Technical feasibility of constructed wetlands to provide for improved environmental and cultural outcomes at Wairoa’s wastewater treatment plant

Abstract

Wairoa’s wastewater discharge consent expires in May 2019. Since April 2016 the Wairoa District Council has worked towards a solution of how an application for a further discharge consent might look like. The Wairoa Wastewater Stakeholder Group was formed to assist the Council to find an adequate option for the future of Wairoa’s wastewater system. One of the most significant goals of this process was to gain cultural acceptance for a new developed future discharge option. Cultural considerations about discharge changes are important for an application for a resource consent, as requirements are regulated by law in the Resource Management Act (RMA 1991), New Zealand Waste Strategy (2002), and the Local Government Act (LGA2002). Currently the treated wastewater is discharged into the Wairoa River. Wairoa’s Tangata Whenua, the native Maori, have a strong spiritual connection to the Wairoa River and big concerns about wastewater entering it. In Maori beliefs water has a spiritual health, which is damaged when water meets waste. Wastewater restoring would only be possible by releasing it back to the earth (earth mother). Stopping the discharge into the river and irrigating all wastewater on land is the favoured option for Tangata Whenua. However, this option is not the most practicable one for Wairoa, due to high costs and limited irrigation areas. Research and consultations with Wairoa’s Stakeholder Group showed the significance of improving the rivers’ health. The outcome is considered to be a package which includes wastewater infrastructure improvements, some wastewater irrigation and develop options to improve the overall health of the Wairoa River. This thesis investigates wastewater infrastructure improvements to address cultural requirements and increase the wastewater effluent quality. The aim is to assess the current wastewater treatment system and develop an upgrade that satisfies both, treatment requirements and cultural values. Natural treatment systems such as wetlands are successfully applied all over the world and are known for being low cost and cultural related wastewater treatment systems in New Zealand. A major goal of this thesis is to prove if and which kind of natural system could be a practicable option for Wairoa. As the wastewater reticulation system is exposed to high inflow and infiltration of storm water, resulting in high fluctuations of the inflow volume, it must be proved if a natural system can be designed and operated in accordance to high flow variations.