Improvements underway at oxidation ponds
People passing the Christchurch Wastewater Treatment Plant may be wondering what is going on presently at the oxidation
ponds. Number 1 pond is being emptied, beginning the next stage of the plant upgrade. Operations and Maintenance Manager
Mike Bourke says that the reconfiguration of the ponds will change how the flow moves through the pond system and will
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 in terms of pathogens present.
“This improvement in natural disinfection is achieved by reducing the short circuiting of the flow from inlet to outlet
of each pond and maximising the time the flow takes to pass through all the ponds,” says Mike Bourke. “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.“
The deepening and reshaping of pond 1 will be completed over this coming summer period, followed by a similar exercise
on the larger pond 2 next summer. At the same time parts of the banks of the ponds will be widened to reduce the
potential for failure of the pond banks in a major earthquake causing property damage. Additional piping between ponds
will also be installed. Some of the sand to be removed from pond 1 will be stockpiled for future use in developing
further sports fields in the east of the city.