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.

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