Find out more about the wastewater treatment plant in your community.
Discharge: Treated wastewater to man-made wetland.
Household sewage gravitates to a low point in the sewer network from where it is pumped in a pressure main to the treatment plant. As it enters the plant it is screened to remove any foreign objects such as cloth or bits of plastic.
Once it is screened, the sewage flows into one end of the pond where it is treated by microbial bugs already there, and bugs within the wastewater. The process is helped by energy from the sun, and wind which assists in mixing and aerating the pond. During this process, solid material falls to the bottom of the pond where it decomposes slowly, eventually producing a small amount of remaining sludge which stays on the floor of the pond until the pond is cleaned – the sludge is then dried and taken to landfill.
At the other end of the pond, the treated effluent is pumped into a purpose-built wetland where it is further treated by the various plants and then either evaporates or filters into the ground. Occasionally, when flows are high after significant rain events, there is a discharge into a centre drain next to the ponds which leads to the Linton Main Drain and ultimately the Tokomaru River.
Our Wastewater Treatment Plant in Tokomaru is scheduled for upgrading. Council is working with local iwi to come up with a solution that allows for treated wastewater to be discharged to land.
Discharge: Treated wastewater to land.
The household sewage gravitates to a pumpstation at a low point in Rua Avenue on the beachfront, from where it is pumped in a pressure main to the treatment plant in the forest. As it enters the plant it is screened to remove any foreign objects such as cloth or bits of plastic.
Once it’s screened the sewage flows into one end of the two connected ponds where it is treated by microbial bugs already there, and bugs within the wastewater. The process is helped by energy from the sun, and wind which assists in mixing and aerating the pond – two mechanical aerators help to boost the process. Solid materials fall to the bottom of the pond where they decompose slowly to produce a small amount of remaining sludge which stays on the floor of the pond until the pond is cleaned – the sludge is then dried and taken to landfill.
At the other end of the pond, the treated effluent is irrigated onto a forest block where the nutrients are absorbed by the growing trees. The irrigation system at Waitārere Beach was recently tripled in size and now a larger forest block is irrigated at a less intense rate.
Discharge: Treated wastewater to land.
The household sewage gravitates to a series of pump stations situated at low points in the town from where it is pumped in a pressure main to the treatment plant on the Old Foxton Road. As it enters the plant it is screened to remove any foreign objects such as cloth or bits of plastic.
Once screened the sewage flows into one end of the ponds where it is treated by microbial bugs already there, and bugs within the wastewater. The process is helped by energy from the sun, and wind which assists in mixing and aerating the pond – a mechanical aerator and floating wetlands. The floating wetlands are plastic floating platforms that contain many different baskets in which different plants are grown. The plants draw nutrients from the pond water and help to aerate the pond at the same time. Any solid material falls to the bottom of the pond where it decomposes slowly to produce a small amount of remaining sludge which stays on the floor of the pond until the pond is cleaned – the sludge is then dried and taken to landfill.
At the other end of the pond the treated effluent is irrigated onto adjacent farmlands. A computer-controlled system is used to manage the irrigation, and ensures that the consent conditions are met. If adverse conditions such as high wind or rain exist, the computer switches off the irrigation and stores the treated effluent within the pond system. It also ensures that the irrigation is spread around the farmlands to prevent areas from being over-irrigated.
Discharge: Treated wastewater to land.
Household sewage gravitates to pump stations that are situated at low points in the town, from where it is pumped in a pressure main to the treatment plant in the forest. As it enters the plant the wastewater is screened to remove any foreign objects such as cloth or bits of plastic.
Once it is screened the sewage flows into one end of the ponds where it is treated by microbial bugs already there, and bugs within the wastewater. The process is helped by energy from the sun, and wind which assists in mixing and aerating the pond – two mechanical aerators boost the process. Any solid material naturally falls to the bottom of the pond where it slowly decomposes to produce a small amount of remaining sludge which stays on the floor of the pond until the pond is cleaned – the sludge is then dried and taken to landfill.
At the end of the process the treated effluent is pumped out into infiltration beds and used to irrigate the forest using a series of sprinklers.
Discharge: Treated wastewater to water (moving to land in 2020).
Household sewage gravitates through the sewers to a single pump station situated near the Transfer Station, from where it is pumped in a pressure main to the treatment plant on Matakarapa Island.
The sewage flows into the first of three ponds where it is treated by microbial bugs already there, and bugs within the wastewater. The process is helped by energy from the sun, and wind which assists in mixing and aerating the pond. Water travels from one pond to the next and the process is repeated in each. Throughout the process solid materials fall to the bottom of the pond where they decompose slowly to produce a small amount of remaining sludge which stays on the floor of the pond until the pond is cleaned – the sludge is then dried and taken to landfill. From there, treated wastewater is discharged into the Manawatū River Loop.
A new way forward for Foxton and the Manawatū River
Following a landmark agreement with iwi, the Environment Court approved Council’s application to move from a water-based discharge for treated waste to a land-based irrigation system.
Currently, Foxton’s sewage treatment system is being upgraded and in future, the treated wastewater will be used to irrigate more than 40ha of land. As well as that, the existing ponds will be made larger, and an additional storage pond will be built for use during wet weather when irrigation is not possible.
The project is expected to be completed in 2020.
Discharge: Treated wastewater to native forest – a world first.
The Levin Wastewater Treatment Plant is a world first as it irrigates a native manuka and kanuka forest.
More than 30 years ago, it became one of the first wastewater treatment plants to discharge treated wastewater to land – then an exotic pine forest which has since been felled.
Located at what is colloquially known as The Pot, it is near the end of Mako Mako Road and the plant, ponds and newly planted manuka and kanuka forest are on land that is both leased and owned by Council.
The wastewater journey begins in Levin, where both household sewage and trade waste either gravitates to, or is pumped to, the treatment plant. After mixing together, the sewage passes through a screen to remove foreign items like cloths and bits of plastic. It then passes through a de-gritter where grit and tiny stones are removed.
The diluted effluent then passes into the primary settling tank where the solids and liquids are separated. From there, solids and liquids are treated separately. Below is a brief summary of what occurs.
Liquid phase
The liquid moves through a trickling filter which is about 1.8m deep and is made of rock media (looks like a riverbed) coated biomass. The biomass is a mix of bacteria and micro-organisms which develop naturally. The trickling filters are designed to remove larger organic particles that are then turned into organic substances known as biomass. Oxygen is provided to the biofilm by exposure to atmosphere on the top, and vents draw in air at the base. Once the biomass thickness reaches a certain thickness it peels off and is carried in the flow out of the base of the trickling filter. Some of the flow out of the base of the trickling filter is recycled back to the top to ensure that the rock media is kept sufficiently wet, and to allow a second pass through the trickling filter – this helps to optimise the removal of carbonaceous material.
From the trickling filters the sewage flows to the humus or secondary settling tank, where the liquid and biomass solids are separated into liquid and solid again. The liquid then flows on to two sequential aeration ponds and is further aerated.
Finally, the treated effluent is then pumped to a pond and aerated again before it is irrigated onto the forest which includes 10-hectare of kanuka and manuka forest through pumps and sprinklers.
Solid phase
Solids are extracted from the base of the primary settling tank and are passed to what is known as a pre-thickener – it optimises the solids content which is then fed into an anaerobic digester. Inside the anaerobic digester the solids are treated in a threefold process:
- Lysis – the solids are broken down into smaller particles by lypases
- Acidogenesis – the small particles are processed by anaerobic bacteria called acidogens to produce volatile fatty acids
- Methanogenesis – the volatile fatty acids are consumed by bacteria called methanogens which convert them to cell mass, methane and carbon dioxide.
These processes are conducted in the anaerobic digesters which purposely exclude oxygen and are heated to approximately 35°C and mixed mechanically – heating and mixing optimises the reaction conditions.
After about 30 days the anaerobically digested sludge that remains is dried and disposed of to the landfill.