Improvements to oxidation ponds well underway

Improvements to oxidation ponds well underway

Improvements to the oxidation ponds at the Christchurch Wastewater Treatment Plant are progressing steadily, with Pond 2 out of service while an earth wall is constructed to divide the pond in two.

The pond is also being deepened and reshaped, and its banks strengthened to reduce the potential for failure in a major earthquake.

Mike Bourke, the Council’s City Water and Waste Operations and Maintenance Manager says the upgrade will improve the pattern of flow through the pond.

“Construction of the dividing wall is well under way and the contractor will soon be stabilising this embankment to reduce the potential for wind blown sand to cause a nuisance.

“The contractor is flooding areas where deepening has been completed to again reduce the potential for sand to blow off the site,” says Mr Bourke.

Work is also being done on the pipe connections between the ponds. Part of this work will involve draining Pond 3, the small pond east of Dyers Road, to enable the construction of connecting pipe work.

“We’re taking this opportunity to deepen and reshape Pond 3, and to construct an island to enhance the wildlife habitat,” says Mr Bourke.

The upgrade of the ponds will change how the flow moves through the pond system and provide significant improvement to the wastewater quality before discharge.

Currently the flow passes through three ponds in series before it is discharged to the estuary. When the pond upgrade is completed in mid-2004 the flow will pass through seven ponds in series, and produce an effluent quality that is expected to be some 10 times better than the current discharge.

“This improved, natural disinfection is achieved by reducing the flow’s short circuit from the inlet to the outlet of each pond and maximising the time the flow takes to pass through all the ponds. Computer modelling of the pond system, coupled with salt tracer testing, has been used to predict the improvements and to determine the optimum shape and depth,” says Mr Bourke.

The first stage of the upgrade, which involved deepening and reshaping Pond 1, was completed in May this year.

Notes:

The upgrades to the oxidation ponds are linked to other upgrades around the city to improve the quality of treated wastewater, better protect the environment and ensure the entire wastewater system will cope with expected city growth, including:

treatment plant improvements; the major sewer upgrade - a $36 million, 10-year project which involves the laying of more than 30km of new pipe; the Ocean Outfall pipeline.