Participate Palmy

Discharge option 1

Majority of treated wastewater is discharged to the Manawatū River via a wetland and/or land passage, with significantly improved removal of contaminants including phosphorus and nitrogen.

All options for treating and discharging our wastewater are still under consideration. The three options we are presenting during this feedback period appear to score the highest across a range of criteria and values.

This option is most similar to how we currently do things, with the majority of treated wastewater from the wastewater treatment plant on Tōtara Road being discharged to the Manawatū River, but with significantly improved treatment.

When the river is at very low levels about 75% of treated wastewater would be applied to land. We’d need about 670ha of land for this.

The river discharge will also treat the wastewater by passing through either a wetland and/or land passage. This ensures the water has had a final filter before entering our awa. Wetlands are like a kidney – filtering out any remaining contaminants.


This wastewater would have one of the highest treatments currently in New Zealand, with advanced removal of contaminants including nitrogen and phosphorus. Nitrogen gets into wastewater from urine and phosphorus comes from cleaning products, food, and fertiliser. We are looking at removing these through anaerobic and aerobic bacteria (biological treatment) and a membrane filtration process.

This would help contribute to a significant reduction of periphyton growth in the river downstream of our discharge, which can impact freshwater species. There are other factors that contribute to periphyton other than wastewater.

By applying some wastewater on land during low flow periods we’d be more confident in meeting guidelines set in the regional One Plan for freshwater.

New innovative technology which uses less energy will be considered.

We’d expect to see an increase in biosolids, the treated sludge produced in the treatment process, which is made up of dead wastewater bacteria and material removed through the treatment process.

We’d be able to further improve treatment over time as new technology is developed, which has the potential to improve wastewater quality.


We’d still use our existing treatment plant, but it would need significant upgrades for the new treatment levels, and to cope with a growing population.

We’d build an even better wetland or land passage for the treated water to run through before entering the river.

We’d also need to build a pipe network to the land discharge site, and purchase irrigation equipment.

Climate change

Climate change wouldn’t have significant impact on this option.


This option has smaller upfront infrastructure costs than some of the other options. The largest costs are associated in the investment in upgraded treatment, purchasing land, installing the pipes to the land discharge site and upgrading the treatment plant.

The operational costs for this option are considered high due to the energy and labour costs of operating a sophisticated treatment plan. This option would have a capital cost of $290 million and an annual operating and maintenance cost of $8 million per year.

Regional growth

We could look at taking other councils wastewater, provided they treat it to agreed standards and contribute to expanding the land application area and treatment plant expansion.


  • We know many members of our community and our neighbours in Horowhenua do not want treated wastewater in the Manawatū River. People may refrain from recreational activities in the river as a result.
  • The discharge of even highly treated wastewater could negatively impact the mauri (life force) of the river and impact the mana of iwi, who are kaitiaki (guardians) of the river.
  • Achieving ever-increasing freshwater standards will be complex, but we believe we can do this with the right technology.