Glossary

A

Activated sludge: The mixture of bacterial matter and wastewater in a sewage treatment plant whereby an environment encouraging bacterial growth is encouraged to metabolise the waste material in the water.
Adsorption: Attachment of a substance to the surface of a solid.
Aeration: The process by which oxygen is introduced to a liquid, usually by means of mechanically circulating air through the liquid so that oxygen can be absorbed.
Aerobic: A condition that occurs in the presence of elemental oxygen
Anaerobic: A condition that occurs without the presence of both elemental oxygen or chemically bound oxygen.
Anaerobic sludge digestion: The process by which activated sludge is broken down anaerobically.
Aquifer: A natural underground layer, often of sand or gravel, which contains water.
Anoxic: A condition that occurs without the presence of free elemental oxygen but in with chemically bound oxygen present.

B

Bacteria: Microorganisms often composed of single cells shaped like rods, spheres or spiral structures.
Biochemical oxygen demand (BOD): Also known as Biological Oxygen Demand, a chemical procedure for determining the rate of uptake of dissolved oxygen by biological organisms in a body of water. Although not as precise as Chemical Oxygen Demand as a quantitative test, BOD is widely used as an indication of the quality of water and a gauge of the effectiveness of wastewater treatment plants.
Biofilter: A waste water treatment process whereby the beneficial bacteria used for treating the water are attached to either fixed or moving media.
Biomass: The total mass of organisms present in a biological system that are responsible for the metabolisation of organic material.
Biosolids: The waste sludge produced from a waste water treatment plant that can be put to beneficial use, such as for soil conditioning or fertilizer.

C

Chemical oxygen demand (COD): A test used to indirectly measure the quality of water by measuring the amount of organic compounds. More accurate than the BOD test, COD indicates the quantity of organic pollutants in the water in milligrams per litre (mg/L).
Chlorination: The process of adding a form of chlorine to water or wastewater.
Clarification: Removal of bulk water from a dilute suspension of solids by gravity sedimentation, aided by chemical flocculating agents.
Clarifier: The settling tank used for the clarification of water.
Coagulation: Irreversible combination or aggregation of particles to form a larger mass.
Coliforms: Named after the test adopted in 1914 for the Enterobacteriaceae family of bacteria that are abundant in the faeces of warm-blooded animals, but can also be found in the aquatic environment, in soil and on vegetation. Escherichia coli (E.Coli), a rod-shaped member of the coliform group, is easy to culture in a laboratory and their presence is used to indicate that other pathogenic organisms of fecal origin may be present.
Colloid: A type of chemical mixture in which one substance is dispersed evenly throughout another in a suspension.
Contact Time: The period of disinfection in water treatment.

D

Detention period: The hydraulic retention period during which part of the flow of water is retained in a tank an calculated as the volume of the tank in m3 divided by the flow rate in m3/hour
Detritus: Heavy material in waste water such as sand and grit.
Disinfection: Destruction of harmful microorganisms, usually by the use of bactericidal chemical compounds.
Disinfection Byproducts: Compounds created by the reaction of a disinfectant with organic compounds in water.
Distribution System: A network of pipes leading from a treatment plant to customers’ plumbing systems.

E

Effluent: The outflow of treated water into the environment from a sewage treatment process at a plant, oxidation pond or other method of treating the waste water.
Endocrine Disruptor Compound (EDC): a foreign substance or mixture that alters the functioning of the endocrine system, consequently harming an individual life form, its offspring, or populations.
Epidemiology: The study of the occurrence and causes of health effects in human populations.

F

Filtration: The operation of separating suspended solids from a liquid (or gas) by forcing the mixture through a porous barrier.
Free Chlorine: The sum of hypochlorous acid and hypochlorite ions expressed in terms of mg/L or ppm.

G

General Standards: A specific quality of water defined by various tests and which promulgated by government as the necessary quality to ensure the return of safe water to the environment where Special Standards are not applicable.
Grit Channel: Also called a grit chamber or de-gritter, the channel that forms part of pre treatment where the velocity of the incoming wastewater is carefully controlled to allow sand, grit and stones to settle, while keeping the majority of the suspended organic material in the water column for treatment in the next stage.
Groundwater: The water that systems pump and treat from aquifers (natural reservoirs below the earth’s surface).

H

Haloacetic Acids: A group of disinfection byproducts that includes dichloroacetic acid, trichloroacetic acid, monochloroacetic acid, bromoacetic acid, and dibromoacetic acid.
Humus: The biomass from biological filters that settles in tanks downstream from the plant and is used as to contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen that is trapped by bacteria in the soil.

I

Influent: The waste water flowing into a treatment plant or oxidation pond etc.

L

Lagoon: Another name for an Oxidation Pond.

M

Microbial Contamination: Contamination of water supplies with microorganisms such as bacteria, viruses and parasitic protozoa.
Microorganisms: Tiny living organisms that can be seen only with the aid of a microscope. Some microorganisms can cause acute health problems when consumed in drinking water. Also known as microbes.

N

Night soil: A euphemism for human feces, “Night soil” is produced as a result of a waste management system in areas without community infrastructure such as a sewage treatment facility, or individual septic disposal. In this system of waste management, the human faeces is collected in solid form.

O

Organic Matter: Matter derived from organisms, such as plants and animals.
Oxidation: Any reaction in which electrons are transferred and most often associated with a reaction involving oxygen.
Oxidation Pond: A large man-made pond designed to provide settlement and further biological improvement during storage. Lagoons are designed to be highly aerobic and colonization by native macrophytes, especially reeds, is often encouraged. Small filter feeding invertebrates assist in treatment by removing fine particulates.
Ozone: (O3) One of the strongest oxidants and disinfectants available, Ozone is typically generated on-site at water treatment plants by passing dry oxygen or air over a system of high voltage electrodes.

P

Parasitic Protozoa: Single-celled microorganisms that feed on bacteria and are found in multi0cellular organisms, such as animals and people.
Pathogen: A disease-causing organism.
pH: A measure of the acidity or alkalinity of an aqueous solution.
Primary treatment: The first stage of sewage treatment whereby sewage flows through tanks called “primary clarifiers” or “primary sedimentation tanks” that are large enough so that the sludge can settle and floating material such as grease and oils can rise to the surface and be skimmed off. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages.

R

Raw Water: Water in its natural state, prior to any treatment for drinking.
Residual: The measurement of chlorine in water after treatment.
Risk Assessment: The process evaluating the likelihood of an adverse health effect, with some statistical confidence, for various levels of exposure.

S

Secondary treatment: The stage in sewage treatment where the biological content, such as that derived from human waste, food waste, soaps and detergents are substantially degraded. The majority of municipal plants treat the settled sewage liquor using aerobic biological processes that are typically either fixed-film or suspended-growth systems.
Secondary sedimentation: The final step in the secondary treatment stage is to settle out the biological floc or filter material and produce sewage water containing very low levels of organic material and suspended matter.
Sedimentation: The water treatment process whereby suspended solids in water are settled out under the influence of gravity.
Settling tank: The large tank where solids in water are settled out under the influence of gravity in drinking water or wastewater treatment.
Sewage: Wastewater that is contaminated with faeces or urine, but is often used to mean any waste water. “Sewage” includes domestic, municipal, or industrial liquid waste products disposed of, usually via a pipe or sewer or similar structure.
Sludge: The residual, semi-solid material separated from suspension in a liquid.
Surface Water: The water that systems pump and treat from sources open to the atmosphere, such as rivers, lakes, and reservoirs.
Special Standards: A specific quality of water defined by various tests and which is government promulgated to ensure the return of safe water to defined environmentally sensitive areas where General Standards are not sufficient.
Stabilization Pond: Another name for an Oxidation Pond.

T

Tertiary treatment: The final treatment or “effluent polishing” stage of waste water to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process.
Total suspended solids (TSS): The quantity of suspended solids present in wastewater as an indicator of how polluted the water is.
Toxicology: The branch of medical science devoted to the study of poisons, including their modes of action, effects, detection, and countermeasures.
Trickling filter: A method of treating sewage whereby the waste water flows downward over a fixed bed of material such as rocks, gravel, slag, or plastic media and causes a layer or film of microbial slime to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced air flowing through the bed or natural convection of air if the filter medium is porous.
Trihalomethanes: A group of disinfection byproducts that includes chloroform, bromodichloromethane, bromoform, and dibromochloromethane.
Turbidity: The cloudy appearance of water caused by the presence of tiny particles. High levels of turbidity may interfere with proper water treatment and monitoring.

U

Ultraviolet Radiation: Radiation in the region of the electromagnetic spectrum including wavelengths from 100 to 3900 angstroms.

V

Viruses: Microscopic infectious agents, shaped like rods, spheres or filaments that can reproduce only within living host cells.

W

Waterborne Disease: Disease caused by contaminants, such as microscopic pathogens like bacteria, viruses and parasitic protozoa, in water.
Wastewater: Any water that has been adversely affected in quality by human influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations. In the most common usage, it refers to the municipal wastewater that contains a broad spectrum of contaminants resulting from the mixing of wastewaters from different sources.
Watershed: The land area from which water drains into a stream, river, or reservoir.