1. Attached Growth Biological WW treatment Systems

2. Biofilm Systems Biofilm a biological slime layer bacteria in biofilm
degrade organics
biofilm will develop
on almost anything

3. Types of Biofilm Systems
Trickling filters
Rotating biological contactors
Fluidized bed reactors
Biofilters
Wetlands systems
Sequencing batch biofilm reactors
(many of these can be aerobic or anaerobic)

4. Trickling Filters

5. Flow Diagram for Trickling Filters

6. Trickling Filters Not a true filtering or sieving process
Material only provides surface on which bacteria to grow
Can use plastic media
lighter - can get deeper beds (up to 12 m)
reduced space requirement
larger surface area for growth
greater void ratios (better air flow)
less prone to plugging by accumulating slime

7. Trickling Filters
Filter Material

8. Typical Trickling Filter

9. Typical Modular and Random Packed Plastic Media
Schematic diagrams of modular and random packed media used in fixed-film treatment systems (Source: Bordacs and Young, 1998)

10. Random Packing
Leonard W. Casson, Ph.D., P.E., DEE

11. Structured Media
Leonard W. Casson, Ph.D., P.E., DEE

12. Bio-towers

13. Trickling Filter Tank is filled with solid media
Rocks
Plastic
Bacteria grow on surface of media
Wastewater is trickled over media, at top of tank
As water trickles through media, bacteria degrade BOD
Bacteria eventually die, fall off of media surface
Filter is open to atmosphere, air flows naturally through media
Treated water leaves bottom of tank, flows into secondary clarifier
Bacterial cells settle, removed from clarifier as sludge
Some water is recycled to the filter, to maintain moist conditions

14. Trickling Filter System

15. Trickling Filter Process

16. Bacteria Removal

17. Types of Trickling Filters
Standard or low rate
single stage rock media units
loading rates of 1-4 m3 wastewater/m2 filter cross-sectional area-day
large area required

18. Types of Trickling Filters
High rate
single stage or two-stage rock media units
loading rates of m3 wastewater/m2 filter cross-sectional area-day
re-circulation ratio 1-3

19. Types of Trickling Filters
Super rate
synthetic plastic media units
modules or random packed
specific surface areas 2-5 times greater than rock
much lighter than rocks
can be stacked higher than rocks
loading rates of m3 wastewater/m2 filter cross-sectional area-day
plastic media depths of 5-10 m

20. Design Criteria for Trickling Filters

21. Design Equation (NRC) Single stage R = Qr/Q F = recirculation ratio
E1 = fraction of BOD5 removal for first stage at 20 oC, including recirculation
and sedimentation
Q = wastewater flow rate, m3/s
Cin = influent BOD5, mg/L
V = volume of filter media, m3
F = recirculation ratio
R = Qr/Q
Qr = recirculation flow rate, m3/s

22. Design Equation (NRC) Second stage
E2 = fraction of BOD5 removal for second stage filter at 20 oC, including
recirculation and sedimentation
Ce = effluent BOD5 concentration from first stage, mg/L

23. Ex. 5-5 Study examples 9-2,9-3 and 9-4 Given: Question:
Single-stage, low rate trickling filter
Volume of filter = 1,443 m3
Hydraulic loading = 1,900 m3/d
F = 2.78; Cin = 150 mg/L
Question:
BOD5 of the effluent
Solutions:
1. Hydraulic loading: Q = (1,900 m3/d) (1d /86400 s) = m3/s
2. Efficiency:
3. Concentration of BOD5: Ce = ( )(150) = 15.8 mg/L

24. Rotating Biological Contactor
Rotating Biological Contactors, commonly called RBC’s, are used in wastewater treatment plants (WWTPs). The primary function of these bio-reactors at WWTPs is the reduction organic matter.

26. RBC Schematic Wastewater Film of Microorganisms Rotation
Leonard W. Casson, Ph.D., P.E., DEE
Wastewater

27. Rotating Biological Contactors

28. Rotating Biological Contactors
RBCs constructed of plastic media on a long shaft
Media is submerged in a tank
Shaft rotates media through water
Bacteria grow on media, degrade BOD in water
Bacteria get air by exposure to atmosphere
Bacteria eventually die, fall off media surface
Dead bacteria and other solids are removed in the secondary clarifier
Media up 12 feet in diameter
Shafts as long as 25 feet
Media areas up to 180,000 square feet per shaft

29. Rotating Biological Contactors
Primary
Settling
Sludge
Treatment
Secondary
Sludge Treatment

30. Flow Diagram for RBCs

31. Rotating Biological Contactor (RBC)
Single RBC

32. Rotating Biological Contactor (RBC)
Defective RBC’s at the Easton Wastewater Treatment Plant

33. Package RBC System
Leonard W. Casson, Ph.D., P.E., DEE