Wastewater glossary of terms

This glossary will help remove the mystery from the lingo.

Activated sludge  

An aerobic wastewater treatment process where microorganisms are grown in a reactor and kept in suspension through mixing and aeration. Wastewater is passed through the reactor where the suspended microorganisms or 'bugs' consume and convert the organic matter. The 'bugs' are then separated from the treated wastewater in a settlement process. The process requires a constant recycling of bugs from the settlement tank back to the reactor to maintain the required microbial population for treatment.

Adsorption

Process that occurs when a gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a molecular or atomic film (the adsorbate). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution.

Aerator (mechanical)

A means of aerating wastewater to increase dissolved oxygen, to enhance aerobic treatment and reduce offensive odours.

Aerobic

Water environment containing enough dissolved oxygen for micro-organisms to break down waste by respiration.

Anaerobic 

Water environment containing insufficient dissolved oxygen to form micro-organisms to break down waste by respiration.

Biological trickling filter 

An attached growth biological process in which the microbial film is attached to non-moving rock or plastic media. Biological treatment Forms of wastewater treatment such as trickling filters, contact beds and activated sludge in which bacterial biochemical action is intensified to oxidise and stabilise the unstable organic matter present.

Biosolids

The material that remains after sludge and septage are stabilised biologically or chemically. Can be beneficially reused as a soil conditioner.

Blackwater 

Human body waste discharged through a flush toilet or urinal.

BOD

Biochemical oxygen demand - the amount of oxygen required to oxidise any organic matter present in a water during a specified period of time, usually five days. It is an indirect measure of the amount of organic matter present in water.

Clarifier 

A tank or basin for the purpose of reducing the concentration of suspended solids in a liquid. Also commonly referred to as a settlement tank.

Digested sludge

Sludge digested under aerobic or anaerobic conditions until the volatile content is reduced to less offensive solids.

Disinfection

The destruction of most micro-organisms in or on a substance so all pathogenic bacteria are killed.

Domestic wastewater

Wastewater derived from human communities - toilet, bathroom, laundry and kitchen waste.

Effluent 

The liquid discharged from a wastewater system component.

Faecal coliform

Bacteria present in waste from warm-blooded animals and used as an indicator of human-derived pollution.

Gravity system

System of conduits (open or closed) in which the liquid runs on descending gradients from source to outlet, and where no pumping is required.

Grease trap

Device for separating grease from wastewater by flotation so that it can be removed from the surface.

Greywater

Household wastes from kitchen, bathroom and laundry, other than blackwater. It usually contains fats and greases, organic matter, nutrients and can also contain pathogens (disease-causing micro-organisms). Sometimes referred to as sullage.

Infiltration

Water entering a public sewer or private drain from groundwater through defects such as poor joints and cracks in pipes and manholes.

Inflow 

Water discharged into a private drain from non-complying connections or other drain laying faults. It includes stormwater entering through illegal down pipe connections or from low gully traps.

Milliscreens

Barrel-shaped screens with mesh sides used as initial screening of large solids. Typically less than 3mm aperture size.

Nutrients

Key nutrients associated with wastewater are nitrogen and phosphorous. Nutrients are an important contaminant in wastewater as they cause prolific weed growth in waterways, adversely affecting ecology. However, some nutrients are required for microbial respiration.

Pathogens

Organisms that can cause diseases - bacteria, viruses and worms.

Oxidation pond

Pond used for treatment of wastewater in which biological oxidation of organic material is carried out by natural or artificial transfer of oxygen to the water from air and from algae, and bacterial reduction is achieved by long detention and exposure to sunlight.

Oxygen demand

The quantity of oxygen utilised in the biochemical oxidation of organic matter in a specified time, at a specified temperature, and under specified conditions (measured as 5-day biochemical oxygen demand - BOD5).

Potable water 

Drinkable/ drinking water.

Plume

Visible or measurable discharge of a contaminant from a given point of origin. Can be visible, sediment, or invisible, such as thermal in water, or visible in the air as, for example, a plume of smoke.

Primary treatment

First (sometimes the only) stage of wastewater treatment to remove large solids. Often the first stage of settlement is called "primary settlement". Preliminary treatment to remove wastewater constituents that may cause maintenance or operational problems in the system eg, grit removal, screening for trash and debris, oil and grease removal.

Residuals 

By-products of wastewater treatment (other than treated effluent). These include sludges, biosolids, grit, grease, fat, air emissions and odour.

Reticulation

Network of pipes, pumps and other devices used to transport sewage to a central point for treatment and/or disposal.

Secondary treatment

More advanced treatment than primary treatment. Stage two of the process which reduces suspended solids and organic matter. Typically require a biological treatment stage to remove/reduce contaminants. Examples include biological trickling filter plants, oxidation ponds, aerated lagoons and activated sludge plants.

Sedimentation 

The process of settling of suspended matter carried by water. See also Clarification.

Septage

The semi-liquid material that is pumped out of septic tanks, consisting of liquid, scum and sludge.

Septic tank

Wastewater treatment device that provides primary treatment for domestic wastewater, involving sedimentation of settleable solids, flotation of oils and fats, and anaerobic digestion of sludge.

Sewage

Wastewater derived from human communities - toilet, bathroom, laundry and kitchen waste. Now more commonly called wastewater.

Sewage sludge

By-product of sewage collection and treatment processes. May consist of primary or secondary sludge (biologically treated).

Sewer 

Pipe that conveys sewage.

Sewerage

A system of piping, with fittings, for collecting and conveying wastewater from source to treatment, and then discharge. The complete sewage collection, treatment and disposal system.

Solid waste

Is all waste generated as a solid or converted to a solid for disposal. It includes wastes like paper, plastic, glass, metal, electronic goods, furnishings, garden and other organic wastes.

Stormwater

Rainwater run-off from solid surfaces (roofs, roads, driveways, paths, parking lots and ground surfaces) that is channelled through drains from roads and urban properties into waterways and the sea.

Sullage

An alternative term for greywater.

Telemetry

Computer-based means of monitoring and communicating with remote sites.

Tertiary treatment

Final stage of wastewater treatment, usually to remove nutrients and pathogens eg, additional biological treatment stage, filtration, chemical flocculation and ultra-violet light disinfection.

Trade waste

Liquid wastes generated by business and disposed of through the sewerage system. Trade waste includes a range of hazardous materials resulting from industrial and manufacturing processes.

Ultraviolet treatment

Disinfection using light waves having wavelengths of 200-300 nm. Ultraviolet (UV) light can be used instead of chlorine, iodine or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction.

Wastewater

Contaminated water from domestic, commercial and industrial activities (see also domestic wastewater).

Wet-weather flow

The maximum flow for which a sewerage system is designed.