A common message weaved into many renewable energy documentaries is that all energy consumed on Earth is ultimately derived from our sun. With the notable exception of nuclear energy, whose heavy fissionable atoms are manufactured in dying stars, this notion is true. The energy within today’s fossil fuel was captured, harvested, and stored by biological systems on Earth long ago. In a way, our energy supply is akin to the Star Stuff of Carl Sagan’s Cosmos.
Thinking of energy in these ubiquitous, philosophical terms makes a bit more palatable the notion of converting human waste into power. To make your sustainable energy contribution just plug your nose, flush the toilet, and imagine the solids going down the drain as star stuff.
As reported by Reuters in “Texas city plans to convert human waste to energy,” San Antonio plans to harvest methane gas from human waste and turn it into methane, the major component in natural gas. San Antonio is the first U.S. city to attempt human waste-to-energy conversion on a commercial scale.
According to the Reuters article, more than 90 percent of San Antonio’s water waste will be recycled for irrigation, compost, and now fuel. San Antonio residents produce about 140,000 tons a year of waste referred to as “biosolids,” which will be processed into about 1.5 million cubic feet of natural gas per day to fuel furnaces, power plants, and generators.
Akin to fossil energy being stored star stuff, human waste is essentially a concentrated store of solar energy. It travels a long conversion path from the sun through our modern agricultural and food distribution system onto a plate. From there it is consumed, and a portion is used to fuel our bodies. The rest is concentrated by the human digestive system to energy-rich biosolids. In a grand manner that perhaps Carl Sagan would appreciate, our planet’s food cultivation infrastructure is also acting as a gigantic solar energy concentrator.
By tapping this previously ignored solar energy store, San Antonio essentially gets paid to further reduce the volume of its municipal waste stream. As reported by Natural Home Magazine. in “Sewer Waste: San Antonio’s Newest Energy Source,” Massachusetts-based Ameresco plans to buy the gas, process it, and sell through existing natural gas pipelines. San Antonio will receive between $200,000 and $250,000 a year as payment.