Sources intimate with the city's "wet" industries say those industries and Wanganui District Council have to hammer out a pre-treatment regime to avoid any repeat of failure in the city's wastewater treatment system.

The wastewater treatment plant (WWTP) has been in strife since it was commissioned in 2007 and now has saddled the council with an upgrade estimated to cost at least $24 million - and possibly more.

While the council acknowledges design faults were an issue, it was also the amount of waste coming from the six major industries that has been highlighted as exacerbating those initial problems.

The six industries that pay to discharge into Wanganui's wastewater system are Imlay, Land Meats, MARS Petcare, Cavalier Spinners, Open Country Dairy and Tasman Tanning.

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An industry insider, who spoke to the Chronicle on the proviso of anonymity, said unless significant pre-treatment processes were in place, similar problems would probably occur.

The source suggested Wanganui was the only major city prepared to accept totally untreated waste from "wet" industries "and probably is the only major council that isn't rating them accordingly".

And he said it was made easier for the council to say the new plant will be able to handle everything "because they have consultants standing in front of them that deflect their responsibility".

"I still believe that the Talleys Group [which owns AFFCO Imlay] should be approached to put in a joint venture ponding and dissolved air flotation (DAF) plant, even if the council had to partially fund it and was then paid back through recoverables," the source said.

He said there was ample scope for such a plant on Imlay property which could also take waste from other processing plants in the Castlecliff area such as Land Meats which is part of the same organisation.

"I think if that was done a cleaned up version of the current ponds would probably suffice. This entire process is totally arse-ended," he said.

Nudging industries toward comprehensive pre-treatment can be achieved and a more recent example has occurred in Morrinsville.

At least two major industries - Greenlea Premier Meats and Fonterra - were facing significant increases in effluent rates when the Matamata-Piako District Council moved to build a new wastewater treatment plant for the township. In one case the rates were set to double from $500,000 to $1 million.

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Those two industries decided to work with the council to build a $19 million pre-treatment plant which saw their discharge rates stay at existing levels.

In the past wastewater from the Greenlea site was screened on site and then pumped from a holding tank directly into the Morrinsville town sewerage system.

The process now involves a two-stage treatment system consisting of a covered anaerobic lagoon followed by another area which helps treat waste from the processing plant before it is sent to the town's sewerage treatment plant.

Don McLeod, chief executive officer for the Matamata-Piako council, said the new arrangement came about because the town's plant was being upgraded and industry discharge was reviewed.

"We entered an agreement allowing discharge from two specific large organisations [Greenlea and Fonterra]. This agreement stipulates effluent parameters and also outlines penalties if these are breached.

"To an extent the industries determined the amount of pre-treatment they would undertake, it is simply the higher the pre-treatment, the lower our charges," he said.

While Fonterra and Greenlea Premier Meats are the only two involved, smaller industries have trade waste agreements with the council that stipulate standards of discharge.

Greenlea is a meat processor while the Fonterra plant produces milk powder and butter products.

Mr McLeod said the Morrinsville pre-treatment plant cost about $19 million.

"The two industry players were asked to fund 40 per cent of this based on the difference between what we would have had to do without their discharge versus what we had to do with their discharge.

"We act as a bank - they pay the debt off over the life of the consent which is 15 years," he said.

Mr McLeod said roughly 40 per cent of the effluent going into the town's treatment system came from those two industries.

"It does depend on how you calculate it based on volume or strength of waste. And paradoxically the meat industry discharge is a source of food for the pond bugs," he said.

But Mr McLeod said no system could cater for open-ended discharge levels either in volume or in strength.

He was not aware of similar pre-treatment regimes around the country, certainly not around a funding agreement.

"But many councils will have trade waste agreements with industry defining what they can and can't discharge. And depending on the industry they will potentially have to pre-treat to meet these standards.

Wanganui mayor Annette Main says she is comfortable with the city's WWTP upgrade.

"The new design is a robust and well-proven process which includes using the existing pond and dividing it into sections.

"The council's confident that the developed design proposed by Cardno BTO is the best option for ensuring we have a properly functioning treatment plant to deal with domestic and trade waste and can meet the conditions of our resource consent."

As part of the upgrade, the council will work with the "wet" industries to create a new trade waste bylaw.

Mark Hughes, council's infrastructure manager, said it would be a joint initiative and would have input from those industries. "This bylaw will determine the charges for the volumes and loads of waste the industries send to the plant.

"If the waste is pre-treated, it will cost industries less. If the quantity of waste increases, industries will be charged accordingly.

"We would expect all industries to look at pre-treatment as part of their business model."

Mr Hughes added: "There is an additional 20 per cent treatment capacity in the new design which can be allocated for new industries.

"The council has a good understanding of the volumes and loads of waste coming from the wet industries. The volumes and loads our new wastewater plant will be able to handle are the equivalent to that of a city of 300,000 residents.

"We'll be gathering further information on the volumes and loads as we progress through the detailed design process between now and Christmas."

Bulk of industrial waste from big 6

Six "wet" industries provide the bulk of industrial discharges into Wanganui's wastewater treatment plant - Affco Imlay, Tasman Tanning (two sites), Land Meat, Cavalier Spinners, Open Country Dairy and MARS Petcare.

According to the Cardno BTO report prepared for the Wanganui council, MARS Petcare is not a meat processor like Affco Imlay and Land Meats but all three have discharges consistent with meat plants. That means higher levels of biochemical oxygen demand (BOD), total suspended solids (TSS), fats, oils and grease, ammonia and sulphides.

Tasman Tanning makes finished leather and carries elevates levels of BOD, TSS, fats, oils and grease, sulphates, sulphides and chromium used in its processing. Like Affco, Tasman Tanning must meet sulphide concentration limits and both have some form of pre-treatment system on-site. So does Land Meats.

Cavalier Spinners has had significantly lower waste than it is consented for. It does use an insecticide to "insect-proof" wool yarn and while most of it is absorbed in the wool, minute amounts remain in the trade waste.

Open Country Dairy makes milk powder and typically trade waste from such plants include higher levels of BOD, TSS, along with fats, oil and grease. It also has on-site pre-treatment.

Cardno BTO's report said the viability of any long-term strategy "is contingent upon management of trade waste contributions".

To this end, it said council should engage an independent facilitator to lead discussions with those industries

Cardno said it was known that some existing industries had plans to expand and some new industries were looking at locating in Wanganui. For that reason "developing a strategy for managing additional trade waste flows in the future is critical".

"Consideration must be given as to whether additional plant capacity should be allocated to trade waste or whether management of trade waste at source is preferred," the report said.

But uncertainty about future demand was the prime reason behind designing an upgraded plant capable of handling more trade waste.