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

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

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

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

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

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

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.

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 http://www.meniscus.co.uk/page.php?article=962&name=Dosing+Syphons

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

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.

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-3 52% 886 kg m-3 Flocor RC 331 m2m-3 91% 98 kg m-3

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.

Psychoda alternata

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

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

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

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

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

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

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

Wastewater Treatment: fixed film systems Unobtrusive installations for sensitive areas

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

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.

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.

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

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

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

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

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

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

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.