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The trash compactor units cycle in about 41 seconds with a maximum compaction force of 1,250 pounds.
Department of Streets, Philadelphia

2008

No. of downtown receptacles: 700

No. of employees responsible: 33

Weekly collections: 17

2009

No. of downtown solar-powered compactors: 500

No. of solar-powered recycling units: 210

No. of employees responsible: 9

Weekly collections: 5

Philadelphia may be the City of Brotherly Love, but it's also the nation's fourth-densest urban area. As the social and geographic hub of the original 13 colonies, the city's a popular tourist destination all year round. But in the hot and muggy summer months, numbers swell as people wander from the Liberty Bell to Independence Hall to the home of Betsy Ross, among other attractions.

All that pedestrian traffic creates a massive challenge for the agency tasked with keeping streets, sidewalks, and other rights of way clean. The volume of waste in the Center City District required 700 trash receptacles that were emptied 17 times/week via four collection routes. Keeping up took 33 employees working three full-time shifts and cost the city $2.3 million annually.

Despite tourism revenues, shortly after his election in 2007 Mayor Michael Nutter asked every department to prepare operational budgets 10%, 20%, and 30% below current levels in anticipation of a $1 billion shortfall over five years. In response, last year the department tried replacing some traditional garbage cans with trash compactors and companion single-stream recycling units. The department “bought” the equipment through a three-year lease-to-own finance program with the manufacturer, BigBelly Solar in Needham, Mass., that eliminates an up-front capital expenditure.

The 300-pound galvanized sheet metal compactor units have a bin volume of 32 gallons.

The compactors are self-powered, requiring no wiring or external electrical connection. They automatically compact the waste when it reaches a certain level. As users deposit waste, it falls into the low-density polyethylene bin inside the machine. When the level of waste eventually rises above the top of the inner bin, the waste interrupts an electric eye beam, triggering the motor to compact the waste down into the bin, making room for more waste.

Users can continue to deposit additional waste during compaction cycles. The machines have an insertion hopper that prevents hands from reaching into the compaction area, and they do not lock users out during compaction.

The process repeats automatically — as needed — until the machine is ready for collection, typically holding about 160 gallons of uncompacted waste. At that point, the LED light indicator on the front panel turns yellow, and the machine sends a wireless message to a central computer server, notifying staff that the unit is ready for collection. The wireless monitoring and notification system uses text-message technology to signal a password-protected Web-hosted database that allows the viewing of machine status and fullness levels from any computer with Internet access. That, in turn, allows managers to ensure that the waste is collected when needed.

The machines continue to receive more waste and run automatic compaction cycles even after signaling they are ready for collection. When the machines are entirely full the LED indicator turns red, notifying staff that immediate collection is required.

“The wireless monitoring system has made it very easy to manage our inventory all across Center City,” explains Scott McGrath, the department's recycling coordinator. “The ability to sort through historical data by collection route and discover collection patterns gives us valuable and actionable information.”

Collection crews empty the compactor units by opening the front door with a key, removing the inner plastic bin, and pulling the liner bag full of waste. After replacing with a new liner bag, crews slide the bin inside the machine, and the LED indicator resets to green.

In just one year the department had cut its weekly collections by more than two-thirds, at an annual operating cost of about $720,000. Performing five weekly collections under the new program requires only nine workers on a single shift; the other workers have been reassigned to trucks that collect household recycling.

By entering into the financing arrangement, the city has no up-front capital cost and will realize collection cost savings in the first year of approximately $850,000. Additionally, the department expects to save nearly $13 million in cumulative collection cost savings over the next 10 years, and the annual operating costs of collecting in Center City is expected to drop by 70%.

The department has since purchased an additional 220 compactors and 100 new companion recycling units, bringing the total to 720 compactors and 310 recycling units. They were installed this spring, according to McGrath.

Then, in October, the department learned that part of a $14.1 million energy-efficiency formula grant from the American Recovery and Reinvestment Act of 2009 would fund the purchase of 260 more units for $973,000. The new units will be placed along commercial corridors later this year.