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.