Levin Water Treatment Plant

Chemical Use

There is a range of chemicals used at the Levin Water Treatment Plant in order to achieve the desired water quality.

Turbidity

Turbidity is a measure of how "dirty" the water is. Under normal circumstances the water is quite clear, but this does not satisfy the Drinking Water Standards, which require that the water be less than 0.5 NTU (Nephelometric Turbidity Units).

In order to reduce the amount of constituents that contribute towards turbidity a combination of chemicals are employed.

PAC (Poly Aluminium Chloride) is used to coagulate the material into larger sized particles so they can be readily trapped on the sand filters. Approximately 4 g/m3 (parts per million) is used at Levin.

A Polyelectrolyte (L3RC Polydadmac) is used to change the electrical charge on each particle so they can be attracted to and adhere to the sand particles in the filter. Approximately 1 g/m3 is used at Levin.

Soda Ash (Sodium Carbonate) is used to raise the alkalinity of the water. This assists with the coagulation process. The alkalinity is also used to limit the corrossiveness of the water, as low alkalinitiy waters will allow some metals from pipes and fittings to dissolve and appear at elevated levels in the water. Some of these metals can have quite toxic effects (ie Lead) Soda Ash is used at the rate of approximately 7 g/m3 at Levin.

Filtration

There are 10 sand filters at Levin where the water is passed through a layer of sand some 0.75m in depth. The coagulated material is trapped on the sand, and then released during a backwash procedure to return to the river though some settling basins.

Disinfection

Chlorine gas is used as a disinfectant to sterilise the water. The chlorine gas is dissolved in the water at a rate of around 1 g/m3. This level is utilised in order to ensure the minimum level stipulated in the Drinking Water Standards of 0.2 g/m3, is available at the extremities of the reticulation (pipework). The water is disinfected to ensure no bacterial or organic material is present in the water, so residents can be confident that it is safe to drink.

The Drinking Water Standards limit the maximum dose of chlorine to 6.0 g/m3.