40,000 new council staff wallow in their work

The Far North District Council's newest employees work 24 hours a day, never demand a pay rise and are quite happy working up to their eyeballs in excrement.

That's because the new workers are tiger worms - 40,000 of them - helping to break down effluent in a natural sewerage system thought to be the first of its kind in the North Island.

A $470,000 upgrade of the council's Kaeo wastewater treatment plant was completed last Thursday after 12 years of planning. The upgraded plant, which serves 164 homes, still has screens and a settling pond to separate solids from liquid effluent, but a secondary process uses red tiger worms to aerate gravel in a filter bed.

That improves the efficiency of natural bacteria, which attach to the gravel and remove dissolved biological matter from the effluent as it trickles through the bed. The treated effluent is then "polished" in a wetland where reeds remove residual nutrients before it is discharged into the Kaeo River.

Council infrastructure manager David Penny said using vermifiltration (worm filtering) instead of a membrane filter cut upgrade costs by $350,000. It would also bring future savings as less power was needed to run the plant.

"We plan to upgrade the wetland and we have the option of adding ultra-violet light treatment if necessary, but we're confident the plant will meet discharge standards in the new resource consent."

The vermifiltration system was based on an international concept but designed by council contractor Transfield Services using ideas provided by council staff, so ratepayers did not have to stump up extra money to buy an off-the-shelf system.

Kaeo residents and directors of Wai Care Environmental Consultants Whangaroa Violet Walker and Bryce Smith are part of a working group formed in 2005 to explore sewage treatment options.

After a change in mayors, a redirection of funds, many meetings and site visits, it was decided that vermifiltration was the best option for Kaeo. It was a first for the North Island and, hopefully, not the last, Ms Walker said. The project showed the community, tangata whenua and the council could work together to achieve an efficient, low-maintenance, cost-effective and environmentally sound result.