Gisborne city sludge treatment wetland trials

NIWA, in close collaboration with the Centre for Integrated Biowastes Research (CIBR), has recently embarked on an exciting new project with the Gisborne/Tairawhiti Wastewater Technical Advisory Group (WTAG) and Gisborne District Council to develop alternative uses and disposal options for the treated effluent and biosolids from Gisborne City.

Implementation of appropriate treatment and discharge options for Gisborne’s wastewater has been a long-standing issue with a high level of Tangata Whenua and wider community involvement. Gradual understanding and co-operation between and within the community and the council has evolved to the stage that a collective solution based around wetland treatment has emerged.

NIWA and CIBR are working together with the community and council to explore the establishment of wetland systems to treat and beneficially re-use wastewater and biosolids from Gisborne’s new Biological Trickling Filter (BTF). Although commonly used in other areas of the world, wetlands constructed for the dewatering and treatment of sludge have not previously been applied in New Zealand. Their efficacy treating BTF sludge is being assessed under local conditions using native plant species, rather than the invasive common reed employed elsewhere in the world. Additionally, the removal efficiency and, the fate and effects of a range of key contaminants of concern in New Zealand (including emerging organic contaminants, pathogens and heavy metals) will be investigated. The initial phases of the work have involved all parties turning out to build some pilot-scale wetlands to evaluate which plant species grow best in Gisborne BTF sludge. NIWA has been investigating the settling and dewatering characteristics of the sludge and developing preliminary wetland treatment options, whilst the community and council in association with CIBR are exploring alternative uses and dispersal options for the treated biosolids and effluent.

This project includes an unprecedented level of community involvement and interest. We are enjoying the close interaction, and the tough and insightful questions being asked.


Principal Scientist - Aquatic Pollution
Bevan Turnpenny, one of the keen tairawhiti/Gisborne wtag members, watering the establishing wetland plants for the upcoming Gisborne sludge treatment trials. [NIWA]
NIWA Scientist Jason Park collecting effluent from the outlet of Gisborne’s Biological Trickling Filter to test settling and dewatering rates of the suspended sludge. [NIWA]