Work on ponds upgrade going well
26 May 2003
Improvements to the oxidation ponds at the Christchurch Wastewater Treatment
Plant are progressing steadily, with the first pond being brought
back into service and the second one about to be emptied.
The first stage
of the upgrade is nearing completion as Pond 1 is refilled
following deepening and reshaping. The next stage is to take
Pond 2 out of service to allow the construction of an earth baffle
to effectively divide
the pond into two cells. Operations and Maintenance Manager Mike
Bourke says this will allow similar deepening and reshaping,
and also strengthening
of the pond banks to reduce the potential for failure in a major
earthquake.
Other major works in the ponds involving new piped connections
between some of the ponds is already well underway.
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
in terms of pathogens present.
“This improved, 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. 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 work in Pond 2 is expected to be completed around April
next year. Mr Bourke says that some odour may be evident as the
pond initially dries,
and any dust potential in the summer will be minimised by restricting
the contractors’ work area.
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