Potable
Water Treatment Plant - Design / Build / Commission July 2004
Background
The Matarangi Urban Water Supply is owned and
operated by the Matarangi Beach Estates. The water
supply system is currently servicing the Matarangi
residents. Due to increasing demand for the water
there was a requirement for a completely new water
treatment plant. The capacity of the plant is
2,600 m3 /day. With principle raw water supplies
coming from Opitonui River and secondly bore water.
Filtration Technology were contracted to complete
the design and build of the new filter by Harrison Grierson Consultants.
The process selection for the contract involved;
- Supply
and install of one 55 m3 contact tank
- Supply and install of one
37 m3 balance tank
- Supply and install of 2 x
1.8 m pressure filters
- Supply and install of clarifier
- Supply and install of polyelectrolyte
mixing and dosing system
- Supply and install of PAC
dosing system
- Supply and install of, Lime
and Chlorine Dosing System
The Process
Raw water enters the plant and is dosed with PACL
and Lime before it enters the contact tank. In
the contact tank the pre Caustic ph adjustment
is added and heavy sludge is allowed to settle.
After leaving the contact tank the water is dosed
with Polyelectrolyte (coagulant).
The water then enters the clarifier tank where
the flocculant allows a sludge blanket to form.
The clear water from the clarifier then flows
through a ballast tank and is processed through
the pressure filters completing its treatment
process and is sent off to the town reservoir.
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Polyelectrolyte
The poly is stored in a powder form in bags,
it is then fed with a wetting eductor into
a mixing tank to be mixed and then transferred
to a day tank. |
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| The clarifier |
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| Pressure
Filters The pressure filters that were
used were Kinetico and operate with a fully
automated backwashing system. The media used
was 70/80 mesh Macrolite media of 0.125 mm
in diameter and a specific gravity allowing
a much larger filtration volume for the size
of the filter than a traditional sand filter. |
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Chemical
Dosing The chemicals dosed into the water
supply are PAC, Lime, Coagulant (Poly) and
Chlorine.
PACl
Poly Aluminium Chloride is stored in a liquid
form in a tank inside the chemical building.
It is dosed into the raw water line with pumps
shown.
Lime
The Lime was feed through a very similar process
to that of the PAC as shown below. |
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Chlorine Dosing
The Chlorine is dosed into the water as a
gas from large supply bottle on site. A Chlorine
Analyser measures the residual chlorine in
the water and feeds back to the PLC to regulate
how much shall be dosed. |
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