Cinema Science: The Power of Waste

In "Back to the Future II," director Robert Zemeckis envisioned a future--now a mere five years away--in which every home comes equipped with a Mr. Fusion Home Energy Reactor. Mr. Fusion can power just about anything, even the flux capacitor of our favorite time-traveling DeLorean, using everything from banana peels to beer cans. Zemeckis may have overestimated the ubiquity of mini fusion reactors--not to mention flying cars--but we have made some progress in transforming waste into power since 1985. Manure and some forms of garbage have been used to produce methane gas, hydrogen gas, and to directly generate electricity. But one of the most surprising of these renewable biomass energy sources is urine.

Urine may not be a particularly powerful energy source, but its abundance and inherent renewability could make up for what it lacks in energy density. Using a technique called urea electrolysis, says Dr. Geraldine Botte of the Center for Electrochemical Engineering Research (CEER) at Ohio University, farms and office buildings could become self-sustaining pee powerhouses.

Urea is one of the main components of urine. If left untreated, urea will react with water and turn into ammonia and other pollutants. To turn this would-be pollutant into power, Botte and her colleagues extract urea from the wastewater and pass an electrical current through it, releasing hydrogen gas. The hydrogen can then be used to power generators or create fuels, and the urea-free wastewater can safely be used for irrigation.

Traditionally, hydrogen has been produced using water electrolysis, but that process is far more expensive and inefficient. Dr. Botte says one cow could provide enough hydrogen to heat water for 19 homes and an electrolyzer could easily fulfill all the electricity needs of a small farm. Some researchers speculate that an office building could be fully powered by the liquid waste of its office workers. And Botte's lab has even used hydrogen made from pee to create a pee-powered car.

In this video Purusha Bonnin, a graduate student working with Dr. Botte, demonstrates how CEER's hydrogen-powered car would work using a small model. But what about the DeLorean? Dr. Botte, like most researchers, thinks that this technology is better suited to stationary purposes for electricity production or perhaps for powering the electrical systems of the car. It is not powerful enough to keep a car engine running efficiently. We are decades away from surmounting the technical and economic hurdles to widespread use of hydrogen cars--and they may never become widely available.

If you're looking to toss some scraps into your coupe and speed off like Doc Brown--minus the time travel--there is a process for that. Those scraps could be transformed into a hydrogen and carbon monoxide synthesis gas, or syngas, through gasification. To create syngas, high-pressured steam and oxygen are combined with the carbon-rich materials to create a chemical reaction, which usually has by-products of molten ash and a negligible amount of carbon dioxide. The syngas is used in some electric powerplants and can also replace natural gas for making ammonia fertilizers and clean-burning synthetic fuels.

Gasification is nothing new. This method was used to power many vehicles during WWII due to gas shortages. Coal is the typical energy source. While the emissions of coal gasification are still relatively clean and carbon neutral, coal is an expensive and finite resource. Gasification could work with just about any dry, solid organic material, but getting it to run consistently and efficiently enough for commercial use has been a challenge.

The team at All Power Labs in California develops gasifiers and successfully drove a Honda Accord using one of their designs. They sell kits for building your own gasifier on their website. While the gasifier worked on a personal scale, the process would be prohibitively expensive for the mass production of cars. Even on this smaller scale, gasifiers are not very dependable, especially when using more irregular kinds of biomass. However, gasifiers, like urea electrolysis, may be well suited for other applications.

One Cambridge dog park found a simple and creative way to reuse waste. Instead of ending up on your shoe, dog poop is deposited into a methane digester called the "Park Spark" which powers a connected lamp. Bacteria in the waste break down into methane gas, which is fed into the park lamp.

These abundant energy sources are all around us. As with all recycling processes, we just need to develop the technology to efficiently convert them. Refuse and waste may not solve all our energy problems, but they could help when combined with other alternative sources and a bit of ingenuity.

Samantha Johnston is currently studying broadcast and print journalism at UCLA Extension. She has traveled through Greece, Ecuador and Peru studying anthropology and archaeology, and earned her BA from the University of California, Santa Barbara, in 2007. On clear, moonless nights, you'll find her stargazing on Southern California's Mount Pinos.

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