Mussel shells help filter contaminants
Christchurch City Council Newsline: 22nd January 2025
Mussel shells are removing contaminants from an urban stormwater wetland, in what could be a world-first.
A mussel shell filter has been installed in the Wigram Basin wetland, located at Canterbury Agricultural Park. The filter is five metres long and one metre deep and contains about 150 cubic metres of shells.
Christchurch City Council Head of Three Waters Gavin Hutchison says it’s the first time he’s aware of that mussel shells have been used for this specific purpose.
“They have been used to remove sediment from roading earthworks after the Marlborough Sounds was hit by large storms in 2021/2 and here in Christchurch we've installed some for sediment removal from Hoon Hay Valley Basin, but this is the first instance we know of they’ve been used for urban stormwater anywhere in the world."
The shells act as a filter by absorbing contaminant material from stormwater.
“They mainly work by absorbing the metals (and other contaminants) which are then bound to the shells. The University of Canterbury has done a lot of research into using mussel shell filters to remove metals from stormwater, particularly zinc. They have developed a product for use on roofs but haven’t looked at anything of the scale that we are doing in Wigram,” Mr Hutchison says.
“Mussel shells are a waste product, so it’s a great opportunity for re-use rather than dumping them. We will be monitoring the installation at Wigram to learn how well they work, but the expectation is that they will significantly improve the quality of water being discharged into our waterways.”
The shells are expected to take many years to become “full,” at which time they can be removed and replaced.
Wigram Basin was upgraded in 2019 to provide additional flood storage and add 3.4 hectares of wetland area for water treatment. The project is part of the wider Ōpāwaho/ Heathcote River floodplain management programme.