Sustainable re-use of processed wastewater - case study: Little River, Banks Peninsula : A dissertation submitted in partial fulfilment of the requirements for the degree of Master of Engineering at Lincoln University

Abstract

Sustainability has many definitions involving the desire to preserve and enhance our natural resources for indefinite use. The aim of this project is to design a system that will work towards sustainable wastewater re-use for the Banks Peninsula town of Little River.

A set of sustainability goals relating to social, cultural, environmental and economic ideals was established to set the scene for the project. It would be difficult to achieve all of the sustainability goals simultaneously. Because of this, the initial design of the land treatment system does not seek to produce a sustainable operation immediately. The management of the system, through response to monitoring environmental changes, will adjust the operation of the scheme to work towards the sustainability goals.

Indicators of the factors deemed most important were identified to form the basis of the monitoring system to accompany the design and management of the system. The key is to design a system that is able to adapt to change, and optimally seeks the sustainability ideal.

Preliminary design of the system involved determining land and storage requirements for the system by comparing two sites (valley and hillside) and two different crops (pasture and eucalyptus). The outcomes of a nitrogen assimilation comparison, a water balance and an economic assessment were compared.

Through both the system design and selection of indicators, it has become evident that the amount of moisture in the soil and the subsequent drainage to groundwater are critical issues at Little River. Soil moisture should therefore be used as the trigger for irrigation in an effort to overcome site limitations.

Regardless of the design and situation of the system, monitoring and management conditions will ultimately determine the success of the system. A suite of indicators is recommended in section 5 in order to monitor progress towards sustainability, and these should be implemented as an integral part of the management system.

In order to achieve the aim of designing a system that will work towards sustainable wastewater re-use for the Banks Peninsula town of Little River, the following list of recommendations is made as a result of the investigations undertaken in this project:

• A pasture crop, of at least 2.25 ha should be planted. • A hillside site would reduce drainage and enable year round harvesting. • Soil moisture is to be used as the trigger for irrigation. • A low application rate irrigation system should be used to reduce the risk of drainage. • A buffer wetland zone of local water tolerant species should be planted around the land treatment site. • An extensive suite of indicators should be used to provide system feedback and monitor progress towards sustainability.