The wastewater service is a core service of the Hauraki Council and involves the process of treating raw wastewater into a final effluent that has removed as many of the harmful characteristics of the original wastewater as possible.
The Council provides and operates piped sewer networks and treatment plants for several urban areas and we ensure that collection, treatment and disposal of wastewater complies with the Public Health Standards and specific resource consent conditions, particularly those requiring the minimising of adverse effects on the receiving environment.
The key reasons for providing a service for treatment and disposal of wastewater are;
- to protect public health
- to mitigate the risks of pollution and disease associated with waste water
- to protect the receiving environments from the effects of waste water products and by-products.
In addition to the Council monitoring the on-going effectiveness and efficiency of the public waste water systems, the Council’s Regulatory Services Group maintains an overview of the adequacy of private collection and disposal systems (such as septic tanks on rural properties), and takes appropriate steps when problems or potential problems are identified.
About our wastewater system
Our wastewater system includes treatment plants, connected to our homes and businesses by pipes, manholes and pumping stations.
Pipes and 47 pump stations convey wastewater (sewage) from homes and businesses to seven treatment plants, located at Kerepēhi, Ngatea, Paeroa, Turua, Waihi, Waitakaruru and Whiritoa.
Wastewater treatment process
Wastewater treatment is the process of taking raw wastewater, and converting it through a variety of treatments into a final effluent that is without the solids and as many of the harmful characteristics of the original wastewater as possible.
There are a variety of different treatments used and available around the world and New Zealand, as there are in the wastewater treatment plants in our District.
They are all quite different in the way they treat but follow the general treatment practice of preliminary, primary, secondary and tertiary treatment.
The treatment process
- Preliminary treatment - removal of floating material, heavy settle-able, and large suspended solids, using structures like screens, grit chambers and flow equalization.
- Primary treatment - the removal of organic solids using sedimentation in primary sedimentation tanks.
- Secondary treatment - aerobic, or anaerobic biological decomposition of organic matter using such things as intermittent sand filters, trickling filters, aeration tanks and imhoff tanks.
- Tertiary treatment - removal of the remaining organic matter and killing pathogens (bacteria, viruses and protozoa) by disinfection with maturation ponds or ultraviolet (UV) light.
The Kerepehi Floating Treatment Wetland
The Kerepehi waste water treatment plant uses a two pond oxidation process which was constructed in 1976 to cater for a population of 800 people.
Oxidation ponds are natural treatment systems in which beneficial bacteria consume bacteria associated with disease. This process causes the growth of algae which is essential to replenish the oxygen in the ponds, however an undesirable effect of this process is that algae is carried in the discharge water to local rivers and ultimately the Firth of Thames.
To address the discharge of algae, the Council upgraded the system by introducing a Floating Treatment Wetland, one of the first of its kind in New Zealand.
The Floating Treatment Wetland consists of woven mats of recycled PET plastics into which wetland species are planted. The plants grow through the mat allowing the roots to be suspended in the water column below the mat. This creates a large surface area which acts as a filter for suspended solids (predominantly the residual algae) and through which natural plant activity removes additional nutrients from the water. Most of the nutrients are retained in the plant until the leaf matter is harvested.
The remaining nutrients either pass into the atmosphere through normal plant activity or are retained in the root mass. The portion of the nutrients and the suspended solids retained by the root mass eventually fall to the pond floor as sludge which is periodically removed using conventional de-sludging methods.
Floating Treatment Wetlands do not require the use of any additional land for treatment, use NZ sourced plants and materials, use low levels of non-renewable resources, do not use chemicals or electricity and are a sustainable approach to treating human waste. Therefore they are a long-term option which is very cost effective and has a very low Carbon Footprint.