Waste equals food—or so we have heard many times from green pundits like William McDonough and Michael Braungart, who view the ways in which contemporary human societies treat waste as a design problem. But waste is not literally equivalent to food—we don't see biological excrement stocked in grocery store shelves, nor serve it at the dinner table. Bio-waste, however, is useful in producing food.
At the globe's largest wastewater treatment plant, the Blue Plains Advanced Wastewater Treatment Plant in D.C., human waste is considered as a valuable resource. The Washington Post recently reported that the District of Columbia Water and Sewer Authority, which operates the plant, will soon be able to convert human excrement into fertilizer, to the tune of about 600 tons per day, that may be used to grow fruits and vegetables.
The new D.C. Biosolids Management Program facility will accomplish a few things simultaneously. It will generate 13 megawatts of electricity, create a "Class A" pathogen-free fertilizer, and reduce the amount (and cost of transporting) of "Class B" waste, which is usable only for inedible trees and sod. According to the Post, this system will save $10 million annually in electricity costs, and will reduce the plant's carbon footprint by a third.
A key element of this facility stems from Norway. Called Cambi's Thermal Hydrolysis Process, the technology pre-treats waste with high-pressure steam in an anaerobic digestion process to produce fertilizer and/or biofuel.
The conversion process also eliminates the smell in the final fertilizer product, since methanogens are first allowed to run a full course of methane gas extraction in enclosed chambers.
With so many benefits, where's the catch? The Post says DC Water's biosolids program required a decade of study and $470 million—hardly insignificant investments in time and money. With further development and testing, the method will hopefully become quicker and cheaper for other utilities to implement. Regardless, a process that more closely approximates nature's approach to dealing with waste as a resource is welcome news—particularly at this significant scale of operations.
Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website each week. His views and conclusions are not necessarily those of ARCHITECT magazine nor of the American Institute of Architects.