Top environmental award for Kawakawa Bay wastewater system
Watercare’s Kawakawa Bay wastewater system has received one of three Environment and Sustainability Awards for large
projects presented by IPENZ, Auckland Branch at the prestigious Arthur Mead Awards Function.
Named after long-serving Auckland City Waterworks Engineer, botanist, and outdoorsman Arthur Mead, who was responsible
for the initial survey and design work on the Upper Nihotupu and Huia Dams, the awards are presented annually to the
projects that best address sustainability, potential adverse environmental effects, waste management and community
involvement.
Watercare Acting Chief Executive Raveen Jaduram said continuing to improve the company’s wastewater treatment services
in order to enhance the health of Auckland’s harbours, estuaries and waterways remained one of Watercare’s main
objectives and a key focus of the company’s capital investment plans. The Kawakawa Bay project also illustrated the
close working relationships Watercare maintained with iwi, residents, and community groups across Auckland.
Designed by Australasian engineering consultancy Harrison Grierson, and constructed by Fulton Hogan, who also managed
the network during its first year of operation, the Kawakawa Bay system was handed over to Watercare last year. The
system enabled the removal of aging septic tanks that had over time polluted groundwater and local streams, leading to
the Bay being declared unsafe for swimming in 2002. Its safe-for-swimming status was restored in November 2012.
Harrison Grierson Technical Director Colin Cranfield said the use of a vacuum system, which was a first for New Zealand,
allowed shallow pipelines to be constructed quickly, minimising disturbance to the residents.
“The spread out nature of the development over four kilometres of coastline, the sandy soils, and the high water table,
made a vacuum system the best option for the Bay,” he said.
In a vacuum collection system, wastewater from individual properties drains to a pit and is then drawn into the vacuum
pipe network through the operation of a pneumatically controlled vacuum interface valve in the pit. Once in the network,
wastewater moves along the pipeline to the vacuum pump station by the differential pressure that is created by the
opening and closing of the vacuum valves throughout the pipe network. Wastewater is subsequently conveyed from the
collection tank at the vacuum pump station to the treatment plant via positive displacement pumps and a pressure rising
main.
The Kawakawa Bay treatment plant employs an advanced, four-stage treatment process similar to that used at Watercare’s
larger Mangere and Rosedale facilities. Wastewater passes through alternating oxygen-rich and oxygen-depleted
environments, enabling a range of different bacteria to break down organic contaminants.
Residual organic contaminants and nitrogen are removed in a biological membrane reactor; bacteria and viruses by
ultrafiltration. The treated effluent then flows to storage lagoons from where it is used to spray irrigate forest
behind the treatment plant, more than two kilometres from the foreshore.
ends