Land APPLICATION OF TREATED MUNICIPAL EFFLUENT: A FIELD TRIAL

The land application of treated municipal effluent has several advantages over disposal into Akaroa Harbour. In addition to its value as irrigation, municipal effluent contains elevated concentrations of plant nutrients, especially nitrogen, which can improve the growth of trees and pasture. In contrast, these same nutrients can provoke eutrophication and algal blooms in water bodies. Effluent application onto land may be more culturally acceptable than disposal into water. Greenhouse studies at Lincoln University have shown that some New Zealand native species not only thrive on soils receiving treated human waste, but kill bacteria and reduce the leaching of contaminants. For example, manuka and kanuka enhance the die off of disease causing pathogens such as Escherichia coli as well as reducing the amount of nitrate leaching from the soil. At Duvauchelle, we aim to determine whether manuka, kanuka, and other native species have potential for the full-scale land treatment of effluent. In a three-year experiment, we will test how native plants respond to the application of treated wastewater in the field. We will also measure the effects of native plants on effluent-irrigated soils. In July 2015, we planted 1350 native trees, divided into 27 blocks of three different vegetation types. Twelve of the 27 blocks are receiving treated municipal wastewater at a rate of 500 mm during the growing season, a similar rate to that used on an irrigated dairy farm in Canterbury. Effluent irrigation started in January 2016. We are measuring the survival, growth and chemical composition of the plants. The concentrations of plant nutrients and contaminants in the soils will be monitored. Our lysimeter experiments at Lincoln University have shown that there are no problems with contaminants in soils irrigated with this treated effluent. Although some plants were stressed during the unusually dry spring, plant survival has been excellent (89%). There are already clear differences between the treatment and the control, with growth visibly better in the blocks receiving effluent. At the conclusion of this 3-year experiment, we will be able to design effluent systems using NZ native vegetation for the land-treatment of wastewater. A key consideration in the design of such systems will be that the NZ native vegetation generates value from the land. This value may come not only from the obvious ecological and aesthetic benefits of native vegetation, but also through the production of NZ native products such as honey (manuka), essential oils (manuka and kanuka), fibre (harakeke), stock supplements (kapuka), and possibly, even NZ coffee (karamu).

Banks Peninsula
We aim to use wastewater to re-establish valuable native vegetation on selected sites around Banks Peninsula.