Water and Sewage Treatment

Question 1

Wastewater treatment process

Answer 1

1. Screening and Grit removal
2. Primary Settlement
3. Secondary Treatment ‘Biological’ Stage
4. Final Settlement
5. Disinfection
6. Outfall

Question 2

Sludge Treatment Process

Answer 2

1. Thickener
2. Sludge digester
3. Sludge storage
4. Sludge dewatering
5. Disposal

Question 3

Sewerage Treatment Works Process

Answer 3

1. Preliminary Treatment (settlement tanks, sedimentation)
2. Primary Treatment (Settlement tanks, Sedimentation)
3. Secondary Treatment (biological treatment, filtration)
4. Tertiary Treatment (Disinfection, further filtration)
5. Final Effluent

Question 4

Preliminary Treatment (STW)

Answer 4

1. Screening (remove plastic, rags, sticks) at 0.03m3/day/1000population
2. Grit Removal (remove inorganic material using constant velocity channel, grit traps or detritors)
3. Flow control (flumes or flow measurement devise and will divert flow to storm tanks)

Question 5

Primary Treatment (STW)

Answer 5

Allows the remainder of the solids to settle out.

• Horizontal flow tanks (4:1 length:breadth)
• Radial Flow
• Upward Flow
• Septic Tank

Question 6

Secondary Treatment (STW)

Answer 6

1. Biofilters (bacteria bed, the settled sewage and oxygen combine with bacteria which eats other organisms)
2. Activated Sludge (conventional treatment of wastewater in an activated sludge plant) - filling, mixing, aeration, settlement and drainage.

Question 7

Tertiary Treatment (STW)

Answer 7

Only required is drinking water abstraction occurs downstream, discharge recharges groundwater or low dilution in watercourse. This is done by:

1. Additional settlement - Lagoons
2. Irrigation - Grass plots
3. Straining - Microstrainer
4. Filtration - Sand filters, membrane filtration
5. Disinfection - UV