After Treatment
The purified liquid (effluent) that comes out at the end of the treatment process is released into Melbourne's waterways in many cases, so it needs to meet strict standards.
Recycling
Following the standard treatment process, the effluent can be further treated to produce Class A recycled water that complies with EPA and the Department of Human Services’ standards.
How clean is the effluent that is discharged to the environment?
All treatment works have to meet Environment Protection Authority requirements to keep their operating licences. It is crucial to avoid certain situations that can happen in some Australian waterways. In warm conditions and slow flowing water, the release of large quantities of effluent can stimulate an excess biological oxygen demand (BOD) which can reduce oxygen available to plants, fish and other aquatic life. If there are too many excess nutrients like nitrogen or phosphorous from farms, industry or sewage getting into the water, it can cause pollution with greenish blooms of algae. These very small plants reproduce rapidly and can eventually block out sunlight, killing off natural plants in the water. Then bacteria get to work on these dead plants and can use up all the oxygen that keeps the river healthy. Without proper treatment, faecal coliforms, the bacteria from human and animal digestive systems, could also get into the water. Tests for coliforms like E coli are useful to estimate water purity. There are varying standards for this, as this chart shows:Water Purpose - Safe faecal coliform colony numbers
Drinking Water = 0 / 100 mLSwimming / Surfing - 200 / 100 mL
Boating / Fishing - 1,000 / 100 mL
Disinfected treated sewerage effluent - No more than 200 / 100 mL