Wetlands trial Q&A
Questions and answers about Gisborne District Council's wetland trials
Q. What's the timeframe?
We need to make the decision to go ahead with the wetlands option by December 2016. It then has 2 years, until December 2018, to gain the consents needed to build the wetlands.
By 2020, the wetlands must be under construction and receiving treated wastewater. By late 2020, all going well, the waters of the bay will be free of wastewater discharge. Treated wastewater from the wastewater treatment plant will go to land to be treated further.
Q. How is wastewater currently treated?
The city’s domestic wastewater is finely screened then passed through a chamber that removes the grit. Industrial wastewater is screened through separate screens.
Here's information on how the wastewater treatment plant works
Q. How much water comes out of the plant each day?
On average, the plant produces about 15,000 cubic metres of treated wastewater a day.
How wetlands work
Some people call wetlands the “kidneys” of the land as they provide a natural filter.
Bacteria and microbes around plant roots combined with the sun help clean up the sludge, get rid of disease-causing organisms (pathogens) and reduce contaminants.
Wetlands are a socially and culturally acceptable way to further treat effluent. They connect traditional and modern practices, and help enhance biodiversity and the life force or mauri of the environment.
Q. How much land is needed for the 2 wetland systems proposed?
About 50 hectares will be needed in total – about 6ha for the planted sludge drying bed wetland; about 45ha for effluent treatment wetland, comprising 12 to 14 beds of 3500m2 each.
Q. Where could wetlands be sited?
That’s still to be decided. The team’s first job is to determine the best type and arrangement of wetlands for Gisborne. Then, after talking further with the public, it will recommend to Council the preferred option, and the type and amount of land needed. Council will decide on the final site or sites.
Q. Where will wetlands water end up?
Whichever wetland system is adopted, a habitat wetland – possibly of about 10ha – is likely to be the last natural treatment stage. By then, the treated effluent will be natural water. Plant health will reflect the health of its ecosystem. A green space may provide places for walking, biking, bird watching and contemplation.
The resulting water will be available for other uses such as irrigation, restoring biodiversity, and developing or restoring wetlands.
Q. What will wetlands-treated water be like?
The aim is for this water to be of a standard similar to any other natural water in the district. The water will have to meet certain standards.
Q. Will this water be drinkable?
No. This water is expected to be free of human components but will contain micro flora and fauna, bacteria and viruses because of the animals, birds, fish and wrigglies living in it.
It will be indistinguishable, in a microbiological sense, from a natural wetland.
Q. How long will wetlands last?
The sludge-drying wetland will treat sludge for up to 10 years after which the clean, usable end product, known as biosolids, can be dug out for uses such as soil conditioning.
The effluent treatment wetland could continue for 50 years or more if built large enough, is properly maintained, and if, before entering the wetland, solids in the BTF-treated water are settled out and removed. After about 25 to 30 years, exposed pipework may need to be replaced, accumulated plant litter dug out from some parts and plants thinned out and re-established to rejuvenate the system.