Sewage under the spotlight

Sewage, and phosphorus treatment in particular is now under the Tararua District Council spotlight as the implications of the Horizons Regional Council One Plan continue to bite.

It seems that even the two years old Dannevirke treatment plant’s sophisticated membrane technology may not be sufficient to meet the new requirements.

Because phosphorus was the most complicated of all the suspended solids and was very fine it would continue to pass through the membranes into the pond without being filtered out, manager district assets Stephen Taylor said.

One solution was to add a coagulant into the pond. This would trap the phosphorus which would eventually sink to the bottom of the pond to become sludge, Mr Taylor said.

He was also critical when the minimum standard levels of phosphorus had to be met in the One Plan. The previous plan indicated that the standard had to be met approximately 25% of the time where as the One Plan required the standard to be met approximately 80% of the time (based on river flows). This meant that the cost of any treatment method was going to increase by over three times for very little (if any) environmental benefit.

Alongside that is the lack of “lead in” time to meet the new standards that was available in the earlier versions of the One Plan but has now been removed, Mr Taylor says.

With consents on three oxidation ponds due to expire the council had already allocated $4.5 million in its Long Term Council Community Plan for upgrades to be completed by 2008/09.

But faced with financing the “unrealistic” standards imposed by the One Plan, Mr Taylor believes that the council will have to rethink its options.

One is to consider the merits of a single treatment plant to service Woodville, Pahiatua and Eketahuna.

Weighed against the advantage of managing one plant rather than multiple plants, is the $14 million price tag for the pipeline required to connect the three towns.

So again, the council grapples with the challenge of impossibly high standards in the face of financial constraints.

The pattern is becoming all too familiar.