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Sewage Characteristics | Sewage Treatment Objectives | Sewage Treatment Methods | Sewage Treatment System | The Evolution Of Sewage Treatment
Sewage Treatment Methods
Historically unit operations have been grouped together to provide various levels of treatment. Preliminary and/or Primary Treatment refers to physical unit operations and is the first stage of treatment applied to any sewage. Secondary Treatment refers to biological and chemical unit processes, while Tertiary refers to combinations of all three.

Preliminary Sewage Treatment
Preliminary sewage treatment is defined as the removal of sewage constituents that may cause maintenance or operational problems with the treatment operations. This includes screening and comminution (grinding) for the removal of debris and rags, grit removal by sedimentation and flotation for the removal of excess oil and grease.

Primary Sewage Treatment
In primary treatment screening and sedimentation remove some of the suspended solids and organic matter. The effluent from primary treatment will contain high amounts or organic matter.

Secondary Sewage Treatment
Secondary sewage treatment is directed at the removal of biodegradable organic and suspended solids, mainly using biological unit processes. Disinfection may be included in secondary sewage treatment.

Tertiary Sewage Treatment
Tertiary sewage treatment includes the removal of nutrients, toxic substances including heavy metals and further removal of suspended solids and organic. Effluent from tertiary treatment is of a high standard and suitable for reuse.

There is no plan to build tertiary treatment systems in Malaysia. The focus has been providing a basic standard of preliminary, primary and secondary treatment.

Sewage inflow Preliminary Treatment Primary Treatment Secondary Treatment Tertiary Treatment effluent discharge
  screening sedimentation activated sludge filtration  
  grit removal floatation biofiltration disinfection  
  grease tank   sedimentation tertiary ponds  
  flow measurement        
  flow balancing        
  removal of rags, rubbish, grit, oil, grease removal of settleable and floatable materials biological treatment to remove organic and suspended solids biological and chemical treatment to remove nutrients and pathogens