Wastewater can be turned into new water

The Manawatu River, looking upstream from near the wastewater discharge.
MURRAY WILSON/ FAIRFAX NZ

The Manawatu River, looking upstream from near the wastewater discharge.

Wastewater can be treated to a standard that is good enough to drink, a forum in Palmerston North has heard.

But the once-favoured option of lower treatment standard and disposal to land is not as easy as it seems.

United States, Australian and New Zealand specialists in wastewater management shared their experiences with about 100 people at the forum on Friday.

It was organised to open public discussions about what Palmerston North should do with its wastewater in future, as it works toward applying for a new discharge consent in 2022.

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Director of water technology and research at Hampton Roads Sanitation District in South East Virginia in the US Charles Bott manages 13 treatment plants handling wastewater from an area with a population of 1.7 million people.

At one of those plants, the treatment system was so sophisticated it produced water at the end of the process that exceeded drinking water standards and was better than the water coming from some traditional supplies.

It was being put back into the ground to feed underground aquifers in an area where water was a scarce resource.

Bott said in urban areas, where there was no room for treatment plant to expand or consider land-based treatment, the only practical option was for treatment plant to become more sophisticated.

The processes included squeezing as much good as possible from the water, including treating for nitrogen and capturing phosphorus that could be used for fertiliser.

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In some plants, bacteria was being used to eat nitrates and discharge nitrogen to the air.

Back in New Zealand, Rotorua Lakes District Council wastewater treatment specialist Alison Lowe said a 26-year experience of minimal treatment and irrigation to forest land had reached its limits.

The water and nutrient load had killed Douglas firs and restricted the growth of pinus radiata.

It was also becoming increasingly difficult to exclude mountain bike enthusiasts from the public-excluded area, posing potential public health risks.

"We would have to disinfect if we were to continue," she said.

As well, infiltration of stormwater into the sewer pipes in recent high-rainfall events had exceeded the capacity of the pumps to deliver wastewater to the discharge site, and there had been overflows of nutrient-rich effluent into the environment.

Rotorua needed a major upgrade of its plant and was working toward improving treatment to a standard where wastewater could be discharged to water rather than land.

"Our proposal is to make water as clean as possible before returning it to the environment, rather than expecting the environment to do the work for us."

The water would also be good enough for people to use, not necessarily for drinking, but possibly for irrigation or industrial use.

Palmerston North City Council water and waste services manager Robert van Bentum said at the end of the forum that it was entirely possible for Palmerston North to produce treated wastewater that exceeded drinking water standards.

"There is still a cultural reluctance to drink it, but there could be a lot of other options for re-use."

Higher levels of treatment, such as nitrogen extraction, as well as land-based options, were in the mix at the early stages of the council's investigations into the best option for future treatment.

Van Bentum said while discharge to land was not an easy option, it was possible, depending on the availability of a large area of land and the cost of securing use of that land.

 - Stuff

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