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By Ciara LaVelle, Kat Bein, Carolina Del Busto, and Liz Tracy
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When a person in the upper or middle Keys flushes his toilet, or a cook in a restaurant pours something down the sink, these substances travel by way of gravity through a pipe to an underground tank typically twice the size of a coffin. Throughout the islands, in 30,000 of these concrete containers, the true leftovers from last night's supper are partially decomposed by anaerobic bacteria. Some solids settle to the bottom of the tank to form a concentrated sludge. Meanwhile, much of the liquid waste drains out of the tank into a crisscross network of small plastic pipes embedded in crushed rock. This subterranean network may measure 20 by 40 feet or more. The plastic pipes are perforated with tiny holes, and so the partially putrefied septic tank effluent dribbles out into the ground, where it is supposed to percolate through the soil and cleanse itself.
What actually happens is that the partially treated wastewater emitted from 30,000 septic tanks seeps through the Keys' porous bedrock -- limestone formed millennia ago by the shells of marine microorganisms -- and finds its way into the nearest waterway. In many cases, it trickles down into the region's groundwater, a geologic layer that in many parts of the nation lies deep in the ground but here lies just three to four feet below the surface. The only thing that keeps Keys residents from continually poisoning themselves with their own fecal material is the fact that they pump in every ounce of their drinking water -- all 13 million to 14 million gallons per day -- from wellfields in southern Dade County.
There are all sorts of chemicals and compounds in household wastewater, but more than one-third of it originates in people's toilets. As such, it contains huge amounts of both phosphorus and nitrogen, in the form of phosphate and ammonium. "Using a series of monitor wells we showed that when the tide goes out, the ground water surges, carrying the leachate from the septic tank toward the canals," says LaPointe, describing a study he performed as a consultant to Monroe County. "But by far the greatest effect on the transport of nutrients from the septic tank drainfield to the canal is when the rain hits. It flows literally like a pipe. The flow rate can go from a base of half a meter to three meters per day up to ten meters per day during rain events. Then the nutrients go way up in the canal." And the canal comes to resemble the dead one behind LaPointe's house, from which the polluted water makes its way to the reefs and Florida Bay.
Six months ago on Pigeon Key, with the help of his long-time assistant, Bill Matzie, LaPointe began building the prototype of a bioengineered wastewater treatment system he believes could eliminate the problem of concentrated nutrient runoff from the Keys' septic tanks, and go a long way toward halting the destruction of the area's reefs and fisheries. While no single element of the treatment system is entirely new, government officials and marine scientists say LaPointe's invention is the first of its type, the cutting edge in a new generation of inexpensive, low-tech additions to conventional sewage treatment that help reduce nutrient poisoning in coastal areas.
LaPointe says his wastewater treatment system is so simple as to be unpatentable, yet he already has his first client, a Keys developer who wants to use an enlarged version of the Pigeon Key prototype to treat sewage at a small, upscale housing project on Upper Sugarloaf Key. This week Florida's Department of Health and Rehabilitative Services is expected to finalize its approval of a two-year pilot program allowing LaPointe to do business with builder Bill Cobb under the terms of an experimental permit. "I want to see a variety of techniques employed to reduce nutrients in the Keys," says Kevin Sherman, an HRS environmental specialist. "But so far give Brian LaPointe credit for being the first to come up with any viable technique at all."
"The way we handle sewage has got to change," says Cobb, who has built houses in the Keys since the early 1970s. "Looe Key has lost 40 percent of its reef just in the last ten years. That tells me that in ten more years they won't have a reef if something isn't done. [LaPointe] has hit on something that is the only cost-effective way I can see to make it happen.
"I personally think this could be the system of the future," Cobb continues. "I honestly believe that in five years, you're going to see this thing made mandatory. The great thing about it is that it could be used retroactively. It could easily be hooked up to thousands of existing septic tanks. It'll work on a small scale and it'll work on a large scale."
LaPointe's prototype on Pigeon Key -- a household-size model developed through a grant from the U.S. Environmental Protection Agency -- uses a series of four 500-gallon tanks to naturally remove phosphate and ammonium from 100 gallons of wastewater per day, the typical amount generated by one household. LaPointe is now using a nutrient solution to simulate sewage, because it allows him to do more exact experimental fiddling than if he used the real thing. In the first tub, Scendesmus, a common green alga, feeds voraciously on the microscopic nutrients contained in the wastewater liquid. Using sunlight as energy, the hungry phytoplankton convert nitrogen and phosphorus into biomass. A tiny air pump keeps the water in the first tank aerated so the algae have plenty of carbon dioxide to use in the photosynthetic process, and also to prevent the septic tank effluent from stinking.