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Waste Wise
Waste Wise: Hard to Swallow

Waste Wise: Hard to Swallow

There’s been a lot of focus lately on diverting the organic waste to non-landfill disposal options such as composting, anaerobic digestion, and alternative technologies like gasification. Food waste is of particular interest because it is energy-rich and, according to EPA, has historically had a recovery rate 16 times lower than total organics in the waste stream (2.5 percent compared to 41 percent, respectively).

Additionally, the recovery rate for total organics has increased over time, while food waste recovery has essentially flatlined. While this trend hints at the challenges inherent in collecting food waste, it also suggests a large unrealized market in organics diversion.

One area of focus has been pure, or nearly pure, organic waste streams like commercial food wastes from restaurants, cafeterias, farmers markets, etc. This material has less contamination and requires less separation compared to mixed waste streams. Yet it poses an interesting dilemma, since areas with large concentrations of restaurants and cafeterias tend to be densely populated cities with little space to deal with waste, much less source-separated food wastes.

An example is New York City, which, due to space limitations, exports most of its solid waste. That waste goes to landfills and other facilities outside the city and, in many instances, is transported out of the region to other states, including South Carolina and Virginia. In fact, many large U.S. cities transport their wastes long distances to regional disposal facilities. But as the municipal solid waste stream continues to fragment, technological limitations and operational considerations affect how the waste is handled and processed, requiring companies to look at each material as its own business model.

Recently, NYC officials and stakeholders have expressed a desire to divert the city’s commercial food waste but, due to space constraints, find themselves faced with maximum facility areas of 1-3 acres. This footprint limits food waste treatment to compact technologies like anaerobic digestion. However, a smaller footprint also means reduced processing capacity, necessitating multiple facilities.

One potential alternative is to transport food waste outside the city to areas that can handle the capacity. This essentially follows current practice, making it an easier sell than trying to shoehorn solutions into the city’s confines.
Some stakeholders have suggested transport distances of roughly 150 miles to composting and other processing facilities would not be uncommon, and a portion of separated food wastes already makes this trek. But transporting the city’s 400,000 tons/year of commercial food waste would be no small task.

Food waste is laden with water. It has a moisture content of roughly 70 percent (the other primary organic component in the waste stream, paper, has a moisture content of less than 6 percent). Ergo, transporting commercial food waste essentially means transporting a lot of water. Our ancestors realized well over 100 years ago that hauling water wasn’t smart, opting to use pipes instead. So, why would we want to haul high moisture content food waste?

This realization suggests that the recent spate of ambitious municipal diversion goals fail to consider operations, particularly if segmenting food waste to non-landfill alternatives is part of the plan. But reducing the moisture content of this material prior to hauling may help make this option viable.

Using the NYC example, the transport of 400,000 tons of food waste annually translates into roughly 11,500 trips from a transfer station. Using smaller trucks raises the number of trips substantially. Reducing the moisture content at either the point of collection or transfer station could yield significant cost savings and environmental benefits.

A moisture content reduction of 30 percent seems plausible given the capabilities of existing technologies like screw presses or belt thickeners. The lower moisture food waste would net a 57-percent reduction in transport. To put this into perspective, transporting food waste with a moisture content of 30 percent rather than 70 percent a distance of 150 miles results in nearly $605,000 in annual fuel savings, 1,700 fewer tons of carbon dioxide emissions per year, and 2 million fewer miles of driving to transport the same material.

Just some food for thought…

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