1. History of and Current Trends in
History of Wastewater Treatment
History of and Current Trends in
Wastewater Treatment
With input by Lee Walker

2. History of Wastewater Treatment
Before 10,000 BC
nomadic tribes allowed the soil to treat it
After establishing townships
approach continued
throw wastes into the streets
street levels rose
raise the doors to their houses
Egypt 2100 BC
only for elite: waste was removed and dumped into rivers

3. History of Wastewater Treatment
1500 BC: Isle of Crete
advanced plumbing and drainage systems
open sewers built of stone
royal household had flushing toilet
last group to use flushing toilets until 1596

4. History of Wastewater Treatment

5. History of Wastewater Treatment
300 BC
Greece: most developed waste management of any civilization prior to the nineteenth century.
Banning the dumping of waste into the streets.
For 800 y Greek government removed waste at the expense of landowners.
Greeks and Romans discovered the link water quality  public health.
Underground sewer network in Rome  Tiber river

6. History of Wastewater Treatment
Dark Middle Ages:
Fall of the Roman Empire  knowledge lost for 1000 y.
Old practice of simply throwing their waste into the streets. 
No separation drinking water and human wastes.
Wastes transferred from waste pits into drinking wells
Epidemics raged in the cities
dysentery, typhus (which comes from bad sanitation)
typhoid fever (from human feces and urine)”
major plagues of the 12th century waste management became a priority

7. History of Wastewater Treatment
16th Century
No change in the understanding and disposal of human wastes.
Some idea of the capacity of polluted rivers to clean themselves (microbes were not understood yet)
Successful for smaller communities.
London collected sewage but dumped into Thames
Cheap method dead river.
With population increases water bodies could no longer treat the high wastewater flows.
What was limiting ? Oxygen  Anaerobic rivers
Alternative treatment became necessary.

8. History of Wastewater Treatment
1860 Septic tank
Perceived link between solids and health
Treat sewage from an entire community
Remove solids, untreated liquid discharged to river
1868 Sand bed filter
to filter septic tank effluent before discharge to river
(No oxygen supply)
1893 Rock Trickling filters
to treat septic tank effluent
(Better oxygen supply, little bacterial biomass present)
Lagoons

9. Effects of Waste Water Disposal
Pathogens  Epidemics
Solid Organics Building up in environment  Long term pollution (river sediments)Oxygen depletion in rivers  Death of higher life
Dissolved organics  Oxygen depletion  Death of higher life
Nutrients (N and P)  Algal blooms  Buildup of solid organics  Decay  Oxygen depletion  Death of higher life
Odor, colour,…

10. Waste Water Analysis Pathogens  Bioessays
Solid Organics Filter or centrifuge sample. Dry residue  Total suspended solids TSS. Ash the TTS Loss is solid organics = volatile suspended solids = VSS
Dissolved organics
COD : Chemical Oxygen Demand (mg/L of O2) = The amount of oxygen required to oxidize soluble organics by an acidic dichromate solution.
BOD : (Biological Oxygen Demand) (mg/L of O2) = The amount of oxygen required for microbial removal of soluble organics over a 5 day period.
Nutrients (N and P) : Present as ammonia and phosphate  algae blooms  algae decay  sec. pollut.

11. Example WW composition
Wastewater Required
composition Levels
BOD (mg/L)
TSS (mg/L)
NH3 Nitrogen (mg/L)
Phosphorus (mg/L) No Limit
Fecal Coliforms (/100 mL) < 14 (CFUs)

12. Why not Lagoon Treatment
Large shallow ponds, 1.2 to 2.4 meters in depth.
Not mixed or aerated  Mostly anaerobic.
Long treatment times, odor emission.
Algae growth  Secondary pollution
Can work as “Integrated System” for agricultural areas
Nutrients  Algae  Zooplankton  Fish 
Not suitable for highly populated areas
Average treatment time = Hydraulic Retention time = HRT = 20 to 200 days  Huge reactor volume
(for Perth about 500 to 1000 Subiaco Stadiums).

13. Why not Lagoon Treatment
Why long treatment times?
Lagoon = chemostat with low productivity. Why?
Efficiency limited by biomass levels and by oxygen.
(Efficiency ~ Productivity (R) of chemostat is proportional to the amount of biomass (X) present)
Design a waste water treatment plant with high X.
Purpose of plant:
Remove organics (COD, BOD)
Remove nutrients (N and P)
Allow re-use of water in the future.
Biomass must be retained longer than the water

14. Theoretical Effect of biomass feedback
Dotted line no feedback:
Washout occuring early
4-fold Feedback approximately:
4*X 4*R  1/4* S
allows 1/4 reactor size to do same work
Feedback essential for pollutant removal. Can be used 100-fold  100-fold smaller treatment plant
Note: same assumed feed concentration (SR) SR X
Steady State Concentration R S D
Dcrit
Biomass Retention in WWTP

15. Biomass Retention in WWTP
How to Retain Biomass ?
Filters don’t work.
Gravity separation needed.
Settling velocity of small particles is proportional to their size (Stokes law).
Floc formation is essential to allow gravity separation.
Settling velocity must be > 1m/h.
Settling can’t happen during aeration and mixing
Use external settlers = Clarifiers
Intermittent stopping of aeration and mixing = Sequencing batch reactor
Biomass Retention in WWTP

16. Problems with floc formation
Pros and Cons of Floc formation for bacteria?
+ Shelter from predators (Protozoa)
- Diffusion problems of BOD and O2
Continuous presence of low levels of BOD (feed) will favour suspended or filamentous bacteria growth
 no settling
 breakdown of plant performance.
Single cells or filaments have
a higher surface area and allow facilitated diffusion.
a lower apparent Ks value for substrate.
Running treatment plant like a chemostat
would result in continuous substrate (BOD) limitation
 no flocs  no settling  low biomass  breakdown
Biomass Retention in WWTP

17. detrimental to gavity settling
Growth of filamentous bacteria favoured by low substrate (BOD) concentrations;
detrimental to gavity settling
floc
Biomass Retention in WWTP

18. Use of Clarifier for Biomass Retention via external biomass feedback
Centrifuging of recycle liquid
Membrane filtration of recycle liquid
Flocculation
Gravity settling of flocculated biomass
Inflow
Outflow
Clarifier
Recycle
(Feedback)
Biomass Retention in WWTP

19. Problems with floc formation
To encourage floc formation: need to expose biomass to high feed levels (BOD) by:
Plug flow system and clarifyer
SBR
Using of a bioselector (not examinable)
Plug Flow system :
The feed and biomass is mixed at entry and moves through the process as plug
Intermixing with the previous and following plug is minimised
Biomass Retention in WWTP

20. Plug flow waste water treatment allowing high BOD levels at the beginning
Clarifier
Influent
BOD Gradient
Effluent
Waste Sludge
Return Activated Sludge
Air Line
A fraction of the sludge is wasted and provides a Solids Retention Time (SRT). SRT is the average length of time the sludge is in the system before being removed.
The liquid retention time (hydraulic retention time = HRT) is a few hours while the SRT is about days
Biomass Retention in WWTP

21. Activated sludge reactors
Thickener
Biomass Sedimentation
Elledge WWTP

22. Use of Sequencing Batch Reactor (SBR) for a) Biomass Retention via internal biomass feedback b) floc formation by oxposing biomass to a sudden high inflow of biomass
Cycle
Fill
Aeration
Settle
Decant
Influent
Effluent
Waste Sludge
Biomass Retention in WWTP

23. Use of Bioselector to allow contact with bacteria and high BOD (not examinable)
Hybrid between plug flow reactor and SBR
Incoming wastewater is mixed with return activated sludge
in an SBR. System used at Woodman Point Treatment plant
Biomass Retention in WWTP

24. SBR treatment plant in Western Australia

25. Comparison between Plug flow and SBR
Traditional plug flow wastewater treatment
liquid pumped from one compartment to another
phases were separated in time and space
Sequencing batch reactor
all phases occur in the one reactor
phases separated only by time
no need for additional clarifyer
Phases of operation
fill, aerate, settle and decant
Not a continuous process - batch
Biomass Retention in WWTP