Saving 30%-plus on irrigation is impressive, but the following system “saves” 100%, by using no potable city water at all. It is also, conceptually, perhaps the most aesthetically intriguing and novel breakthrough for underground irrigation in quite some time.
Called the Living Machine, it first emerged in the 1990s and has gone through steady improvement since.
David Hicks, a wastewater and environmental consultant based near Greensboro, NC, runs a Living Machine that was commissioned in 2008 at the Northern Middle School in Guilford County, NC. It’s now watering a school football field and two soccer fields, plus two other plots, sized 100 yards by 50 yards—“quite a bit of land,” says Hicks. It eliminates the need for aboveground watering, apart from rainfall. It’s also getting “quite a bit of water savings,” considering that it uses nothing from the tap, because all of the supply is treated wastewater from the school.
As a compact, in-ground, natural wastewater treatment system—a sort of partially buried tiny wetland—the “Living Machine” produces effluent that meets EPA and local standards as safe and suitable for landscape needs.
“It’s not exactly a constructed wetland,” says Will Kirksey, P.E., who is senior vice president, engineering and manufacturing, for the Living Machine’s developer, Worrell Water Technologies LLC, of Charlottesville, VA. Rather, he says, the process is rendered below ground, in a series of sewage treatment cells that work on a similar principle.
Beneath the surface, pumps and gravity work to circulate, oxygenate, and activate the flow. At ground level, porous crushed aggregate lets air go down to do the aerobic work below. The basic treatment principles are routine, says Kirksey, “but the real backbone of the technology is the design idea and the know-how.”
At the school site that Hicks manages, the resulting treated effluent is piped out through a “fairly standard sub-surface” irrigation loop 18 inches below ground. Burial reduces runoff, thereby saving 30% to 50% of the reuse water, compared to surface irrigation, and extending the amount of turf being watered that much more.
An 18-inch depth is deeper than would have been done using potable water, Hicks notes, and this extra gap forces the Bermudagrass to push roots deeper for it. But the extra few inches are a cushion, desirable “for sanitation purposes … to make sure there wouldn’t be any surface wetness.” Ideally, in hindsight, a shallower pipe might have been better, he suggests.
In any case, plants and grass “have done real well,” says Hicks. Salts in the effluent—the accumulation of which is a problem for soils wetted by such water—is being canceled-out by having a 2-foot layer of sand just below the turf—“so normal rainfall gives a good flushing to prevent salt buildup.” That’s an unusual design concession, he adds.
Hicks runs the whole plant by himself and finds the task quite easy, thanks to its automated controls and Internet accessibility. Every element can be remotely monitored. The system text messages him at any sign of trouble. There’s even an iPhone app to control most functions. Trouble signals “are fairly rare” anyway, he says; the most frequent being local power outages.
Next to the school building sits the Living Machine’s surface wetlands, with cattails, bulrushes, reeds, water irises, willow shrubs, and natural vegetation, covering a rectangle of two-thirds the size of a football field, and mixing in pleasantly with the natural landscape.
Regarding the wetlands aspect, Kirksey notes that this can be compacted and situated indoors instead of out, and rendered as a decorative feature, like giant planter boxes. They’re biologically safe, with no odors or exposed water.
The Port of Portland, OR, offices, occupied by 300 people, showcases a 750-square-foot version in its lobby. In Florida, there’s an even smaller one measuring just 10 by 10. All told, two-dozen Living Machines are in operation nationwide, with another half-dozen under development, he says.
