Glossary
Key terms from wastewater and sludge treatment, explained briefly.
TSS
Total suspended solids - solid particles that can be separated from wastewater by filtration. Measured in mg/l.
BOD5
Biochemical oxygen demand over five days - a measure of biologically degradable organic pollution.
COD
Chemical oxygen demand - overall measure of oxidisable organic and inorganic substances.
DAF
Dissolved Air Flotation - separation of suspended and floating matter by micro bubbles.
Decanter
Centrifuge for mechanical solid-liquid separation of sludge at high throughput.
Discharge limit
Legally defined maximum value for pollutants in the effluent of a treatment plant or indirect discharge.
Precipitation
Chemical process converting dissolved substances such as phosphorus into settleable solids.
Flocculation
Agglomeration of fine particles into larger flocs by adding flocculation aids (polymers).
Float sludge
Sludge accumulated at the water surface by flotation and skimmed off.
Indirect discharger
A plant discharging wastewater into the public sewer rather than directly into a water body.
Coagulation
Destabilisation of colloidal particles by adding coagulants such as ferric chloride or PAC.
Membrane filtration
Pressure-driven filtration through semipermeable membranes (MF, UF, NF, RO).
P removal
Targeted removal of phosphorus from wastewater by precipitation or biological processes.
Pile cloth media
Special filter fabric with a pile structure for fine particle filtration.
Polymer
Long-chain molecule (cationic or anionic) used for flocculation and conditioning of sludge and wastewater.
Screw press
Mechanical dewatering unit with a slowly rotating screw inside a screen basket.
Tertiary treatment
Third treatment stage in wastewater treatment - polishing filtration after biology.
DS
Dry solids - solids content of a sludge after drying, given in percent.
Cloth filter
Filter unit with textile filter media (cloth discs) for fine and ultra-fine filtration.
Retention time
Average residence time of the wastewater in a treatment step.
Water reuse
Treatment and reuse of treated wastewater as service or process water.