According to the EPA, in 2013, Americans threw away 35 million tons of food. That’s over 100 kilograms (220 pounds) of food for every person in the country. Therefore, it is imperative that we find alternative uses for nutrient-rich food waste; keeping it from taking up valuable landfill space represents an important environmental challenge. The nutrients this waste contains could be cycled back into the environment, making it available for use in natural and human-dominated ecosystems.

Several non-profit organizations, such as Waste No Food in California and the industry-backed Food Waste Reduction Alliance, are working to raise awareness of the problem and create a roadmap for industry and consumers to reduce food waste. It’s important to note that problems of food waste differ in the developed and the developing world. In the latter, about one-third of crops are spoiled or wasted before they even reach consumers. A lack of refrigeration and poor transportation systems in these parts of the world make food spoilage a fact of life; food waste can only be reduced through the development of mobile processing technologies and improved methods for getting food to where it’s needed most.

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In the developed world, however, food waste occurs primarily among end users, restaurants, and residences. For instance, a restaurant may stock too much of a perishable ingredient, which can’t be used in its entirety before spoiling. Preventing such problems requires making a periodic “dumpster dive” and seeing what ingredients are consistently getting thrown out. Of course, it’s not always possible to run a business—or a family kitchen—and be certain which items will get used and which will not. Many restaurants have partnered with humanitarian organizations to make daily or weekly donations of surplus food they no longer anticipate using. A significant amount of food waste comes from unused trimmings and leftovers, some of which can be used in animal feed. Finally, used cooking oil and grease can be sold to biofuel manufacturers (see Chapter 10, page 309).

Rather than dumping food scraps and yard waste in landfills, such material can be composted. Composting is a method for returning the nutrients found in organic matter back to the environment, using processes that mimic the natural biogeochemical cycling of matter. The process involves naturally occurring bacteria, fungi, and invertebrates that gradually break down organic wastes into “compost,” a dark-colored substance resembling soil. Compost, which adds both nutrients and organic matter to soils, makes a great fertilizer for growing crops.

An example of an effective composting program is found in the sanitation system of San Francisco, California. This city has a food scrap collection program in areas with high numbers of restaurants. The food waste is collected in special bins every week by garbage trucks in a separate run. The waste is delivered to a facility that grinds and mixes it, then places it in huge black plastic bags for about 2 months. Once the composting process is complete, the “black gold” is delivered to farms and wineries throughout the state, where it is used as organic fertilizer. San Francisco’s composting system mimics the nutrient cycles found within nature and does an effective job of preventing this biodegradable waste from entering landfills. Home gardeners can also compost in their own backyards, layering food waste from the kitchen with leaves and sawdust and turning it periodically.

When organic material such as food waste ends up in landfills, naturally occurring bacteria gradually break it down. However, landfills are largely anaerobic, meaning very little oxygen is available. Therefore, the bulk of decomposer organisms found in landfills are anaerobic bacteria. In this anaerobic environment, bacteria produce methane (see Chapter 2, page 36) as a waste product—methane is a potent greenhouse gas (see Chapter 14, page 437). This biologically generated methane is chemically identical to the main constituent of the natural gas used for household heat and cooking, as well as for industrial purposes (see Chapter 9, page 268). However, so-called landfill gas is usually a 50-50 mixture of methane and carbon dioxide. Nonetheless, in the United States, landfills are the third largest source of methane emissions to the atmosphere, after industry and agriculture.

Increasingly, landfills have systems that collect emerging gas to reduce their emissions of methane, which can be used as an energy source. The level of treatment needed for landfill gas depends on the intended use. Direct use of landfill gas to heat boilers and kilns generally requires only primary treatment, which removes moisture, particulates, and the trace amounts of sulfur dioxide generally present (Figure 12.19). Because primary-treated landfill gas still consists of roughly half carbon dioxide, it has lower energy content than does natural gas. For use in applications where higher energy content is required, such as heating homes and running natural gas vehicles, secondary treatment is required. The additional treatment involves removal of carbon dioxide, nitrogen, oxygen, and other trace gases. The result is “pipeline quality gas,” which is nearly pure methane and approximately equivalent in energy content to natural gas.

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