Glossary

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D

Dealkalinisation

Any process that serves to reduce the alkalinity of water.

Decarbonation

The process of removing carbon dioxide from water, using contact towers or air scrubbers.

Degasification

The process of removing dissolved gases from water, using vacuum or heat.

Deionisation

Process that serves to remove all ionised substances from a solution. Most commonly is the exchange process where cations and anions are removed independently of each other.

Demand management

Measures taken by water companies and others to manage households and non-household demand for water. Measures include leakage management, water efficiency and metering.

Demineralisation

Processes to remove minerals from water, usually the term is restricted to ion exchange processes.

Denitrification

Removal of nitrate and nitrate product from water to produce a quality that answeres common water standards.

Desalination

The removal of dissolved salts from water by distillation, reverse osmosis, de-ionization, electrodialysis or freezing.

Descriptive consent

A consent under which discharges are controlled by imposing general rather than numerical standards.

Dewater

The separation of water from sludge, to produce a solid cake.

Digester

A closed tank for wastewater treatment, in which bacterial action is induced to break down organic matter.

Direct run-off

Water that flows from the ground surface directly into streams, rivers and lakes.

Discharge consent

A legal document which gives permission to discharge and sets out the terms under which the discharge should be made.

Disconnection

Separation of a customer's supply from the public water network.

Disinfection

The destruction of pathogens by physical or chemical means.

Disinfection by-products (DBPs)

The residual substances formed by disinfection.

Dissolved air flotation (DAF)

A procedure of induced flotation with very fine air bubbles or 'micro bubbles'.

Dissolved oxygen (DO)

Oxygen dissolved in a liquid, the solubility depending on temperature, partial pressure and salinity, expressed in milligrams per litre. Tables giving values for the solubility of oxygen in water have been published in standard methods.

Dissolved solids

Solids material that totally dissolves in water and can be removed by means of filtration.

Drought

A prolonged period of dry weather; said to exist if, for at least 15 days, on each day, rainfall has been less than 0.25mm.

DWF

Dry Weather Flow.

DWI

Drinking Water Inspectorate. The body responsible for assessing the quality of drinking water in England and Wales.

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