Biofilm Process

Attached growth biological processAttached growth biological process

(Fixed-film process(Fixed-film process 、、 Biofilm process)Biofilm process)

farid khan farid khan

PD Dr. Ursula Obst, National Research Center Karlsruhe, Germany

What is a biofilm?

A biofilm is a structured community of bacterial and other microbial cells enclosed in a polymeric matrix and adhered on an inert or living surface. Biofilms consists of three components:a. microorganismsb. extracellular polymeric substances (EPS, glycolax)c. surface


Microbes are not lonely threavers in the environment but love to live in community.

BiofilmBiofilm

Adhesive growth of mixed microbial population Adhesive growth of mixed microbial population

on surfaces (on surfaces (microbes microbes ++ surface surface))

PlanktonicPlanktonic vs. vs. fixedfixed

Biofilm formation is induced due to bacterial Biofilm formation is induced due to bacterial

Extracellular Polymeric SubstanceExtracellular Polymeric Substance (EPS) (EPS) 胞外胞外

聚合物聚合物 − − slime layerslime layer黏液層黏液層 (glycocalyx(glycocalyx醣外被 ))




Glycocalyx or ‘slime’ formation

Biofilm bacteria excrete extracellular polymeric substances, or sticky polymers, which hold the biofilm together and cement it to a surface. In addition, these polymer strands trap scarce nutrients and protect bacteria from biocides.

Attachment is mediated by extracellular polymers that extend outward from the bacterial cell wall (much like the structure of a spider’s web). This polymeric material, or glycocalyx, consists of charged and neutral polysaccharides groups that not only facilitate attachment but also act as an ion-exchange system for trapping and concentrating trace nutrients from the overlying water. The glycocalyx also acts as a protective coating for the attached cells which mitigates the effects of biocides and other toxic substances.

heat exchanger overgrown by biofilms after treatment with degradable anti-corrosives (courtesy HC Flemming)

huge biofilm from a warm water pool, Yellowstone NP


Summarizing:

Cell surface structures such as fimbriae, other proteins, LPS, EPS, and flagella all clearly play an important role in the attachment process.

The attachment of microorganisms to surfaces is a very complex process, with many variables affecting the outcome. In general, attachment will occur most readily on surfaces that are rougher, more hydrophobic.

Biofilm ProcessesBiofilm Processes

advantages of biofilm processes:

- higher process productivity (loading rates)- higher biomass holdup- higher mean cell residence time- no need for biomass recirculation- creates suitable environment for each type of bacteria- sustains toxic loads

Biofilm ProcessesBiofilm Processes

• types :- Trickling filters滴濾池- Rotating Biological Contactors 生物圓

盤法- Biological Contact Oxidation 接觸曝氣法、

生物接觸氧化法 (Contact biofilter 接觸濾床法 )

滴濾池 RBC

Source: www.aqua-medic.de

一些接觸曝氣法之填料

建鑫環境工程有限公司

三越企業股份公司

Trickling FiltersTrickling Filters

Rotating distribution arm sprays primary Rotating distribution arm sprays primary effluent over circular bed of rock or other effluent over circular bed of rock or other coarse mediacoarse media

Air circulates in pores between rocksAir circulates in pores between rocks

““Biofilm” develops on rocks and micro-Biofilm” develops on rocks and micro-

organisms degrade waste materials as organisms degrade waste materials as they flow pastthey flow past

Organisms slough off in clumps when film Organisms slough off in clumps when film gets too thickgets too thick


Filter Material

BOD5

NH4+

NO3-

trickling filter

nitrification

oxidation of BOD

Trickling filters are operated aerobically and need additional denitrification steps.


Aerobic secondary wastewater treatment processes (Trickling Filter)

Rocks:10–15 cm in diameter, the bed is 2 m deep


Not a true filtering or sieving processNot a true filtering or sieving process

Material only provides surface on which Material only provides surface on which bacteria to growbacteria to grow

Can use plastic mediaCan use plastic media– lighter - can get deeper beds (up to 12 m)lighter - can get deeper beds (up to 12 m)– reduced space requirementreduced space requirement– larger surface area for growthlarger surface area for growth– greater void ratios (better air flow)greater void ratios (better air flow)– less prone to plugging by accumulating slimeless prone to plugging by accumulating slime

Rotating Biological Contactors

Called RBCsCalled RBCs

Consists of series of closely spaced discs Consists of series of closely spaced discs mounted on a horizontal shaft and rotated mounted on a horizontal shaft and rotated while ~40% of each disc is submerged in while ~40% of each disc is submerged in wastewaterwastewater

Discs: Steer or light-weight plasticDiscs: Steer or light-weight plastic

Slime is 1-3 mm in thickness on discSlime is 1-3 mm in thickness on disc

Rotating Biological Rotating Biological ContactorsContactors

Rotating Biological ContactorsRotating Biological Contactors

Aeration

Shearing of excessmicroorganisms

Attached microorganismspick up organics

Filmmixes withwastewater

Rotating Biological ContactorsRotating Biological Contactors

PrimarySettling

SludgeTreatme

nt

SecondarySettling

Sludge Treatment

Fixed-film bioreactor

Cost-effective -low capital and O&M costs

Small operation land requiried

High biomass density & low sludge production

Minimizes washout of slow-growing organisms

Capable of handling both hydraulic and organic shock loads

Modifications of Basic Biological Methods

Activated sludge with fixed-film packing– Submerged Aerobic Filter (SAF)Synthetic packing materials developed for use in AS processes, may be suspended in the liquid or fixed in the aeration tankEnhance the AS process by providing a greater biomass concentration and reducing the basin size requirementsImprove nitrification rates and accomplish denitrification in aeration tanks by having anoxic zones within the biofilm depth

Modifications of Basic Biological Methods

Because of the complexity of the process and issues related to understanding the biofilm area and activity, the process designs are empirical and based on prior pilot-plant or limited full-scale results.

There are now >10 different variations of processes with suspended packing, including the Captor®, Linpor® and Kaldnes®.

Kaldnes®Moving-Bed Biofilm Reactor (MBBR)

Developed by a Norwegian company

AS process added with small cylindrical shaped polyethylene carrier (10 mm in diameter and 7 mm in height; 0.96 g/ml) in aerated or non-aerated basins to support biofilm growth

N removal through both nitrification (with O2) and denitrification (without O2)

http://www.kaldnes.com/

• Effluent rate : 30 L/day

• Sludge return rate : 15 L/dat

• HRT : 12.5 hr

• DO : 2~3 mg/ L

Documents

Biofilm Process