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Out-of-the-box thinking

The life of four odour-control biofilter beds at the Tahuna wastewater treatment plant in Dunedin has been extended with some remediation work by Citycare Water developed through some out-of-the-box thinking.

A Citycare Water team rehabilitated the beds for the Dunedin City Council, with the assistance of Clearwater Civil, using eight-tonne diggers lifted onto the site with an 80-tonne mobile crane, Project Manager Stephen Adam says.

Video equipment was used to review the digger movements to track any effects of the weight of the diggers on the extensive pipe network in the biofilter beds before, during and after the clean-up, he says.

There was no visible impact and vegetation was successfully removed with the top layer of 10 centimetres of deteriorated bark, another 40-60cm of bark was root raked and loosened by excavators with specialist root rake blades, and new bark was added to top up the biofilter beds, Stephen says.

“We were asked to help and needed an outside-of-the-square solution to protect the pipes.

“We resolved a challenging situation with no damage or displacement of any of the pipes,” he says.

The biofilter beds at the Tahuna plant play a critical part in treating around 30 million litres of wastewater each day from Dunedin residents and businesses.

They needed to be rejuvenated as part of essential maintenance to ensure bacteria in the biofiltration system media effectively reduces odours from the treatment plant.

How the beds work is the saturated air containing organic contaminants (odour) pass through the beds of bark and through the process of bio-oxidation are broken down into harmless by-products by the micro-organisms or bacteria present.  (For more information see here)

Tahuna biofilter 5

crane lifting a digger

Tahuna biofilter 4

diggers at work

Tahuna Biofillter 1

before shot


Tahuna Biofilter 3