The hybrid treatment system can be a combination of various
unit operations and processes in order to improve the wastewater
effluent quality. Fig. 1 shows a broad spectrum of the possible
combinations of the hybrid system between physical, chemical
and biological processes. Hybrid system can be defined as any
processes which fall inside the green region. Unit operations and
processes are grouped together to provide various levels of treatment
usually known as preliminary, primary, advanced primary,
secondary (without or with nutrient removal) and advanced (or
tertiary) treatment.