Treated water may go out to sea

Palmerston North’s treated wastewater could be piped out to sea in one of the future scenarios the city council has put out for public comment.

The latest stage of the ‘‘Nature Calls’’ project to find an improved solution to dealing with the city’s wastewater proposes 26 different options.

Council transport and infrastructure manager Robert van Bentum said none of the proposals had been fully investigated at this stage and cost estimates had not been done.

But the council wanted to hear how people felt about discharging wastewater to seven different environments, or a combination of them.

The options are the Manawatu¯ River, land, the sea, evaporation into the air, piping deep into groundwater, treating to a standard high enough to go into the drinking water supply, or a split between the river and land.

‘‘This is not about technology, but asking where in the environment we are comfortable with discharging some or a portion of our treated wastewater.’’

He said some of the options, like discharge to drinking water, were likely to require the most expensive treatment technology.

The coastal option might seem surprising to many inland city people, but most of New Zealand’s metropolitan areas already discharged into the ocean, he said. The cost of installing pipes about 2 kilometres out to sea would be the expensive element of that option.

Evaporation would require a large surface area for the volume of liquid, which would need to be heated. ‘‘It’s conceivable, but we are not sure it there is practical and affordable technology.’’

A continued discharge to the river would require treatment to a higher standard.

Another twist could be to discharge some or all of the wastewater at a location downstream of the O¯ piki bridge, where the river had a muddy bottom.