1. Wastewater Treatment Fixed Film Reactors
Professor Nick Gray
Centre for the Environment
Trinity College
University of Dublin
© Tigroney Press

2. Wastewater Treatment Sludge treatment
Learning Objectives:
The design of percolating filters
Operational basis of percolating filters including problems
Concept that FFRs can be aerobic, anoxic and anaerobic
Explore modern FFR designs
What you should know after this lecture:
The basic design of a percolating filter
Operational basis of the process
Most likely operational problems
Application and design of other FFRs

3. Wastewater Treatment: fixed film systems
The standard design of a fixed film reactor is the percolating or trickling filter

4. Wastewater Treatment: fixed film systems
1.8 metre deep, blast furnace slag filter. Single pass low rate system

5. Wastewater Treatment: fixed film systems
Surface irrigation of settled sewage via nozzles with a motor driven distributor arm. Air is supplied by passive ventilation. 30m diameter

6. Wastewater Treatment: fixed film systems
Fish tailed nozzles or splash plates ensure good distribution and also reduce fly emergence. Problem is that they encourage surface ponding

7. Wastewater Treatment: fixed film systems
Industrial filter using a reciprocating arm. Surface dries out in between wetting resulting in top layer of filter not covered with film.

8. Dosing syphon Splash Plate fixed pipes Tipping trough
Lower diagram…as sewage level rising in chamber increases pressure forcing air out of U bend at base…the water floods into distribution pipes until air lock activated.
Tipping trough
Operates 8-10 times per hour to provide sufficient energy from jets to drive distribution arm

9. Wastewater Treatment: fixed film systems
Current designs are normally built above ground
Older filters are often neglected in Ireland and become overgrown
They are however, very robust and easy to bring back into service

10. Wastewater Treatment: fixed film systems
High rate filters contain modular plastic media and may require assisted aeration/ventilation.
Often very tall (12 m) but free standing so require little support from walls.

11. Wastewater Treatment: fixed film systems
The film requires a high surface area on which to develop.
Critical depth for O2 penetration is 0.2 mm then anoxic and anaerobic layers develop causing biofilm destabilization
Medium Surface area Voidage Weight (dry)
50 mm slag 151m2m % 886 kg m-3
Flocor RC m2m % kg m-3

12. Wastewater Treatment: fixed film systems
The media is covered by a thick layer of micro-organisms, mainly heterotrophic bacteria but also fungi and micro and macro-colonizers.

13. Psychoda alternata

14. Wastewater Treatment: fixed film systems
Garden pond filters are very compact and use smaller media
Also include filter mats to remove algae and larger solids
Some include solids separation, others multi-chambered for large ponds
Different media used to support bacteria but also to trap solids

15. Wastewater Treatment: fixed film systems
Rotating Biological Contactors (RBCs)

16. Wastewater Treatment: fixed film systems
Biofilm develops on both sides of the plates which rotate at 1 rpm

17. Wastewater Treatment: fixed film systems
Plates are arranged in blocks sat in different sections - plug flow configuration

18. Wastewater Treatment: fixed film systems
The Units are fully enclosed in a GRP shell reducing noise, smell and fly nuisance

19. Wastewater Treatment: fixed film systems
Smaller designs are often innovative but less robust

20. Wastewater Treatment: fixed film systems
Larger designs up to
25,000 pe commonly
used in Europe

21. Wastewater Treatment: fixed film systems
Unobtrusive installations for sensitive areas

22. Wastewater Treatment: fixed film systems
BAF Biological Aerated Filters can be used for secondary and tertiary treatment. Characterized by having a backwash facility and no secondary settlement tank.
Floating media for tertiary treatment

23. Wastewater Treatment: fixed film systems
SAF – Submerged Aerated Filter
Each cell houses a number of fine bubble membrane diffusers, which are mounted below a packed rigid corrugated PVC media.
Can also be built completely underground.

24. Wastewater Treatment: fixed film systems
SAF/BAF systems are often categorized by action:
Carbonaceous removal and nitrification
dF BAFsm – Downflow Biological Aerated Filter with sinking media
uF BAFsm – Upflow Biological Aerated Filter with sinking media
uF BAFfm – Upflow Biological Aerated Filter with floating media
Denitrification (anoxic)
dF dNBFsm – Downflow Denitrifying Biological Filter with sinking media
uFdNBFmm – Upflow Denitrifying Biological Filter with mobile media
Originally SAF and BAF systems were based on the use of a secondary settlement tank, or regular (daily) backwashing respectively…now the difference is less clear.

25. Wastewater Treatment: fixed film systems
Integrated Biological Processes using submerged media
Integrated fixed film activated sludge (IFAS)
conventional activated sludge system with the use of submerged media
Moving bed bioreactor (MBBR)
aerated lagoon with moving submerged media
Submerged bed biological reactor  (SBBR)
aerated lagoon with fixed (stationary) submerged media

26. Wastewater Treatment: fixed film systems
Integrated fixed film activated sludge (IFAS)
conventional activated sludge system with the use of submerged media

27. Wastewater Treatment: fixed film systems
Moving bed bioreactor (MBBR)
aerated lagoon with moving submerged media

28. Wastewater Treatment: fixed film systems
Submerged bed biological reactor  (SBBR)
aerated lagoon with fixed (stationary) submerged media

29. Wastewater Treatment: fixed film systems
Other types of fixed (stationary)
submerged media
PVC rope media
Bioweb-PVC rope mesh

30. Wastewater Treatment: fixed film systems
Pilot Scale Filters for Research and Design Studies

31. Wastewater Treatment: fixed film systems
Read: Chapter 12 of the course text as a brief overview or for more detail see Gray, N.F. (2004) Biology of Wastewater Treatment, Imperial College Press, London..
References:
Mara, D. and Horan, N. (eds) (2003) Handbook of Water and Wastewater Microbiology. Academic Press, London.