1. ENG421 (12c) – Desalination and Waste Handling
- types of residuals
Residual Treatment
Management of Residual Liquid Streams
Management of Membrane Concentrate
Management of Residual Sludges

2. General Water Treatment Technologies (Week 4)
Treatment technologies (unit operations and processes) used determined by what needs to be removed, inactivated or modified

3. Waste Handling (1 of 9) - aka residuals management
planning, design and operation of facilities
to reuse or dispose of water treatment residuals
- wish to minimise amount of material that must ultimately be disposed of, by
recovering recyclable materials
reducing water content of residuals
- cost of transporting and ultimately disposing of residuals
major fraction of residual management costs
→ reduce quantity of material (economic solution)
- must also minimise environmental impacts and meet regulatory discharge requirements
- may impact on design and operation of water treatment plant

4. Waste Handling (2 of 9) Residuals from the treatment of water
- sludges from water treatment processes
- liquid wastes from water treatment processes
- liquid wastes from processes
to thicken process sludges
to treat liquid wastes
- gaseous wastes (e.g. offgases)
from specialised water treatment processes

5. Waste Handling (3 of 9)
Sources of solid residuals from the treatment of water

6. Waste Handling (4 of 9)
Sources of liquid residuals from the treatment of water

7. Waste Handling (5 of 9)
Sources of miscellaneous residuals from the treatment of residuals from water treatment

8. Waste Handling (6 of 9)

9. Waste Handling (7 of 9)

10. Waste Handling (8 of 9) Amounts of residuals generated
up to 5 % of raw water entering treatment plant
most becomes filter waste washwater (granular and membrane)
contains <10% removed solids
underflow from sedimentation basins
contains only 0.1 – 0.3 % of plant flow
but has most of solids removed

11. Waste Handling (9 of 9)
Constituents in residuals (sludges and liquids) to consider :
pathogenic micro-organisms
Giardia cysts, Cryptosporidium oocysts
turbidity, particles
disinfection byproducts (DBPs)
precursors in DBP formation (natural organic matter)
total organic carbon (TOC)
taste-causing compounds
odour-causing compounds
synthetic organic compounds (SOCs)
manganese and iron
arsenic and other toxic compounds
radioactive material
dissolved solids and salt
normally return liquid from these wastes to treatment plant
but may treat with separate facilities if concerns significant

12. Residual Treatment (1 of 6)
Past treatment of residuals :
discharge to nearby streams or rivers
stored in lagoons
spread on land (little or no processing)
this approach led to :
discolouration or increased turbidity of receiving waters
build up of sludge deposits in receiving waters
occupying large areas of land with constructed lagoons
impacts on fish via
increased water turbidity, pH, water hardness
high salt levels in some situations
sludge spread on land prevents or inhibits plant growth
sludge mixed with soil has reduced impact (not too much)

13. Residual Treatment (2 of 6)
Treatment of residuals :
must understand properties of residuals (measure)

14. Residual Treatment (3 of 6)
Treatment of residuals (cont) :
Coagulation sludges
produced by coagulation and natural settling of particles
sludges collected in sedimentation basins and on filters

15. Residual Treatment (4 of 6)
Treatment of residuals :
Coagulation sludges (cont)

16. Residual Treatment (5 of 6)
Treatment of residuals (cont) :
Granular Media Filter and Membrane Filter Waste Washwater
from the cleaning of granular or membrane filters

17. Residual Treatment (6 of 6)
Treatment of residuals (cont) :
Reverse Osmosis and Nanofiltration Concentrate
liquid wastes high in dissolved solids and low in suspended solids
concentrations of dissolved salts much higher than feed stream
5 – 10 times higher

18. Management of Residual Liquid Streams (1 of 2)
treatment options
flow equalisation with or without chemical addition
reduces impact of intermittent high volume backwash flows
lagoons with or without chemical addition
batch sedimentation with or without chemical addition
high-rate sedimentation with or without chemical addition
dissolved air flotation
granular filtration
membrane filtration
disinfection
UV oxidation
discharge to
surface waters
wastewater collection
sewers

19. Management of Residual Liquid Streams (2 of 2)
Management of residual liquid streams (cont) :
High-rate clarification

20. Management of Membrane Concentrate (1 of 5)
must consider
volume of concentrate
may be 50% of flow to plant
environmental classification and regulations
due to high salt levels
treatment options
membrane concentration
may be followed by crystallisation or solar evapouration
evapouration/distillation
solar evapouration
crystallisation
deep-well injection
discharge to
surface waters
wastewater collection
sewers

21. Management of Membrane Concentrate (2 of 5)
Management of membrane concentrate (cont) :
evapouration/distillation
boiling with submerged tube heating surface
boiling with long tube vertical evapourator
flash evapouration
forced circulation with vapor compression
solar evapouration
rotating surface evapouration
wiped surface evapouration
vapor reheating process
vertical tube falling film evapourator

22. Management of Membrane Concentrate (3 of 5)
Management of membrane concentrate (cont) :
solar evapouration
evapouration ponds
glass covered solar ponds
consider effects of
relative humidity
wind velocity
barometric pressure
water temperature
salt concentration
rain

23. Management of Membrane Concentrate (4 of 5)
Management of membrane concentrate (cont) :
crystallisation
convert thickened concentrate into crystals
crystals dewatered in centrifuge or belt press
dispose of crystals to landfill

24. Management of Membrane Concentrate (5 of 5)
Management of membrane concentrate (cont) :
deep-well injection
pump concentrate into an injection well (1000s m deep)
injection zone is usually brackish or saline aquifer
under thick layers of impermeable rock
prevents contamination of shallower freshwater aquifers

25. Management of Residual Sludges (1 of 8)
treatment options

26. Management of Residual Sludges (2 of 8)
Management of residual sludges (cont) :
alum sludge
1. gravity thickening → chemical conditioning → centrifuge → landfill
2. sludge lagoons → decant recovery and recycle → landfill (or sewerage)
membrane concentrate
directly to :
brackish surface water
ocean
deep-well injection
sewerage

27. Management of Residual Sludges (3 of 8)
Management of residual sludges (cont) :
gravity thickening

28. Management of Residual Sludges (4 of 8)
Management of residual sludges (cont) :
dissolved air flotation thickening

29. Management of Residual Sludges (5 of 8)
Management of residual sludges (cont) :
sludge lagoons
non-mechanical
requires sufficient, cheap land (makes lagooning cost effective)

30. Management of Residual Sludges (6 of 8)
Management of residual sludges (cont) :
vacuum filtration

31. Management of Residual Sludges (7 of 8)
Management of residual sludges (cont) :
plate and frame filter presses

32. Management of Residual Sludges (8 of 8)
Management of residual sludges (cont) :
belt filters

33. References
Masters, G.M., 1998, Introduction to Environmental Engineering and Science, Prentice Hall, Upper Saddle River, pages 286 – 287
MWH, 2005, Water Treatment Principles and Design, 2nd ed., John Wiley and Sons, New York (TD430 .W ), pages 1429 – 1506, 1641 – 1708
Nemerow, N.L. et al, 2009, Environ Eng : Water, Wastewater, Soil and Ground, 6th ed., John Wiley and Sons, New York (TD430 .E ), page 162
Parsons, S.A. and Jefferson, B., 2006, Introduction to Potable Water Treatment Systems, Blackwell, Oxford (TD430 .P ), pages 165 – 176