1. Biological Treatment Processes

2. Outline Overview 3.1 Criteria for Successful Biological Treatment
3.2 Principles of Biological Reactions
3.3Wastewater Treatment Ponds
3.4 Anaerobic Treatment Processes

3. Wastewater Treatment Primary Physical process Secondary Biological
Tertiary
Combination

4. 2.1 Overview of Treatment Processes
Preliminary & Primary Treatment
Physical / chemical processes to prepare wastewater for biological treatment
Removal of solids mainly
Usually cheaper/ easier than secondary processes
Examples:
a. equalisation (flow and load),
b. neutralisation,
c. settling of solids,
d. flotation of oil and grease,
e. filtration etc

5. 2.1 Overview of Treatment Processes
Secondary Treatment
Biological removal of biodegradable, mostly soluble organic compounds (carbon removal)
Aerobically
activated sludge plants,
aerated ponds
trickling filters etc.
Anaerobically
non-aerated ponds,
high rate anaerobic (biogas) plants

6. In general, costs increase with increasing degree of treatment
Tertiary Treatment
Removal of specific pollutants with physical, chemical and/or biological methods
Examples:
a. adsorption of organics by activated carbon
b. precipitation or flocculation of phosphate etc.
c. biological nitrogen removal
d. disinfection
In general, costs increase with increasing degree of treatment

7. Wastewater Treatment Primary Physical process Secondary Biological
Tertiary
Combination

8. Outline Overview 3.1 Criteria for Successful Biological Treatment
3.2 Principles of Biological Reactions
3.3Wastewater Treatment Ponds
3.4 Anaerobic Treatment Processes

9. 3.1 Criteria for Successful Biological Treatment
Produce biological catalyst (biomass)
source of energy
source of cellular components (C, H, N, O, P, S etc.)
Maintain biomass
adequate environment (T, pH, toxics)
adequate retention time (rate of treatment)
Separation of biomass
grow suitable types of organisms ie. floc forming bacteria

10. Outline Overview 3.1 Criteria for Successful Biological Treatment
3.2 Principles of Biological Reactions
3.3 Wastewater Treatment Ponds
3.4 Anaerobic Treatment Processes

11. 3.2 Principles of Biological Reactions
A. Three Important Biological Reactions
Aerobic
CHO + O2  biomass + CO H2O
≈ 50 % ≈ 50 %
respiratory metabolism
Anaerobic
CHO  biomass + CO2 + CH4 + H20
% %
fermentative metabolism
Photosynthesis
CO2 + H2O  biomass + O2
energy supplied externally (light)

12. B. Aerobic or Anaerobic ?
1000
100
10000
100000 1 10
0.1
Wastewater COD (mg/L)
Hydraulic Retention Time (days)
Aerobic treatment
Anaerobic digestion
High Rate Anaerobic
Treatment
Low Rate Anaerobic

13. 3.2 Principles of Biological Reactions
C. Nutrient Requirements
"Major" elements: C, H, O, N
"Minor" elements:
P  DNA/RNA, phospholipids, ATP
S  for proteins, amino acids
K  in RNA, coenzymes
Mg  in RNA, coenzymes, as cation
Trace elements
Often essential: Ca, Mn, Fe, Co, Cu, Zn
Rarely essential: B, Na, Al, Si, Cl, V, Cr, Ni, As, Se, Mo, Sn, I

14. Outline Overview 3.1 Criteria for Successful Biological Treatment
3.2 Principles of Biological Reactions
3.3 Wastewater Treatment Ponds
3.4 Anaerobic Treatment Processes

15. 3.4 Wastewater Treatment Ponds
Applied mostly in rural industries and small communities
Main benefits are low construction and operating cost
Classification based on biological activity, form of aeration and influent composition
POND TYPE
BIOLOGICAL
ACTIVITY
TYPE OF
AERATION
Anaerobic
Avoided
Facultative (Stabilisation)
Anaerobic/ Aerobic
Natural
Aerated
Aerobic
Mechanical
Aerobic (Maturation, Oxidation)

16. 1. Anaerobic Ponds Characteristics: High organic load; Deep (3-6m);
Biomass formation small (5-15% of C in feed)

17. Anaerobic Pond Design & Operation
Parameter
Unit
Typical values
Loading (volumetric)
kg BOD5/m3/d
Temperature °C
25-35
Mean HRT
days
6-25
Influent COD
mg/L
Effluent COD
Operational Considerations:
BOD removal 60-80%
Scum formation to contain odour emissions
Monitor pH (should be )

18. 2. Facultative Ponds Characteristics:
“two zone” environment, depth m; large
microbial diversity; medium organic load; odour free

19. Facultative Pond Design & Operation
Design: Area Loading Rate
kg BOD5/ha/d T>15oC
kg BOD5/ha/d T<15oC
HRT days
Operational Considerations:
Maintain aerobic conditions. Beware of over-loading causing the pond to turn anaerobic - odour problems

20. 3. Aerated Ponds Characteristics:
Mode is determined by the mixing intensity
Completely mixed: P/V = W/m3
Facultative: P/V ≈ 0.8 W/m3

21. Aerated Pond Design & Operation
HRT days
Aeration capacity ≈ 2*BOD load
Aerators: kg O2/kWh
ΔBOD: %
Operational Considerations:
Can be very efficient for soluble BOD/ COD removal but solids concentrations too high for discharge (irrigation ok).

22. 4. Aerobic (Oxidation) Ponds
Characteristics:
Natural oxygenation (wind, photosynthesis); large surface area; shallow ( m); low organic loading.
Suitable for treating effluent from anaerobic ponds

23. Aerobic Pond Design & Operation
Design: kg BOD5/ha/d
Operational Considerations:
Maintain aerobic conditions. Beware of over-loading causing the pond to turn anaerobic.

24. Outline Overview 3.1 Criteria for Successful Biological Treatment
3.2 Principles of Biological Reactions
3.3Wastewater Treatment Ponds
3.4 Anaerobic Treatment Processes

25. 3.4 Anaerobic Treatment Processes
Treatment under exclusion of oxygen
Carbon mainly converted to methane (CH4) and carbon dioxide (CO2)
Used for high organic loadings
Efficient and economic COD/BOD removal
Low rate systems use very long HRT eg. Anaerobic ponds
High rate systems use low HRT but need biomass retention mechanism eg. UASB
Increase rate of biological action by increasing temperature.

26. Anaerobic Process Principles
Pathways of organics in anaerobic treatment
Fast growing,
robust bacteria
Slow growing, pH
sensitive archaea

27. Process types A. Single-stage processes
Long solids & hydraulic retention times (HRT)
Eg. Anaerobic digesters (20-30 d HRT)
Anaerobic ponds (10-30 d HRT)
B. Two-stage (high rate) processes
Short HRT in first stage, no biomass retention
Short HRT but with biomass retention in second stage, usually pH controlled
Eg. UASB, Hybrid, fluidised bed reactors etc.

28. A. Single Stage Process SLUDGE DIGESTER Biogas Treated effluent
Wastewater
SLUDGE DIGESTER
Mixing mechanically
or often by biogas
recirculation

29. 1. Upflow Anaerobic Sludge Blanket (UASB)
Treated effluent
Biogas
From
Pre-acidification
Tank
Gas collector
Granular biomass
Gas collection
below water
level to reduce
turbulence at
overflow
Uniform flow
distribution
essential
Sludge blanket

30. 2. Hybrid Reactor Biogas Treated effluent Packed bed
From
Pre-acidification
Tank
Granular biomass
Uniform flow
distribution
essential
Packed bed
(plastic material)
for biofilm growth
Sludge blanket

31. B. Two-Stage Reactor Performance
COD removal %
BOD removal %
Gas production m3/kg CODremoved
Methane production m3/kg CODremoved
Methane conc %
Sludge production kg VSS/kgCODremoved

32. Two-stage high-rate hybrid reactor for abattoir & industrial wastewater

33. Anaerobic Reactor Design
1. Pre-acidification tank
Often on the basis of an equalisation tank (also variable volume operation)
Typical HRT h
pH 5-6 if controlled, 4-5 if uncontrolled
Mixing usually only by inflow 􀃎 importance to minimise solids in influent
Covered tank, gas vented and treated or incinerated (with biogas in boiler or flare)

34. Anaerobic Reactor Design
2. Methanogenic (2nd stage) reactor
Volume-based organic loading rate (OLR)
Cin  biodegradable COD conc. in influent mg/L
Q  wastewater flow rate m3/d
VR  methanogenic bioreactor volume m3
Typical HRT h, Solids RT days
Usually heated to operate at °C

35. High Rate Anaerobic Treatment
Typical process flowsheet using Upflow Anaerobic Sludge Blanket (UASB) reactor
Acidif. Tank
Mix Tank
Sludge
blanket
Methanogenesis
Acidogenesis
Biogas
Biomass
retention as
granules
Recycle and mix tank reduce pH
control dosing
CSTR-type tank usually not heated

36. Anaerobic Reactor Design
OLR designs for various reactor types:
UASB  6-12 kg COD/m3/d
Internal Circulation  kg COD/m3/d
Fluidised/expanded bed 12-20 kg COD/m3/d
Hybrid Reactor  6-12 kg COD/m3/d
OLR varies with degradability, temp., pH…
Hydraulic loading up to 24 m3/(m2reactor area d)
Gas loading m3 gas /(m2reactor area d)

37. Questions?

38. Documentation

39. Terima Kasih