Worms now on council payroll

An innovative sewerage plant that uses worms as part of the effluent treatment process, the first of its kind in the Far North, is now up and running at Kaeo.

The Far North District Council completed a $470,000 upgrade of the town's wastewater treatment plant last week, after a 12-year planning exercise that involved the Whangaroa community. The upgraded plant, which treats sewage from more than 160 homes, still has screens and a settling pond to separate heavy solids from liquid effluent, but the secondary treatment process uses red tiger worms to aerate gravel media in a filter bed.

That improved the efficiency of natural bacteria which attached to the media and removed dissolved biological matter from effluent as it trickled through the bed, FNDC general manager (infrastructure and asset management) David Penny said. The treated effluent was then 'polished' in a wetland where reeds stripped the effluent of residual nutrients before it was discharged into the Kaeo River.

Mr Penny said using vermifiltration instead of a membrane filter had reduced the upgrade cost by $350,000. It would also result in on-going energy cost savings because less power was needed to operate the plant.

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

The vermifiltration system was based on an international concept, but designed by council contractor Transfield Services, using research and design ideas provided by council staff, Mr Penny saying ratepayers had been saved further expense by the council developing its own system instead of buying one off the shelf.

"We are constantly looking for innovative approaches that result in good environmental outcomes while reducing costs for ratepayers," Mr Penny said, adding that the council might use vermifiltration at its other wastewater plants if it worked at Kaeo.

Kaeo residents Violet Walker and Bryce Smith, directors of Wai Care Environmental Consultants Whangaroa and key members of a working group that was formed in 2005 to explore treatment options for the plant, hoped the process would have wider application.

"After a change in mayors, a redirection of funds, many meetings and many site visits, it was determined that vermifiltration was the best option for Kaeo, a first for the North Island, and hopefully not the last," Ms Walker said.

The working group had worked alongside the council to ensure the upgraded plant met the needs of the community and tangata whenua.

"This project shows how the community, tangata whenua and the council can collaborate on an innovative initiative and achieve an efficient, compliant, low-maintenance, cost-effective and environmentally-sound result," she added.