Iron and Manganese Removal with AVG Filters

Western Bay of Plenty District Council
- Automatic Valveless Gravity Filter
Western Bay of Plenty District Council planned to augment their existing water management system by building a new water treatment plant at Pongakawa. The water supply was to be a new bore with generally good properties but with an elevated Iron and Manganese content.
Filtration Technology Ltd was contracted to supply and install an Automatic Valveless Gravity Filter (AVG) with sand filter media to bring the water into compliance with NZDWS 2005.
Because of its essential feature of being a gravity filter without valves within a filter system, AVG’s provide an excellent solution to unmanned remote WTP’s. The AVG’s backwash after attaining a pre-decided headloss and the cleaning/backwashing cycle continues without operator intervention.

Project Description
To design, supply, install and commission 2x AVG filters and associated chemical dosing and monitoring equipment to achieve compliance with NZDWS 2005.

Operational Features
The bore water is injected with Chlorine and liquid Sodium Hydroxide prior to a static mixer located before a contact tank.

The increase of water pH effects oxidation of the Iron and Manganese causing precipitation. The water passes through a contact tank to the two AVG headers and then by gravity through the filters where the oxidised impurities are removed.

The water exits from underdrain filter nozzles and traverses to an upper filter tank through a transfer pipe.
Water level rises to the outlet weir and exits at the elevated filtered water outlet.
After a period of operation the material collected on the sand bed leads to an increase in headloss, which causes the filter into backwash mode. After removal of dirt by reversing
the flow, the normal filtering operation restarts. The agitated and expanded bed settles, and clean water begins to flow at outlet of filter. Interlocks are provided on the two filters to ensure only one filter backwashes at one time.
Post filtration chlorination and monitoring of chlorine, pH and turbidity are carried out on the water leaving the plant.

Process Specification