The Pines II WWTP near Rolleston was designed for an ultimate population of 60,000. This stage was completed in 2013 for a population of 30,000. It currently consists of inlet works, bioreactors, clarifiers, UV disinfection and irrigation to pasture.
An evaluation of the relative merits of different irrigation methods found the centre pivot irrigators to be the most cost effective and efficient irrigation system for the site.
Most pasture species have a high nutrient uptake rate and a high nutrient export value when the end use is cut and carry. For the soil type at the Pines II WWTP a hydraulic loading rate of up to 8 mm/d is being used. The use of treated wastewater to irrigate pastures also helps to conserve groundwater.
The arrangement with the local contractor to cut and carry the pasture negates any costs to the Selwyn District Council (SDC) for cutting of the grass whilst also adding value to the local economy in the form of animal fodder which would otherwise be a waste product. Overall the cut and carry operation is likely to be carbon negative due to the removal of the grass.
Since the treated effluent has been applied to the land there have been no measured negative effect(s) on groundwater quality and soil characteristics.