Archive for December, 2008

14
Dec
08

subtlety and sweetness: bioreactor landfill

Andries Vierlingh, a 16th-century Dutch dike master, specialized in small interventions—subtle alterations in the natural environment that would bend the forces of nature to his purpose. He studied tides and currents to understand how to encourage the waters to deposit silt where he needed a dike, how to set the tides to scour a channel where he was looking for better drainage. “With subtlety and sweetness,” he wrote, “you may do much at low cost.”   He recommended patience, gentleness, and cleverness. His minimalist approach was mostly inspired by necessity. He had dirt, and he had labor in ample supply, as well as spades to bring the two in fruitful alliance. He had primitive, wind-driven pumps but often unobliging weather. Very little wood, except profusions of willow shoots with which to weave mats. No stone, except prohibitively expensive imports. Small wonder that he looked to subtlety.

In the U.S. today, true want of resources is an unaccustomed circumstance. Vierlingh’s spirit of patient minimalism is rarely practiced, I suspect in part because greater glory lies in bigger budgets and more fantastic equipment. So it is something of a surprise to find an experiment in such minimalism at Yolo County Central Landfill, in the middle of the grasslands just west of Sacramento, California.

The experiment in question is an effort to render our trash into a geologic formation, cheaply and expeditiously. That is the description of the project offered by Don Augenstein of the Institute of Environmental Management in Palo Alto. Don is a somewhat other-worldly presence, a fount of information on garbage, renewable energy, and climate change, and one of the movers behind the Yolo County outdoor garbage lab. He invited me along on a tour of the dump on the dreary Wednesday before Thanksgiving, together with a gaggle of junior college students who didn’t look wildly enthusiastic about their field trip.

yolo, trash arriving

yolo, trash arriving

Since this was a regular working day, the landfill was as busy above ground as below.  Trucks drove in large loads and small, coming in thick and fast enough to cause a backup at the gate.  Heavy equipment trundled over the mounds, compacting and molding and pushing around the fresh leavings. Piles of stuff that can be snatched from the abyss were being moved from one place to another. Concrete was being mauled into its constituent parts. A sorry pile of bathroom porcelain, sat pale and forlorn in the middle of this bustle, the still center in a vortex of industrial activity. Flocks of gulls, inevitably, wheeled above the scene, screaming as they always do.

bioreactor cell

bioreactor cell

Much of what is to be seen at Yolo is just conventional landfill and its attendant recycling activities. The proceedings remind me of a landfill in Amersfoort, in the Netherlands. But several “cells”—the lined landfill compartments in which our trash is stored until we can think of a better thing to do with it—have been rigged at Yolo as bioreactors. Leachate is judiciously circulated through these cells, which have been constructed very much like the usual layer cake of trash and daily cover, but with a subtle difference.  The daily cover itself is permeable so as to facilitate the even movement of moisture. The whole thing is topped with a layer of shred tire and then wrapped in plastic, which in turn is held in place by whole tires and wheelhubs and other  paper weights that sanitary engineers typically have ready to hand. The shred tire layer on top is to encourage the desired flow of methane gas through the dump, for more efficient extraction. The plastic wrapper prevents its escape into the atmosphere. The whole sandwich is built and monitored under the watchful eye of Ramin Yazdani, whose business card lists him as senior civil engineer at the Yolo Planning and Public Works Department.

methane to electricity

methane to electricity

The purpose of the bioreactor is to more effectively collar methane, a significant part of which goes on the lam at conventional “dry tomb” landfill despite methane capture systems. Methane doesn’t directly harm humans (as many of the other landfill effluents have the potential to do), but it is a potent greenhouse gas. “Fugitive” landfill emissions contribute significantly to global warming. However, when captured, methane is an effective fuel, and the idea behind the bioreactor is to get the trash to give up all the gas in a short, sharp burst. In this way, the trash becomes less of an environmental menace and at the same time a more economical source of fuel—a double whammy in favor of the planet.

Experiments to do the same thing are being conducted in Spain, France, Belgium and elsewhere, but in vessels specially built for the purpose. These “digesters” are expensive and require significant energy inputs. They can’t handle all the waste in the waste stream, even after recyclables are removed. And they extract far less methane from the “feed stock” than the landfill bioreactor at Yolo—which has an extraction rate of more than 95% over the course of a year.

This excellent result is achieved at low cost, both in terms of funding and energy inputs. The most remarkable “energy in” lies in the dedication and inexhaustible inventiveness of the human motors behind the experiment—Augenstein’s genius with numbers and Yazdani’s wizardry in building things that work almost out of nothing. Vierlingh would be very pleased to find out that throwing more resources at the problem delivers a less effective solution than an attentive eye and subtle adjustments in the way a landfill is put together.

ramin yazdani, monitoring underground activity

ramin yazdani, with monitoring equipment

In the meantime, the garbage at Yolo is monitored as carefully as a patient in the ICU. Continuous measurements of moisture, temperature, and pressure inside the stewing trash heap are taken, while the composition of gases that arise from it is analyzed. Workers collect leachate samples that go off to a different lab for analysis.

Regulators have yet to be persuaded that simple and subtle solutions may be more sound than big-muscle engineering, and so the collection and analysis of data proceeds patiently as does the effort to present results. I hope they succeed, because their solution seems important in a world where landfill still is the most common trash management approach. What’s more, their spirit of inspired minimalism seems to be the right recipe for a hot and nearly exhausted planet.




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