Biochar is organic matter burned in an anaerobic atmosphere. Mixed into soil, this porous carbon offers tiny housing to microorganisms. It also functions as a sponge for nitrogen and phosphorous, preventing them from washing away. You can make it by incinerating any kind of organic trash--agricultural waste, manure, bodies and bones. Controlled pyrolizing processes also yield bio-oil that can be burned for heat or to generate electricity. Climate change geoengineers believe the biochar "miracle substance" to be an extremely stable form of carbon sequestration, while organic farmers hype its productivity as a soil amendment.* Archaeologists say the terra preta (black earth) in ancient tracts of agricultural land in the Amazon are still fertile after thousands of years. Biochar gives even James Lovelock a little hope in human survival: "There is one way we could save ourselves and that is through the massive burial of charcoal. It would mean farmers turning all their agricultural waste--which contains carbon that the plants spent the summer sequestering--into non-biodegradable charcoal, and burying it in the soil."**
But isn't there another massive flow of organic trash to burn? The Hornsby Bend Biosolids Management Plant processes 1 million gallons of sewer sludge a day, which is only 1% of the total sewage water treated daily in Austin. The grounds are beautiful and a little stinky, located right along a bend in the Colorado River.
The sludge water treated here settles out of sewage in the first stage of processing at Austin's two wastewater treatment plants, and is then pumped to Hornsby Bend. Here, the treatment process begins by passing sludge over conveyor belt screens that allow solids to settle out. Sludge then enters anaerobic digesters--six huge pressurized floating domes--where it is metabolized by bacteria kept warm by gas combustion. The gas itself is methane farted out by bacteria in these digesters. In 2012 the domes were retrofitted with "co-gen"--electricity generators that run on gas combustion, such that burning methane from the digesters simultaneously heats the domes and generates electricity sold back to Austin Energy. The treatment facility's 112 acres are also an agriculture research facility that experiments with fertilizing alfalfa and hay fields with biosolids and irrigating with wastewater. Current research focuses on the persistence of emerging contaminants (from pharmaceuticals like birth control and viagra) in treated biosolids.
After the digesters, biosolids are mixed with mulched leaves and sticks from curbside pickup and composted for several weeks. Compost then ages up to three months and is screened and trucked to Organics By Gosh for bagging. It winds up in Home Despot as DilloDirt for all your landscaping needs. And this year Hornsby Bend's new product DilloChar hit the market--bioslids and mulch, pyrolized in a methane-powered furnace.
Once most of the biosolids are removed from the raw sludge in the conveyor belt stage of processing, wastewater flows to three pools that draw bird populations and recreational birders. When I visited in the winter, koots and shovel bill ducks paddled around, picking through the pools' banks. Migratory herons, painted buntings, and swifts nest in the summer. Red shoulder hawks and osprey also hunt here, likely drawn to rodents that live in the hay fields and topsoil hills from gravel mines that surround the treatment facility. The pools are divided by raised levees that are open to the public year round during daylight hours. Public sludge is remediated into a park for urbanature--ecosystems that thrive in the world only because of highly technical large scale human-made systems, in this case, collective intestines of post-poop.
After percolating through the three pools, the water flows into narrow ponds inside a football field-sized greenhouse. The ponds were once stocked with water hyacinth plants for further treatment (to draw out metals) until the water hyacinth babies clogged up the aeration pumps. Next they tried duckweed, which was recently all washed away when the water flow rate went too fast. Now algae have taken over the ponds, and management are throwing around ideas on what to do with the greenhouse. The banks of the ponds have little holes dug out where turtles have been laying their eggs.
Hornsby Bend and other municipal facilities in the US have succesfully transformed sewage--the ultimate worthless garbage--into commodites, energy forms, and urbanature. But biosolids can also start backing up in some kind of megacity-scale hoarder scene: in 2006, Kern County outlawed Los Angeles' dumping of its processed biosolids as agricultural fertilizer. As sludge piled up, LA responded with an experimental geothermal anaerobic digester at Terminal Island. EPA permit in hand, they inject biosolids into five thousand foot deep wells that tap depleated oil and natural gas tables. The earth heats these pits of hell to 150°F. The wells are filled with briny wastewater (from a desalination facility or fracking?). Like the domes at Hornsby Bend, bacteria digest the biosolids, producing CO2 sequestered by the water (turning it into carbonated water) and methane gas collected at a second well's vent.
Of course, some people are just waiting for some mutant bacteria to evolve in the pits, infecting LA with a pandemic. Others say demons will crawl out. Or the deep wells will activate fault lines, mega-volcanoes. Meanwhile the methane vents power whole neighborhoods and the biosolids facilities themselves.
This summer Ephemerata Garden's DilloChar test patch yields dinner plate poppies. The sunflowers grow fifteen feet tall, absurdly propping up the sky, sequestering carbon. Curbside pickup accepts diapers, pet poop, and meat for pyrolization. The crumbly biochar could have been somebody's shit, or dinner bones, or just branches from a dying hackberry. Smells like burned dollar bills.
*Stewart Brand, Whole Earth Discipline: An Ecopragmatist Manifesto, New York and London: Viking, 2009, 240-1.
**Quoted in ibid., 288.