Rosedale Wastewater Treatment Plant
Wastewater is pumped to the site and is treated in a series of different processes to ensure it is safe to be returned into the environment. Solids and liquids in the wastewater are separated at different times through the overall process. Biological processes, similar to those used in our own stomachs, are used to help purify the waste. The main treatment process for liquids is called “activated sludge”, where bacteria in the activated sludge solids use the wastewater as a source of food.
After solids are removed through settlement, the liquids take around two weeks to travel through the pond system, where sunlight provides natural disinfection of remaining bacteria. Further disinfection using ultraviolet light is provided before the treated wastewater is discharged by gravity almost three kilometres out to sea through a completely new discharge system. This was completed in 2010. The treated wastewater easily meets New Zealand Recreational Water Quality guidelines before it reaches the surface. Some of the treated wastewater is used on site for process wash water and irrigation.