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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

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2017

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University of Bath

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Download date: 26. Sep. 2023

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 1

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 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,

2 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. 3

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 -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

4 m Mass flow rate kg.s-1 mactual Actual measured flow rate kg.s-1 mideal Ideal calculated flow rate kg.s-1 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

Um Mean pipe flow velocity m.s-1

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 5 zFDG Zero-discharge fluid dynamic gauging Į Angle of gauging nozzle contraction at the tip 0

Ȗa Surface free energy of surface a

Ȗab Interfacial tension between surfaces a and b

į Fouling layer thickness m

ǻ Gibbs free energy

ǻ12 Pressure drop between points 1 and 2 Pa

ș Contact angle 0

Ȝ Cell culture lag period s, min, hr

Ȝ Thickness of gauging nozzle rim m

µf Fluid dynamic viscosity kg/(m.s)

µm Increase in cell number over time (log gradient)

µFD Microfluidic device

ȡf Fluid density kg.m-3

IJmax Maximum applied shear stress Pa

IJo Orbital shear stress on shaking table Pa

IJw Wall shear stress Pa

6

Contents

ABSTRACT ................................................................................................................................................ 1

Nomenclature ......................................................................................................................................... 3

Figures ................................................................................................................................................... 11

Tables .................................................................................................................................................... 24

1. INTRODUCTION ............................................................................................................................. 26

1.1 Context .................................................................................................................................. 26

1.2 Structure of Report ............................................................................................................... 27

2. LITERATURE REVIEW ......................................................................................................................... 28

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