Fouling Deposition Research Articles

Heat transfer and fouling deposition investigation on the titanium coated heat exchanger surface

Fouling is the undesired deposition on heat exchanger surfaces which enhance heat transfer resistances and retard heat exchanger performance. This paper investigates fouling mitigation of calcium carbonate by the application of coatings on SS316L heat exchanger. Titanium (Ti) was selected as coating material due to its high resistance to corrosion and good surface adhesion. Physical vapor deposition method was adopted to coat Ti on the SS316L surface. Heat transfer investigation at different flow rates were conducted to observe the effect of coating and then fouling experiments were carried out to investigate the deposition of Calcium Carbonate to the coated and uncoated surfaces. The test section was taken under microscopic investigation to study the surface texture before and after the fouling effect. It was observed that the Ti coated SS316L surface of heat exchanger surface experienced less corrosion, enhanced heat transfer and reduced fouling deposition.

Superhydrophilic polyvinylidene fluoride membrane with hierarchical surface structures fabricated via nanoimprint and nanoparticle grafting

The sustainable development of membrane separation technology is facing the severe challenge of membrane fouling problem. This paper proposed a novel strategy that combined nanoimprint lithography and nanoparticle grafting technology to fabricate antifouling polyvinylidene fluoride membranes. The nanoimprint process brought about a wave-like micro-scaled surface pattern with alternate concave and convex structures. The subsequent grafting process with amine-terminated nanoparticles further decorated the pattern into a hierarchically structured surface, which allowed a rapid (<1 s) complete wetting (i.e., contact angle = 0°) by water thus superhydrophilic. Besides, the obtained membrane (designated as imprinted_G) achieved an enhanced capability of solute rejection while maintaining a water permeability of ~8.4 × 10−7 m s−1 kPa−1 comparable with that of the pristine membrane (~8.6 × 10−7 m s−1 kPa−1). Furthermore, the superhydrophilic and hierarchical surface potentially led to a local hydration layer and turbulent flow, which resisted the adhesion and deposition of foulants, thereby endowing the membrane with dramatically enhanced antifouling capability. The imprinted_G membrane achieved the highest water production yield (~36% higher than the pristine membrane) with stable flux recovery rates in the filtration experiments with practical membrane bioreactor mixed liquor (containing activated sludge). Furthermore, the imprinted_G membrane exhibited a conspicuously improved capability in resisting biofouling of Bacillus thuringiensisd and Escherichia coli, demonstrating a promising prospect for practical applications.

Performance Evaluation of Portable Hot Water Jet for Frozen Meat Industry Application

High temperature-induced water jet has important cleaning factors for effective cleaning at food industries because it can provide mechanical, heat, and chemical effects during cleaning. It can also reduce cleaning time, labor load, and utility consumptions, hence reducing the operating costs and enhance sustainability. However, it has not been used widely in small and medium food industries due to a lack of cleaning awareness and small budget allocation for cleaning and disinfection. In this article, we evaluated the performance of a portable water jet in the laboratory before it was introduced to the frozen meat industry. Removal of invisible fat-based fouling deposits which remained on the surfaces of the meat processing equipment is quite a challenge. In this work, stainless steel surfaces were fouled with the fat-based fouling deposit. The fouled stainless-steel surfaces were used for the cleanability tests. The tests were conducted at different parameters which were cleaning parameters (temperature (35 °C and 65 °C) and cleaning detergent presence), cleaning operations (nozzle distances (5 cm and 30 cm)) and surface geometries (vertical and horizontal) which representing the different equipment’s geometry. Physical cleanliness (visual and touch) and protein residue swab test was used as the cleaning indicators. The target cleanliness was achieved at a high cleaning temperature of 65°C and with the presence of cleaning detergent. Results from these tests will be used as a guide to design an optimal cleaning program for SMEs frozen meat patty factory.

Experimental Investigation of Microbial Fouling and Heat Mass Transfer Characteristics on Ni-P Modified Surface of Heat Exchanger

Fouling deposition problem on heat transfer surface is widely distributed in the field of energy and chemical industry, and microbial fouling is a common fouling type in heat exchanger. In this article, the surface modification was used for inhibiting or mitigating the microbial fouling deposition on heat exchange surface. Firstly, the experimental system for real-time monitoring the fouling deposition process was built, and then the Ni-P modified surface was prepared. Further, the slime forming bacteria (SFB) microbial fouling characteristics and corresponding influencing factors on Ni-P modified surface were investigated experimentally. The results indicated that Ni-P modified surface had an excellent fouling inhibition property. Comparing with carbon steel, Ni-P modified surface reduced the fouling heat resistance by 80%. Accordingly, the influencing factors of microbial fouling deposition including temperature, flow rate and microbial concentrations were discussed. With cooling water temperature increasing given in the experiment arrangement, the microbial fouling resistance was increased first and then decreased, while with bacteria concentration and flow rate increasing, the fouling resistance was increased and decreased separately. The work can provide experimental reference for the fouling inhibition surface development and fouling inhibition mechanism study.

Mechanical comparison of milk and whey protein isolate fouling deposits using indentation testings

Whey protein products have been previously used as a surrogate to mimic fouling and cleaning processes of dairy production. The basic idea builds on the fact that the main components of milk fouling are whey proteins and that the process from the solution to the fouling deposit is guided by similar chemical reactions. However, it remains unknown whether the resulting mechanical behaviour reflects that of milk deposits. Therefore, the objective of the present study is threefold: In the first step, the mechanical characteristics of raw milk and whey protein fouling deposits were determined and compared with each other. In a second step, we aimed to quantify the amount of whey protein isolate needed to obtain a similar mechanical behaviour. For the determination of the time-dependent mechanical characteristics of milk and whey protein deposits, indentation and indentation relaxation experiments were performed. The outcomes of this study show that whey protein deposits, generated from a solution featuring a whey protein powder concentration of 0.1g/l, lead to comparable mechanical characteristics to that of raw milk deposits. Furthermore, a significant influence of the milk deposit thickness on the mechanical behaviour was identified, resulting from the fouling generation process. Finally, a three-dimensional material modelling approach is suggested that can predict the time-dependent mechanical behaviour of milk fouling deposits.

Contributions of surface and pore deposition to (ir)reversible fouling during constant flux microfiltration of secondary municipal wastewater effluent

Reversible and irreversible fouling mechanisms for polyvinylidene fluoride (PVDF) hollow fiber membranes during constant flux microfiltration (MF) of secondary municipal wastewater effluent are reported. Infrared spectra of fouled membranes revealed a two-step mechanism for hydraulically irreversible surface deposition of foulants; initial binding of relatively hydrophobic molecules, which served as platform for further deposition of comparatively more hydrophilic molecules with progressive MF. Compressible cake filtration quantitatively described forward MF of the raw wastewater effluent. In contrast, analysis of fouling behavior after effluent organic matter (EfOM, measured as DOC) removal by different pretreatments revealed that the foulants deposited on the membrane surface are not the dominant reason for irreversible loss in permeability instead pointing to internal pore deposition as the main reason, which was verified by blocking law modeling over multiple filtration/backwashing cycles. Additionally, the extent of EfOM removal during pretreatment was not proportionally linked to consequent fouling, signifying the role of specific EfOM fractions in the feed water as being responsible for (ir)reversible fouling. Interestingly, MF of the raw wastewater effluent resulted in lower irreversible permeability loss when compared with pretreated wastewater, which was attributed to the cake layer serving as a dynamic membrane that reduced exposure of membrane pores to foulants.

Experimental Study on Microbial Fouling Inhibition Performance of Ni‐P‐NanoTiO2 Composite Surfaces

AbstractMicrobial fouling of heat exchangers causes serious issues including increased fuel consumption, flow resistance, and maintenance cost expenditure. Composite Ni‐P‐nanoTiO2 coatings were prepared for inhibiting and mitigating the heat exchanger microbial fouling deposition. The surface energy components and wall adhesion work of microbial fouling medium had a significant effect on the microbial fouling deposition process. Compared with carbon steel coupons, the microbial fouling deposition on Ni‐P‐nanoTiO2 coatings was reduced by about 90 % and the wall adhesion work and microbial fouling deposition rate of these coatings were less. The Ni‐P‐nanoTiO2 coatings might not only be advantageous for controlling the initial microbial adhesion, but also effective for reducing the fouling deposition rate.

Facile Preparation of a Superhydrophobic iPP Microporous Membrane with Micron-Submicron Hierarchical Structures for Membrane Distillation.

A facile method combining micro-molding with thermally-induced phase separation (TIPS) to prepare superhydrophobic isotacticpolypropylene (iPP) microporous membranes with micron-submicron hierarchical structures is proposed in this paper. In this study, the hydrophobicity of the membrane was controlled by changing the size of micro-structures on the micro-structured mold and the temperature of the cooling bath. The best superhydrophobicity was achieved with a high water contact angle (WCA) of 161° and roll-off angle of 2°, which was similar to the lotus effect. The permeability of the membrane was greatly improved and the mechanical properties were maintained. The membrane prepared by the new method and subjected to 60h vacuum membrane distillation (VMD) was compared with a conventional iPP membrane prepared via the TIPS process. The flux of the former membrane was 31.2 kg/m2·h, and salt rejection was always higher than 99.95%, which was obviously higher than that of the latter membrane. The deposition of surface fouling on the former membrane was less and loose, and that of the latter membrane was greater and steady, which was attributed to the micron-submicron hierarchical structure of the former and the single submicron-structure of the latter. Additionally, the new method is expected to become a feasible and economical method for producing an ideal membrane for membrane distillation (MD) on a large scale.

Facile dual-functionalization of polyamide reverse osmosis membrane by a natural polypeptide to improve the antifouling and chlorine-resistant properties

Long-term durability is of significant importance for the polyamide thin film composite (PA-TFC) reverse osmosis (RO) membranes under the complicated operation conditions of the water treatment. Herein, dual-functional RO membranes with improved antifouling and chlorine-resistant properties were facilely fabricated. A natural polypeptide, ε-poly-l-lysine (PL), was employed as the surface modifier for RO membrane, and covalently immobilized on the PA-TFC membrane surface through one-step chemical coupling under ambient conditions, without sacrificing the permselectivity. Surface properties of the PL-modified membranes were systematically characterized, and the modification method was also optimized. The greatly enhanced surface hydrophilicity derived from PL layer resulted in less propensity to the deposition of organic foulants. Moreover, the topmost PL sacrificial layer effectively improved the membrane chlorine-resistance, with the normalized salt rejection higher than 99.5% after accelerating chlorination. The readily available modifier and straightforward modification process make PL modification on PA layer a potential strategy for the fabrication of antifouling and chlorine-resistant RO membrane.

Antifouling behaviour of a photocatalytic modified membrane in a moving bed bioreactor for wastewater treatment

Membrane fouling is a major bottleneck in the application of moving bed-membrane bioreactors. A novel moving bed-UV-photocatalytic-modified membrane bioreactor (MB-UVPMBR) was proposed for efficient wastewater treatment and membrane fouling mitigation. Herein, the modified membrane served as photocatalysis and membrane processes simultaneously. Compared with the conventional moving bed-membrane bioreactor (MBMBR) and MB-UVPMBR without UV light irradiation, the MB-UVPMBR exhibited good effluent quality and anti-fouling ability with UV light irradiation. The cake layer resistance was reduced by 83%, and the pore blockage resistance was reduced by 88%, thus reducing the total membrane filtration resistance. The hydrophilicity of the modified membrane helped mitigate foulant deposition and cake layer formation on the membrane surface. The modified membrane effectively reduced the contents of soluble microbial products and foulants deposited on the membrane surface by photocatalysis. Additionally, the fouled membrane could be effectively regenerated by self-cleaning.

Investigation on ash fouling formation of induced fan blade and heat exchanger surface in a 1000MW coal-fired power plant

The control of fouling deposition on the main equipment has always been an im-portant issue concerned by scientific research and industrial application. How-ever, severe fouling deposits on the induced fan blade and the low temperature economiser were found in a 1000 MW coal-fired power plant with ultra-low emission. The deposit samples were collected and analysed through X-ray dif-fraction spectrometer, X-ray fluorescence, elemental analyser and SEM with en-ergy dispersive spectrometers. The result shows that the deposits are mainly composed of tschermigite (NH4)Al(SO4)2 ? 12H2O, letovicite (NH4)3H(SO4)2, cal-cium sulphate CaSO4, and quartz SiO2. The ammonium sulphate is the main component of the fouling deposits. It acts as an adhesive and makes an important contribution to the deposition. The analysis shows that the ammonia slip from denitrification system and the unreasonable temperature setting are the main reasons for fouling deposition. It is suggested that the high concentration of am-monium slip at denitrification system and the rapid condensation of the sulphuric acid mist at heat exchanger should be paid more attention in coal-fired power plants.

Study on dynamic measurement of fouling thermal resistance in a boiler

A fouling thermal resistance method is introduced, for evaluating water quality in real time through measuring fouling thermal resistance on heat transfer surface. A simple device as a boiler heat transfer model was designed for measuring the deposition of dirt by the fouling thermal resistance method. The change in the thermal resistance of the fouling was measured with regard to samples with different water quality. The temperature-time curves were plotted with respect to the measured data of various temperatures over the whole process of temperature rise and fall to examine the feasibility of the method in evaluating the thermal resistance of the fouling contributed by the hardness of the water, finding that the fitted curve can characterize the fouling deposition of high hardness water. It has been shown that this experimental device can be improved further in the hope of being applied in practical use.

Membrane Filtration of Effluent from a One-Stage Bioreactor Treating Anaerobic Digester Supernatant

A challenge in side-stream treatment of anaerobic digester supernatant is that the effluent does not meet discharge standards. To address this challenge, this study tested tubular multichannel ceramic microfiltration (MF) and ultrafiltration (UF) membranes for the post-treatment of anaerobic digester supernatant. Pollutant rejection (total suspended solids (TSS), COD, total nitrogen (TN), and total phosphorus (TP)), color removal, and membrane susceptibility to fouling were determined at various transmembrane pressures (TMPs) (0.2, 0.3, 0.4, 0.5 MPa). Both methods completely removed TSS. In MF, COD was removed with 48–76% efficiency at 0.2–0.4 MPa. In UF, COD removal efficiency was slightly higher, reaching 83.7% at 0.4 MPa. With both methods, pollutant removal did not increase at TMP of 0.5 MPa. With both MF and UF, color was reduced by 54–100%, irrespective of the TMP. At 0.2–0.4 MPa, membrane resistance was lower and permeate flux was much higher with MF than UF. At 0.5 MPa, the methods differed only slightly from each other. Due to the larger cut-off, flux decline was slower in MF (0.7 h−1) than in UF (1.1 h−1), as the larger pore-size favors less foulant deposition. Thus, taking into account rejection efficiency, capacity, washing frequency, and cost (pressure), these results indicate that MF at 0.4 MPa is the most effective variant for post-treatment of anaerobic digester supernatant. With this variant, the almost colorless permeate contained 25 mg COD/L, no TSS, 55 mg TN/L (75% in the form of nitrites and nitrates), and 8.5 mg TP/L, thus meeting criteria for water to be used in irrigation or algae cultivation.

Heat transfer and fouling characteristics during falling film evaporation in a vertical sintered tube

Heat transfer and fouling performance of water in a sintered porous stainless-steel tube were investigated experimentally. The test tube has a porous tube wall composed of stainless-steel powder with a typical diameter of 0.3 μm, and the special wall was designed to improve the thermal performance during falling film evaporation by increasing the nucleation site densities and relieve the foul processing through vapor transmission. Heat transfer tests were implemented at a saturation temperature of 373.2 K, over a mass velocity range of 0.42–1.47 kg/ (m s), with a subcooled degree of 0.5 K at inlet, and the temperature, pressure and mass flux of steam fixed, while the fouling tests were carried out using high-rigidity water as work fluid at a fixed mass velocity of 0.84 kg/ (m s). Heat transfer coefficient of the sintered tube is about 30% lower than that of the plain tube, and the inferior effect of the porous structure is caused by the weak thermal conductivity steam filled in the wall void and possible vapor film formed in the inner surface of tube. There is a flatten relationship between the heat transfer coefficient of the plain and the mass velocity, while that of the porous tube increases as the mass flux increases. As for the fouling process, the fouling resistance for the porous tube seems to make little difference on the overall thermal performance of the test section, contrary to the heat transfer deterioration for the smooth tube during the fouling deposition process.

Performance evaluation of modified nanohybrid membrane polyethersulfone-nano ZnO (PES-nano ZnO) using three combination effect of PVP, irradiation of ultraviolet and thermal for biodiesel purification

The main problems in biodiesel purification using membrane are low selectivity and fouling issue. Therefore, this research was developed on the modification polyethersulfone nanohybrid membranes which have excellent selectivity performance and anti-fouling behavior. The PES-nano ZnO nanohybrid membrane was fabricated by preparing dope solution composed of PES, nano ZnO and N-methyl Pyrrolidone as a solvent. UV irradiation, PVP addition, and thermal treatments were conducted to modify fabricated nanohybrid membranes. The modified membrane exhibited significant enhancement of hydrophilicity by lowering the water contact angle value from 66.17° to 52.33°. The initial flux of modified membrane increased up to 200% of the unmodified membrane’s initial flux. Both of modified and unmodified membranes have rejection more than 91% that can lowering the glycerol content from 3.98 to 0.34 wt-%. The modified membrane presented less foulant deposition on the membrane surface. This membrane also performed excellent stability in term of permeate flux and rejection efficiency. It is verified that the concept of modified PES-nano ZnO membrane can achieve a higher membrane performance for biodiesel purification such as increased of flux, lowering the glycerol content, better anti-fouling behavior and excellent stability.

Characterisation of organic matter in membrane photobioreactors (MPBRs) and its impact on membrane performance

Understanding the behaviour of organic materials in bioreactors is an important part of system assessment. This paper focuses on the combined use of liquid chromatography – organic carbon detection and fluorescence excitation–emission matrix spectroscopy for characterising the fate of dissolved organic compounds in membrane photobioreactors operated under different hydraulic and solids retention time. It was found that small amino acids/peptides were largely removed in the reactors, which coincided with the production of biopolymers. The biopolymers were effectively retained (>84%) by the ultrafiltration membrane, in contrast with other algal-derived substances, such as quinones, flavonoids and extracellular chlorophyll a. During long-term low-flux operation (4.5L/m2h), preferential deposition of organic matter (e.g. biopolymers) and particles on different fouling layers was observed. The upper fouling layer (obtained by rinsing) was found to contain the greatest amount of organic foulants (211–348mg/m2) and solids (7.5–15.5g/m2). By contrast, chemically desorbing layer showed the lowest degree of organic matter build-up, whereby low molecular weight acids were the most abundant organic material. The short-term flux-stepping trials conducted for the same microalgal biomass revealed distinct results, presumably due to the different fouling mechanism involved, where preferential deposition of foulants was not expected given the high driving force.

Constructing zwitterionic polymer brush layer to enhance gravity-driven membrane performance by governing biofilm formation

In this study, zwitterionic polymer brushes with controlled architecture were grafted on the surface of gravity-driven membrane (GDM) via surface-initiated reaction to impart antifouling property. A variety of membrane characterization techniques were conducted to demonstrate the successful functionalization of zwitterionic polymers on PVDF hollow fiber membrane. The membrane underwent 90 min of reaction time possessing strong hydrophilicity and high permeability was determined as the optimal modified membrane. Long-term GDM dynamic fouling experiments operated for 30 days using sewage wastewater as feed solution indicated zwitterionic polymer modified membrane exhibit excellent membrane fouling resistance thus enhanced stable flux. Confocal laser scanning microscopy (CLSM) imaging implied that zwitterionic polymer modification significantly inhibit the adsorption of extracellular polymeric substances (EPS) which dominates fouling propensity, resulting in the formation of a thin biofilm with high porosity under synthetic functions of foulants deposition and microbial activities. Interfacial free energy prediction affirmed the presence of zwitterionic functional layer on membrane surface could substantially decrease the interactions (e.g., electrostatic attractions and hydrophobic effects) between membrane and foulants, thereby reduced flux decline and high stable flux. Our study suggests surface hydrophilic functionalization shows promising potential for improving the performance of ultra-low pressure filtration.

Effect of H2S on the corrosion-fouling behaviors of Cu-base surface

Based on the First-principles method of density functional theory (DFT), the adsorption of H2S on the primary growth surface (001)(111)(110) of Cu-base was investigated. The results demonstrate that the stable adsorption position of H2S on Cu(001)(111)(110) surface is t-parallel, b-H-down-c and h-H-down-c, respectively. And the corresponding adsorption energy is the minimum of −0.580 eV, −0.560 eV, −0.527 eV. After doping Zn in Cu, b-parallel, b-parallel and h-H-down-p are the stable adsorption position of H2S on Cu–Zn(001)(111)(110) surface. More chemical bonds form on adsorption sites of Cu and Cu–Zn substrate. Crystal structure of Cu doping Zn becomes unstable and easy to be corroded. Additionally, the experimental results reveals that copper shows better corrosion resistance of H2S than that of brass. Trends of fouling deposit curve of copper and brass are similar while the fouling is prone to deposit on the surface of brass after H2S corrosion. The consequences evidence that the fouling deposition can be influenced by the corrosive surface of materials and the fouling is prone to deposit on the corrosive pits and cracks. Furthermore, the crystal form of calcium carbonate on the surface of brass and copper after H2S corrosion is primarily aragonite and calcite. The corrosion products can promote the fouling adhesion.

An analysis of the effects of pressure-assisted osmotic backwashing on the high recovery reverse osmosis system

AbstractThe low cost simplified method for implementation of pressure-assisted osmotic (PAO) backwash (BW) for spiral wound reverse osmosis (RO) membrane module is presented in this work. The effect of membrane design and an operating parameter concerning the efficiency of PAO membrane BW is analyzed. The following design and operating parameters are considered in this study: (i) spacer thickness, (ii) dimension of the permeate channel, (iii) number of leaves, and (iv) BW water pressure. The performance of PAO BW with respect to membrane cleaning efficiency is analyzed for three different high recovery RO systems by purifying 1,500 liters of water. The membrane cleaning efficiency is measured by examining the rate of permeate quality and quantity decline using ASTM D4516 method. Finally, to quantify the membrane fouling with respect to different high recovery configurations, the thickness, and composition of foulants present in the used membrane's surface are measured by using field emission scanning electron microscope with energy dispersive X-ray (FESEM-EDX). The result concludes that the RO membrane operated at high recovery with PAO BW is found to have less fouling deposits than membrane without PAO BW.

Ultrafiltration of oil-in-water emulsion stabilized with surfactants

Application of ultrafiltration membrane in the separation of oil-in-water emulsion has a consequence of fouling formation and relate to significantly flux reduction. Filtration of oil-in-water emulsions is challenging since both oil and surfactant have interaction with the membranes. In addition, there is a possibility of droplet deformation to enter the membrane pores. This research was focused on the effect of surfactant type on the ultrafiltration performance. Models of oil-in-water emulsion consisted of crude oil, diesel oil and lubricant oil as dispersed phase and mixture of distilled water with the addition of 0.1% of Tween 80 or Alkyl Benzene Sulfonate as the continuous phase. Flat-sheet Polyethersulfone having 10 kDa molecular weight cut-off was selected as the membrane. The result showed that there were fluxes decline during 2 hours of operation in ultrafiltration of oil-in-water emulsion stabilized with a non-ionic surfactant (Tween 80). On the other hand, when oil-in-water emulsion was stabilized with anionic surfactant (Alkyl Benzene Sulfonate), the fluxes were relatively constant during 2 hours filtration. The COD rejection was in the range of 98-97%, 94-96% and 90-94% for oil types of crude oil, diesel oil and lubricant oil respectively. Total oil content rejection was found as 98-99% for both crude oil and lubricant oil and 98-97% for the diesel oil. Based on Scanning Electron Microscopy, images of the membrane after filtration of oil-in-water emulsion stabilized with Tween 80 showed foulant deposit which was predicted as oil and surfactant. However, when filtering oil-in-water stabilized surfactant only less deposit on the membrane surface was observed.