De-dusting - Process designed to remove particulate matter created in the power generation process. Electrostatic precipitators create an electric field that essentially captures particulates; up to 99% of particulates in gas can be captured in this way.

De-NOx (Denitration) - System that removes nitrogen oxides from flue gas.

Desalination - Process that removes salt and other minerals from saline water (such as sea water) in order to make it suitable for human consumption or irrigation.

De-SOx (Desulfurization) - System that removes sulfur oxides from flue gas.

Diesel oxidation catalysts (DOC) - Designed to oxidize carbon monoxide, gas phase hydrocarbons and the sulfur component of diesel particulate matter thereby creating carbon dioxide and water. Has been shown to reduce emission by up to 50%.

Diesel particulate filters (DPF) - Filters that use silicon carbide blocks in the exhaust systems of locomotives to trap particulate matter. Can reduce emission by up to 80%.

Digital substations - Automated and computerized substations that provide greater transparency, higher reliability and efficiency of operations.

Dimethyl ether (CH₃OCH₃) - Considered a clean burning hydrocarbon fuel, CH₃OCH₃ is produced by the gasification of coal or natural gas. Considered to have potential as a synthetic biofuel.

Discharge rate - Rate at which pollutants or other materials are emitted into the environment, i.e. the amount of solid, liquid or gaseous material emitted over a period of time.

Disinfection - Process that involves the removal of pathogenic organisms from water via the use of chlorine and ultraviolet light, among other applications.

Distributed generation - Small-scale power generation technologies (typically in the range of 3 kW to 10,000 kW) used to provide an alternative to or an enhancement of the traditional electric power system. Power generation is achieved on-or-off-grid, as opposed to large-scale centralized power plants.

Distribution materials and components - Pipes, valves and nozzles that are used to transport water, primarily between treatment plants and usage points.