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Administration - Sustainability at Lehman College

Food Composting at Lehman College

Starting in 2009, Lehman College made the commitment to compost food-preparation scraps (raw, unprocessed vegetables peels, cores, stalks, inedible or unappetizing parts of fruits and vegetables, whole vegetables that have begun to “turn”) with the purchase of a closed-system, automated food composter. The cafeteria kitchen generates an average of 50 pounds of compostable food scraps every day the cafeteria is in operation (247 days/year; approximately 6 tons per year). Prior to the adoption of food composting, food scraps had been disposed in the regular garbage.

Food scraps are processed first in a pulper (prototype model from Somat Company, Lancaster, PA), which pounds scraps into small particles and reduces water content. Pulping accelerates the composting process by increasing the exposed surface area and doubles the weight of food waste that can be processed by the composter.

The composter, named “The Rocket®” (Tidy Planet Ltd., Macclesfield, Cheshire, UK), accelerates natural decomposition processes. The Rocket can process a volume of 11.4 gallons of food waste per day (approximately 57 pounds). A rotating, central, interior shaft with projecting blades mechanically turns the compost at pre-programmed intervals, aerating it and draining excess moisture.

Equal volumes (not weights) of pulped food-preparation scraps (source of nitrogen) and wood chips or dry leaves (source of carbon and a bulking agent) are added to the composter. Food scraps and wood chips/dry leaves are thoroughly mixed so that there are no contiguous pockets of predominately nitrogen or carbon sources. Thorough mixing maximizes exposure to oxygen – highly important to the composting process.

Once the composting process is established in the Rocket, the composting process itself maintains temperatures around 65°C (149oF) in the first third of the Rocket for a minimum of 2 days, ensuring the destruction of pathogens (which are responsible for composting odors) and seeds. Although the Rocket has a heating element, it has never been activated, even in the coldest winter. System heat is generated by thermophilic (heat-loving) bacteria that thrive at high temperatures only. Temperatures of material in the first third of the Rocket can easily scald!

The mesophilic phase of the composting process occurs after the thermophilic phase. Temperatures decrease to ambient and a different group of microorganisms takes over the composting process.

Excess moisture (particularly in a closed system) prevents introduction of oxygen needed during composting. Excess moisture is slowly gravity-drained from the composting chamber and collected in a container at a rate of approximately 5 gallons in 24 hours. The collected liquid has a strong, objectionable odor because it contains odor-producing bacteria that have not spent sufficient time at high temperatures to inactivate them.

From initial addition of food waste to the production of finished compost, the process takes approximately 2-4 weeks. In stark contrast to the material from the beginning of the process, the finished compost has only a subtle “earth” smell. Although this material can be used immediately as a soil amendment, it is added to the “finished” end of the outdoor food composting pile to cure for at least one season. Carbon:Nitrogen ratio of the finished, cured compost is 25-30:1.

Diverting organic materials from the solid waste stream and composting these materials instead is beneficial to the environment. Compost is used to replace depleted nutrients in soil, decreasing the need for artificial chemical fertilizers and pesticides. In addition, a significant component of waste is removed from landfills, an environment not conducive to natural decomposition processes.

Lehman’s Rocket for composting food waste is the second in operation in New York City and the third in New York State. For a tour of Lehman’s food composting operations, please contact the EH&S Office, (718) 960-8988, or email.

Food Composting Links