Classification of Unit Processes
Physical Process
Processes that remove pollutants using physical properties of pollutants or water.
Example: Sedimentation, flotation, screening, and filtration.
Chemical Process
Processes that utilize chemical properties of water and require the addition of chemicals to remove impurities.
Example: Neutralization, softening, absorption, precipitation.
Physiochemical Process
Term used when both physical and chemical processes are combined.
Biological Process
Processes that use microorganisms (bacteria) to remove organic pollutants.
Example: Activated sludge process, trickling filter, rotating biological contactor, etc.
Classification of Treatment
1. Primary Treatment
Physical and chemical processes, such as screening, sedimentation, and filtration, used to remove floating and suspended solids.
Approximately 30% of BOD (biological oxygen demand) is typically removed in primary treatment.
2. Secondary Treatment or Biological Treatment
Biological processes are used to remove dissolved organic matter, converting it into biomass (concentration of bacteria).
3. Tertiary or Advanced Treatment
Combination of physical, chemical, and biological processes used to remove nutrients and pollutants not efficiently removed in primary and secondary treatments.
Tertiary treatment focuses on removing nutrients (nitrogen, phosphorus) and achieving disposal standards.
Advanced treatment ensures treated wastewater meets permissible limits set by regulatory authorities (e.g., GPCB or CPCB).
If treated wastewater is not to be used for beneficial purposes (re-use).
Examples: Irrigation, recreational activities.
If treated wastewater is to be recycled:
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