Sootblowing is a process in which supersonic steam jets are used to periodically blast deposits off heat transfer tubes in kraft recovery boilers. However, sootblowing significantly consumes the valuable high pressure steam generated by the boiler, hence it should be optimized. A recovery boiler consists of three convective sections - superheater, generating bank and economizer. The tube arrangement in these sections, particularly the tube spacing is different from each other. Moreover, tubes in an economizer are finned. A sootblower jet will interact differently with these tube arrangements, potentially affecting its strength, and hence deposit removal capability. The objective of this work was to characterize jet/tube interaction in the three sections of a recovery boiler. Lab-scale experiments were conducted in which these interactions were visualized using the schlieren technique coupled with high-speed video, and were quantified by pitot pressure measurements. This work is the first to visualize the interactions. The offset between the jet and tube centrelines, the nozzle exit diameter relative to the tube diameter, and the distance between the nozzle and tube were varied to examine their effects on jet/tube interaction. Results showed that due to the very low spreading rate of a supersonic jet, a jet (primary jet) stops interacting with a superheater platen when the jet is only a small distance away from it. When the jet impinges on a tube, the jet deflects at an angle, giving rise to a weaker ‘secondary’ jet. Due to the large inter-platen spacing, a secondary jet has an insignificant impact in a superheater. In a generating bank, the primary jet weakens between the closely spaced tubes due to increased mixing. However, a secondary jet impinges on the adjacent tubes exerting a high impact pressure on those tubes. The primary jet also weakens between finned economizer tubes, but remains stronger for a greater distance than in a generating bank. As in the case inside a generating bank, a secondary jet also impinges on adjacent rows of tubes in an economizer. The results imply that in a superheater, a sootblower jet must be directed close to the platens to yield useful jet/deposit interactions, and to avoid wasting steam by blowing between the platens. In a generating bank, deposits beyond the first few tubes of a row experience a weaker sootblower jet, and thus may not be removed effectively. However, secondary jets may contribute to removing deposits from the first few adjacent tubes. They may also induce erosion-corrosion of those tubes. Secondary jets may also help remove deposits from adjacent rows in a finned tube economizer. In an economizer, the strength and hence, the deposit removal capability of a sootblower jet diminish only slightly beyond the supersonic portion of the jet. A mathematical model was also developed to determine the feasibility of using inclined sootblower nozzles in recovery boiler superheaters, and suggests that it may be possible to clean superheater platens more effectively with slightly inclined nozzles.

Una de las aplicaciones más importante de los procesos de filtración por membrana es en el área de tratamiento de agua por ultrafiltración, nanofiltración u ósmosis inversa. Entre los problemas más serios encontrados en estos procesos destaca la aparición de los fenómenos de ensuciamiento y envejecimiento de las membranas que limitan la eficacia de la operación tanto en la separación de los solutos, como en el flujo de permeado, afectando también el ciclo de vida de las membranas.Para reducir el coste de la producción y mejorar la robustez y eficacia de estos procesos es imprescindible disponer de modelos capaces de representar y predecir la eficiencia y el comportamiento de las membranas durante la operación. Una alternativa viable a los modelos teóricos, que presentan varias particularidades que dificultan su postulado, la constituyen los modelos basados en el análisis de los datos experimentales, entre cuales destaca el uso de las redes neuronales. Dos metodologías han sido evaluadas e investigadas, una constando en la caracterización de las interacciones entre las membranas y los compuestos orgánicos presentes en el agua de alimentación, y la segunda basada en el modelado de la dinámica de operación de las plantas de desalinización por ósmosis inversa.Relaciones cuantitativas estructura‐propiedad se han derivado usando redes neuronales de tipo back‐propagation, para establecer correlaciones entre los descriptores moleculares de 50 compuestos orgánicos de preocupación para la salud pública y su comportamiento frente a 5 membranas comerciales de ósmosis inversa, en términos de permeación, absorción y rechazo. Para reducir la dimensión del espacio de entrada, y para evitar el uso de la información redundante en el entrenamiento de los modelos, se han usado tres métodos para seleccionar el menor número de los descriptores moleculares relevantes entre un total de 45 que caracterizan cada molécula. Los modelos obtenidos se han validado utilizando un método basado en el balance de materia, aplicado no solo a los 50 compuestos utilizados para el desarrollo de los modelos, sino que también a un conjunto de 143 compuestos orgánicos nuevos. La calidad de los modelos obtenidos es prometedora para la extensión de la presente metodología para disponer de una herramienta comprensiva para entender, determinar y evaluar el comportamiento de los solutos orgánicos en el proceso de ósmosis inversa. Esto serviría también para el diseño de nuevas y más eficaces membranas que se usan en este tipo de procesos.En la segunda parte, se ha desarrollado una metodología para modelar la dinámica de los procesos de ósmosis inversa, usando redes neuronales de tipo backpropagation y Fuzzy ARTMAP y datos experimentales que proceden de una planta de desalinización de agua salobre Los modelos desarrollados son capaces de evaluar los efectos de los parámetros de proceso, la calidad del agua de alimentación y la aparición de los fenómenos de ensuciamiento sobre la dinámica de operación de las plantas de desalinización por osmosis inversa. Se ha demostrado que estos modelos se pueden usar para predecir el funcionamiento del proceso a corto tiempo, permitiendo de esta manera la identificación de posibles problemas de operación debidas a los fenómenos de ensuciamiento y envejecimiento de las membranas. Los resultados obtenidos son prometedores para el desarrollo de estrategias de optimización, monitorización y control de plantas de desalinización de agua salobre. Asimismo, pueden constituir la base del diseño de sistemas de supervisón capaces de predecir y advertir etapas de operación incorrecta del proceso por fallos en el mismo, y actuar en consecuencia para evitar estos inconvenientes. / One of the more serious problems encountered in reverse osmosis (RO) water treatment processes is the occurrence of membrane fouling, which limits both operation efficiency (separation performances, water permeate flux, salt rejection) and membrane life‐time. The development of general deterministic models for studying and predicting the development of fouling in full‐scale reverse osmosis plants is burden due to the complexity and temporal variability of feed composition, diurnal variations, inability to realistically quantify the real‐time variability of feed fouling propensity, lack of understanding of both membrane‐foulants interactions and of the interplay of various fouling mechanisms. A viable alternative to the theoretical approaches is constituted by models developed based on direct analysis of experimental data for predicting process operation performance. In this regard, the use of artificial neural networks (ANN) seems to be a reliable option. Two approaches were considered; one based on characterizing the organic compounds passage through RO membranes, and a second one based on modeling the dynamics of permeate flow and separation performances for a full‐scale RO desalination plant.Organic solute sorption, permeation and rejection by RO membranes from aqueous solutions were studied via artificial neural network based quantitative structure‐property relationships (QSPR) for a set of 50 organic compounds for polyamide and cellulose acetate membranes. The separation performance for the organic molecules was modeled based on available experimental data achieved by radioactivity measurements to determine the solute quantity in feed, permeate and sorbed by the membrane. Solute rejection was determined from a mass balance on the permeated solution volume. ANN based QSPR models were developed for the measured organic sorbed (M) and permeated (P) fractions with the most appropriate set of molecular descriptors and membrane properties selected using three different feature selection methods. Principal component analysis and self‐organizing maps pre‐screening of all 50 organic compounds defined by 45 considered chemical descriptors were used to identify the models applicability domain and chemical similarities between the organic molecules. The ANN‐based QSPRs were validated by means of a mass balance test applied not only to the 50 organic compounds used to develop the models, but also to a set of 143 new compounds. The quality of the QSPR/NN models developed suggests that there is merit in extending the present compound database and extending the present approach to develop a comprehensive tool for assessing organic solute behavior in RO water treatment processes. This would allow also the design and manufacture of new and more performing membranes used in such processes.The dynamics of permeate flow rate and salt passage for a RO brackish water desalination pilot plant were captured by ANN based models. The effects of operating parameters, feed water quality and fouling occurrence over the time evolution of the process performance were successfully modeled by a back‐propagation neural network. In an alternative approach, the prediction of process performance parameters based on previous values was achieved using a Fuzzy ARTMAP analysis. The neural network models built are able to capture changes in RO process performance and can successfully be used for interpolation, as well as for extrapolation prediction, fact that can allow reasonable short time forecasting of the process time evolution. It was shown that using real‐time measurements for various process and feed water quality variables, it is possible to build neural network models that allow better understanding of the onset of fouling. This is very encouraging for further development of optimization and control strategies. The present methodology can be the basis of development of soft sensors able to anticipate process upsets.

Water resources are increasingly precious, so wastewater reclaiming has become an important source of water nowadays. There are many types of industry including conventional and hi-tech ones in the selected industrial processing zone, where different process wastewaters are treated by a centralized wastewater treatment plant. The effluent is then discharged into the ocean (EDO). On the other hand, among several other industries backside grinding (BG) wastewater generated by the IC (integrated-circuit) packaging and testing industry is treated by their owned wastewater treatment plants and then discharged onto land (EDL). Normally, BG wastewater is huge in quantity and it contains microscale and nanoscale particles. The objectives of this research were two-fold: (1) to evaluate the feasibility of using two tubular ceramic membranes (microfiltration and ultrafiltration) coupled with the electrocoagulation/electrofiltration (EC/EF) process to effectively treat the effluent discharged into the ocean, effluent discharged onto land, and BG wastewater for the purpose of reclamation; and (2) to investigate the best time for backwashing of membranes through the analysis of components of membrane fouling using resistances in series model. The experimental results showed that the ultrafiltration (UF) membrane (i.e., tubular TiO2/Al2O3 composite membrane) outperformed the mictrofiltration (MF) membrane (i.e., tubular Al2O3 membrane) in terms of permeate quality. But, generally, the later yielded a greater membrane flux. In the case of BG wastewater by UF and EC/EF, the quality of permeate met the tap water standards in terms of water quality items analyzed. As for EDO and EDL further treated by UF and EC/EF, all the analyzed water quality items of permeate, except pH and total dissolved solids, met the tap water standards in Taiwan. Thus, more efforts have to be made to reclaim these two types of effluent. Finally, the components of membrane fouling were analyzed using resistances in series model for the tested water specimens. The results showed that generally the irreversible resistance component (Rirr) had a greater contribution to a better quality of permeate than that of the reversible resistance component (Rr). It was also found that the magnitude of Rirr of BG wastewater was greater than Rirr values of the other two effluents. This might explain why the quality of permeate of the former was better than the latter. The results further indicated that Rr increased more than Rirr as the operating time elapsed, resulting in a limited improvement of permeate quality even a longer treatment time was employed. To recover the membrane flux to its optimum, in this study the best time for backwashing of membrane was determined based on the time at which Rr was greater than Rirr. However, the flux recovery was found to be in the range of 60-77% as compared with the initial flux for a virgin membrane in treating new batch of water specimens. The fraction unable to recover by backwashing might be contributed by Rirr in the membrane pores. A further acid washing would resolve this problem.

In Taiwan, more than 25% of all water uses comes from groundwater, and thus groundwater is a very valuable water resource for both domestic and industrial uses. However, groundwater at many existing former industrial sites and disposal areas was contaminated by halogenated organic compounds that were released into the environment. The chlorinated solvent trichloroethene (TCE) is one of the most ubiquitous of these compounds. In this laboratory-scale feasibility study, a hybrid two-stage process combining fiber filtration (FF) and nanofiltration (NF) was applied to remove to suspended solids (SS) and TCE from contaminated groundwater for water purification. In this study, a man-made kaolin solution was used to simulate groundwater purification using FF system. Then, microfiltration (MF), ultrafiltration (UF), and NF systems were applied for TCE removal. The hybrid membrane process using FF and NF units was used to evaluate the feasibility on TCE removal. The scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) were used to investigate membrane morphology and structure after use. A 3-D excitation emission fluorescence matrix (EEFM) was used to evaluate the potential of membrane organic fouling. Results show that the optimization filtration velocity of FF was 15.3 m/hr, and the observed TCE and SS removal efficiencies were 80% and 60%, respectively. Removal mechanisms for MF and UF were mainly sieving, and the removal mechanism for NF was mainly electrostatic repulsion. Results indicate that NF had the highest TCE removal efficiency (98.2%). When initial TCE concentration was 1 mg/L, NF membrane pore might shrink caused increased TCE removal (rejection). When TCE concentration was higher 1 mg/L, membrane damage and pore enlargement was observed with decreased TCE removal efficiency. The observed SS, sulfate, and hardness removal efficiencies were 99.8%, 98.7%, and 98.7% respectively, when FF and NF hybrid process was used. Higher TCE concentration might enlarge membrane pore, which caused decreased membrane separation and increased flux. Approximately 46% of flux drop was observed when NF was used alone compared to the hybrid membrane process using FF as the first treatment stage. Membrane analyses show that residual TCE was adsorbed on the membrane. Low zeta potential of groundwater was observed due to the compressed electric double layer, which caused aggregation of particle. High zeta potential of permeate was due to the particle dispersive through hybrid process. Results from SEM analysis show that membrane morphology was damaged by TCE, and heavy metal in groundwater deposited on membrane. Results of EEFM analysis indicate that groundwater contained humic acid (HA) and soluble microbial by-product (SMP). HA and SMP might be adsorbed on fiber filter, and extracellular polymeric substances (EPS) that attached on fiber filter might be washed out. The organic powders on the surface of the fiber filter might be washed out causing the increased in NPDOC concentrations. Humic acid could be removed through NF process, and SMP might be adsorbed in membrane pore caused organic fouling, and SMP might be washed out after treatment by the FF+NF hybrid process. Results indicate that FF as pre-treatment can maintain higher flux. Higher TCE concentration caused membrane destruction and decreased membrane separation. TCE contaminated groundwater can be affectively treated by the hybrid membrane system to meet the groundwater standard and reclaimed water standard. Reclaimed water could be used for industrial cooling water and irrigation purposes.

The objective of this study is to develop a membrane-based generic treatment scheme for wastewaters of indigo dyeing process of denim industry, based on water reuse. For this purpose, firstly the performances of microfiltration (MF), coagulation, and ultrafiltration (UF) processes were evaluated as pretreatment alternatives and the best pretreatment alternatives appeared to be single stage 5 &micro / m MF and sequential 5 &micro / m MF followed by 100 kDa UF providing high permeation rate and high color retention. These two pretreatment alternatives were compared based on the performance of nanofiltration (NF) using NF 270 membrane, and the best pretreatment process was evaluated as 5 &micro / m MF that provided 87-92% color and 10% chemical oxygen demand (COD) retention. After the pretreatment tests, three different NF (NF 270, NF 90, Dow Filmtec, USA and NF 99, Alfa Laval, Denmark) and two different reverse osmosis (RO) membranes (HR 98 PP and CA 995 PE, Alfa Laval, Denmark) were tested to produce reusable water. Permeate COD and color performances of the tested NF and RO membranes were similar and satisfactory in meeting the relevant reuse criteria, while permeate conductivity was satisfactory only for HR 98 PP RO membrane and for NF 90 membrane. On the other hand, NF 270 membrane was superior to the other membranes in terms of permeation rate. For NF 270 membrane / cumulative color, COD and conductivity retentions were found to be 93 %, 92 %, and 60 %, respectively. When the developed process chain (5&micro / m MF+ NF 270) was also tested for a dilute indigo dyeing wastewater, it was found out that the developed scheme works similarly and is generic for indigo dyeing wastewaters.

Water is becoming increasingly scarce as the demand for fresh water continues to rise. One potential new water resource is purified produced water. Produced water is generated during oil and gas production, and it is often contaminated with emulsified oil, high levels of salt, and particulate matter. Produced water purification using polymer membranes has been investigated, but its implementation is limited by membrane fouling. This study focused on the preparation and application of poly(ethylene glycol) (PEG) hydrogels as fouling-resistant coatings for commercial reverse osmosis (RO) membranes. To prepare fouling-resistant coatings for RO membranes, three series of copolymer hydrogel networks were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as the crosslinker and acrylic acid (AA), 2-hydroxyethyl acrylate (HEA), or poly(ethylene glycol) acrylate (PEGA) as comonomers, and their transport properties were evaluated. The hydrogels have high water uptake and high water permeability, and crosslink density strongly influences water uptake and water permeability. For example, a 100 mol% PEGDA hydrogel contained 61% water by volume, but 80PEGA, which has essentially the same chemical composition but lower crosslink density, contained 72% water by volume. Hydrogel water permeability ranged from 10 to 26 (L [mu]m)/(m² hr bar) and correlates well with water uptake; high water uptake often leads to high water permeability. Additionally, the copolymers have hydrophilic surfaces with a low affinity for oil, based on contact angle measurements using n-decane in water. Commercial RO membranes (AG RO membrane from GE Water and Process Technologies) were coated with PEG hydrogels, and the desalination and fouling resistance properties of the coated membranes were tested. The water flux of coated membranes and a series-resistance model were used to estimate coating thickness; the coatings were approximately 2 [mu]m thick. NaCl rejection for both uncoated and coated membranes was 99.0% or greater. As determined by zeta potential measurements, both uncoated and coated RO membranes are negatively-charged, but coated membranes are less negatively-charged than uncoated RO membranes. Model oil/water emulsions, prepared with either a cationic or an anionic surfactant, were used to probe membrane fouling. In the absence of oil, surfactant charge, and therefore, electrostatic interactions play a significant role in membrane fouling. In the presence of DTAB, a cationic surfactant, the AG RO membrane water flux immediately dropped to 30% of its initial value, but in the presence of SDS, an anionic surfactant, its water flux gradually decreased to 74% of its initial value after 24 hours. However, in both cases, coated membranes exhibited less flux decline than uncoated membranes. Coated membranes also experienced little fouling in the presence of an n-decane/DTAB emulsion. After 24 hours, the water flux of a PEGDA-coated AG RO membrane was 73% of its initial value, while the water flux of an AG RO membrane fell to 26% of its initial value. Conversely, both coated and uncoated membranes fouled significantly in the presence of an n-decane/SDS emulsion, indicating that oil fouling is controlled both by electrostatic and hydrophobic interactions. Overall, this work provides answers to some of the fundamental questions posed regarding the viability of using modified membranes for produced water treatment. / text

No description available.

Delisea pulchra is a red macroalga that produces furanones, a class of secondary metabolites that inhibit the growth and colonization of a range of micro- and macroorganisms. In bacteria, furanones specifically inhibit acyl homoserine lactone (AHL)- driven quorum sensing, which is known to regulate a variety of colonization and virulence traits. This thesis aims to unveil multiple aspects of the chemically mediated interactions between an alga and its bacterial flora. It was demonstrated that the quorum sensing genetic machinery of bacteria is laterally transferred, making traditional 16S rRNA gene based-diversity techniques poorly suited to identify quorum sensing species. Previous studies had shown that AHL-producing bacteria belonging to the roseobacter clade can be readily isolated from D. pulchra. Because of this, it was decided to use a roseobacter epiphytic isolate from this alga, Ruegeria strain R11, to conduct a series of colonization experiments on furanone free and furanone producing D. pulchra. Furanones were shown to inhibit Ruegeria strain R11's colonization and infection of D. pulchra. In addition, it was demonstrated that Ruegeria strain R11 has temperature-regulated virulence, similar to what is seen for the coral pathogen Vibrio shiloi. Rising ocean temperatures may explain bleached D. pulchra specimens recently observed at Bare Island, Australia. To assess whether quorum sensing is common within the roseobacter clade, cultured isolates from the Roseobacter, Ruegeria and Roseovarius genera were screened for AHL production. Half of the bacteria screened produced the quorum sensing signal molecules, AHLs. These AHLs were identified using an overlay of an AHL reporter strain in conjunction with thin layer chromatography (TLC). The prevalence of quorum sensing within the roseobacter clade, suggests that these species may occupy marine niches where cellular density is high (such as surface associated communities on substratum and marine eukaryotes). Diversity studies in marine microbial communities require appropriate molecular markers. The 16S rRNA gene is the most commonly used marker for molecular microbial ecology studies. However, it has several limitations and shortcomings, to which attention has been drawn here. The rpoB gene is an alternate ???housekeeping??? gene used in molecular microbial ecology. Therefore, the phylogenetic properties of these two genes were compared. At most taxonomic levels the 16S rRNA and rpoB genes offer similar phylogenetic resolution. However, the 16S rRNA gene is unable to resolve relationships between strains at the subspecies level. This lack of resolving power is shown here to be a consequence of intragenomic heterogeneity.

Fouling of heat treatment equipment in the dairy processing industry is an expensive and persistent problem. The objective of this work was to develop a better understanding of the mechanisms of dairy fouling in heat exchangers and identify methods to control this build-up. This was part of a larger project investigating the interaction between spore-forming thermophilic bacilli (thermophiles) contamination and fouling deposits on internal surfaces of equipment. Two systems were developed to monitor the onset and build-up of fouling on the internal surfaces of two research heat exchangers. The first used a commercial sensor to measure the local heat flux and the temperature on the hot side of a plate type heat exchanger. The heat transfer coefficient was calculated and normalised with its value at the start of the run to reflect the contribution of fouling deposits to the thermal resistance, thus giving a real-time estimate of the rate of fouling. The second system used an energy balance over a tubular type heat exchanger and measured inlet and outlet temperatures to estimate the overall heat transfer coefficient thus giving a global measurement of fouling over the tubular heat exchanger. In both systems the plot of normalised heat transfer coefficient over time often stayed constant over an induction period, which was followed by a falling period indicative of growth in the fouling layer thickness and/or mass. Each system was validated by comparing the final value of the normalised heat transfer coefficient with direct measurements of fouling made at the end of a run namely: fouling deposit height for the local measurement and fouling deposit mass for the global measurement. The normalised heat transfer coefficient reported by each system correlated well with the corresponding direct measurement of the fouling layer. An important factor identified in this study was the effect of air bubble nucleation on fouling deposits. It was shown that bubbles that formed on the heated surface greatly reduced the length of the induction period to a matter of seconds rather than hours, as found in previous studies of fouling in the absence of surface bubbles. The rate of fouling was also enhanced while the bubbles remained at the surface. The structure of bubble type fouling layers was linked to the behaviour of the bubbles at the heated surface. Visual observations of these bubbles showed evidence of growth, vibration and coalescence during their period of attachment to the heated surface. Deposits from bubble type fouling consisted of all solid components found in the original milk solution, except lactose, in approximately the same ratio. By contrast fouling deposits reported in the literature with systems operating under the traditional protein denaturation mechanism were reported to consist mainly of whey proteins. Bubble induced fouling can be limited in a number of ways, the most effective being to maintain a high operating pressure in the equipment to ensure nucleation does not occur. Experiments conducted in this study showed that a pressure of 130 kPa.g was sufficient to suppress all bubble nucleation at the heated surface at a temperature of 90°C. Another method identified was the use of high linear fluid velocities to entrain any surface bubbles into the processing stream immediately upon nucleation. Linear velocities above 1.0 m/s were shown to achieve this goal in the miniature plate heat exchanger tested. However, this method is only partially successful because the local linear velocity varies with position in heat exchange equipment of complex geometries and can drop below the mainstream average velocity causing surface bubbles to form, especially in recirculation regions behind flow obstacles. A more reliable method, in situations where high operating pressures could not be used, involved conditioning the heated surface with a thin protein layer during the first few minutes of a run. Conditioning the surface resulted in bubble suppression even at high temperatures and low pressures, thus greatly extending the length of the induction period. Trials performed in this study showed that the addition of a proteolytic enzyme produced by psychrotrophic microbes greatly increased fouling. The enzyme destabilised the caseins which could attach directly to the heat exchange surface independently from the bubble fouling mechanism. Thus the quality of the milk is another important factor to consider. However, the addition of enzymes produced by thermophilic bacilli isolated from milk powder plants did not increase fouling. A theory describing the air bubble induced fouling mechanism is presented along with recommendations on how to reduce this fouling contamination in processing equipment.

Fouling of heat treatment equipment in the dairy processing industry is an expensive and persistent problem. The objective of this work was to develop a better understanding of the mechanisms of dairy fouling in heat exchangers and identify methods to control this build-up. This was part of a larger project investigating the interaction between spore-forming thermophilic bacilli (thermophiles) contamination and fouling deposits on internal surfaces of equipment. Two systems were developed to monitor the onset and build-up of fouling on the internal surfaces of two research heat exchangers. The first used a commercial sensor to measure the local heat flux and the temperature on the hot side of a plate type heat exchanger. The heat transfer coefficient was calculated and normalised with its value at the start of the run to reflect the contribution of fouling deposits to the thermal resistance, thus giving a real-time estimate of the rate of fouling. The second system used an energy balance over a tubular type heat exchanger and measured inlet and outlet temperatures to estimate the overall heat transfer coefficient thus giving a global measurement of fouling over the tubular heat exchanger. In both systems the plot of normalised heat transfer coefficient over time often stayed constant over an induction period, which was followed by a falling period indicative of growth in the fouling layer thickness and/or mass. Each system was validated by comparing the final value of the normalised heat transfer coefficient with direct measurements of fouling made at the end of a run namely: fouling deposit height for the local measurement and fouling deposit mass for the global measurement. The normalised heat transfer coefficient reported by each system correlated well with the corresponding direct measurement of the fouling layer. An important factor identified in this study was the effect of air bubble nucleation on fouling deposits. It was shown that bubbles that formed on the heated surface greatly reduced the length of the induction period to a matter of seconds rather than hours, as found in previous studies of fouling in the absence of surface bubbles. The rate of fouling was also enhanced while the bubbles remained at the surface. The structure of bubble type fouling layers was linked to the behaviour of the bubbles at the heated surface. Visual observations of these bubbles showed evidence of growth, vibration and coalescence during their period of attachment to the heated surface. Deposits from bubble type fouling consisted of all solid components found in the original milk solution, except lactose, in approximately the same ratio. By contrast fouling deposits reported in the literature with systems operating under the traditional protein denaturation mechanism were reported to consist mainly of whey proteins. Bubble induced fouling can be limited in a number of ways, the most effective being to maintain a high operating pressure in the equipment to ensure nucleation does not occur. Experiments conducted in this study showed that a pressure of 130 kPa.g was sufficient to suppress all bubble nucleation at the heated surface at a temperature of 90°C. Another method identified was the use of high linear fluid velocities to entrain any surface bubbles into the processing stream immediately upon nucleation. Linear velocities above 1.0 m/s were shown to achieve this goal in the miniature plate heat exchanger tested. However, this method is only partially successful because the local linear velocity varies with position in heat exchange equipment of complex geometries and can drop below the mainstream average velocity causing surface bubbles to form, especially in recirculation regions behind flow obstacles. A more reliable method, in situations where high operating pressures could not be used, involved conditioning the heated surface with a thin protein layer during the first few minutes of a run. Conditioning the surface resulted in bubble suppression even at high temperatures and low pressures, thus greatly extending the length of the induction period. Trials performed in this study showed that the addition of a proteolytic enzyme produced by psychrotrophic microbes greatly increased fouling. The enzyme destabilised the caseins which could attach directly to the heat exchange surface independently from the bubble fouling mechanism. Thus the quality of the milk is another important factor to consider. However, the addition of enzymes produced by thermophilic bacilli isolated from milk powder plants did not increase fouling. A theory describing the air bubble induced fouling mechanism is presented along with recommendations on how to reduce this fouling contamination in processing equipment.