About UNEP
United Nations Environment Programme
Division of Technology, Industry and Economics
top image
space space space
Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

Heavy metals Metals such as copper, zinc, cadmium, chromium and lead. In wastewater treatment they are usually concentrated in the sludge.
Human excreta Faeces and urine.
Incinerating toilet Incinerating toilet refers to a dry toilet where the solids are combusted. Used usually in isolated area (e.g. permanent snow).
Incineration (sludge) Combustion of sludge. Usually in a multiple hearth or fluidised bed furnace. It is relatively costly and may produce air pollution.
Infiltration trench (stormwater) A trench into which stormwater run-off is directed and is allowed to infiltrate to the groundwater. See also Chamber soakway.
Integrated waste management Integration of the management of solid waste, wastewater and stromwater to achieve protection of public health and the environment. The integration can also be seen in a wider context with hygiene promotion, community consultation and participation and matters associated with the above.
Lagoon Lagoons or ponds are natural or engineered excavations in the ground and used to treat wastewater and stormwater. Settling of solids and degradation of organic materials by micro-organisms take place in the lagoons. They are therefore also called stabilisation lagoons or waste stabilisation lagoons.
Landfill(ing) A landfill is usually an excavation in the ground where waste is buried, and landfilling refers to the method of waste disposal by burying the waste in the ground.
Leach pit or drain Pit or drain into which the overflow from a septic tank is directed. Water leaches (infiltrates) into the ground. The soil surrounding the pit or drain must be permeable and not close to the water table.
Lime stabilisation Lime stabilisation refers to the addition of lime (calcium oxide) to waste (e.g. sludge). In this way the pH of the sludge is increased usually to above 11 and hence bacteria (including pathogens) are killed.
Mesophilic The conditions of composting where the temperature initially rises, but still below 40 oC. See Thermophilic.
Membrane filtration Membrane filtration uses a membrane that passes water and some salts. In this way the water passing through (the permeate) contains less salt and bacteria. A high pressure is required to push the water through the membrane.
Micro-organisms Micro-organisms in wastewater treatment include bacteria, fungi, protozoa and crustaceans which convert organic wastes to more stable less polluting substances
Natural cycles See Biogeochemical cycles
Natural purification Processes occurring in nature which remove pollutants or convert them or render them less harmful to the environment. Examples are the removal of suspended solids in quiescent stretches of a river and removal of organic wastes through consumption by naturally occurring bacteria.
Night soil Night soil refers to human excreta that is stored in buckets and collected nightly for reuse, treatment or disposal.
Nitrification Conversion of ammonium in wastewater to nitrate. This process is carried out by nitrifiers under aerobic conditions.
Nitrifiers Bacteria carrying out the nitrification process.
Nitrogen An essential and important plant nutrient. It occurs in several forms: organic nitrogen, ammonia, nitrite and nitrate.
Nitrogen cycle See Biogeochemical cycles.
Nutrients Nutrients refer to the elements that are required by plants and animals, although nitrogen and phosphorus are generally the major nutrients of concern in wastewater. See Eutrophication and Environmentally sensitive zones.
On-site systems Waste treatment systems that are located where the waste is produced. See Centralised systems.
Overhung latrine Latrine located above water (river or coastal water) and human excreta drops directly into the water.
Overland flow Overland flow refers to the treatment of wastewater by passing it through land. Purification of the wastewater takes place as it flows through the soil. Grasses growing on the soil transpire part of the water and take up nutrients.
Oxidation ditch Channel in the form of a ring for the treatment of wastewater. The wastewater is moved along the channel to assist with aeration. Treatment processes are similar to what takes place in a lagoon.
Pathogens Bacteria, viruses, protozoa and helminths which cause illnesses.
pH pH indicates the degree of acidity or alkalinity of water. Neutral pH is seven, whereas a value below 7 indicates acidic conditions and above 7 alkaline conditions. Living organisms usually tolerate a pH of between 6 and 9.
Pit privy Pit privy or latrine is a latrine built on top of a dug pit. Human excreta is deposited into the pit. When the pit is full the content is dug up, or the latrine relocated and the pit covered with soil.
Phosphorus Phosphorus is an essential and important plant nutrient. It occurs as organic phosphorus and phosphate.
Pond See Lagoon
Pour flush toilet A pour flush toilet has a water seal and is flushed by pouring 2 to 3 L of water into the pan.
Primary sludge Sludge produced from primary treatment of wastewater.
Primary treatment The treatment of wastewater by screening and sedimentation to remove solids.
Pyrolysis (sludge) Heating of sludge to a very high temperature in the absence of oxygen or in the presence of controlled small amounts of oxygen. Under these conditions the sludge is converted into water, gas, oil and char.
Rapid rate land application See Soil Aquifer Treatment
Rainfall run-off Water from rainfall that flows over surfaces.
Retention basin Basin or pond used to store stormwater run-off. Flooding potential is therefore reduced. Settling of solids and infiltration of water into the ground occur during retention.
Return activated sludge Activated sludge that is returned to the aeration tank of an activated sludge process to assist with treatment of wastewater. See Activated Sludge.
Rotating Biological Contactor (RBC) A rotating biological contactor is used to treat wastewater and consists of rotating disks that are partly immersed in the wastewater. In this way the wastewater is entrained in the rotating disks and aerated, and aerobic bacteria consume organic wastes.
Run-off See Rainfall run-off.
Sand filtration The operation of passing water through a bed of sand to remove suspended solids from the water.
Secondary treatment Secondary treatment refers to the treatment of wastewater after primary treatment. Aeration is introduced to supply oxygen to the bacteria consuming the organic materials in the wastewater. See Activated sludge and Trickling Filter.
Sedimentation The removal of suspended solids by slowing the velocity of flow of the wastewater. In this way solids settle to the bottom of the sedimentation tank or pond.
Septage The sludge that accumulates in a septic tank.
Septic tank On-site tank for the storage of solids in wastewater. Regular emptying of the accumulated solids is required so that it can function properly. See Septage, Leach drain/ pit and STEP.
Septic tank effluent pumping (STEP) STEP refers to the conveyance of the overflow from septic tanks by pumping it to a central collection point. Pumping overcomes the need to have large diameter pipes which rely on gravity flow.
Sequencing batch reactors (SBR) An Activated Sludge Process that is operated batchwise (rather than with a continuous flow of wastewater). Each step of the Activated Sludge Process is done in sequence. Two tanks in parallel are required to deal with continuous flow of wastewater.
Settled sewerage Sewerage that conveys wastewater that has undergone settling to remove suspended solids.
Sewage Sewage is wastewater produced from human activities in a household, and consists of human excreta, kitchen waste, bathing water and washing water. See Sewerage.
Sewerage Sewerage refers to the pipes and drains which convey sewage. A sewerage system includes the pumps that may be required if gradient for gravity flow is not sufficient. Sewerage usually also conveys stormwater and industrial wastewater. See Sewage.
Sewer mining Withdrawal of wastewater from a sewer pipe for reuse purposes. Treatment of the wastewater is required to meet the requirement of reuse.
Shallow sewerage See Simplified Sewerage
Simplified sewerage In simplified sewerage pipes are laid relatively shallow in the ground when traffic above is light. Design horizon is shorter compared to conventional sewerage. As a result pipes are smaller in size and are laid shallower compared to conventional sewerage. Costs are correspondingly lower.
Sludge (sewage sludge) Sludge is the solids that are produced from human excreta or from the treatment of wastewater.
Solids Solids refer to materials which are in solid form. They are generally in the solid phase, but may dissolve in water (e.g. salts and sugar). Hence the reference to Dissolved Solids or Total Dissolved Solids. See Suspended Solids.
Solids free sewerage See Settled Sewerage
Stabilisation Stabilisation refers to the decomposition of organic materials by micro-organisms. The organic materials are converted into more stable less biodegradable materials and therefore do not produce as much odour and less attractive to insects.
Stormwater Stormwater is water which results from storm and rainfall generally. See run-off.
Suspended solids (SS) Suspended solids are solid particulate matter contained in water. They are generally removed by settling, but for light particulates by floating. See Dissolved Air Flotation.
Suspended growth system A suspended growth system retains micro-organisms in a wastewater treatment system in the form of flocs suspended in the wastewater. An activated sludge process is an example of a suspended growth system. See Attached Growth System.
Swales (stormwater) Long shallow channels which intercept stormwater run-off (e.g. from a Filter strip). They act to store the water temporarily and allow it to infiltrate to the ground.
Tertiary treatment The treatment of wastewater beyond secondary treatment, but may be used to refer specifically to the removal the nutrients nitrogen and phosphorus. See Secondary Treatment.
Thermophilic The conditions of composting where the temperature is above 45 oC. Heat is generated from the activities of micro-organsims consuming the organic materials in the compost. Oxygen requirement is highest in this active period. Can be taken advantage for compost sterilisation purposes.
Thickening (sludge) The process of removal of water/moisture from the sludge. This is usually done by allowing the solids in the sludge to settle and decanting the excess water.
Toilets Facilities for urination and defecation including the housing required for such facilities.
Total Dissolved Solids (TDS) See Solids
Total Suspended Solids (TSS) See Suspended Solids
Trickling filter A trickling filter is an example of an Attached Growth System. Wastewater is allowed to flow through the filter bed. Organic materials in the wastewater are consumed by the micro-organisms attached to the surfaces of the filter bed. See Attached Growth System.
Ultraviolet disinfection Ultraviolet disinfection utilised ultraviolet radiation (e.g. from the sun) to achieve disinfection. See Disinfection.
Upflow Anaerobic Sludge Blanket (UASB) An anaerobic process for the treatment of wastewater (usually with a high BOD). Wastewater is passed through a tank from below through a bed of sludge containing the micro-organism which consume the organic wastes.
Vault latrine A latrine where human excreta is stored in a vault, which is emptied regularly of the sludge.
Waste management hierarchy A waste management method which considers prevention of waste as the highest priority, followed by waste minimisation, recycling, reuse and treatment prior to disposal. The latter is considered to be of the lowest priority.
Wastewater Wastewater refers to water that has been used in households and also in other activities, e.g. industry producing industrial wastewater. See Sewage.
Waste stabilisation pond See Lagoon.
Wetlands Water bodies that are generally shallow and may not have permanent water. Artificial wetlands (constructed wetlands) are wetlands that have been created to receive stormwater, or treat wastewater.
Waste Activated Sludge (WAS) Activated sludge that is in excess of the requirement of an activated sludge process and is wasted from the process. See Activated Sludge and Activated Sludge Process.
Water cycle The natural cycling of water in the environment, which include evaporation of water from the oceans, seas, rivers and lakes, the condensation of the evaporated moisture as rainfall, the resulting rainfall run-off, water infiltration to the groundwater, uptake by plants, and water flowing in rivers to the seas and oceans.


Main Menu  

  • Brochure
  • IETC Brochure

  • International Year of Forests
  • International Year of Forests

  • World Environment Day
  • ??????

  • UNEP Campaign
  • UNite to Combat Climate Change