The effect of electromagnetic fields on biofouling in a heat exchange system using seawater

Synergistic Benefits of Micro/Nanostructured Oil-Impregnated Surfaces in Reducing Fouling while Enhancing Heat Transfer

Liquid-liquid heat exchangers that operate in marine environments are susceptible to biofouling, which decreases the overall heat exchange between hot and cold liquids by increasing the conduction resistance. Recently, micro/nanostructured oil-impregnated surfaces have been shown to significantly reduce biofouling. However, their potential as a heat exchanger material has not been studied. Neither is it obvious since the oil used for impregnation increases the wall thickness and the associated conduction resistance. Here, by conducting extensive field and laboratory studies supported by theoretical modeling of heat transfer in oil-infused heat exchanger tubes, we report the synergistic benefits of micro/nanostructured oil-impregnated surfaces for reducing biofouling while maintaining good heat transfer. These benefits justify the use of lubricant-infused surfaces as heat exchanger materials, in particular in marine environments.

Effect of magnetic field on calcium - silica fouling and interactions in brackish water distribution systems

Fouling growth in brackish water distribution systems (BWDS), especially calcium-silica fouling, is inevitable issue in brackish water desalination, chemical and agricultural industry, eventually threaten the cleaner production process and environment. Magnetic Field (MF) has been a greener and effective technology to control calcium carbonate fouling. However, the effects of MF on composite calcium-silica fouling are still elusive. Therefore, this paper assessed the effect of MF on calcium and silica fouling. We found that MF not only significantly reduce the calcium carbonate fouling, but also obviously decreased the silica fouling. The MF reduced the calcite fouling reached 38.2%-64.3% by changing water quality parameters to trigger the transformation rate of CaCO₃ crystal from compact calcite to looser aragonite, as well as increase the unit-cell parameters and chemical bond lengths of calcite and aragonite. The MF also decreased the content of silica fouling (silica and silicate) reached 22.4-46.3% by reducing the concentration of soluble silica and accelerating the flocculation settlement to form large size solid particles in BW. Furthermore, MF broke the synergistic interactions among calcium and silica fouling. In addition, the anti-fouling ability of permanent MF was higher by 12.3-35.1% than electric MF. Overall, these findings demonstrate that MF is an effective and chemical-free technology to control calcium-silica fouling in BWDS, and provide a new perspective for sustainable application of brackish water.

Using electromagnetic fields to inhibit biofouling and scaling in biogas slurry drip irrigation emitters

Reusing biogas slurry (BS) in agricultural drip irrigation systems may provide a solution to deal with the adverse environmental impacts of applying BS. Biofouling and scaling are two leading issues in drip irrigation emitters. This study investigated a practice that applied electromagnetic fields (EMFs) to control biofilms and scales. The bacterial communities and mineral precipitations in the clogging substances of emitters were determined. Results showed that EMFs inhibited the growth of microbes, and influenced BS physicochemical parameters. Consequently, EMFs shifted the bacterial communities with reduced diversities. Network analyses revealed that bacterial species under EMFs treatments showed lower average connectivities and simpler interactions, which were responsible for the decreases of extracellular polymers substances (EPS). Moreover, EMFs treatments not only reduced the carbonates in emitters, but also prevented the depositions of phosphates, silicates, and quartzes. EMFs also had impacts on the lattice parameters and crystal volumes of carbonates. In addition, the changes in bacterial communities and EPS contents were associated with the reductions of various minerals. Accordingly, EMFs effectively mitigated biofilms and scales with the fixed clogging substances reduced by 29.1-53.8 %. These findings demonstrated that applying EMFs is an effective anti-biofouling and anti-scaling treatment with potential applications in BS irrigation systems.

Electromagnetic fields for biofouling mitigation in reclaimed water distribution systems

Biofouling is ubiquitous in reclaimed water distribution systems and causes various industrial, economic, and health issues. This paper investigated the anti-biofouling efficacy of electromagnetic fields (EMFs) for agricultural emitters used for two types of reclaimed water. 16S rRNA gene sequencing and X-ray diffraction were applied to determine the microbial communities and mineral compositions in biofilms. The obtained results revealed that EMF treatment significantly changed the bacterial communities and reduced their diversities in biofilm by affecting water quality parameters. Network analysis results indicated that EMFs were detrimental to the co-occurrence patterns of mutualistic relationships among bacterial species, destroyed the connectivity and complexity of the networks, and inhibited biofilm formation [decreased total biomass and extracellular polymeric substance (EPS) content]. EMF treatment could also decrease the deposition of mineral precipitates, reducing the carbonate and silicate content in biofilm. The decrease of EPS content appeared to reduce biofilm-induced mineral crystallization, while the ion precipitations accelerated by EMFs caused an erosive effect on biofilm. The results demonstrated that EMF treatment is an effective, chemical-free, and anti-biofouling treatment method with great potential for biofouling control in reclaimed water distribution systems.

CUSUM chart method for continuous monitoring of antifouling treatment of tubular heat exchangers in open-loop cooling seawater systems

A CUSUM chart method is presented as an alternative tool for continuous monitoring of an electromagnetic field-based (EMF) antifouling (AF) treatment of a heat exchanger cooled by seawater. During an initial experimental phase, biofilm growth was allowed in a heat exchanger formed of four tubes until sufficient growth had been established. In two of the tubes, continuous EMF treatment was then applied. The heat transfer resistance and heat duty (heat transfer per unit time) results showed that biofilm adhesion was reduced by the EMF treatment. EMF treatments resulted in a 35% improvement in the heat transfer resistance values. The proposed CUSUM chart method showed that the EMF treatment increased the useful life of the heat exchanger by ∼20 days. Thus, CUSUM charts proved to be an efficient tool for continuous monitoring of an AF treatment using data collected online and can also be used to reduce operation and maintenance costs.

Low-frequency electromagnetic fields as an alternative to sanitize water of drinking systems in poultry production?

Low-frequency electromagnetic fields (LF-EMF) may present an alternative to conventional sanitation methods of water supply lines in animal production. The objective of this study was to evaluate the effect of the application of LF-EMF on bacterial concentrations and biofilms at scale-models of different drinking systems (circulating and non-circulating) conventionally used in poultry holdings. Treated systems were equipped with commercial devices producing pulsed electromagnetic signals of low frequency up to 10,000 Hz; max. 21 mT. Exposure of water to LF-EMF resulted in changes of the culturable bacterial counts, although with high standard deviations. Differing between systems types, LF-EMF treatment seemed to be responsible either for a limitation or for an increase of colony forming unit counts, with partly statistically significant differences, especially in early stages of treatment. In contrast, neither biofilm formation nor counts of cells suspended in water differed between treated and control lines over 28 days of experiment, as determined by fluorescence microscopy. Although this study indicates that LF-EMF may influence culturability of water microorganisms, no clear inhibitory effects on bacterial biofilm formation or on planktonic microbes by LF-EMF treatment were confirmed in the experiments.

Pseudomonas aeruginosa in Swimming Pool Water: Evidences and Perspectives for a New Control Strategy

Pseudomonas aeruginosa is frequently isolated in swimming pool settings. Nine recreational and rehabilitative swimming pools were monitored according to the local legislation. The presence of P. aeruginosa was correlated to chlorine concentration. The ability of the isolates to form a biofilm on plastic materials was also investigated. In 59.5% of the samples, microbial contamination exceeded the threshold values. P. aeruginosa was isolated in 50.8% of these samples. The presence of P. aeruginosa was not correlated with free or total chlorine amount (R² < 0.1). All the isolates were moderate- to strong-forming biofilm (Optical Density O.D.570 range 0.7-1.2). To control biofilm formation and P. aeruginosa colonization, Quantum FreeBioEnergy© (QFBE, FreeBioEnergy, Brisighella, Italy), has been applied with encouraging preliminary results. It is a new, promising control strategy based on the change of an electromagnetic field which is responsible for the proliferation of some microorganisms involved in biofilm formation, such as P. aeruginosa.

Mitigation of marine biofouling on tubes of open rack vaporizers using electromagnetic fields

This study quantitatively evaluates the antifouling action of the continuous physical treatment with electromagnetic fields (EMFs) of seawater used as heat exchanger fluid in an open rack vaporizer (ORV) pilot plant to reduce the growth of biofouling on external rib-tube surfaces. The results demonstrate that the biofilm adhered on the treated rib-tubes was reduced by 33% in thickness and by 44% in dissolved solids regarding the biofilm adhered on the untreated control rib-tubes. The lower conductivity and Ca(2+) and Mg(2+) ionic content in the effluent of the treated seawater confirmed that the EMFs accelerated the process of ionic calcium nucleation and precipitation as calcium carbonate. The precipitation of ions dissolved affected the inter-molecular interactions among extracellular polymers, thereby weakening the biofouling film matrix and reducing its adhesion capacity. The drag of small particles by the flow of seawater had an erosive action and decreased the biofouling film thickness. Consequently, the antifouling methods treatment with EMFs allowed reduce the negative effect that the biofouling have for the heat transfer equipment used in the regasification process and keep the highest techno-economic operating conditions.

Characterization of biofilm formation in natural water subjected to low-frequency electromagnetic fields

Electromagnetic field (EMF) treatment has proven to be effective against mineral scaling in water systems. Therefore, it should be assessed for the treatment of other deposits such as biofilms. In this study, a commercial device producing low-frequency EMF (1-10 kHz) was applied to a reactor fed with natural water for 45 days. The treatment promoted the concentration of microorganisms in suspension and limited the amount of sessile microorganisms in the biofilm, as determined by the measurement of total DNA, qPCR and microscopy. The structure of the bacterial community was assessed by t-RFLP and pyrosequencing analysis. The results showed that EMF treatment affected both planktonic and sessile community composition. EMFs were responsible for a shift in classes of Proteobacteria during development of the biofilm. It may be speculated that the EMF treatment affected particle solubility and/or microorganism hydration. This study indicated that EMFs modulated biofilm formation in natural water.