OXIDATION IN PORANGAHAU
CLEANING UP OUR ENVIRONMENT
A NEWSLETTER FROM THE
PORANGAHAU ENVIRONMENTAL MANAGEMENT TEAM
The Porangahau Environmental Management Team (PEMT) was set up from the resource consents issued by the Hawke’s Bay Regional Council for the wastewater treatment plants at Porangahau and Te Paerahi.
The PEMT is investigating suitable wastewater treatment systems for the Porangahau and Te Paerahi townships that will improve the quality of wastewater treatment. The PEMT’s aim is to find a way to deal with the wastewater, endeavour to stop discharge of treated effluent into waterways, and to make the Te Paerahi oxidation pond obsolete so that it can be removed.
A public meeting will be held in Porangahau on 11th February 2012 to discuss the work of the Porangahau Environmental Management Team.
Existing Wastewater Treatment
At present all of the wastewater collected in Porangahau township and Te Paerahi township is piped to oxidation ponds near each township. In these ponds, the natural actions of wind, time and bacterial action improve the quality of the wastewater.
PORANGAHAU OXIDATION POND
After treatment the wastewater at Porangahau flows through a wetland and drain before finally flowing into the Porangahau River.
TE PAERAHI OXIDATION POND AND WETLAND
At Te Paerahi extra oxygen is added to the wastewater in the oxidation pond to help the treatment process. The oxygen is added by aerators which mix air into the wastewater. The treated wastewater flows into a wetland and soaks into the sand dunes.
Options looked at
The PEMT has looked at many ways to treat wastewater. This includes:
· Addition of aerators, baffles, filters, floating wetlands and ultraviolet disinfection to the existing oxidation ponds.
· High tech treatment plants such as activated sludge, membrane technology and chemical dosing.
· Land treatment by wetlands, forests, or cut and carry operations.
SPRAY IRRIGATION INTO A FOREST
The PEMT considers that the most desirable treatment process to investigate further is:
· Use worm farms to treat the effluent.
· Use the by-products from this treatment – nutrient enriched liquid and composted matter – to improve soil quality in the Porangahau area.
· Dispose of any excess liquid on to land, either through wetlands and soakage into the ground, or by watering trees in a forest or grass and other crops.
The use of worms to treat wastewater was developed in Chile. It was brought to New Zealand by BioFiltro, a company in Southland. Biofiltro have installed 6 worm-based wastewater treatment plants in Southland, and are about to start 2 other plants. A bed is created with sawdust on top of a filter layer, and the effluent is sprayed on to this bed. Worms that have been added to the sawdust bed digest the effluent, producing “worm liquid” which is collected at the bottom of the bed. The “worm liquid” can be used as a liquid fertiliser on gardens and farms. Every year, the top layer of the bed is removed and replaced with a new layer of sawdust. The old layer is full of worm casts, and is a very good soil conditioner and fertiliser.
WORMS AT WORK
Ideally both of these by-products could be used to improve the soil and crop growth. However there will be times when there is excess liquid. This liquid could be stored in a storage dam to be used when the weather is better for applying it to the ground. It could be further treated by filtering it through a wetland or irrigating it into a forest.
Page last updated 14 Jan 2012