Background The Eltham Urban Water Supply is owned and operated
by the South Taranaki District Council. The water
supply system is currently servicing the Eltham
Township, Riverlands Eltham Ltd, Dairy Meats NZ
Ltd, Pastoral Foods (NZ) Ltd and Mainland Products
Ltd.
Due to increasing demand for the water and the
existing filter’s deteriorating state, there
was a requirement to upgrade the water treatment
plant by design and building a second sand filter
as well as refurbishing the existing filter. This
would double the maximum capacity of the plant
to 10,800 m3 /day. However this is limited to
a maximum of 5,520 m3 /day due to the current
Resource Consent.
Filtration Technology were contracted to complete
the design and build of the new filter as well
as the refurbishment of the existing filter. The
main objective was to provide plant redundancy
and improve the overall water quality.
The process selection for the upgrade involved;
The
addition of a new 6 metre diameter gravity filter.
Replacement
of the existing PLC.
Supply
of access platforms to access both new and old
filter tanks
Supply
of weir to allow for the raw water supply to
enter either the new filter tank or the old
filter tank.
Supply
of new backwash pumps and blowers and pump house.
Filters/Automation The existing filter was very much in an ‘as
built’ condition, largely unchanged since
construction circa 1970. To relieve production
pressure, an epoxy coated steel filter was constructed
and installed adjacent to the existing plant.
In the process all dose lines and
dose points were relocated from their original
position of which the new filter is now on.
Other additions to the process include supply
and install of a new blower and Grundfos backwash
pumps with a large flow rate of 250 l/s. Two backwash
pumps were supplied one for duty and one for standby.
To accommodate these additions a 24 m2 pump shed
was supplied.
Filter floor
The filter floor was designed and built by
Filtec. The design was one in which the laterals
were concreted into the base of the filter.
Eliminating the need for the extra fabrication
involved on building a nozzle floor. Altek
nozzles were placed into the laterals. Sand
of grade 0.6-1 mm was used to cover the nozzles
to a height of 600 mm above the filter floor.
Combining
the old filter with the new
A weir was designed and built by Filtec in
order to allow the raw water in to be diverted
either to the new filter or the old filter,
while also allowing the option of running
both should it be necessary.
