|
Our complex wastewater system services a population of 199,000 predominantly urban with some commercial and industrial customers. The systems consists of:
We're working to repair this ageing network and introducing new systems to accommodate the needs of our growing city. Our topography is hilly and borders sensitive beaches and the Hauraki Gulf. Our wastewater network is managed by the North Shore City Council Water Services Division and our maintenance contractor, Techscape, a council owned Local Authority Trading Enterprise (LATE). Wastewater collection and treatment Societies around the world collect and treat waste according to cultural tradition, technological knowledge and financial ability. Wastewater collection and treatment is the basis of a modern civilisation and is essential to a community's health. A modern wastewater system (like we have in North Shore City) meets public health standards unknown 150 years ago, when cities had open sewers in the streets. Even when sewerage pipes were laid, raw sewage was still discharged directly into our harbours until the 1960s when the wastewater treatment plants in North Shore City and Auckland City were built. Wastewater (sewerage) system Every time you flush the toilet, pull the plug from a sink or have a shower, the wastewater drains into a sewer pipe on your property. If you live in North Shore City, that pipe connects to our wastewater (sewerage) system, which carries the wastewater to the wastewater treatment plant at Rosedale. Here the wastewater is treated to produce effluent (or liquid waste) and biosolids (or sludge). The way we treat and dispose of effluent and sludge from our wastewater treatment plant is an important issue and we are continually seeking more environmentally friendly ways of doing this. Effective treatment protects public health, the local environment and our coasts and harbours. Following consultation with the public in 1991, we've been working continually to upgrade the treatment plant to achieve more environmentally and economically sustainable ways to improve wastewater treatment. The wastewater treatment plant speeds up the natural purifying processes. Nature’s process of waste treatment in waterways was in the past considered adequate by some cultures. We know now that this pollutes seafood and damages aquatic and marine ecosystems. The natural capacity of the environment to treat waste has been exceeded by population expansion and industrial development. When a small amount of wastewater enters a stream, the volume of the water in the stream dilutes it. Bacteria and other small organisms consume the waste and other organic matter turning it into new bacterial cells, carbon dioxide and other products. The bacteria normally present in the water must have oxygen to do their part in breaking down the waste. Water acquires oxygen from the plants that grow in the water itself and from turbulent flow that aerates the water. The plants use sunlight to turn the carbon dioxide present in water into oxygen. The life and death of any body of water depends mainly upon its ability to maintain a certain amount of dissolved oxygen. This dissolved oxygen (or DO) is what fish breathe and without it they suffocate. Problems begin when the wastewater load is excessive. In the worst case, the water could lose all of its oxygen, which results in death of both fish and vital plant life. At this point the water may give off odours. Since dissolved oxygen is the key element in the life of water, the demands on it are used as a measure to tell how well a treatment plant is working. This measuring device is called biochemical oxygen demand, or BOD. If the treatment plant has a high content of organic pollutants the effluent has a high BOD. In other words, it will demand more oxygen from the water to break down the wastewater and will leave the water with less oxygen (it will also be dirtier). The Rosedale Wastewater treatment Plant removes the BOD so there is no depletion of dissolved oxygen in the receiving water.
|
Complex
wastewater system 
Water
introduction