Hi Daniel,

I presume you're talking about activated sludge plants rather than trickling filters?

In activated sludge the biofilm is in small free floating clumps called 'flocs - the bacterium Zooglea ramigera is a major player in producing flocs. The flocs are exopolysaccharide holding bacteria and prozoa and so attract other organic particles, as well as having a charged surface that will assist in binding other charged molecules.

The flocs are colonised by a range of organisms that degrade the organic compounds, including bacteria and protozoa, especially ciliates. Since the flocs are not attached to a surface they have a much larger surface area to interact with their environment, and the entire floc will be aerobic leading to higher metabolic rates. The process is highly aerobic and there is plenty of nitrogen and phosphorus around so it goes very quickly indeed! Once the aeration stops the flocs flocculate (funny that eh?!) and then settle trapping any free organic matter etc as it settles ( just like the finings used in wine and beer making).

There is plenty of literature out there and the text books 'Brock: the biology of microorganisms' and Alcamo 'Fundamentals of microbiology' have some coverage by way of an introduction. Biofilms are extremely complex environments and the interactions between different species, genera, and domains is not well understood, so don't worry if there are gaps you can't fill in.

Try these for light reading!:

Costerton WJ, Wilson M (2004) Introducing biofilms. Biofilms 1:1–4

Donlan RM (2002) Biofilms: microbial life on surfaces. Emerg

Infect Dis 8:881–890

Nicolella, C; van Loosdrecht, MCM; Heijnen, JJ (2000 ) Wastewater treatment with particulate biofilm reactors JOURNAL OF BIOTECHNOLOGY 80:1 1-33

Hi Daniel,

I presume you're talking about activated sludge plants rather than trickling filters?

In activated sludge the biofilm is in small free floating clumps called 'flocs - the bacterium Zooglea ramigera is a major player in producing flocs. The flocs are exopolysaccharide holding bacteria and prozoa and so attract other organic particles, as well as having a charged surface that will assist in binding other charged molecules.

The flocs are colonised by a range of organisms that degrade the organic compounds, including bacteria and protozoa, especially ciliates. Since the flocs are not attached to a surface they have a much larger surface area to interact with their environment, and the entire floc will be aerobic leading to higher metabolic rates. The process is highly aerobic and there is plenty of nitrogen and phosphorus around so it goes very quickly indeed! Once the aeration stops the flocs flocculate (funny that eh?!) and then settle trapping any free organic matter etc as it settles ( just like the finings used in wine and beer making).

There is plenty of literature out there and the text books 'Brock: the biology of microorganisms' and Alcamo 'Fundamentals of microbiology' have some coverage by way of an introduction. Biofilms are extremely complex environments and the interactions between different species, genera, and domains is not well understood, so don't worry if there are gaps you can't fill in.

Try these for light reading!:

Costerton WJ, Wilson M (2004) Introducing biofilms. Biofilms 1:1–4

Donlan RM (2002) Biofilms: microbial life on surfaces. Emerg

Infect Dis 8:881–890

Nicolella, C; van Loosdrecht, MCM; Heijnen, JJ (2000 ) Wastewater treatment with particulate biofilm reactors JOURNAL OF BIOTECHNOLOGY 80:1 1-33

Thank you, Richard. In what aspects can we improve the performance of biofilm in organic matter decomposition? I think there is a lot of space for engineering to improve the operation system, but do we need science too? I mean to study the formation of mixed-species biofilm, bacteria communication, synergism and antagonism, bacterial consortia, regulation of digestive enzyme production, and so on. How can this basic knowledge explored apply to the development of higher-performance technology.

in fact, there are some factors influence the biofilm process, you have to be considered, such pH effects, alkalinity, oxygen concentration, temperature, substrate concentration, and others. the structures and functions of biofilm varies according to the type of bacteria. in general biofilm development process goes through four stages are conditioning film, binding colonization, irreversible attachment, and situation. In practice way for removing organic matter, you must look after organic loading rate (OLR), and hydraulic loading rate (HLR). May i suggest to you that fundamental book "wastewater engineering treatment and reuse" written by: Metcalf & Eddy, 4th edition chapter 7&8.

Hi Daniel,

as far as improving the process goes I think it could be pretty difficult. genetic modification of a such a diverse microbial community would be extremely difficult, and cause major problems re: ethics and release of GMO's. These days the more modern systems are highly engineered and constantly monitored for all those things that Ahmed mentioned above. I think the difference in activated sludge is that there is no attachment process, so the formation of flocs or granules (another form of biofilm - especially useful in anaerobic digestion) does not follow the same processes or have the same limitations as conventional surface associated biofilms. An area of interest is that floc formation appears to be stimulated by the 'sensing' of predatory protozoa (ciliates). This causes the flocs to form as a protection against ingestion , but leaves the no floc forming enteric bacteria (pathogens) exposed to grazing from the protozoa. Investigating the mechanism by which floc or granule formation is stimulated might be a useful area of research?

good luck!

cheers,

Richard