By Jan TenBruggencate
Advertiser Columnist

Old-timers in the Islands, particularly people raised on plantation camps, can remember the days when faucets frequently were fitted with filters.

Most often, the filters were cotton tobacco-bags with drawstrings — the kind men carried in their shirt pockets with the tag hanging out.

The simple filters caught dirt and bits of rust that often came out of the ancient lines.

These days, modern filtration systems are used to do the same thing, but much more efficiently.

Kaua'i County's Water Department and Grove Farm Co. are discussing a filtration plant that would use tubes with minuscule holes in them. A partial vacuum on the inside of the spaghetti-like tubes would suck water through the porous tubes, but would leave behind any contaminants.

In the Kaua'i situation, the system would convert stream and ditch water into drinking water, but without the extensive use of chemicals or other disinfection technologies.

A related technology is being promoted to filter sewage, converting it into something that's likely safe to drink, although that's not recommended.

A Texas firm, Enviroquip, has built a pilot plant for the City and County of Honolulu at its sewer plant in Honouliuli, and recently made a proposal for a similar system to a West Kaua'i firm, Kikiaola Land Co.

Enviroquip uses a "submerged flat plate membrane bioreactor" system developed by the Japanese industrial firm Kubota.

Sewage first goes through an aerobic biological treatment, similar to those used in many sewer plant designs, although it's tweaked a bit to increase efficiency, said Dennis Livingston, the firm's membrane bioreactor project manager.

Then the liquid, minus the solids that have been filtered out, is run past sets of membrane cartridges, with air bubbles preventing the particles from clogging the surface of the membrane.

The Kubota membrane is made of a polyethylene material with filter holes sized at 0.40 microns. That's so small that bacteria and viruses can't get through. Nutrients such as nitrogen and phosphorus are reduced to levels so low they often can't be detected in lab tests.

"Basically, there's nothing left" but water, Livingston said.

In other countries, the recycled water from similar plants is used to run toilets and irrigate fields.

In the Islands, it would meet standards for irrigating landscaping or agricultural products, said Raymond Hoe, managing partner of Clear Water Technology, which markets the systems.

Jan TenBruggencate is the Advertiser's Kaua'i bureau chief and its science and environment writer. Contact him at (808) 245-3074 or e-mail jant@honoluluadvertiser.com.