Alternative anti-fouling strategies and the role of monitoring

Transcription

1 Alternative anti-fouling strategies and the role of monitoring Hans-Curt Flemming Biofilm Center IWW Water Centre, Mülheim an der Ruhr - Consulting - Research - Service - 1

2 What is Fouling? Definition adopted from heat exchanger technology: Fouling is the undesired deposition of material on surfaces (Epstein, 1981) Inorganic fouling (precipitation of inorganic crystals), Scaling Organic fouling (deposition of fat, oil, protein etc.) Particle fouling (deposition of silt, clay, humic particles etc.) Biofouling (deposition and growth of microorganisms on surfaces) particles which can multiply on the expense of nutrients 2

3 Bright future for biofouling An example: Washing machines - Slime formation in washing powder fill-in box - Slime formation in tubes - Clothes are smelly if not dried fast enough - Insufficient disinfection, infections spreaded Cause: Biofouling due to protection of environment and clothes Biologically readily degradable washing soaps Water saving increasing washing soap concentrations Liquid washing soaps stick stronger to walls higher local concentrations at interfaces Low temperatures while washing No more peroxides or other bleaching agents in washing soap Water with washing soap remaining in tubes for extended periods of time because it is not completely drained after washing 3

4 An ideal biofouling environment: Paper mill, an environment with free access of bacteria from air, water and paper components (see Michael Meiers presentation) Fouling chances increased by - chlorine-free process - neutral ph - higher concentrations of nutrients - temperatures between 30 and 45 C - Use of contaminated additives 4

5 How good intentions cause inexpected problems: Massive biofilm development in a heat exchanger due to biodegradable corrosion inhibitor 5

6 The Quest for the Silver Bullet Get rid of biofouling once and forever! The ultimate anti-fouling coating: Tributyltin paints a Silver Bullet too powerful Normal oister shell Oister shell, exposed to TBT 6

7 Time scale for fouling protection Kevin Marshall: The organism always wins (Question: how fast!) Anti-Fouling requirements in different time scales: Hours to days -SomeCatheters - Surfaces in contact with food Days to weeks - Environmental sensors - Dialysis units Weeks to months - Heat exchanger systems - Membranes and filters for water treatment Months to years - Ship hulls, oil rigs - Drinking and process water pipes and reservoirs 7

8 What to do? Steps in fouling cases 1. Detection 2. Sanitization 3. Prevention 8

9 Biofilm sampling: On surfaces! Scratching, scratching, scratching (razor blades, rubber scrapers, cotton swabs etc.) Removal of parts of support material with biofilms laboratory Expose test surfaces ( coupons ), remove after given time laboratory 9

10 Verification of biofouling: Field tests: - Visual observation: slime - Smell - Texture (slimy) - Smolder test: heat sample, go for smell of burnt hair Laboratory: - Microscopical observation, cells/cm² - Cultural methods (cfu/cm²) - Chemical analysis (water content, org./inorg.) - Spectroscopical analysis (e.g., FITR) 10

11 The medicine-based strategy Biofouling is considered a technical disease Microorganisms cause this disease Kill microorganisms and the problem is solved Adoption of medical term: Disinfection to cure the system Drawback of this strategy: - In many cases ineffective because biomass, not activity is the problem, dead or alive - Killing does not necessarily remove biomass: dead biomass can still cause problems (heat exchanger, membranes, process waters etc.) - Disinfection means only Inactivation of pathogenic organisms - Frequent failure of this strategy creates jobs and contributes to the gross national product but not to sustainable solution of problems 11

12 Regrowth of P. aeruginosa on test surfaces after application of H 2 O 2 and Ag + Disinfection 2 1,0E+8 1,0E+7 Disinfection 1 colony counts [cfu ml -1 ] 1,0E+6 1,0E+5 1,0E+4 1,0E+3 1,0E+2 1,0E+1 without silver with silver - 1,0E time [d] Application of 600 mg L -1 H 2 O 2 alone and with 300 µg L -1 AgNO 3 added for 24 h at room temperature Determination of colony counts (PAP, 24 h, 36 C) at reactor outlet (courtesy of S. Schulte) 12

13 Killing vs. removal colony count biocide treatment colony count control total cell count biocide treatment total cell count control colony count and total cell count [cm -2 ] biocidetreatment 2. biocidetreatment 3. biocidetreatment time [d] 4. biozidetreatment Cells/cm² cfu Total cell count with DAPI Colony counts on R2A agar, incubation 7 days at 20 C Repeated H 2 O 2 treatment for 15 min (Courtesy of Simone Schulte) 13

14 Five fundamental problems in conventional anti-fouling strategies 1. Monitoring by process performance or product quality No early warning systems 2. Sampling of water phase and not on surfaces No information on biofilm site / extent 3. Disinfection No cleaning: dead biomass on surface, good regrowth conditions 4. No nutrient limitation Nutrients = potential biomass; not reduced by biocides 5. Efficacy control by process/product quality No optimization of countermeasures 14

15 Alternative: Strategies based on better understanding of biofouling Biofouling: Undesired deposition and growth of microorganisms at interfaces Biofouling is a biofilm problem Dissolved substances are converted into locally accumulated biomass Operational definition: Biofilm growth exceeding threshold of interference Biofouling: A biofilm reactor in wrong place & time 15

16 Elements of an integrated Anti-Fouling Strategy: Holistic approach, based on understanding the principles of biofilm development Surface design and modification Cleaning friendly design Biofilm management Biofilm engineering Biofilm analysis Monitoring of deposit development 16

17 Anti fouling toolbox 17

18 The most obvious target: Surfaces Surface modification to influence primary adhesion (see sessions on Tuesday) - Material selection (however, on a long term, all materials can be colonized) - Surface properties (hydrophobic, hydrophilic; hydrogels selection for specialized organisms) - Surface topography (roughness, nanostructures, lotus effect - needs 3 phases, beware of surfactants!) - Antiadhesive coatings (Can be fouled by abiotic matter) - Surface bound biocides (Mechanism obscure; sometimes even effect on water phase claimed; fate of dead cells; Fouling) - Biocide releasing surfaces (Water contamination) - Self polishing surfaces (Water contamination) - Functional surfaces (H 2 O 2 +Catalyst; UV-light) (Fouling) - Conductive coatings, application of electrical current (Fouling) - Reversible change of surface properties (Fouling) How long does the effect last? Toxicity Most promising: Low adhesion surfaces, easy to clean 18

19 Biofilm Management Threshold of interference 19

20 Biofouling Potential: 1. Ubiquitous, always hungry biofilms 2. Nutrients from medium and support, representing potential biomass 3. Surfaces inviting for colonization 4. Undisturbed growth conditions, e.g., infrequent cleaning 20

21 Strategy: Put the biofilm into the right place Example: membrane system for treatment of heat exchanger water Biofilter ahead of the membrane 21

22 Biofilm Biofilm Membrane Porous support Membrane Porous support Before biofilter After biofilter Thin cut of biofilm on membrane 22

23 Biofilm parameters before/after filter Parameter unit before filter after filter Cell number [#/cm 2 ] 1,0 x ,5 x 10 6 CFU [#/cm 2 ] 1,0 x ,2 x 10 6 Protein [µg/ cm 2 ] 78 4 Carbohydrates [µg/ cm 2 ] 26 3 Uronic acids [µg/ cm 2 ] 11 2 Humic subst. [µg/ cm 2 ] Biofilm thickness [µm] 27 3 Flux decline [%] 35 <2 23

24 Biofilm engineering Mitigating adverse effects of a biofilm which cannot be removed Living with biofilms * Improved permeation properties * Improved heat transfer * Reduced friction resistance 24

25 McDonogh, R., G. Schaule and H.-C. Flemming (1994): The permeability of biofouling layers on membranes. J. Membr. Sci. 87,

26 Confocal laser scanning microscopy (CLSM) Vertical view of biofilm: change of structure Control 10 8 cells/cm² After 10 treatments with H 2 O 2 Still 10 8 cells/cm² 26

27 Natural Anti-Fouling Strategies I Options: - Tolerance - Avoidance - Defense Organisms we can learn from (see Tuesday section): Microalgae Macroalgae Terrestrial plants Echinodermata (Stachelhäuter) Worms Water plants (e.g., seaweed) Fish 27

28 Natural Anti-Fouling Strategies II Mechanical defense - Intense surface production of mucus - Surface-bound cilia-driven migration of a mucus film - Scraping of surface with specialized appendices ( windshield wiper ) - Surface renewal ( scinning ) - Cleaning by friction between body and sediment surface - Specific surface structures 28

29 Natural Anti-Fouling Strategies III Chemical defense - Surface-bound or excreted secondary metabolites * Toxins (some are very toxic) * Pheromones (AHL s) Extrinsic defense - Selected epibionts (inhibitory to others) - Specialized epibiont predators (grazers) Combined strategies 29

30 Monitoring - the key to successful anti-fouling strategies Early warning saves remedy efforts Efficacy control of cleaning procedures Optimization of cleaning Control of anti-fouling strategies 30

31 Biofilm monitoring: Observation of biofilm development over time What do we want to know? Site/location Quantity Thickness Distribution Nature of deposit - organic/inorganic - biological/abiological - chemical composition Stability (how easy to clean?) Kinetics of formation and removal 31

32 The optimal monitoring method: in situ in real time on line non destructive fast and accurate Integrates over large surface areas easy to handle, stable Has predictive power Early warning capacity Saves value 32

33 On-line Monitoring Sensors System Biofilm Cleaning Biofilm procedures Biofilm Hard-/Software Fouling Critical fouling boarder line Documentation/ Visualisation Defined alarm boarder line Defined effectivity boarder line time 33

34 The concept: use of monitors for automatic fouling control Modem Additives Dosage Modem Local data processing -> control systems 34

35 3 levels of information of monitors: Information Level I Detection of a deposit on a surface Example for parameter Scattered light Differential turbidity Optical fouling monitor Pressure drop Heat transfer resistance Weight increase Velocity of sound Photoacoustic spectroscopy Quartz crystal microbalance Level II Biological aspects of deposit FTIR-spectroscopy Tryptophane fluorescence Direct microscopy Level III Detailed information FTIR-spectroscopy Raman spectroscopy X-ray photoelectron spectroscopy 35

36 Conclusions: Five principles of alternative anti-fouling strategies 1. Learn to live with biofilms and keep them under control 2. Monitoring: crucial for timely detection of biofilms and countermeasure optimization 3. Cleaning is more important than killing biofilm organisms 4. Biofilm management: Nutrient limitation (nutrients are potential biomass) 5. Biofilm engineering: Mitigating of biofilm effects (hydraulic resistance) It is possible to live with biofilms! 36