Glossary
Activated sludge process This process involves using naturally occurring micro-organisms to feed on the organic material in the sewage. Activated sludge is a rich mixture of bacteria and minerals. The process is used in sewage treatment plants to break down organic matter and nitrogen compounds.
Aeration Adding oxygen (usually in air) by mixing air into sewage processes or water bodies by mechanical aerators or blowing air through diffusers to ensure that aerobic processes are maintained.
Algae Large group of generally aquatic, non-flowering plants, many microscopic.
Algal bloom A rapid increase in the numbers of algae, usually caused by a change in the flow, light, temperature or nutrient levels of the water in which it lives.
Ammonia A chemical compound made up of carbon and hydrogen that can be toxic, and also contribute to the nutrient enrichment of waters.
Biodiversity The range of plants and animals, and the habitat that they live in.
Biogas A by-product of the sewage treatment process that includes carbon dioxide and methane. Melbourne Water uses biogas as a source of renewable energy.
Biosolids The treated and stabilised solids in sewage.
Catchment The area of land drained by a creek or river system, or a place set aside for collecting water which runs off the surface of the land. Catchments provide the source of water for the dams and reservoirs in which our drinking water is collected.
Coliforms Bacteria that are used to indicate the presence of pathogens from faecal contamination of water. They are not generally pathogenic themselves.
CSIRO Commonwealth Scientific and Industrial Research Organisation.
Dam Technically, the dam is the wall that holds the water in and the reservoir is the water.
Disinfection Any process that destroys or removes disease-causing organisms such as viruses, bacteria or protozoa. It is used as part of the purifying of drinking water.
E. coli Escherichia coli is a bacteria/bacterium found in the stomachs of mammals, for example humans, and used as an indicator of recent faecal contamination.
Ecosystem The system of animals and plants and the environment they inhabit.
Effluent Treated sewage that flows out of a sewage treatment plant.
Environmental flow The minimum designated flow in a waterway needed to satisfy specified ecological requirements. Water released from a reservoir to maintain water levels downstream of a dam.
Greenhouse gases Vapours, including water, in the lower atmosphere, which reflect solar radiation back to earth.
Greywater Sewage from the kitchen, laundry and bathroom (but not the toilet). It usually contains soap, detergents and fats.
Groundwater Water collecting below ground level in an aquifer or water table.
Heavy metals General term for cadmium, chromium, copper, iron, mercury, nickel, manganese, lead, zinc, arsenic and selenium.
Hydrology The study of water occurrence, distribution, movement and balances in ecosystems; the seasonal patterns of a river’s flow.
Irrigation The use of water to nourish cultivated land or open space to promote the growth of vegetation.
Mega A factor of one million. Therefore, a megalitre of water is one million litres. Melbourne’s Thomson Reservoir holds 1,068,000 million litres.
Methane A chemical compound made up of carbon and hydrogen produced as a by-product of anaerobic sewage treatment. Methane can be used as a fuel source for energy generation.
Nitrogen A chemical element essential for the growth of plants and animals. Our atmosphere is comprised of 79% of nitrogen.
Nutrients Substances such as nitrogen and phosphorus in various forms required for the growth of plants. Excess concentrations of nutrients can be harmful in rivers, creeks and bays.
Outfall Pipeline discharging treated effluent.
Phosphorous A chemical element essential for growth. It is present in many fertilisers and its overuse may contribute to the formation of algal blooms in waterways.
Pollution The results of activity that is detrimental to beneficial use by plants, animals or humans of water, air or land.
Protected catchment Protected catchments have no farms, houses or factories, so they provide water free of any pollutants these and other human activities produce. Most of Melbourne’s catchments are protected.
Reservoir A major body of water created in a river valley by building a dam (see Dam).
Run-off Rain or water, which flows from a catchment into a river, stream, lake or reservoir.
Sediment Sand, clay, silt, pebbles and organic material deposited in water.
Sewage and sewerage Sewage is the waste carried in our sewers. Sewerage is the system of pipes, pumps and treatment plants to manage sewage.
Stormwater Rainfall that runs off roofs, roads and other surfaces where it flows into gutters, streams, rivers and creeks, and eventually into the bays. This water can carry contaminants such as plastic bags, detergents, nutrients and heavy metals.
Suspended solids Solids that float on the surface or are suspended in water, and which are largely removable by filtering.
Tertiary treatment A level of sewage treatment that is beyond secondary treatment by further reducing the level of nutrients and suspended solids.
Toxicants Harmful substances, including heavy metals, chemical compounds and excessive concentrations of nutrients.
Trihalomethanes Formed during the disinfection of water with free chlorine.
Turbidity The presence of fine suspended matter such as clay or silt in water causing the water to be cloudy or muddy in appearance.
Weir A structure across a waterway to stop and raise water levels.
Wetlands Low-lying areas of land intermittently or permanently covered with either fresh or salt water. Wetlands occur naturally and can be constructed.