Absorption1 - The taking up of a substance, especially a fluid, into the body of another material.
Absorption2 - The reduction of intensity of any form of radiated energy as a result of energy conversion in a medium.
Abstraction - The withdrawal of water from any source of supply.
Acetate - Any salt or ester of acetic acid (vinegar), containing the monovalent ion CH3COO¯ or the group CH3COO-
Acid - Any substance that dissociates (splits) in water to form a solution containing hydrogen ions. Strong acids have a high degree of dissociation and are usually corrosive. Acids have a pH which is less than 7. Acids neutralize alkalis, forming salts in the process.
Acid rain - Rain that contains a high concentration of the pollutants sulphur dioxide or nitrogen oxide; forming sulphuric acid and nitric acid respectively. N.B. carbon dioxide also dissolves in rainwater to form carbonic acid, but this is not usually considered in this context.
Actinic - Producing a photochemical effect; relating to radiation.
Activated Carbon - A porous, highly absorptive form of carbon used to remove impurities from fluids or for the separation and extraction of chemical compounds or solvent recovery. Activated carbon is usually produced by heating organic matter in the absence of air. Its porous nature means that it has a very large surface area to mass ratio, ideal for good adsorption. Activated carbon is frequently used in either powered (PAC) or granular (GAC) form. Powdered activated carbon is much finer and therefore has a larger surface area to volume ratio. Granular activated carbon is larger but has the advantage that it can be reused, after regeneration; which usually involves burning off the collected impurities by heating in a regeneration kiln.
Activated Sludge - The process of sewage treatment whereby wastewater (mixed liquor) is aerated (agitated with forced air or oxygen) to develop a biological floc (of microorganisms) that will break down the organic matter in the sewage. The mixed liquor is then discharged to a settling tank and the supernatant is run off for further treatment before discharge. The sludge (settled solids) in the mixed liquor tank is the activated sludge; some of this is pumped back to the aeration tank to seed (re-introduce bacteria to promote growth of biological floc) incoming wastewater, this is known as return activated sludge (RAS). The remaining sludge (surplus activated sludge or SAS) is further treated prior to disposal.
Adiabatic - Taking place without loss or gain of heat.
Adsorption - When molecules of a dissolved substance collect on and adhere to the surface of an adsorbent solid. Activated Carbon is an example of an adsorbent solid.
Aerobic - Dependent on free oxygen or air. e.g. Aerobic digestion of sewage; microorganisms, which rely on oxygen for their metabolic processes, oxidize organic compounds in sewage; this is an aerobic process.
Aerobiosis - Life in the presence of free oxygen.
Aerosol - Very fine liquid or solid particles which are suspended in a gas. Condensation aerosols are created when gases with moisture content are cooled; condensed liquid droplets in suspension. Dispersion aerosols are created when solid or liquid particles are broken up and introduced into a gaseous medium.
Afforestation – Establishing or increasing tree plantation in an area.
Afterburner - A device in the exhaust system of an internal combustion engine intended to offer complete combustion thereby removing or rendering harmless potentially dangerous pollutants in exhaust gases. The term ‘afterburner’ is frequently used in the context of offering additional thrust or propelling force by burning additional fuel after the main cycle of combustion.
Agrestal - Uncultivated plants growing on cultivated land, e.g. weeds.
Agroforestry - A method of farming which combines herbaceous and tree crops.
Air - A mixture of gases that forms the Earth’s atmosphere. Composition of dry air at sea level is roughly as follows: Nitrogen (78%), oxygen (20.95%), argon (0.93%), carbon dioxide (0.03%) and other (0.09%).
Albedo - The ratio of the intensity of light reflected from an object, such as a planet, to that of the light it receives from the sun. A term often used in relation to SRM (solar radiation management).
Algae - Single or multicellular organisms that have chlorophyll and rely on photosynthesis for life. These plants can be found growing in moist ground, fresh water or salt water. Algal blooms can occur in rivers and lakes that are rich in organic and mineral nutrients (eutrophic). This can be problematic once the plants start to decay as they can deplete the oxygen supply.
Alkali - A substance that dissociates (splits) in water to form a solution containing an excess of hydroxyl ions (OH¯) relative to hydrogen ions. Alkaline solutions have a pH which is greater than 7. Acids neutralize alkalis, forming salts in the process.
Alkalinity - A water quality parameter which is used to measure the buffering capacity (of a water sample) against changes in pH. i.e. its ability to neutralize acids to the stoichiometric equivalent in bicarbonate, carbonate or hydroxide content. Units are expressed in mg/l (equivalent CaCO3 [calcium carbonate or limestone]).
Alternative Energy – Energy produced from sources other than fossil fuels.
Aluminium Sulphate – Chemical formula Al2(SO4)3. It is a white crystalline solid used as a coagulant (to bind suspended solids together so they can settle out) in water treatment processes.
Amino Acid – An essential building block of protein, which consists of amino ( – NH2) and acidic carboxyl (– COOH) groups.
Ammonia – Chemical formula NH3. Ammonia is usually encountered as a colourless pungent gas (low boiling point -33.3⁰C). It is highly soluble and is used in the manufacture of fertilizers, nitric acid and other nitrogenous compounds. It can also be used to control emissions of nitrogen oxides when used with a vanadium based catalyst in combustion engines; the products of this reaction are nitrogen and water vapour.
Ammonia can be produced biologically by nitrogen fixing bacteria (nitrogen cycle) or industrially using the Haber process; both processes use nitrogen from the atmosphere.
Amphoteric– Able to function either as an acid or a base.
Anaerobe – An organism (esp. bacteria) that does not require oxygen or air for respiration.
Anaerobic – Without oxygen.
Anaerobic Digestion – The decomposition of organic matter, in the absence of oxygen, by anaerobes; resulting in the formation of methane and carbon dioxide. This process is used to produce biogas.
Anaerobiosis – Life in the absence of free oxygen.
Anion – A negatively charged ion; an ion that is attracted to the anode during electrolysis.
Anode – An electrode which is at a positive potential.
Anoxic – Without oxygen.
Anthropogenic – Produced as a result of human activity.
Aquifer – A deposit of porous rock, containing water, which can be used to supply wells. Groundwater.
Aquifer Depletion – When the rate of consumption of water from an aquifer is greater than the rate of replenishment from natural or artificial recharge.
Arable Land – Land that can be cultivated.
Arid – Very dry due to lack of rainfall, typically when less than 25cm or 10 inches of rainfall is received annually.
Artificial Recharge – The process of augmenting ground water supplies by flooding the surface at a higher rate than would be achieved by natural precipitation (rain) or infiltration. Slightly polluted water may be used for this purpose because the natural filtering action of the rocks would improve its quality. Artificial recharge is mainly used to restore supplies that have been excessively depleted or store surplus water for later use but is sometimes (e.g. in India) used to dilute the existing groundwater, if it contains a high concentration of a given impurity and the above ground treatment resources are no longer matched to treat the quality of existing groundwater.
Asset Management Plan (AMP) – These are investment plans for water infrastructure. Water companies in England and Wales must put forward their proposals for spending every five years.
Atmosphere – The gaseous envelope surrounding the Earth or another celestial body.
The composition of the Earth’s atmosphere is maintained by the carbon and nitrogen cycles.
Autotrophic – An organism that is capable of manufacturing complex organic compounds for food from simple inorganic sources such as water, carbon dioxide and nitrates. e.g. Green plants.
Background Concentration of Pollution – The extent of pollution from a local source can be quantified by comparison against the background concentration of a given pollutant. This is the concentration that would exist if the local source was not present.
Backwash – In water treatment, it is the process used to clean filter media by reversing the flow through the filter bed to remove the trapped impurities. Backwashing is necessary to prevent the filter clogging up or leaking through contaminated water.
Bag Filter – A tightly woven bag used for removing dust from dust laden gases.
Band Screen – (Also known as travelling band screen). A continuously moving wire mesh band that is usually installed on raw water intakes, headworks or combined sewer overflows in order to remove solids and so protect pumps and process plants.
Bar Screen – See also band screen. This is also used to remove large solids at headworks etc. but it is a fixed screen, with a set of regularly spaced bars which has to be mechanically raked.
Barnes’ formula – Used for calculating the flow velocity in a sewer.
Flow Velocity (m/s) = 107 x Hydraulic Mean Depth0.7 (m) x Slope of Sewer0.5
Base – See Alkali.
Base exchange – An ion exchange process used for removing hardness from water (softening) whereby calcium (Ca2+) and magnesium (Mg2+) ions are exchanged for sodium ions (Na+).
Biochar – Is biomass which has been treated by pyrolosis (heated in the absence of oxygen in kilns) to form charcoal. Usually biomass (e.g. plant life) would release carbon dioxide as it decomposes but by creating biochar the cycle is interrupted and the carbon can be locked away in soil. This is part of an effort to reduce the concentration of greenhouse gas emissions and tackle climate change. Biochar is said to have many soil benefits for crop growth, such as increased water retention, however there is some debate about how much carbon actually remains locked in the soil over a period of time.
Biochemical Oxygen Demand (BOD) – Is a measure of the organic pollution of water. The standard test measures the amount of dissolved oxygen used up (in mg/l) by bacteria, in decomposing organic matter, in a water sample after being incubated in darkness for 5 days at 20⁰C. The test is not infallible and is affected by a number of factors such as the presence of toxins that inhibit bacterial growth, the additional chemical uptake of oxygen (COD) and the availability of oxygen and nutrients during the test. Some of these factors can be controlled e.g. by the addition of allythiourea (ATU) to selectively inhibit the oxidation of any ammonia that may be present in the sample. It is standard practice to use both COD and BOD readings in order to gain a more complete understanding of a particular water sample.
BOD and COD ratios have been established for a number of different types of effluent.
Biodegradable – Capable of being decomposed by bacteria or other biological means.
Biodiesel – Diesel fuel derived from vegetable or animal fats. It consists of long chain alkyl esters and is made by combining the fats (lipids) with an alcohol in the presence of a catalyst such as sodium or potassium hydroxide. Glycerine (used in cosmetics and pharmaceuticals etc.) is also formed as a by-product of this process.
Biodiversity – The existence of a wide variety of plant and animal species in their natural environments.
Bioethanol – Ethanol made by fermenting common crops, such as sugar cane, corn or wheat, intended primarily for use as an alternative to petroleum and diesel. Its use is hailed as being helpful to the environment in the sense that overall emissions will be partially offset by the uptake of carbon dioxide by new energy crop growth as they are continually replaced. However it attracts criticism for the amount of land required and the conversion of land which is needed to grow food crops.
Biogas – Gas formed by anaerobic digestion of organic materials; used as fuel.
Biological Aerated Filter – In wastewater treatment; a reactor filled with filter media (usually plastic) which is either in suspension (upflow) or supported by gravel (downflow). The media supports a film of microorganisms that decompose organic matter. The reactor is aerated and incoming flow can be upflow (rising) or downflow (by gravity) depending on the reactor design.
Biomass1 – The total number of living organisms in a given area, usually expressed in weight per unit area.
Biomass2 – Organic matter, of recent origin, that is used as a source of energy. It is classified as being renewable on the account that it can be quickly replaced in contrast with fossil fuels.
It is considered to be carbon neutral over its life cycle in that it absorbs carbon dioxide during the growth phase and releases the same amount when it is burned as fuel.
Bioremediation – A process that uses microorganisms to return an environment, which has been altered by contaminants, to its original condition.
Biosolids – Treated sludge from sewage treatment.
Bisphenol A (BPA) – A compound used in the production of epoxy resins and polycarbonate plastics. e.g. It can be found in the plastic lining inside a tin can which enables the can to be heated to kill off bacteria without the metal contaminating the food. BPA is a cause for concern because it is a known endocrine disruptor.
Borehole – A hole driven into the ground to obtain geological information or to extract resources such as water, oil or gas.
Brackish Water – Water which has a higher salinity (is saltier) than potable (drinking) water but is not as salty as sea water. The salt concentration of brackish water is said to be in the range 0.5 to 30 grams per litre (or the equivalent 0.5 to 30 ppt [parts per thousand]). By comparison sea water typically contains around 35 grams per litre.
Breakpoint Chlorination – When chlorine is used as a disinfectant; the breakpoint is the dosage of chlorine required to satisfy the chlorine demand of organic impurities (to oxidise them) that are present in a sample. Any more chlorine that is added is available as free chlorine.
Breeder Reactor – Nuclear fission; a type of nuclear reactor that produces more fissionable material than it consumes.
Brine – Water containing large amounts of salt esp. sodium chloride (NaCl). Salt concentration is over 50 g/l (or equivalent 50 ppt [parts per thousand]). Water can be evaporated from brine solution to yield salt. Electrolysis of brine can be used to produce sodium hydroxide, hydrogen and chlorine gas.
Bubble Policy – A policy that allows polluters to discharge more pollutants at one source if the equivalent cuts are made at another.
Buffer Solution – Is an aqueous solution consisting of a weak acid and its conjugate base or a weak base and its conjugate acid. e.g. Citric acid and sodium citrate. It can resist changes in pH when small amounts of acid or base are added to it.
Caesium-137 – A radioactive isotope that is formed mainly by nuclear fission. It has a half-life of around 30 years and decays by pure beta decay to a metastable nuclear isomer of barium-137m. Barium-137m has a half-life of 2.55 minutes and is responsible for all of the gamma ray emission.
Calcium carbonate (CaCO3) – Commonly referred to as limestone.
Carbonates can cause temporary hardness in water if carbon dioxide is in solution. Temporary hardness is so called because it can be easily removed by boiling, whereas hardness attributed to noncarbonates is ‘permanent’. Hardness in water which is caused by calcium, magnesium and other ions is usually described as calcium carbonate equivalent.
Calcium carbonate is used in the manufacture of cement and quicklime.
Calcium oxide (CaO) – Commonly referred to as quicklime.
It is manufactured by heating calcium carbonate (limestone) at 900⁰C; a process which releases carbon dioxide.
CaCO3 → CaCO + CO2
Calorific Value – The quantity of heat produced by the complete combustion of a given mass of fuel. Usually expressed in units of joules per kilogram.
Calibration – A procedure which checks or adjusts an instrument's accuracy by comparison with a standard or reference.
CAM Plant – Any plant that undergoes a form of photosynthesis known as crassulacean acid metabolism, in which carbon dioxide is taken up only at night.
Cancer – Abnormal cell growth, in which cancerous cells invade and destroy other cells and tissues. A large proportion of cancers are thought to be linked to environmental factors, chemicals and other substances known as carcinogens.
Carbohydrate – A group of organic compounds; which includes sugars (such as sucrose) and polysaccharides (such as cellulose, glycogen and starch). Carbohydrates contain carbon, hydrogen and oxygen, with the general formula Cx(H2O)y.
Carbon (C) – A non metallic element that exists in three allotropic forms; graphite, diamond and amorphous carbon. Carbon has an atomic number of 6, an atomic weight of 12.011 and a valency of 2,3 or 4. All organic compounds contain carbon. The carbon in fuels (such as coal, oil and natural gas) is released as carbon dioxide during combustion.
Isotopes of carbon:
Carbon – 12 is used as the standard for atomic mass. Its atomic mass is defined as 12.
Carbon – 14 is a radioisotope used in radiocarbon dating. It has a half-life of 5700 years.
Carbonaceous – Containing carbon.
Carbonate – A salt or ester of carbonic acid. Carbonate salts contain the divalent ion CO32-.
Carbon Capture & Storage (CCS) – A method of carbon dioxide sequestration where carbon dioxide is separated (e.g. from combustion waste gases) and stored in underground reservoirs, in order to prevent release into the atmosphere.
Catalyst – A substance that modifies and increases the rate of a reaction without being consumed in the process.
Pending update.
Decrepitation – The breaking up of certain crystals when exposed to heat. In terms of metal hydrides which can be cyclically heated to store and release hydrogen. This repeated making and breaking of bonds in the alloy’s structure can weaken it and eventually render it un-useable.
Diazotrophic Bacteria – Are bacteria that fix nitrogen gas (N2), taken from the atmosphere, into a bio-available form, such as ammonia, that can be used organisms.
Galvanic Cell Experiment: A common school experiment where an acidic fruit or vegetable, such as a lemon or potato, is used to demonstrate how a battery works. It involves converting chemical energy into electrical energy using a lemon (citric acid) or potato (phosphoric acid) and inserting two different metals as electrodes. The potential difference between the metals allows current to flow.
The electrodes used are usually a galvanised nail (i.e. zinc coated metal) and a copper penny. Copper is the positive electrode (cathode) and zinc is the negative electrode (anode). An electrochemical Redox reaction occurs. Zinc has a lower reduction potential than copper so it will be oxidised (lose electrons). The lemon / potato juice acts as an electrolyte allowing free movement of ions.
The acid in the lemon or potato contains H+ ions which are reduced to hydrogen gas in the reaction.
Zn → Zn2+ + 2e- (Oxidation)
2H+ + 2e- → H2 (Reduction)
If zinc and copper were connected by conductive wire in air; current would flow as a result of the difference in reduction potentials, with the zinc anode losing electrons to the copper cathode. This would continue until the force of repulsion, from the build up of electrons, equalled the force of attraction at the cathode.
However, when the electrodes are immersed in a conductive solution (lemon or potato), this is continuous (until the elements are consumed). So when the zinc and copper electrode are connected, using conductive wire, in a lemon / potato battery arrangement, the hydrogen ions are reduced at the copper cathode and a current is established in the conductive wire.
GCMS: Gas Chromatography Mass Spectroscopy. Technology combining gas chromatography and mass spectrometry that is used in the analysis of chemical substances.
Hypoxia – Low oxygen. The dissolved oxygen concentration of hypoxic water is usually less than 2 to 3 mg/l. Compare Anoxic.
Osmotic Power – Also known as salinity gradient power. Is the energy derived from the electrochemical potential difference between a concentrated salt solution (such as seawater) and a dilute salt solution (such as freshwater).
There are two practical methods; Reverse ElecroDialysis (RED) and Pressure Retarded Osmosis (PRO).
In Pressure Retarded Osmosis, a semi-permeable membrane is used which separates the freshwater and seawater. Freshwater permeates into the seawater compartment in order to equalize the salt concentration on both sides; which results in hydrostatic pressure build up in the seawater compartment which can be harnessed for energy production e.g. through application of this pressure to turn a turbine.
In Reverse ElectroDialysis, two membranes are used; one that is selectively permeable for positive ions and one for negative ions. Salt water is separated from the fresh water between the two membranes. Freshwater will lose both positive ions and negative ions. This charge separation produces a potential difference that can be utilized directly as electrical energy. The voltage obtained depends on the number of membranes in the stack, the absolute temperature and the ratio of the concentrations of the solutions, the internal resistance and the electrode properties.
According to current research (last updated November 2009), Reverse ElectroDialysis is seen as the most attractive option. See related article Green Light for Blue Energy.
Oxy-fuel combustion – The process of burning fuel using oxygen instead of air. Due to the composition of air, which contains mainly nitrogen, nitrogen oxides in the flue (waste) gas are greatly reduced. The resultant flue gas largely consists of carbon dioxide and is therefore much easier to sequester for carbon capture schemes.
Peak oil - Is the point in time when the maximum rate of global petroleum extraction is reached; after which the rate of production will start to decline until all the oil is used up. With less of it available, oil will become much more expensive as the reserves are depleted further.
The theory is based on the observed production rates of individual oil wells and the combined production of a field of related oil wells. The Hubbert Curve was proposed by, geoscientist, Marion King Hubbert; it depicts the aggregate rate of production increasing exponentially until peak oil is reached, followed by an exponential fall.
A comprehensive study of data relating to global oil reserves and peak oil was conducted by the UK Energy Research Centre in October 2009.
Permafrost - is ground that is permanently frozen, often to great depths. The surface can sometimes thaw in the summer; this thin surface layer is called the active layer.
Pressure Retarded Osmosis – See Osmotic Power.
The theory is based on the observed production rates of individual oil wells and the combined production of a field of related oil wells. The Hubbert Curve was proposed by, geoscientist, Marion King Hubbert; it depicts the aggregate rate of production increasing exponentially until peak oil is reached, followed by an exponential fall.
A comprehensive study of data relating to global oil reserves and peak oil was conducted by the UK Energy Research Centre in October 2009.
Permafrost - is ground that is permanently frozen, often to great depths. The surface can sometimes thaw in the summer; this thin surface layer is called the active layer.
Pressure Retarded Osmosis – See Osmotic Power.
Pending update.
Salinization: Occurs when there is a build up of salt in soil. This usually takes place in arid regions where the rate of transpiration is greater than the rate of precipitation and salts have been transported to surface soils; when the water evaporates the build up of salt is left behind. This effect is most common in desert regions, although mismanagement of irrigation can also lead to soil salinity, e.g. through use of saltwater or over abstraction leading to water table ingress from the seawater.
Excess salts hinder the growth of crops by limiting their ability to take up water. This is a problem exacerbated in desert regions where inhibited plant growth means that effective shielding using plants to prevent available water from evaporating, in the sun’s glare, cannot be used.
Stratosphere – The upper part of the Earth’s atmosphere where temperature decreases with altitude.
Subtropics - are the geographical zone of the Earth immediately north and south of the equatorial region, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S. The term "subtropical" describes the climatic region found adjacent to the tropics, usually between 20 and 40 degrees of latitude in both hemispheres.
Tillage – (In agriculture) It is the preparation of soil by ploughing, ripping or turning it.
Troposphere – The lower (ground level) part of the Earth’s atmosphere where temperature increases with altitude.
Volatile Organic Compounds (VOCs): Are organic compounds that evaporate readily under normal conditions; having a high vapour pressure and low water solubility. The European Union definition (April 2004) is; ” ..any organic compound having an initial boiling point less than or equal to 250°C measured at a standard pressure of 101,3 kPa”.
They can contribute to air pollution directly or by producing secondary pollutants through chemical or photochemical reactions. Methane, a potent greenhouse gas, is one example of a VOC. An example of a secondary pollutant is ozone which can be created when some VOCs react with nitrogen oxide in the presence of sunlight; when ozone is present in the lower atmosphere it poses a risk to human health by causing respiratory or cardiovascular problems (see post).
Man-made VOCs are used in the manufacture of paint, refrigerants and pharmaceuticals and are typically industrial solvents. In an enclosed area use of such substances can contribute to “sick building syndrome”.
Zooplankton – Are organisms that drift in columns of water in the oceans or in bodies of fresh water. They are usually heterotrophic which means they use organic carbon sources for growth. Their tiny size means that they can often be too small to distinguish, individually, with the naked eye. The name ‘zooplankton’ is derived from the greek for zoon (ζῴον) which means ‘animal’ and planktos which means ‘drifting’.
Pending update.
