Wastewater, also known as sewage, is the used water that goes down sinks, washing machines, showers, baths and toilets.

Most of it is water. The rest includes organic matter such as human waste, food scraps, cooking fats, oil and grease, and debris such as sand, grit and plastic.

Wastewater can also include household and business chemicals, paint and medicines. These can be harmful to our health, our harbours and waterways, so effective treatment is very important.

Where does your wastewater go?

Each time you flush the toilet, pull the plug from a sink or have a shower, the water drains into a wastewater pipe on your property.

Our plants are always operating, treating wastewater so that it is safe to release back into the environment. We never shut down and we always keep running, even during the worst of weather and power outages.

More than 90 per cent of Auckland’s wastewater goes to our plants at Māngere and Rosedale. Here it is treated to standards that protect public health, the local environment and our coasts and harbours. We are continually seeking more environmentally friendly ways of doing this.

Screening

Before treatment, raw wastewater goes through screens to filter out any solids such as rags, debris and other objects. Rotating drum screens feed this material into a conveyor and deposit it in a large bin. Trucks then take it out to landfill.

Treatment stages

Treatment takes about 12 hours from start to finish, and we cannot stop it or slow it down.

1. Separating solids from liquid

The wastewater goes into sedimentation tanks where sand and grit is removed, and any solids (sludge) sink to the bottom.

The sludge is then thickened and pumped to anaerobic digesters, where it is stabilised. It is then dewatered and limed to become biosolids – ready for disposal or reuse.

The liquid then moves to the next treatment stage.

2. Biological nutrient removal

This natural, chemical-free process uses ‘activated sludge’, which contains an army of micro-organisms. They eat the carbon in the liquid wastewater, and reduce the amount of phosphorus and nitrogen. These nutrients can pollute waterways and be toxic to fish.

3. Settling, filtering and disinfecting

The microorganisms are removed as the wastewater passes through clarifiers and filter blocks containing anthracite, a very hard form of coal.

The liquid is then disinfected under powerful ultraviolet lamps. This results in a 10,000-fold reduction of harmful pathogens, bacteria and viruses. There are no chemical byproducts, and it is safe for the environment.

About 12 hours after it enters the plant, the treated wastewater is safely discharged from the Māngere Wastewater Treatment Plant into the Manukau Harbour. This takes place on an outgoing tide to ensure the discharge is well mixed with the harbour water. At our Rosedale Treatment Plant, treated wastewater is held in two large ponds before being discharged 2km out to sea in the Waitemata Harbour.

The final effluent meets standards that protect public health, the local environment, and Auckland’s coasts, estuaries and harbours.

Biosolids are a product of the nutrient-rich, organic sludge produced when we treat wastewater.

Our aim is to make the best use of this resource, so that we protect and enhance the environment.

At our Māngere plant we are using biosolids to restore a former quarry on nearby Puketutu Island. At other plants, we dispose of biosolids in commercial landfills.

We’re also seeking ways to use biosolids in environmentally friendly ways. To explore other options, we are continually working with local iwi and businesses. As well as our own investigations, we draw on the experiences of wastewater utilities around the world.

Our initiatives include:

• Considering how biosolids can be reused to benefit the environment.

• Taking part in an industry working group looking at national environmental standards for biosolids used on land.

• Finding ways to recycle wastewater at our sites and with external customers.

• Maximising the harvesting of biogas from wastewater to create energy.

• Changing technology to minimise our carbon footprint and greenhouse gas emissions.

• Exploring other opportunities including: extracting valuable end products from the biosolids, creating bio polymers, creating safe-to-use compost and producing phosphorus-rich fertilisers.

Our laboratory performs a range of analyses on wastewater, trade waste and biosolids for waste treatment plants.

The Network Discharge Consent was issued by Auckland Council in 2014 for a 35-year period. Its purpose is to protect the health of Auckland’s communities and environment (such as beaches and waterways) by setting performance standards for the wastewater network.

It authorises an average of two spills per year or an alternative discharge frequency based on the best practicable option. Currently, there are areas in Auckland that do not meet this criterion. Therefore, we are required to rectify this situation and document this in the Wastewater Network Strategy.

We are required to consult with mana whenua, council, local boards and the Auckland Regional Public Health Service on our strategy. We are also engaging with special interest groups and people in Auckland.

The Wastewater Network Strategy sets out the actions we plan to take over a six-year period to improve the performance of our wastewater network. It is a requirement of the Network Discharge Consent.

What is wastewater?

Wastewater, also known as sewage, is the used water that goes down sinks, washing machines, showers, baths, and toilets. Most of it is water. The rest includes human waste, detergents, food scraps, cooking oils and debris.

Wastewater drains into private wastewater pipes. These connect to the public wastewater network which carry household wastewater to treatment plants. At the treatment plants, wastewater is cleaned so that it is not harmful to people or the environment. Depending on the treatment plant, the treated wastewater will be released to sea, rivers or land.

The public wastewater network is managed by us.

What is stormwater?

Stormwater is rain. In towns and cities, rain that falls on buildings and roads cannot be absorbed fully by the ground. It needs to be collected into a public stormwater network so that it does not cause flooding. Stormwater that is collected passes through the network and empties directly into streams and the sea.

The public stormwater network is managed by Auckland Council. We are not consulting on their network. But if you'd like to learn more, please visit their stormwater infrastructure page.

In some of the older parts of central Auckland, combined networks collect both wastewater and stormwater flows in a single pipe. Combined networks are designed to overflow during rainfall events. To ensure that these overflows occur in a controlled manner, rather than on private property, the network has dedicated engineered overflow points. These discharge through a piped system or designated flow path to the local receiving environment.

What are we doing about overflows from the combined network?

We want everyone to be able to enjoy clean waterways and open spaces, so we’re building a wastewater tunnel across central Auckland called the Central Interceptor. We also have projects such as the western isthmus, which are separating the stormwater and wastewater pipes. Together, the Central Interceptor and our western isthmus strategy will significantly reduce wastewater overflows in central area. The area that the Central Interceptor project will address has its own consent, due to the timeframe of the project and associated work.

What is an overflow?

A wastewater overflow occurs when wastewater (sewage) spills out from gully traps, manholes, engineered overflow points or pump stations and flows into public or private property. It can flow into waterways and the sea.

There are three types of overflows:

Type one: These are from pump stations. These may occur due to power outages or equipment failures, in addition to wet weather and blockages.

Type two: These are from engineered overflow points. They are designed to overflow during heavy storms.

Type three: These are from points in the network, such as manholes and private gully traps. We rely on people reporting these overflows.

Why do overflows occur?

Overflows can occur anytime, anywhere. The causes may be lack of capacity in the network or blockages or a combination of both. The blockages may be caused by fat, rubbish and tree roots clumping together and restricting the flow. When this happens, wastewater can spill through private gully traps, manholes, engineered overflow points or pump stations.

Overflows can also occur on rainy days when stormwater enters our wastewater network and overwhelms it.

Did you know? In heavy rain, the amount of stormwater that drains from an average roof can be equivalent to the wastewater flows from more than 40 households. That’s why it is essential for houses to have rainwater plumbed into approved stormwater outlets, rather than allow it to flow into the wastewater network.

Child’s play? No way! Our staff have pulled numerous toys out of the wastewater network over the years. Other objects include false teeth, ropes, bricks and even wine bottles. But they say cleaning up overflows is no child’s play. They respond very quickly, clear blockages and thoroughly clean the affected area. Our focus is on minimising the risk to public and environmental health.

What happens when an overflow occurs?

When we are notified of an overflow, our crews respond as quickly as possible. They water blast the sewer to clear any blockages. Then they clean and disinfect the area, removing debris and ensuring the area is safe.

Our operations and planning teams work closely together. The role of the planning team is to investigate the cause of an overflow. They may use a hydraulic model to work out if an overflow was caused by a lack of capacity in the network, a severe storm, or by blockages. They may also arrange CCTV inspections or smoke testing. CCTV checks the condition of the sewer and smoke testing helps to identify cracked drainage as well as incorrect stormwater connections. Sometimes, stormwater drainage is connected to the wastewater network by accident.

If the planning team find that the cause of an overflow is a lack of capacity, they will scope upgrade work. This involves securing funding as well as carrying out site and design investigations. Depending on the location and complexity of the upgrade, they may need to coordinate a response with the Local Board, Auckland Transport, Auckland Council, mana whenua, local interest groups and the local community.

Our engineered overflow points are designed to operate during extreme weather events. These overflows – which consist of wastewater that is heavily diluted with stormwater – flow along waterways to the sea. Auckland Council has a website called SafeSwim that lets the public know if a beach is safe to swim at from a health and safety perspective. If there is a direct wastewater overflow onto a beach, it is signalled on the website with a black flag.

You and your whānau have a big role to play in keeping our neighbourhoods, local waterways and beaches healthy by reducing overflows. While we take care of the public wastewater network, we need you to maintain your private drainage. We also need you to be mindful about what you pour down the sink and flush down the toilet.

We plan to invest $10.7 billion in wastewater infrastructure between 2021 and 2041. This is to ensure our ageing network continues to operate reliably as our city grows and climate changes. It is also to ensure we protect the environment by meeting our consent conditions, including the Network Discharge Consent.

In our next Wastewater Network Strategy, we will identify the work we need to do to improve the performance of our wastewater network. Our aim is to invest in the network, reduce overflows and improve operation of the network over time – in terms of achieving an average of two spills per year per engineered overflow point or an alternative discharge frequency based on the best practicable option.

Our strategy will outline three workstreams:

1. Infrastructure delivery: construction work to upgrade our assets.

2. Inflow and infiltration programme: inspection work to identify where stormwater is entering the wastewater network.

3. Community education: educating you and your whānau on the causes of overflows and how we all have a role to play in preventing them.

A water and wastewater servicing strategy is a long-term plan that helps ensure communities have clean and safe water to use and drink, and that the water used is treated properly before being returned to the environment.

A servicing strategy considers things like finding water sources, making sure we don't waste water, and building treatment plants to clean water and safely dispose of wastewater. The strategy also thinks about how we can ensure we have enough water for the future, and that our assets are durable and resilient to factors such as climate change.

Servicing strategies will be progressively developed for the 30 catchments across our network. In some cases, multiple catchments will be grouped together for a servicing strategy. A good example is the large metropolitan servicing strategy which will include many catchment areas from the North Shore through to South Auckland.

Our servicing strategies will:

• Be long-term, looking out at least 70 years

• Be cognisant of mana whenua and local community values and aspirations

• Consider long-term impacts of external factors such as population growth, network demand, climate change, and changing regulatory requirements

• Be flexible and adaptable for future uncertainty, providing resilience for future generations

• Provide options and high-level cost estimates

• Inform choices about water sources, discharge points, sea-level rise, resource allocation and priorities

• Inform our Asset Management Plan (AMP) for future-focused investment planning and prioritisation.

The diagram below shows some of the many factors that the servicing strategies will consider when planning for future decisions and investment. This includes various aspects of community wellbeing such as environmental, social, cultural, and economic. In the process of decision-making, trade-offs between various factors will be important. Making the right trade-offs and investment choices will help future communities remain healthy but also resilient to future challenges.

Infrastructure servicing strategies are plans that ensure our water systems and physical assets are well-maintained and upgraded over time because they play a critical role in our daily lives. We plan for 70 years because infrastructure is expensive to build and maintain, and we want to make sure it lasts. To do this, we use an approach that breaks down the 70-year timeframe into smaller planning periods called horizons (refer to the below image). This helps decision-makers anticipate future needs, plan infrastructure development accordingly, and avoid costly last-minute investments. Anticipating future infrastructure needs can help build community resilience.

By anticipating major changes and being willing to adjust the servicing strategies and plans as conditions change, we can develop large-scale infrastructure projects that are aligned with future needs and prepared for potential challenges

Our relationship with mana whenua is a partnership. It is a collaborative relationship between local iwi or hapū, which recognises mana whenua as kaitiaki or guardians of the land. The partnership ensures that cultural values, knowledge, and aspirations are respected and integrated into our decision-making processes. This partnership involves the sharing of information, resources, and decision-making to address community and environmental issues. Working together, we can achieve better outcomes for the community, enhance cultural understanding, and promote environmental sustainability.

We recognise the significance of Mātauranga Māori (Māori knowledge systems) and their valuable contribution towards preserving natural resources with a long-term vision. When we develop the servicing strategies and make decisions, these principles provide us with fresh perspectives and opportunities to achieve outcomes that are agreed to by everyone. Through our joint efforts, we can create positive outcomes for the community and safeguard our natural resources for generations to come. ­­