1. Prepared by: Pn. Hairul Nazirah Abdul Halim
ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRY CH 9 - Attached Growth Process
Prepared by:
Pn. Hairul Nazirah Abdul Halim

2. Attached-Growth Process
3 general classes:
1. Nonsubmerged attached growth process
2. Suspended growth process with fixed-film packing
3. Submerged attached growth aerobic process

3. Advantages of aerobic attached growth processes over the activated sludge process:
Less energy required
Simpler operation
No problems of bulking sludge in secondary clarifiers
Better sludge thickening properties
Less equipment maintenance needs

4. 1. Nonsubmerged attached growth process
Liquid flow over the attached biofilm
Example: Trickling Filter
Concept of Trickling Filter:
Bed/basins filled with broken stones
Bed is filled with w/w from top
The w/w was allowed to contact with the packing for a short time.
The bed was then drained allowed to rest before the cycle was repeated.

5. 2. Suspended growth process with fixed-film packing
Use of packing material that are suspended in the aeration tank.
The advantages:
Increased treatment capacity
Greater process stability
Reduced sludge production
Enhanced sludge settleability
Reduce solid loading on the secondary clarifier
No increase in operation and maintenance costs

6. 3. Submerged attached growth aerobic process
Does not required secondary clarification
Upflow and downflow packed bed reactors and fluidized-bed reactors
Advantage: area requirement is 1/5 to 1/3 of that needed for activated-sludge treatment
Disadvantage: capital costs higher than activated-sludge treatment

7. Trickling Filters

8. Flow diagram for biological process used for w/w treatment:
c) Trickling Filters

9. Trickling Filters Non submerged fixed-film biological reactor
using rock or plastic packing
Depth of rock packing: 0.9 to 2.5m (averages 1.8m)
Primary clarification is necessary before trickling filter
A slime layer develops on the rock or plastic packing in the trickling filters
Contains microbs for biodegradation of substrates

10. Trickling Filters
Biological community in the filter – aerobic & fucultative bacteria, fungi, algae and protozoans. Animals – snails, worms, insect larvae.
Bacteria species in trickling filter: Achromobacter, Flavobacterium, Pseudomonas and Alcaligenes
Fungi – Fuzazium, Mucor, Penicillium, Geotrichum, Sporatichum and various yeasts
Algae – do not take direct part in waste degeneration.
But during the daylight, add oxygen to w/w.

11. Trickling Filters Slime layer thickness – up to 10mm
Organic material from the liquid is adsorbed on to the biological film or slime layer
The organic material is degraded by aerobic microbs in the outer portion of the biological slime layer.

12. Trickling Filter classification
Low-rate filters
Intermediate-and High-Rate Filters
Roughing Filters

13. Design of Physical Facilities
Factor that must be considered in the design of trickling filters:
Type and physical characteristic of filter packing to be used
Dosing rate
Type and dosing characteristics of the distribution system
Configuration of the underdrain system
Provision for adequate airflow
Settling tank design

14. Filter packing
Ideal filter packing – high surface area per unit volume
- low cost
- High durability
- High porosity (so clogging is minimized)
Depth of rock filters - 2m

15. Typical packing material for trickling filters: (a) rock, (b) and (c) plastic vertical-flow, (d) plastic cross-flow, (e) redwood horizontal, and (f) random pack.

16. Dosing Rate
Dosing rate - the depth of liquid discharged on top of the packing for each pass of the distributor
Higher distributor rotational speed = lower dosing rate
High dosing rate – better performance because:
1. larger water volume applied per revolution
2. Provides greater wetting efficiency
3. Results in greater agitation – which cause more solids to flush out of the packing
4. Results in thinner biofilm – creates more surface area

17. Distribution System
Consist of two or more arms that are mounted on a pivot in the center of the filter and revolve in a horizontal plane.
The arms are hollow and contains nozzles through which the w/w is discharged over the filter bed.
Driven by electric motor

18. view of conventional rock filter with two-arm rotary distributor

19. (c) view of top of tower trickling filter with four-arm rotary distributor.

20. Underdrains
Carry away the treated w/w and solid discharged from the filter packing for conveyance to the final sedimentation tank.
Airflow
Adequate airflow is importance to provide efficient treatment and to prevent odors.
Use of forced or induced-draft fans to provide a reliable supply of oxygen.

21. Settling Tank
Function – to produce a clarified effluent
Solids are separated from the treated w/w
All sludge from trickling filter settling tanks is sent to sludge-processing facilities or return to primary clarifier.

22. Rotating Biological Contactors
Consist of a series of closely spaced circular disks of polystyrene or PVC that submerged in w/w and rotated through it.
Standard size – 3.5m in diameter and 7.5m in length.
As RBC disks rotate out of the w/w, aeration is accomplished by exposure to the atmosphere.
Microbs grow on the medium surface remove substrates from the w/w and oxygen from the air to sustain their metabolic process.
RBC require pretreatment of primary clarification.

23. Flow diagram for biological process used for w/w treatment:
d) Rotating Biological Contactors.

24. (a) conventional RBC with mechanical drive and optional air input

25. submerged-type RBC equipped with air capture cups (air is used both to rotate and to aerate the biodisks),

26. Submerged RBC is 70-90% submergence
Air-drive units are used to provide oxygen and rotation.
Advantages:
Reduce loadings on the shaft and bearings
Improve biomass control by air agitation
Ability to use larger bundles of disks

27. Disadvantages:
Low level of dissolved oxygen in liquid – biological degradation activity may be oxygen limited.
To prevent algae growth, protect the plastic disks from UV – RBC units are covered (Fig. 9-11b).

28. Fig. 9-11(b) conventional RBC in enclosed reactor,

29. Designing a Rotating Biological Contactor
Flow from the primary clarifier is 20,000 m3/d with BOD of 150 mg/L. The hydraulic loading rate is found to be 0.05 m3/m2.d. It is required to produce an effluent with a soluble BOD5 of 10 mg/L. Determine the surface area required for an RBC system to treat the wastewater.

30. effluent with a soluble BOD5 of 10 mg/L.
SOLUTION
Influent BOD = 150 mg/L
effluent with a soluble BOD5 of 10 mg/L.
hydraulic loading rate = 0.05 m3/m2.d.
Disk area = 20,000 m3/d = 4 x 105 m2
0.05 m3/m2.d