Alternative Treatment Techniques

Question 1

Why do we need to look to alternatives

Answer 1

• Global perspective - western system of using drinking water to flush toilets is unsustainable
• N and P resources are treated as waste
• Central, large scale approach is expensive

Question 2

What criteria do we use to judge treatment techniques

Answer 2

affordability, sustainability (technology, expertise), acceptability, ecological footprint

Question 3

Individual Treatment of WW

Answer 3

• Robust performance:
  > strongly varying flow rate e.g. having guests over versus going on holiday
  > biofilm - prevents wash out of microorganisms
• User friendly installation and O&M

Question 4

Septic Tank

Answer 4

• Removal mechanisms: settling and flocculation of suspended material, flotation of fats and oils, partial biodegradation of organic matter (in anaerobic conditions)
• Suspended growth system
• No pre treatment but post treatment is required
• Not too much space needed
• No N or P removal

Question 5

Soil Adsorption Field

Answer 5

-treatment of water when percolating through soil
- Removal mechanisms: biofilm system
- Need pre treatment to remove suspended solids, often used as post treatment of septic tanks
- Large footprint/space required
- Limited N and good (initial) P removal

Question 6

Slow and fast sand filter

Answer 6

• Removal mechanism: physical filtration, aerobic microbial degradation
• Biofilm system
• Need pre treatment to remove suspended solids
• Small footprint
• Limited N and P removal

Question 7

Waste Stabilisation Ponds

Answer 7

• man made basins in series of:
  > Anaerobic pond: removal of BOD, sized according to volumetric organic loading (quantity of organic matter e.g. g of BOD5 per day applied to each m3 of pond)
  > Facultative pond: removal of BOD, removal of eggs and cholera, sized according to surface organic loading (quantity of organic matter e.g. daily applied per hectare of pond surface area)
  > Maturation pond: removal of viruses and bacteria, removal of N and P
• Removal mechanisms: sedimentation, (anaerobic and aerobic) microbial degradation, pathogen removal (pH and oxygen gradients), bacteria and algae interactions
  > Bacteria use wastewater BOD and O2 to produce new cells and CO2. Algae use light and CO2 produced from bacteria to make new cells and O2 for bacteria to use
  » Suspended growth system
  » Screening and grit removal needed for pre treatment
  » Very large footprint
  » N and P removal possible
• Suited for tropical countries - sunlight and ambient temperature are important
• High removal of pathogens means suitable for reuse in agriculture