Sanitation Terminology

The following are terms commonly found in content describing the management of human waste.

Activated sludge

A central component of conventional wastewater treatment, where the ability of microbes to remove nitrogen, organic matter and other contaminants is harnessed in sequential aerobic and anoxic processes.


A process where a thin layer of atoms, ions, or molecules adhere to a surface. Often used in wastewater treatment to remove pollutants such as viruses, bacteria, heavy metals and volatile organic compounds, or in tertiary treatments to dechlorinate or remove odors. Activated carbon, which is extremely porous, is a popular material used for adsorption, but existing rocks and soil systems are more commonly relied upon.


Describes a process in conventional wastewater treatment where microbes use oxygen in a metabolic process that removes nitrogen from the water. Typically requires the use of blowers and mixers to whisk oxygen into the wastewater. This process accounts for a significant portion of a treatment plant's energy usage.

Aerobic Treatment Units (ATU)

Multi-chamber tank or a series of tanks that applies a series of treatment processes to the wastewater. The wastewater enters the first tank or chamber, which serves as a small gravity settling tank where large, heavy solids settle out of the water. The clarified water from the settling tank or chamber then passes into the aeration chamber where it is aerated to digest (or stabilize) the biological waste. By periodically stopping the aeration pump in the aeration tank much of the nitrogen in the wastewater can also be gassed off. Finally, the effluent from the aeration tank is pumped into the clarifier where the biological solids settle to the floor and the treated water is pumped out of the tank to an absorption field.


An organism which is able to thrive without molecular oxygen (O2).

Anaerobic bacteria

Bacteria that only grow in the absence of free elemental oxygen. [EPA, 2004]; Microorganisms that live in oxygen deprived environments [DOE].


An environment where there is no molecular oxygen (O2). In the water, dissolved oxygen is absent.


A living collection of diverse microbes that form a plasma and can work together to filter out and digest contaminants from wastewater.


Gas resulting from the decomposition of organic matter under anaerobic conditions. The principal constituents are methane and carbon dioxide [EPA, 2004].

Biological nitrification

When microbes convert ammonia/ ammonium into nitrite and nitrate. In wastewater treatment, the ammonia primarily comes from urine and feces.

Biological oxygen demand (BOD)

The amount of dissolved oxygen needed by aerobic organisms to break down organic matter in a water sample at a given temperature and time period. BOD is commonly expressed as milligrams of oxygen consumed per liter of sample over 5 days at 20°C (Delzer & McKenzie, 2003). It is often used to describe the level of organic pollution of water. Total BOD is the amount of oxygen required to completely oxidize the organic compounds to carbon dioxide and water through microbial metabolism.


Liquid and solid human body waste and the carriage water generated through toilet usage [EPA, 1996].


A concentrated animal feeding operation. CAFOs are agricultural facilities that house and feed a large number of animals in a confined area for 45 days or more during any 12-month period.


(a term often used interchangeably with cesspit) A tank pit, sometimes lined with bricks or concrete, used for the temporary collection and storage of human waste. In cases where the pit is constructed water-tight, it needs to be emptied frequently, which can result in high operation and maintenance costs. If not watertight, liquids leach out, while solids decay and collect in the base. Cesspools offer a high risk of contaminating nearby ground, surface, and coastal waters. Prone to overflowing during heavy rain, and if located near low coastal areas, are at risk of being inundated by rising sea-levels.

Constructed wetlands

Shallow water bodies or gravel or engineered media filled basins vegetated with plants adapted to continuous or periodic inundation. Constructed wetlands are engineered to improve water quality by creating a flow system that maximizes contact between water, wetland sediments, and its associated biological communities.

Container-based sanitation

Service in which toilets collect excreta in sealable removable containers, which need to be collected regularly and transported to treatment facilities. Qualifies as a type of 'improved sanitation' under the UN's Joint Monitoring Programme (See Sustainable Development Goal 6.2).


The general term for a liquid that leaves a technology, typically after blackwater or sludge has undergone solids separation or some other type of treatment. Effluent originates at either a Collection and Storage or a (Semi-) Centralized Treatment technology. Depending on the type of treatment, the effluent may be completely sanitized or may require further treatment before it can be used or disposed of.

Effluent organic matter (EfOM)

Carbon, hydrogen, and oxygen. Can also contain nitrogen, phosphorus, sulfur, and many other compounds. Measured by its Biological Oxygen Demand.


(from Greek eutrophos, meaning 'well-nourished') When a body of water becomes overly enriched with minerals and nutrients, which induce excessive growth of algae and cause hypoxia.


Urine and feces not mixed with flush water or other waste components.

Fecal sludge

A component of on-site sanitation systems, made up of a mixture of human excreta, water, and items such as toilet paper and tampons that people dispose of in pits tanks or vaults. Also called 'night soil.' Sludge composition determines treatment and potential disposal and/or end use options.


A chemical compound such as alum that causes molecules to coagulate. Added during primary stages of wastewater treatment.

Flush water

The carriage water generated through toilet usage.


Wastewater other than effluent containing human waste, such as sink drainage or washing machine discharge [EPA, 2009].


In ocean and freshwater environments, refers to low or depleted oxygen in a water body. Hypoxia is often associated with the overgrowth of certain species of algae, which can lead to oxygen depletion when they die, sink to the bottom, and decompose [NOAA].

Improved sanitation

A facility that hygienically separates human excreta from human contact and includes flush toilet, pit latrine with slab, composting toilet, ventilated improved pit latrine, septic and other examples.

Leach field

(also drain field, disposal field, soil absorption system) The area in which treated wastewater is discharged and filtered as it trickles through gravel and sand layers. More advanced systems may include trenches and perforated pipes to evenly distribute the water.

Nitrification of effluent

Nitrification is a two-step microbial process by which reduced nitrogen compounds (primarily ammonia) are sequentially oxidized to nitrite and nitrate. In the first step, ammonia-oxidizing bacteria oxidize ammonia to nitrite, and in the second step, nitrite-oxidizing bacteria oxidize nitrite to nitrate.


An essential element necessary to life. Nitrogen gas (N2) makes up about 78% of the atmosphere (NASA, 2016) and is a key component of proteins.

Non-point source pollution

Pollutants that come from multiple sources / can't be traced to one single source. Encompasses chemicals, oils, toxins (e.g., nitrogen, phosphorus, bacteria from septic tanks).


Chemical forms of nitrogen, phosphorus and silica, that are essential building-blocks of plant and algae cells. These chemicals can have toxic impacts when present in ratios higher than normal.

Open defecation

The practice of defecating outside on the ground, or in a body of water, instead of contained and concentrated within a designated place, such as a latrine.

Oxygen demand

Mass of dissolved oxygen needed by microorganisms to degrade organic and some inorganic compounds. A measure used in wastewater treatment systems as an indicator of how much organic content is in the wastewater. For instance, ammonia creates an oxygen demand as it is converted to nitrate. (Also called BOD for biological oxygen demand.)

Pit humus

Material that has been removed from a double pit technology --- such as a fossa Alterna, double ventilated improved pit, or twin pits for pour-flush toilets, composting toilets, terra preta toilets, or arbor loss --- because it's produced underground passively and is made up slightly differently than standard compost. It contains a high volume of nutrients and organic matter.

Point-source pollution

Includes wastewater and illegal chemical dumping. The pollution originates from a single source.

Primary treatment

Mechanical screening, active screening or settling of solids, and some reduction of organic matter (that is, biological oxygen demand, or BOD). No focus on nutrients, typically.

Safely managed sanitation

Refers to facilities that are not shared and incorporate treatment of human waste, either in-situ, through storage, collection and eventual treatment, or sewer systems.


Refers to conditions related to public health, especially the provision of clean drinking water and adequate disposal of human waste.

Sanitation system

Sanitation systems are a combination of different functional units that together allow managing and reusing or disposing the different waste flows from households, institutions, agriculture or industries in order to protect people and the environment. The systems are designed to address the whole water as well as the nutrients cycle, from the toilet user where wastewater is generated, over the collection, treatment up to reuse or discharge. In order for sanitation systems to function reliably, the technical know-how for the installation of functional units as well as their management, operation, and maintenance must be guaranteed.

Secondary treatment

Biological treatment for removal of BOD (see biological oxygen demand) which may also achieve some reduction of nutrients.

Septic system

An on-site system that consists of an underground septic tank and a drain field.


Technically the term sewage refers to human excrement that has been conveyed through a conduit, using water. However, outside the sanitation sector, sewage has come to mean any human excrement, regardless of where and how it has been stored or transported.


Mainly excreta and water that may contain other matter such as sand, grit, metals, trash and/ or various chemical compounds, depending on the source of the sludge.

Stabilization ponds

Engineered water bodies most commonly used for treating wastewater (aerobically).


Generated when precipitation from rain and snowmelt events flows over land or impervious surfaces and does not percolate into the ground.


Precipitation from rain and snowmelt that flows over land or impervious surfaces without being absorbed into the land.


A layering of water, with lighter water on top. Water that is fresh (contains little salt) and warm is lighter than cool salt water.

Tertiary treatment

Filtration (may also include chemical removal of phosphorus with clarification), aeration, and nutrient removal through biological or chemical processes.


Used water and solids, including sewage, from a community that flow to a treatment plant. Used water includes water from industrial processes. Stormwater, surface water, and groundwater infiltration also may be included in the wastewater that enters a wastewater treatment plant [University of Florida].

Wastewater treatment

Preparation and transformation of wastewater and related products (e.g., blackwater, fecal sludge, greywater, non-biodegradable waters, etc.) for safe reuse or disposal in order to minimize health risks for people and protect the environment from pollution.