ch 9 - attached growth process
TRANSCRIPT
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ERT 417/4WASTE TREATMENT IN BIOPROCESS
INDUSTRY
CH 9 -Attached Growth Process
Prepared by:
Pn. Hairul Nazirah Abdul Halim
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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
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Advantages of aerobic attached growth processes overthe activated sludge process:
1. Less energy required
2. Simpler operation
3. No problems of bulking sludge in secondary clarifiers4. Better sludge thickening properties
5. Less equipment maintenance needs
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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 cyclewas repeated.
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2. Suspended growth process with
fixed-film packing
Use of packing material that are suspended in the
aeration tank.
The advantages:
1. Increased treatment capacity
2. Greater process stability
3. Reduced sludge production
4. Enhanced sludge settleability
5. Reduce solid loading on the secondary clarifier
6. No increase in operation and maintenance costs
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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 foractivated-sludge treatment
Disadvantage: capital costs higher than activated-sludge
treatment
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Trickling Filters
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Flow diagram for biological process used for w/w treatment:
c) Trickling Filters
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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
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Trickling Filters
Biological community in the filter
aerobic & fucultativebacteria, fungi, algae and protozoans. Animals snails,
worms, insect larvae.
Bacteria species in trickling filter:Achromobacter,Flavobacterium, Pseudomonas andAlcaligenes
FungiFuzazium, 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.
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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.
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Trickling Filter classification1. Low-rate filters
2. Intermediate-and High-Rate Filters
3. Roughing Filters
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Design of Physical Facilities Factor that must be considered in the design of trickling
filters:
1. Type and physical characteristic of filter packing to be
used2. Dosing rate
3. Type and dosing characteristics of the distribution system
4. Configuration of the underdrain system
5. Provision for adequate airflow6. Settling tank design
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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
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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.
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Dosing Rate
Dosing rate - the depth of liquid discharged on top of thepacking 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
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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
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view of conventional rock filter with two-arm rotary distributor
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(c) view of top of tower trickling filter with four-arm rotary
distributor.
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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 reliablesupply of oxygen.
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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.
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Rotating Biological Contactors
Consist of a series of closely spaced circular disks of
polystyrene or PVC that submerged in w/w and rotatedthrough 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 substratesfrom the w/w and oxygen from the air to sustain their
metabolic process.
RBC require pretreatment of primary clarification.
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Flow diagram for biological process used for w/w treatment:
d) Rotating Biological Contactors.
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(a) conventional RBC with mechanical drive and optional airin ut
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submerged-type RBC equipped with air capture cups (air is
used both to rotate and to aerate the biodisks),
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Submerged RBC is 70-90% submergence
Air-drive units are used to provide oxygen and rotation.
Advantages:
1. Reduce loadings on the shaft and bearings
2. Improve biomass control by air agitation
3. Ability to use larger bundles of disks
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Disadvantages:
1. Low level of dissolved oxygen in liquid biological
degradation activity may be oxygen limited.
2. To prevent algae growth, protect the plastic disks from UVRBC units are covered (Fig. 9-11b).
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Fig. 9-11(b) conventional RBC in enclosed reactor,
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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 producean effluent with a soluble BOD5of 10 mg/L.
Determine the surface area required for an RBC
system to treat the wastewater.
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SOLUTION
Influent BOD = 150 mg/L
effluent with a soluble BOD5of 10 mg/L.
hydraulic loading rate = 0.05 m3/m2.d.
Disk area = 20,000 m3/d = 4 x 105m2
0.05 m3/m2.d