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Thesis Submitted for the Degree of Doctor of Philosophy University of Bath PHD An investigation into the strength and thickness of biofouling deposits to optimise chemical, water and energy use in industrial process cleaning Peck, Oliver Award date: 2017 Awarding institution: University of Bath Link to publication Alternative formats If you require this document in an alternative format, please contact: [email protected] General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 07. Oct. 2021 An investigation into the strength and thickness of biofouling deposits to optimise chemical, water and energy use in industrial process cleaning Oliver Philip Wayland Peck A thesis submitted for the degree of Doctor of Philosophy University of Bath Department of Chemical Engineering March 2017 COPYRIGHT Attention is drawn to the fact that copyright of this thesis/portfolio rests with the author and copyright of any previously published materials included may rest with third parties. A copy of this thesis/portfolio has been supplied on condition that anyone who consults it understands that they must not copy it or use material from it except as permitted by law or with the consent of the author or other copyright owners, as applicable. This thesis/portfolio may be made available for consultation within the University Library and may be photocopied or lent to other libraries for the purposes of consultation with effect from Signed on behalf of the Faculty/School of Chemical Engineering ................................... ABSTRACT Biofouling is both a human health hazard and detrimental to process efficiency. Biofilm growth is inevitable on exposed surfaces, so an informed approach to cleaning and timely management are essential. Chemicals can readily kill cells, but the biofilm structure must be removed to prevent re- growth and maintain sterility. Chemical agents also pose health and environmental risks, but the typical alternative is to pump unsustainable volumes of cleaning solution through pipelines for mechanical cleaning. The aim of this research was to apply green cleaning principles to biofouling removal in industry, reducing the amount of chemicals, water and energy used in cleaning. Biofilms of Escherichia coli and Burkholderia cepacia were grown on polyethylene, glass and stainless steel 304, in single and mixed species cultures. Fluid dynamic gauging (FDG) utilises hydrodynamics to measure both the thickness and attached strength of the biofilms and therefore the optimum water usage for removal can be estimated, and is both relatively simple and inexpensive to operate. As well as using a static culture method, a drip flow reactor was built to develop biofilms under flow conditions. The use of FDG offers an original way of monitoring both the attachment strength and thickness of mixed species biofilms, and drip flow is an alternative to traditional biofilm growth methods for analysis of removal behaviours, with particular relevance to food production environments. The adhesive and cohesive strengths of both single and mixed species biofilms increased up to 14 days‘ growth, and as previous studies suggest that this will be sustained over longer periods under flow conditions, cleaning prior to peak strength would be prudent – at later stages the risk of pathogens developing and contaminating the process would likely become too great, particularly if the biofilm is experiencing significant detachment which increasingly occurs with age. The development of greater, sustained thickness over time can also pose problems with heat transfer and enhanced pressure drop. Protein, a key component of the extracellular matrix, showed a strong correlation with the adhesive strength of mixed species biofilms. Biofilms grown on polyethylene attached more strongly in the early stages of growth than those on glass or steel, which may be due to the greater hydrophobicity of the surface. Chemicals can be used most effectively to weaken the outer layers, and sodium hypochlorite was also shown to be useful for weakening surface adhesion – the required shear stress for 95% removal was reduced by approximately 60% for 5 and 10-day old biofilms. There are more risks associated with chlorine-based disinfectants than the alternative, peracetic acid, although finding a suitable low concentration would be simple using this method. There is no simple solution, complicated further by the unpredictability of the species present in industrial biofouling. The best way of minimising the risk of spoiling and contamination would be to clean surfaces with regularity, in the region of every 5 days rather than after a more prolonged period, 1 which would also serve to minimise the resources used by preventing biofilms from becoming too strongly attached or too thick. A chemical input would need to be determined by testing for the optimum concentration necessary for a suitable effect, thus eliminating excess use, and thereby reducing water and energy use in the process. Taking a multispecies sample from a process flow could offer a more realistic approximation of industrial biofilms. Surface coatings to prevent adhesion are the focus of much research, and could be an alternative to reactive methods. 2 Nomenclature Symbol Description Units a Orbital radius of shaking table m A Maximum cell number [-] A Surface area m2 AB Lewis acid-base polar interactions AFM Atomic force microscopy ATP Adenosine tri-phosphate BAC Benzalkonium chloride BCA Bicinchoninic acid BHI Brain-heart infusion BR Brownian movement forces BSA Bovine serum albumin CBD Calgary biofilm device CBR CDC biofilm reactor Cd Discharge coefficient [-] CDFF Continuous depth fluid fermenter Cf Fanning friction factor [-] CFD Computational fluid dynamics CFU Colony-forming units [-] ci Concentration of chemical species i in solution CIP Cleaning-in-place CLSM Confocal laser scanning microscopy COD Chemical oxygen demand CSH Cell surface hydrophobicity DAPI 4‘,6-diamidino-2-phenylindole DBNPA 2,2-dibromo-3-nitrilopropionamide DFR Drip flow reactor dh Hydraulic diameter of duct m DLVO Derjaguin-Landau-Varwey-Overbeek theory DNA Deoxyribonucleic acid DO Dissolved oxygen DSS Dimethyldichlorosilane dt Diameter of gauging nozzle m dtube Diameter of gauging tube m EDTA Ethylenediamenetetraacetic acid EL Electrostatic surface charge interactions EPDM Ethylene propylene diene monomer EPS Extracellular polymeric substances f Frequency of shaking table rotation s-1 FDG Fluid dynamic gauging FISH Fluorescent in situ hybridisation FTIR Fourier transform infrared spectroscopy h Interparticulate distance m h Clearance distance between gauging nozzle and surface m H Hydrostatic head m h0 Clearance distance between nozzle and clean surface m HVAC Heating, ventilation and air conditioning I Ionic strength Moles LB-EPS Loosely-bound EPS Leff Tube effective length m LW Lifschitz-van der Waals interactions 3 m Mass flow rate kg.s-1 -1 mactual Actual measured flow rate kg.s -1 mideal Ideal calculated flow rate kg.s MBC Minimum bactericidal concentration parts per million (ppm) MDPE Medium density polyethylene MIC Microbially influenced corrosion M.I.C. Minimum inhibitory concentration parts per million (ppm) MRD Modified Robbins device n Number of moles Moles n Number of cell generations [-] N Number of cells in a culture [-] N0 Number of cells in previous generation [-] NMR Nuclear magnetic resonance spectroscopy OCT Optical coherence tomography OD Optical density P Hydrostatic pressure kg/(m.s-2) PBS Phosphate-buffered saline PCA Plate count agar PE Polyethylene PEX Cross-linked polyethylene PFA Perfluoroalkoxy tatrafluoroethylene PMMA Poly(methyl methacrylate) PVC Poly(vinyl chloride) PVDF Polyvinylidene fluoride r Radial distance from nozzle centre m Ra Average roughness µm Rf Thermal resistance parameter Rrms Root mean square roughness µm Rz Average peak-to-valley height µm RDE Rotating disk electrode Re Reynolds number [-] RFC Radial flow cell RM Raman spectroscopy RNA Ribonucleic acid RO Reverse osmosis SEM Scanning electron microscopy SEM-EDS SEM with energy dispersion spectroscopy SEPS Soluble extracellular polymeric substances SS Stainless steel SWR Standard working reagent TB-EPS Tightly-bound extracellular polymeric substances TBT Tributyltin TDR Time-domain reflectometry TSB Tryptic soy broth -1 Um Mean pipe flow velocity m.s uPVC Unplasticised poly(vinyl chloride) UV Ultraviolet v Velocity m.s-1 VBNC Viable but non-culturable cells w Width of gauging nozzle rim m XDLVO Extended DLVO theory z Elevation head m zi Charge of chemical species i in solution 4 zFDG Zero-discharge fluid dynamic gauging α Angle of gauging nozzle contraction at the tip 0 γa Surface free energy of surface a γab Interfacial tension between surfaces a and b δ Fouling layer thickness m ΔG Gibbs free energy ΔP12 Pressure drop between points 1 and 2 Pa 0 θ
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