WASTEWATER (sewerage)
Manukau Water operates the wastewater treatment plant that serves Beachlands and Maraetai.
What is Wastewater?
Wastewater is used water, it is the waste from our homes and workplaces and it is also known as “sewage”. It is the waste that goes down the drain every time you flush the toilet, wash your hands, have a shower or a bath, wash the dishes, clean your teeth, wash your clothes, or run your garbage waste disposal. It also includes similar wastes that go down the drains at schools, hospitals and other institution, businesses and industry. It does not include the rain that runs off your roof. This goes into a separate stormwater system.
Wastewater is 99% water; the other 1% consists of
- organic matter such as human waste and food scraps
- oil and grease
- traces of heavy metals such as silver, lead, zinc and copper
- debris such as sand, grit, wood and plastic
- bacteria and viruses that can make people ill
- nutrients such as nitrogen and phosphorus can harm our harbours and waterways. These nutrients can deplete oxygen and cause fish to die, create excessive plant growth, and result in toxic algal blooms.
Whether you are at home or work every time you flush the toilet, take a shower, turn on the tap or let the plug out the water that goes down is classed as wastewater.
This waste goes into the sewer pipe for the property and then connects into the main bulk sewage pipe which transports all waste to the Mangere Treatment Plant which is managed by Watercare Services Ltd. This waste contains soaps, detergents, food scraps, fat and anything else that we dispose of down the drain.
Did you know…
About 280 million litres of treated wastewater is released into the Manukau Harbour every day from the Mangere Treatment Plant. This is equivalent to one petrol tanker every three seconds!
Wastewater and the Environment
Wastewater is a major risk to health and the environment. Wherever it escapes from the sewer pipes in an untreated form it creates an immediate health risk to humans as well as being unsightly and smelly. It consumes the oxygen in the water which kills fish, shellfish and plants and those that survive are likely to be infected with dangerous viruses. It takes very little wastewater to pollute a stream, estuary or harbour and completely destroy it for food gathering or recreational purposes.
Growing and Ageing
The 1900km of wastewater drainage and 80 pumpstations in Manukau’s system will eventually need replacing. The cost of doing this is some $400 million, much of which will be required over the next 30 years.
In addition to this cost is the need to provide further capacity to provide for the city’s growth. Some of this will be paid for directly by developers, but the extra load on the system will affect everyone and place more stress on the environment.
What is infiltration and why is it so important?
Infiltration is stormwater or ground water feeding or seeping into a sewer line. Property owners may have illegally connected downpipes from their roof gutters so they feed into a sewer gully trap, rather than into a separate stormwater drain. So in heavy rain, the stormwater dramatically increases flow though that sewer line. Some others may feed their stormwater into a soak hole, where it permeates the ground in heavy rain.
If you have an old sewer line, which has not been properly maintained those pipes may have deteriorated, joints may have opened, or tree roots may have damaged the pipes. In heavy rain, ground water can seep into the line – so boosting load on the line.
If the gully trap outside the house is not at correct distance above the ground level then the surface flooding can directly enter the wastewater system.
Consequently, during heavy rain, stormwater infiltration can overload sewer mains by 5 to 15 times there design capacity. When that happens the system cannot cope and the sewage overflows into street gutters or onto private or public property, before polluting creeks, streams and beaches as the runoff carries the untreated sewage to the sea.