Evaluating the Economic and Environmental Cost for Onsite and Offsite Composting

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With people getting increasingly familiar with climate change adaptation, composting has become a popular way for people to take action on protecting the earth. In the U.S., 30-40% of the food supply is wasted, and in restaurants, 74% of the waste is organic material. In 2018, the EPA estimated that 2.6 million tons of food (4.1% of food waste) was made into compost. However, there are two different kinds of composting: sending waste to a composting company (offsite composting) or composting at the place where waste creates (onsite composting). The author conducted a case study at a high school in Pennsylvania, USA, and designed a Bokashi composting experiment and an evaluation model to compare the economic cost and carbon dioxide (CO₂) emission for onsite and offsite composting. The study finds that the cost of 1 kg of food waste for onsite composting is $0.29 and that for offsite composting is $0.22 (a 24% reduction). However, in this case, the onsite composting causes 0.014 kg of carbon dioxide equivalent (CO₂e) per kg of food waste, while the mission of offsite composting is 0.035 kg of CO₂e. It means that switching from offsite to onsite composing would result in a reduction of 21 kg of CO₂e for 1000 kg of food waste, which is the amount of waste produced by a high school campus with 400 people within just about five days to a week. It is worth knowing that 21 kg of CO₂e equals the amount of CO₂ a mature tree can capture in an entire year. Therefore, onsite composting costs are higher but have more environmental benefits than offsite composting.