Filtering sewage

The new sewage-treatment system from Wyndham company BioFiltro uses technology originating from Chile to treat effluent in a small and low-cost plant.

The system digests sewage on a bioactive sawdust bed supported by a rock drainage layer.

The system works in a three-treatment process. The wastewaters are applied to a bioactive sawdust bed supported by the rock drainage layer.

Within these layers exist aerobic and anaerobic bacteria, along with higher level organisms including rotifers (microscopic aquatic animals, similar in size to plankton) and worms.

The organic waste is first broken down by bacteria, but later worms process solids to form a low-volume humus (soil-like solid residues) and a liquid. In the final stage, the clear liquid can be treated by a UV unit to help kill the faecal coliform bacteria before liquid is discharged.

The amount of organic material consumed is dependent on the available oxygen within the system - this is why the sawdust bed and organisms such as worms are important, to aerate the system.

• In late 2006 BioFiltro Ltd was formed in New Zealand, and was granted the exclusive international rights for the Chilean technology, excluding Latin America and Spain.

• The Southland District Council installed a BioFiltro plant for the Edendale/Wyndham sewage scheme in 2009.

• The system is used for the treatment of domestic wastewater for the 250 personnel at the Chilean Air force base, Eduardo Frei, in the Antarctic.