8/12/2019 CH 9 - Attached Growth Process

1/30

ERT 417/4WASTE TREATMENT IN BIOPROCESS

INDUSTRY

CH 9 -Attached Growth Process

Prepared by:

Pn. Hairul Nazirah Abdul Halim

8/12/2019 CH 9 - Attached Growth Process

2/30

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

8/12/2019 CH 9 - Attached Growth Process

3/30

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

8/12/2019 CH 9 - Attached Growth Process

4/30

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.

8/12/2019 CH 9 - Attached Growth Process

5/30

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

8/12/2019 CH 9 - Attached Growth Process

6/30

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

8/12/2019 CH 9 - Attached Growth Process

7/30

Trickling Filters

8/12/2019 CH 9 - Attached Growth Process

8/30

Flow diagram for biological process used for w/w treatment:

c) Trickling Filters

8/12/2019 CH 9 - Attached Growth Process

9/30

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

8/12/2019 CH 9 - Attached Growth Process

10/30

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.

8/12/2019 CH 9 - Attached Growth Process

11/30

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.

8/12/2019 CH 9 - Attached Growth Process

12/30

Trickling Filter classification1. Low-rate filters

2. Intermediate-and High-Rate Filters

3. Roughing Filters

8/12/2019 CH 9 - Attached Growth Process

13/30

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

8/12/2019 CH 9 - Attached Growth Process

14/30

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

8/12/2019 CH 9 - Attached Growth Process

15/30

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.

8/12/2019 CH 9 - Attached Growth Process

16/30

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

8/12/2019 CH 9 - Attached Growth Process

17/30

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

8/12/2019 CH 9 - Attached Growth Process

18/30

view of conventional rock filter with two-arm rotary distributor

8/12/2019 CH 9 - Attached Growth Process

19/30

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

distributor.

8/12/2019 CH 9 - Attached Growth Process

20/30

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.

8/12/2019 CH 9 - Attached Growth Process

21/30

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.

8/12/2019 CH 9 - Attached Growth Process

22/30

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.

8/12/2019 CH 9 - Attached Growth Process

23/30

Flow diagram for biological process used for w/w treatment:

d) Rotating Biological Contactors.

8/12/2019 CH 9 - Attached Growth Process

24/30

(a) conventional RBC with mechanical drive and optional airin ut

8/12/2019 CH 9 - Attached Growth Process

25/30

submerged-type RBC equipped with air capture cups (air is

used both to rotate and to aerate the biodisks),

8/12/2019 CH 9 - Attached Growth Process

26/30

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

8/12/2019 CH 9 - Attached Growth Process

27/30

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).

8/12/2019 CH 9 - Attached Growth Process

28/30

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

8/12/2019 CH 9 - Attached Growth Process

29/30

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.

8/12/2019 CH 9 - Attached Growth Process

30/30

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