Sewage Treatment
An article called Plants that Purify on page 9 of the Jan/Feb '92 issue of Audubon describes how marsh plants
effectively cleanse the effluent from sewage water. The marshes emit no unpleasant odors and are home to birds,
turtles, and fish. Excerpts of the article follow:
- A floating, wind-driven aeration device anchored in the pond's center churns and oxygenates the resulting
soup, allowing aerobic bacteria to slowly break down the solids, which then settle to the bottom as sludge. In
this airless gunk, anaerobic bacteria continue the decomposition process. The time bacteria are given to
consume nutrients is one of the main differences between a natural and mechanical sewage-treatment system.
[The] sewage remains in its settling pond for three months, ample time for bacteria to chew on and break
down pollutants.
- Rows of nutrient-absorbing plants such as African calla lilies, water irises, arrowheads, and miniature and
giant bulrushes grow in the waterlogged gravel. A small group of plants with large leaf surfaces, such as the
African calla lily, can suck up water at a prodigious rate - about 1,000 gallons per day, depending on sunlight
- and release it into the air through evapotranpiration. Wastewater spends a month trickling through the rocks
and roots of the filter, where bacteria and microbes attached to plant roots further break down pollutants. ...
The key processes of natural sewage treatment are entirely invisible. Plant roots nurture and shelter countless
microorganisms that not only consume ammonia, nitrogen, and phosphorous but also attack and break down
such pollutants as industrial chemicals, detergents, and pesticides into simple compounds that the plants can
then absorb.
- B.C. Wolverton, Ph.D., a pioneer in natural wastewater treatment ... has been researching the ability of plants
to clean polluted water for more than 20 years. He spent much of that time at NASA's Strennis Space Center,
in Picayune, Mississippi, developing a way to recycle waste at the agency's planned moon base. Now retired,
he heads Wolverton Environmental Services, which advises towns and cities on natural treatment systems.
Rock-reed filters like the one at [Benton, Louisiana] are his design, though the basic idea has long been used
in European countries, principally Germany and the United Kingdom.
- In a 30 by 120 foot [Providence, Rhode Island] greenhouse ... rows of huge translucent cylinders contain
water hyacinths, watercress, bald cypress seedlings, ginger, and philodendrons, as well as snails and tilapia
(a fish species), which break down the waste as it flows from tank to tank. This unique system is the
brainchild of John Todd, Ph.D., a visionary and former scientist at the Woods Hole Oceanographic Institution.
An article called Space-Age Sewage System on page 30 of the June '93 issue of Popular Science magazine
describes a natural biofilter for processing sewage. Excerpts of the article follow:
- Ocean Arks International in Falmouth, Mass., has developed a down-to-Earth alternative to conventional
wastewater treatment. By mimicking pond and marsh processes, his greenhouse-based "living machine"
cleanses sewage without intensive energy or chemicals. ... Sewage flows into aerated tanks inside a small
greenhouse, then to a series of solar silos inside a larger greenhouse. The silos contain microorganisms,
snails, shellfish, and plants such as hyacinths and watercress; some also hold fish. In a clarifier, solids settle
to the bottom for removal. The remaining liquid flows through a "biofilter" of plants such as bulrushes and
cattails. ... Pilot projects are already being used to treat waste from septic tanks in Harwich, Mass.; municipal
sewage in Providence, R.I.; and dairy wastes at the Ben and Jerry's ice cream factory in Waterbury, Vt.
