1. Unit 2.2 Treatment Mechanims
Online Course Faecal Sludge Management
Developed by UNESCO-IHE and SANDEC
January 2016
Unit 2.2 Treatment Mechanims
Mariska Ronteltap,
Senior Lecturer Sanitary Engineering UNESCO-IHE

2. Treatment mechanisms
Many treatment systems for FS: based on systems for wastewater treatment and treatment of wastewater sludge
Not the same thing!
Major differences: high variability in concentration of all constituents

3. Important properties of FS
Degree of stabilisation
Organic load
Particle size and density
Dissolved oxygen (typically low!)
Temperature pH
Water content
Viscosity

4. Treatment mechanisms for FSM
Current understanding limited; mainly empirical
More knowledge -> better design of treatment technologies!
Physical
Chemical
Biological

5. FSM treatment processes
Physical treatment

6. Physical treatment FSM
Dewatering
Drying
Volume reduction
Dewatering most important:
Water expensive to transport!
No water = (almost) no pathogens
Essential for resource recovery (compost, fuel)

7. Physical treatment FSM - processes
Evaporation
Evapotranspiration
Filtration
Gravity separation
Centrifugal force
Pressure

8. Water content in FS Free / bulk water Interstitial water
Surface / colloidal water
Intracellular water

9. Water content in FS Free: most easily removed
Interstitial: bound in pores, by capillary forces
Surface: bound to solids via adsorption / adhesion
Intracellular: within cells, only removed by destructing cells
Physically bound water: only removed by chemicals, centrifugation, pressure and evaporation

10. Filtration Media through which filtration can take place: Membranes
Sand
Rocks, gravel
Types:
Slow filtration (0.1 – 0.4 m/h)
Gravity driven
Pressurised
Granular media

11. Filtration in FSM
Most common: unplanted and planted sludge drying beds

12. Evaporation Transpiration Energy provided by the sun
Functionality influenced by climate
Factors: heat; humidity; wind (to transport moist air)
Transpiration
By plants
Factors: plant species; growth phase; plant density; leaf shape and colour; water availability in root zone
Evapotranspiration: combination

13. Centrifugation of FSM Quite common for WWTPs
In FS: for partial removal of bound water (cells break up)
However: high energy costs!

14. Heat drying Evaporation of free water at the surface
After that: internal water is brought to the surface for evaporation
Direct drying systems: principle is convection
Indirect drying systems: conduction
Infrared drying systems: radiation
Restriction: again energy, and ammonia gas!

15. FSM treatment processes
Chemical treatment

16. Chemical treatment FSM
To improve performance of physical treatment
To inactivate pathogens
However: keep costs in mind!
Typically two forms:
Alkaline addition
Ammonia addition

17. Alkaline addition
Alkaline addition typically for stabilisation of sludge
After addition:
pH rises to 12
Microbes are inactivated
Smell and pathogens are reduced
Larger molecules are broken up / hydrolysed
With CaO: also temperature goes up, double effect!
Concerns: NH3 volatilisation; scaling

18. Ammonia addition Aqueous ammonia also inactivates microorganisms
pH has to be >8.5 because of NH3/NH4+ equilibrium
Addition typically in the form of urea
As long as pH is high -> no regrowth
When applied to the soil: pH goes down, and NH4+ becomes available as a fertiliser, which is a benefit over other chemicals
Dosing: trial! pH is important indicator (combined with duration)

19. Chemical addition: MSc research 2014
Biodigester in India
10 cows, 1 family toilet
40 days HRT (long)
Good results with lime and urea!
Urea subsidised -> cheaper in India

20. Different additions to dried slurry
lime treatment
Faecal contamination is reduced to less than 1 cfu/g using;
10 g/l industrial grade lime or
20 g/l locally available lime
urea treatment
12.5 g/l urea
chemical or natural treatment
High solid concentration hence require dilution with raw/grey water. Further studies require for possibility of use of grey water.
When compared, urea and natural both has no additional cost burden on user.

21. Results- lime treatment- E.coli in different type of slurry

22. FSM treatment processes
Biological treatment

23. Biological treatment
In theory, the following biological treatments are possible:
Aerobic treatment
Anaerobic treatment
Composting
Main reason: stabilisation!
“Stabilisation involves the degradation of putrifiable, readily degradable material, leaving behind more stable, less degradable organics.
Stabilised organic matter does not have an exact agreed upon scientific definition, but in general refers to resistant to further biodegradation.”

24. Biological treatment
However, depending on the source of the sludge, it may be more resistent to biological treatment.

25. Mechanisms -> applied in technologies
Physical
Chemical
Biological
Treatment taking place in technologies.
These technologies will be discussed in the next units!