curbside.
Operational considerations span more than identifying the best collection approaches.
“For example, sometimes in our evaluations, we find efficiencies through methods to accomplish more than one function in one stroke, perhaps co-shredding leaves and branches at the same time. Or using compostable bags instead of plastic ones that require a separate debagging operation.
Or we may make suggestions around the deployment of equipment, sometimes replacing a truck or tractor tow-behind compost turner method with a self-propelled windrow turner. It’s a one-time investment that could save time and money in the long run,” Duckett says.
Early planning is a consistent theme.
Preliminary work should include market research to identify the quality and quantity of available feedstocks. And it should involve stakeholder engagement with potential feedstock suppliers, haulers, city departments, and citizens.
“You must make sure everyone is on board because there are a lot of considerations, such as estimating the participation rate to design the size and type of processing facility. Mitigating contamination also takes forethought. It’s a big issue in the compost world.
Among Duckett’s recommendations to deter contamination from the start is implementing a ban on plastics mixed with yard waste. And setting up to provide paper in lieu of plastic bags for collecting materials, as plastics are a big problem for composters.
Duckett does site visits before going into design mode in keeping with the mantra of planning ahead. He’s looking from a technical lens for details to address to circumvent barriers later.
“One issue we give special thought to is that there are a lot of rules around buffers. Buffers could be from schools, playgrounds, adjacent residents, or water bodies, among community resources. We have to keep in mind that these are not potentially usable areas when planning the layout and design. So, we look at available space after accounting for them,” he says.
There are also rules around the proximity of compost pads to water tables, so the team is heedful of groundwater fluctuations. As important are soil characteristic studies to determine if pad construction will require outside soil or a different pad type. And key to the design process is evaluating stormwater management systems, as McCarron exemplifies with the Queensbridge project.
The considerations are vast, with no single right answer, but quite a few options exist to make composting work well in highly populated spaces. Regardless of the circumstances, local composting can provide burgeoning communities a viable, sometimes profitable, way to manage what typically is at least 30 to 40% of their waste stream. And keeping the processing site at home, close to the generator, comes with multiple benefits beyond.
Mr. McCarron, PE, is a Vice President of SCS Engineers and our National Expert on Organics Management. He has nearly 35 years of progressively responsible experience in solid waste management, including waste composition studies, solid waste planning, composting, recycling, transfer stations, waste-to-energy systems, landfill design, and landfill gas systems. His expertise is in the design, permit, construction, and operation of compost systems and facilities for public and private clients.
Ryan Duckett, PE, is a Senior Project Professional experienced in solid waste research and consulting. He serves as a project engineer for a variety of design projects, financial analyses, feasibility studies, and overall planning efforts in support of solid waste assets such as collection, transfer stations, recycling facilities, and landfills. He is a Professional Engineer licensed in Virginia and North Carolina and has a BS in Environmental Engineering and an MBA.