ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY

CH 9 - Attached Growth Process

Prepared by:Pn. Hairul Nazirah Abdul Halim

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

• Advantages of aerobic attached growth processes over the activated sludge process:

1. Less energy required

2. Simpler operation

3. No problems of bulking sludge in secondary clarifiers

4. Better sludge thickening properties

5. Less equipment maintenance needs

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.

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

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

Trickling Filters

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

c) Trickling Filters

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

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.

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.

• Trickling Filter classification

1. Low-rate filters

2. Intermediate-and High-Rate Filters

3. Roughing Filters

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 used

2. Dosing rate

3. Type and dosing characteristics of the distribution system

4. Configuration of the underdrain system

5. Provision for adequate airflow

6. Settling tank design

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

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.

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

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

view of conventional rock filter with two-arm rotary distributor

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

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.

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.

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.

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

d) Rotating Biological Contactors.

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

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

• 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

• 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 UV – RBC units are covered (Fig. 9-11b).

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

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.

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