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| Fig. 1: This is an image of wasted food and wasted energy. (Source: Wikimedia Commons) |
You wouldn't leave the lights on and the television running when you leave your house; we don't want to waste energy. So why do we waste food? Americans discard an estimated 1.3 Billion tons of food per year (see Fig. 1), roughly a third of all food we eat. [1,2] Not only are we wasting the food, but also fresh water (used to grow the food), oil (used in transportation), money (spent to buy and dispose of the food), and space and land in landfills to hold the waste, adding up to about 160 Billion dollars of wasted money each year. [2] This waste problem found in the US (1.3 Billion tons wasted) is similar to other food waste problems found around the world. To discard food in this great of a quantity is to squander and waste huge amounts of potential clean energy that our world so desperately needs.
Breaking down the energy in food is relatively easy actually (we've all done an experiment in high school that asks us to calculate the energy in a "cheeto" or another food). Different foods have different amounts of energy, but the Atwater factors assign energy values to macronutrients as follows: Fat has 8.5 kCal per gram, Protein has 3.5 kCal per gram and Carbohydrates have 3.5 kCal per gram. [3] For reference, lightbulbs are found standard at 60 watts (producing about 800 lumens). A watt is a unit of power while a joule is a unit of energy (1 kCal is equal to 4.184 kJ). One watt is equal to a joule per second. Meaning 100 grams of strawberries, which has an estimated 29 kCals of energy (120,000 joules), could power a 60 watt light bulb for 30.55 minutes. If just 100 grams of strawberries can provide this much power, think of all the energy we waste with our food nation and worldwide. Finding ways to repurpose our food waste will massively impact our overall human energy efficiency.
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| Fig. 2: This is a photo of a large pile of compostable food waste. (Source: Wikimedia Commons) |
Researchers at Cornell University have been investigating ways to effectively and efficiently transfer food waste into a viable source of energy. They have discovered that by using a pair of simple chemical processes: hydrothermal liquefaction and anaerobic digestion they can breakdown food waste into a useful biofuel. The process involves heating waste food effectively pressure cooking it to create an oil that can be refined into a fuel. The waste from the liquefaction is then subject to anaerobic digestion where microbes break down the food into gases that can be used to produce heat and electricity. [1] These researchers envision a world where garbage trucks don't deliver to landfills, but rather treatment plants where our food waste can be directly converted into clean and renewable energy we can use.
Another option that utilizes and repurposes our food waste is a more traditional composting approach. A recent scientific study found that even residentially operated composting systems are found to have on average 77% efficiency in organic capture of waste. [4] This compost fertilizer can be put back into the soil to help grow additional food and crops, effectively recycling past waste products (se Fig. 2). This system doesn't produce direct useable energy, but recycles the energy put into the waste food for later use in food production.
Both approaches are pathways to making use of our waste. The latter one is more feasible residentially and most likely attainable at this moment in time, but as we progress as a world, reducing waste and increasing energy efficiency will become paramount in order to protect our world from climate change.
© Dylan Woodhead. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. Chow, "The Simple Way We Might Turn Food Waste into Green Energy," NBC News Mach, 12 Dec 17.
[2] S. Sengupta, "How Much Food Do We Waste? Probably More Than You Think," New York Times, 12 Dec 17.
[3] A. J. Fascetti and S. J. Delaney, eds., Applied Veterinary Clinical Nutrition (Wiley-Blackwell, 2011).
[4] M. A. Vázquez and M. Soto, "The Efficiency of Home Composting Programmes and Compost Quality," Waste Manage. 64, 39 (2017).
