Definition of pretreatment:
Pretreatment is a process in which a facility reduces, alters, or eliminates pollutants in wastewater before releasing it to the CETP or the environment. The pretreatment process may or may not generate sludge.
Some examples of treatment processes (but not limited to) are listed below and may be installed as standalone systems or integrated into a complete treatment system in the facility, which may or may not generate sludge.
Screening, grit removal
pH correction
Chemical/electro-chemical coagulation and flocculation
Lamella settling
Dissolved air flotation
Primary sedimentation
Activated sludge process (ASP)
Oxidation ditch
Sequential batch reactor (SBR)
Rotating biological disks
Moving bed bioreactor (MBBR)
Membrane bioreactor (MBR)
Anaerobic digestion
UASB reactor
Aerated ponds
Filtration (sand/disk/high rate)
Activated carbon adsorption
Chemical/UV/Ozone disinfection
Membrane technologies (MF/NF/UF/RO)
Thermal/Membrane evaporation
Crystallization
Electrochemical oxidation/Fenton’s reaction
Ion exchange
Photocatalytic degradation
The processes below, when installed as a standalone system, cannot be considered as pretreatment :
●Equalisation tank/homogenisation tank (if no chemicals are added in the equalisation tank/homogenisation)
The processes below, when installed as a standalone system, are to be considered as pretreatment:
● Grit removal irrespective of the mesh size (In this case, the residue collected from the filters or mesh, irrespective of its size, should not be classified as sludge, as this generally consists of textile fibres or solid waste and not sludge; it should be classified as Indirect with pretreatment (without sludge) if installed as a standalone treatment step).
● Equalisation tank/homogenisation tank (if chemicals are added in the equalisation tank/homogenisation and generate sedimentation, which is collected and disposed of by the facility, then this should be classified as sludge)