1. Prepared by: Pn. Hairul Nazirah Abdul Halim
ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRY CH 10 – Anaerobic Suspended & Attached Growth Process
Prepared by:
Pn. Hairul Nazirah Abdul Halim

2. The purpose of this chapter – to present anaerobic treatment processes used to remove organic material from liquid streams.

3. Rationale for Anaerobic Treatment
Advantages of Anaerobic Treatment Processes:
Energy Considerations
Lower Biomass Yield
Fewer nutrients required

4. 1. Energy Considerations
Net energy producers instead of energy users

5. 2. Lower Biomass Yield
Sludge processing and disposal cost reduced greatly.
3. Fewer Nutrients Required
Aerobic process require nutrients to support the growth.
Anaerobic need less nutrient because less biomass is produced.

6. Disadvantages of Anaerobic Treatment Processes
Operational Considerations
Need for Alkalinity Addition
Need for Further Treatment

7. Operational Considerations
Longer start-up time (months for anaerobic versus days for aerobic processes)
Sensitivity to possible toxic compounds
Potential for odor production
Corrosiveness of the digester gas
However, with proper w/w characterization and process design these problems can be avoided/managed.

8. 2. Need for Alkalinity Addition
2000 to 3000 mg/L CaCO3 may be needed to maintain an acceptable pH with high CO2 concentration.
Cost to purchase alkalinity
3. Need for Further Treatment
May require further treatment with aerobic process to meet discharged requirements.

9. Examples of types of w/w treated by anaerobic processes:
Alcohol distillation
Breweries
Chemical manufacturing
Dairy and cheese processing
Domestic w/w
Fish and seafood processing
Pulp & paper
Soft drink beverages
Sugar processing
Pharmaceuticals

10. General Design Considerations for Anaerobic Treatment Processes
Characteristic of the Wastewater
The presence of toxic streams, flow variations, inorganic conc., seasonal load variations.
2. Flow and Loading Variations
Wide variation in influent flow and organic loads can upset the balance between acid fermentation and methanogenesis.
Lower pH inhibit methanogenesis

11. 3. Organic concentration and temperature
Optimal biological rxtn: 25 – 35 oC
COD > 1500 to 2000 mg/L are needed to produce sufficient methane to heat w/w without external heat source.
Aerobic treatment can be applied at lower temp (10-20oC)
- slower rxtn rates
- longer SRT
- larger reactor volumes
- lower organic COD loading is needed
- degradation of long chain fatty acids is limited

12. 4. Fraction of Nondissolved Organic Material
High solid conc., are treated in suspended growth reactor than by upflow and downflow attached growth processes
5. Wastewater Alkalinity
Alkalinity in the range mg/L as CaCO3 typically required to maintain pH at/or near neutral.
The level of alkalinity needed is seldom available in the influent w/w
Requirement to purchase chemical to control pH – impact on economic

13. 6. Solid Retention Time (SRT)
SRT larger than 20d are needed for anaerobic processes at 300C.

14. Anaerobic Suspended Growth Processes
3 types of anaerobic suspended growth processes:
1. Complete-mix suspended growth anaerobic digester
2. Anaerobic contact process
3. Anaerobic sequencing batch reactor

15. Complete-mix suspended growth anaerobic digester
SRT in the range 15 – 30d
Without sludge recycle – for high conc. Of solid or extremely high dissolved organic conc.

16. View of typical pilot plants : (a) pilot-scale anaerobic reactors at a food-processing facility

17. 2. Anaerobic contact process
Overcomes the disadvantaged of a complete-mix process without recycle
Biomass is separated and returned to the contact reactor

18. 3. Anaerobic sequencing batch reactor (ASBR)
Four step: Feed, React, Settle and Decant

19. Attached Growth Anaerobic Processes
Upflow attached growth anaerobic treatment reactors differ by type of packing used and the degree of bed expansion.
3 types:
Upflow packed-bed reactor
Anaerobic expended bed reactor
Fluidized bed anaerobic reactor

20. Upflow packed-bed reactor
The packing is fixed and the w/w flows up
Suitable for w/w with low suspended solid conc.
Advantages:
- high COD loadings
- relatively small reactor volumes
- operational simplicity
Limitations:
- cost of packing material
- maintanance associated with solids accumulation
- possible packing plugging

21. 2. Upflow Attached Growth Anaerobic expended bed reactor
Packing material – silica sand ( mm)
Smaller packing provide greater surface area per unit volume
Packing void fraction 50%
upflow liquid velocity – 2 m/h
Advantages and limitations are similar to fluidized bed reactor.

22. 3. Fluidized bed anaerobic reactor
Packing material – sand, anion and cation exchange resins and activated carbon
Packing size 0.3 mm sand
Operate at higher upflow liquid velocity – 20 m/h
Advantages
– ability to provide high biomass conc.
- high biomass loading
- high mass transfer characteristic
- minimal space requirements
Disadvantages:
- pumping power required to operate fluidized bed
- cost of reactor packing
- length of start up time