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The Living Machine

As you approach the recycled truck trailer, your ears are filled with the soft gurgling sounds of water. When you reach the top of its platform, your eyes are filled with river birch, water hyacinth and willows. And you wonder, as you detect the faint aroma of wild mint, if you really are in a sewage treatment plant. Parked outside San Franciso's Oceanside Sewage Treatment Plant, the Living Machine runs secondary effluent through a series of ecosystems to remove contaminants including excess nitrogen, phosphate and coliform bacteria. Twenty thousand gallons a day receive tertiary treatment. The machine can be also adapted to provide both primary and secondary treatment.

Developed by John Todd of Ocean Arks International, the Living Machine consists of a 28-foot-long steel tank divided into two purifying trains of seven cells which serve as ecosystems. The first five cells maintain aerobic, or oxygenated, conditions to promote growth of nitrifying bacteria, which convert ammonia (NH3) to nitrate (NO3). The last two cells provide anaerobic conditions in which other bacteria reduce nitrate (NO3) into nitrogen gas (N2), which returns to the atmosphere. Although ammonia and nitrate occur naturally in the water system, too much of these chemicals can be lethal to aquatic organisms. In the aerobic cells, plants with extensive root structures provide habitat for a variety of zooplankton, beetles and other freshwater invertebrates. In the anaerobic cells, surface covering plants such as water hyacinth prevent the growth of algae which would add unwanted oxygen back into the system.

Microbiologist Michele Hallahan, who operates the facility, chose plants that have a preference for wet conditions and are adaptable San Francisco's climate. Ten percent of the final effluent is returned to the beginning of each train to recycle bacteria into the system. (Hallahan has not needed to add commercial bacteria in over a year.) In addition, the purified effluent from one of the trains runs into a fish tank filled with ornamental and bait fish. According to Hallahan, aquaculture is part of the Living Machine's design. Proceeds from the sale of plants and fish grown in the machine help cover operating costs. The fish tank also tests the final water quality. Little is left to chance. State of the art technology is employed to monitor and maintain these ecosystems.

Every 15 seconds water quality measurements such as pH, dissolved oxygen, and turbidity are taken by a computer, which subsequently adjusts flow rates, carbon-dosing levels and other biological procedures. Weekly, effluent is tested in a certified lab for the EPA (see chart). According to Hallahan, effluent from the Living Machine is clean enough for swimming, and ideally, can be released into a large body of water. However, to meet California title 22 requirements (standards for water reuse), the effluent is treated with UV to remove remaining coliform bacteria. Currently, the effluent is returned to the Oceanside facility as raw sewage.

This month, the EPA-funded two-year-long project in alternative, wastewater treatment comes to a close. Whether the Living Machine will remain at the Oceanside plant as an educational facility is still to be determined.

Contact: Ocean Arks International (508)540-6801

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