Back Pressure
A pressure that can cause water to back flow into the water supply when a user’s water system is at a higher pressure than the public system.

Background Level
In air pollution control, the concentration of air pollutants in a definite area during a fixed period of time prior to the starting up or on the stoppage of a source of emission under control. In toxic substances monitoring, the average presence in the environment, originally referring to naturally occurring phenomena.

Bag Filter
Device containing large fabric bags, used to trap particles entrained in gas streams.

BATNEEC
Best Available Technique Not Entailing Excessive Cost.

BCURA
British Coal Utilisation Research Association.

Beryllium
An airborne metal hazardous to human health when inhaled. It can be discharged by machine shops, ceramic and propellant plants, and foundries.

Bioaccumulants
Substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolised or excreted.

Bioassay
Study of living organisms to measure the effect of a substance, factor, or condition by comparing before-and-after exposure or other data.

Biochemical Oxygen Demand (BOD)
A measure of the amount of oxygen consumed in the biological processes that break down organic matter in water. The greater the BOD, the greater the degree of pollution.

Biodegradable
Capable of decomposing rapidly under natural conditions.

Biomass
(1) the amount of living matter in an area, including plants, large animals and insects; (2) plant materials and animal waste used as fuel.

Bioremediation
Use of living organisms to clean up oil spills or remove other pollutants from soil, water, or wastewater; use of organisms such as non-harmful insects to remove agricultural pests or counteract diseases of trees, plants, and garden soil.

Biosphere
The portion of Earth and its atmosphere that can support life.

Bottom Ash
The non-airborne combustion residue from burning pulverised coal in a boiler; the material which falls to the bottom of the boiler and is removed mechanically; a concentration of the non-combustible materials, which may include toxics.

BS
British Standard.

BSI
British Standards Institute.

BSP
British Standard Pipe.

Buffer
A solution or liquid whose chemical makeup neutralises acids or bases without a great change in pH.