With the floating wetlands, the new treatment system also used screening of the influent, biological attachment surfaces curtains and aeration, dosing with aluminium sulphate, and ultraviolet irradiation.
In a CHBDC report this year the system's problems were outlined. After starting operations in June 2013, difficulties developed with the filter and the quality of the pond effluent.
It was found that the five filters sent to New Zealand from the Czech Republic, where they had been built, had a problem with the sand screws where the sand was washed.
A larger version of the Waipawa upgrade was installed at Waipukurau, with two filters instead of one, and the filters were modified from the experience at Waipawa.
However, regional council has raised concerns the nutrient Amm.N and SRP and E.Coli bacterium have now exceeded the limits.
"Urgent action is required to rectify the situation," the report said. If the limits continue to be exceeded, CHBDC will breach its consent at the sixth sampling after the upgrade date.
The sampling is scheduled for December 18, with the results expected to return to the HBRC after Christmas.
Discharge records show the treatment plants have not been able to operate at the design capacity and a bypass from the outlet of the treatment pond has been used to balance the inflow and outflow.
"The discharge of this partially treated wastewater is believed to be the cause of the exceedances," the report said.
The CHBDC said the reason the sand filters have not been able to operate at the design capacity is due to tannin in the wastewater reacting with the alum coagulant and binding the sand in the beds of the sandfilters triggering an overload shutdown.
The CHBDC has been working to overcome the problem, however initial attempts were unsuccessful and a new trial was commissioned in late November, too late to be assessed against the last reported wastewater sample.
The regional council report said if the plants are operated in a manner that does not meet the required standards or the regional council is not satisfied that CHBDC has a "clear plan", then enforcement action may be required in 2015.
Chief executive John Freeman said the CHBDC has been in discussions with regional council about the wastewater issue but reserved comment on the matter until after the Hawke's Bay Regional Council Environment and Services Committee meeting tomorrow in Napier.
CHB Mayor Peter Butler also declined to comment.
Conditions imposed on the Waipukurau and Waipawa treatment plants by the existing resource consents also required samples to be taken of the discharge at 14-day intervals and the results reported to the HBRC.
The next set of samples is due back about December 15.
