Partially treated sewage is being discharged into a Motueka wetland area after a fault in the town’s wastewater treatment plant.
In a statement on Thursday, the Tasman District Council said engineers had noticed degradation in the Motueka plant’s filtration system. Polyolefin
Team leader water supply and wastewater Becky Marsay said the area causing concern was the membranes in the final filtering stage of the wastewater treatment process.
The membranes that remove the remaining bacteria and minute particles before water is discharged were becoming blocked by solids building up on their surface, and proving tough to remove by cleaning, limiting the amount of wastewater that can be treated at the plant.
Engineers and the wastewater team were at a loss as to why this was happening, and were urgently investigating options, the council said. However, it was likely the membranes would need to be replaced, at an estimated cost of $500,000.
They were expected to have an operational life of seven to 10 years, but are only two years old.
To avoid uncontrolled overflows, partially treated wastewater is being pumped into a wetland area, described as a soakage area where the wastewater would be filtered through the ground.
As a precaution people have been warned not to take whitebait or shellfish from the area or have contact with the water in the adjacent area until further notice. Warning signs would be put up.
Marsay said the discharge to the area was the way the plant operated prior to 2016 when the membranes were installed. The soakage area was retired several years ago.
Asked about the response from iwi given that discharge of wastewater to water was repugnant to Māori, Marsay said iwi had been kept informed every step of the way.
“But yes, this is not a good situation, we find ourselves in.”
Councillor Kit Maling, in Thursday’s operations committee, said the plant’s screens had never met specification as far as he could recall.
Maling said the current screens came in from overseas and it had been a “real struggle” to get them to work.
“Will the new screens be a different spec, so that it actually operates better?”
Group manager community infrastructure Richard Kirby said the question had been asked at what point did you throw good money after bad.
The membranes would be modified and staff were trialling filters in front of them to try to capture some of the solids before they hit the membranes and hopefully extend their life.
He said starting over with a new system would have significant costs.
Kirby said one of the advantages of the filtration system was that if it didn’t work, it could be utilized somewhere else, and was not a sunk investment.
However, he understood Maling’s concerns, the membranes having been a problem when he arrived seven years ago.
“Certainly, I know my predecessor had chased up the designers and everything, and of course they ran away and we ended up with basically a system that just doesn't have the resilience that we expected. So it's one of those situations where we're carrying the baby because of poor design.”
Marsay said 2300m³ of wastewater was coming into the plant a day. With the reduced capacity,they were only able to treat about 1000m³ a day.
Wood FR While there was generally a four-month delay in getting the membranes, there was the possibility of obtaining some from a council that were not quite ready for theirs yet, she said.