1. ENG421 (4c) – Water Quality Management
Water Treatment Plant
- for surface water
- for groundwater
- for residual management

2. Water Treatment Plant for Surface Water (1 of 9)
Alternative water treatment trains may be used
depends on :
quality of surface water
water standard to be met
conventional water treatment
direct- and inline filtration treatment
direct-microfiltration treatment
reverse-osmosis treatment

3. Water Treatment Plant for Surface Water (2 of 9)
Conventional Water Treatment
used for surface waters with :
high turbidity (> 20 NTU)
high colour (> 20 cu)
high Total Organic Carbon (TOC > 4 mg/L)
process :
coagulation
flocculation
sedimentation
granular media filtration
disinfection
advantages :
good operational flexibility
hydraulically stable
low operator attention
disadvantage :
low surface loading rates
→ large process surface area requirements
consider land availability

4. Water Treatment Plant for Surface Water (3 of 9)
Conventional Water Treatment (cont)

5. Water Treatment Plant for Surface Water (4 of 9)
Direct- and Inline Filtration Treatment
used for higher quality surface waters with :
low turbidity (< 15 NTU)
moderate to low colour (< 20 cu)
low Total Organic Carbon (TOC < 4 mg/L)
process :
flash mixing
flocculation
granular media filtration (often coarse deep bed monomedia filters)
disinfection
Inline Filtration
same as direct filtration except
flocculation occurs in pipe (not in flocculation basin)
used for excellent quality surface waters with :
very low turbidity (< 5 NTU)
low colour (< 10 cu)

6. Water Treatment Plant for Surface Water (5 of 9)
Direct- and Inline Filtration Treatment (cont)

7. Water Treatment Plant for Surface Water (6 of 9)
Direct-microfiltration Treatment
used for good quality surface waters with :
low turbidity (< 10 NTU)
moderate to low colour (< 10 cu)
low Total Organic Carbon (TOC < 4 mg/L)
process :
screening system
cartridge filters or microscreens (and maybe coarse screens)
microfiltration membranes
configured in modules
disinfection
advantage :
plant may be readily automated
good for small or isolated sites

8. Water Treatment Plant for Surface Water (7 of 9)
Direct-microfiltration Treatment (cont)

9. Water Treatment Plant for Surface Water (8 of 9)
Reverse-osmosis treatment
used for
desalination of
seawater (35 g/L)
brackish water (0.5 – 30 g/L)
specific contaminant removal
e.g. natural organic matter (NOM) from surface water
colour from groundwater
process :
screening system
cartridge filters or microscreens
reverse osmosis (RO) membranes
disinfection

10. Water Treatment Plant for Surface Water (9 of 9)
Reverse-osmosis treatment (cont)

11. Water Treatment Plant for Groundwater (1 of 9)
Alternative water treatment trains may be used
depends on :
quality of groundwater
water standard to be met
conventional lime-softening treatment
membrane water softening
gas removal treatment
iron and manganese treatment

12. Water Treatment Plant for Groundwater (2 of 9)
Conventional Lime-softening Treatment
used to remove hardness from groundwater
hard water has total hardness > 150 mg/L
hardness is total of carbonate and noncarbonate hardness
high mineral content due to calcium (Ca2+) and magnesium (Mg2+)
process :
when hardness is mainly calcium (magnesium < 40 mg/L)
lime (and/or soda ash) is added (single stage process)
soda ash removes noncarbonate hardness
coagulation/flocculation/sedimentation
may occur in single basin

13. Water Treatment Plant for Groundwater (3 of 9)
Conventional Lime-softening Treatment (cont)

14. Water Treatment Plant for Groundwater (4 of 9)
Membrane Water Softening
used to remove
hardness from groundwater
colour
total organic carbon (TOC)
disinfection by-products (DBP)
process :
nanofiltration (more common)
membranes configured in modules
removes divalent ions
may be automated
good for small, remote plants
reverse osmosis
removes monovalent ions
disadvantage :
disposal of concentrated waste stream

15. Water Treatment Plant for Groundwater (5 of 9)
Membrane Water Softening (5)

16. Water Treatment Plant for Groundwater (6 of 9)
Gas Removal Treatment (aka air stripping)
used for groundwaters with :
undesirable gases
hydrogen sulphide
volatile organic compounds (VOC)
concentrations above maximum contaminant level (MCL)
process :
stripping tower
pressurised granular media filtration
disinfection
disadvantage :
must consider (and treat) off-gas from stripping tower

17. Water Treatment Plant for Groundwater (7 of 9)
Gas Removal Treatment (cont)

18. Water Treatment Plant for Groundwater (8 of 9)
Iron and Manganese Treatment
used for groundwaters containing inorganic iron and magnesium
process :
oxidation
oxidants used : chlorine
(when iron < 2 mg/L, little manganese)
potassium permanganate
(when iron and manganese are present)
oxygen
(effective with iron)
ozone
precipitation on pressure filters
disinfection

19. Water Treatment Plant for Groundwater (9 of 9)
Iron and Manganese Treatment (cont)

20. Treatment Processes for Residual Management (1 of 2)

21. Treatment Processes for Residual Management (2 of 2)

22. References
MWH, 2005, Water Treatment Principles and Design, 2nd ed., John Wiley and Sons, New York (TD430 .W ), pages