Fouling Dynamics Research Articles

Coke Formation in Steam Cracking Reactors: Deciphering the Impact of Aromatic Compounds and Temperature on Fouling Dynamics

Coke Formation in Steam Cracking Reactors: Deciphering the Impact of Aromatic Compounds and Temperature on Fouling Dynamics

Evaluation of diffusion coefficients as surrogate indicators for electrostatic repulsion in ultrafiltration membrane fouling

Impacted by the electrostatic repulsion between ultrafiltration (UF) membranes and natural organic matter (NOM), organic fouling precipitates significant operational difficulties in water treatment facilities. This study investigated the applicability of diffusion coefficients as surrogate indicators to evaluate the electrostatic repulsive forces between NOMs and UF membrane surfaces. We utilized three distinct types of NOMs and three different UF membranes, each possessing different charge characteristics. Notably, we found that the reduction in diffusion coefficients was markedly pronounced when membranes rich in ionizable functional groups with strong negative charges were involved, indicating heightened electrostatic repulsion. To confirm the reliability of diffusion coefficient reduction as a surrogate indicator of the electrostatic repulsive force, a comprehensive membrane fouling test was conducted. The results revealed a strong correlation between the two parameters, enhancing our understanding of the intricate dynamics of membrane fouling (R2 = 0.9744–0.9907). Thus, this study proposes the concept of utilizing the reduction in the diffusion coefficient as a surrogate indicator to represent the electrostatic repulsive force between NOMs and the UF membrane surface. This innovative approach contributes to enables proactive and predictive assessments of membrane performance, fostering a shift toward proactive maintenance and enhances the operational efficiency of water treatment facilities.

Dynamics of fouling of plastic waste fragments by microorganisms in the Gulf of Finland

In recent years, the problem of the aquatic environment pollution with synthetic polymers - plastic and microplastics - has become more urgent than ever, which causes an increasing interest of the scientific community in this topic, both in our country and abroad. The development of organic synthesis chemistry at the beginning of the last century led to the emergence of synthetic polymers – plastics; the chemical properties of plastic, making it an inexpensive, durable, and useful material, led to its widespread, mass distribution, but they are also the cause of difficulties with its disposal – the decay, decomposition, and disposal of many types of plastic takes decades, which much lower than the production rate of new plastic. As it is known, plastics are materials that are synthetic or natural high-molecular compounds (polymers); the term “microplastic” refers to particles of synthetic polymers or plastic copolymers (less than 5 microns), they are insoluble in water and non-degradable. Such characteristics of microplastic components as the area, the particle surface relief, the type of polymer will affect the biofilm formation rate. This indicator also is influenced by the flow rate, the bio-productivity of the waters, and the position of the particles in the water column.

Membrane Distillation: Pre-Treatment Effects on Fouling Dynamics.

In the research reported in this paper, membrane distillation was employed to recover water from a concentrated saline petrochemical effluent. According to the results, the use of membrane distillation is technically feasible when pre-treatments are employed to mitigate fouling. A mathematical model was used to evaluate the fouling mechanism, showing that the deposition of particulate and precipitated material occurred in all tests; however, the fouling dynamic depends on the pre-treatment employed (filtration, or filtration associated with a pH adjustment). The deposit layer formed by particles is not cohesive, allowing its entrainment to the bulk flow. The precipitate fouling showed a minimal tendency to entrainment. Also, precipitate fouling served as a coupling agent among adjacent particles, increasing the fouling layer cohesion.

Evaluation of membrane cake fouling mechanism to estimate design parameters of a submerged AnMBR treating high strength industrial wastewater

A mathematical model, which was previously developed for submerged aerobic membrane bioreactors, was successfully applied to elucidate the membrane cake-layer fouling mechanisms due to bound extracellular polymeric substances (eEPS) in a submerged anaerobic membrane bioreactor (SAnMBR). This biofouling dynamic model explains the mechanisms such as attachment, consolidation and detachment of eEPS produced in the bioreactor on the membrane surface. The 4th order Runge-Kutta method was used to solve the model equations, and the parameters were estimated from simulated and experimental results. The key design parameters representing the behaviour of cake fouling dynamics were systematically investigated. Organic loading rate (OLR) was considered a controlling factor governing the mixed liquor suspended solids (MLSS), eEPS production, filtration resistance (Rt), and transmembrane pressure (TMP) variations in a SAnMBR. eEPS showed a proportional relation with OLR at subsequent MLSS variations. The consolidation of EPS increased the specific eEPS resistance (αs), influencing the cake resistance (Rc). The propensities of eEPS showed a positive correlation with Rt and TMP. The outcomes of the study also estimated a set of valuable design parameters which would be vital for applying in AnMBRs treating industrial wastewater.

Multiple fouling dynamics, interactions and synergistic effects in brackish surface water distribution systems

Dissolved salts, colloidal particles, and active microorganisms in brackish surface water distribution systems (BSWD) cause multiple fouling, poses potential threat to the environmental pollution, and raising technical and economic issues as well. So far, the co-occurrence and interactions of multiple fouling remains largely unknown. Multiple fouling behaviors were assessed in agriculture BSWD under different nitrogen (N) fertilizers. X-ray diffraction, Rietveld refinement analysis, 16S rRNA, and microbial network analysis were conducted to determine the fouling characteristics. Statistical analysis was applied to reveal the relative contributions and interaction of multiple fouling. Our results demonstrated, multiple fouling of precipitates, particulates and biofoulings were co-occurred. Fouling growth was largely attributed to the strong interactions of different fouling. The binary interactions of precipitates - particulates contributed 51.1%, and ternary interactions of precipitates - particulates - biofouling contributed 25.4% to explain the decline of system performance, while the contribution of each single type fouling was minimal. Thereby indicating the significant role of calcium silica, biomineralization and bio-silicates in fouling. The lower acid N fertilizer broken the interaction of multiple fouling by increasing the precipitate crystal parameters and repulsive forces amongst particulates, as well as destroyed microbial interactions in biofouling. Overall, this study open frontier for multiple fouling in-depth profiling and antifouling guidance for effective utilization of BSWD.

RF‐LSTM‐based method for prediction and diagnosis of fouling in heat exchanger

AbstractFouling degrades the thermal and hydraulic performances of the heat exchanger (HE), leading to failure if undetected. It occurs due to the accumulation of undesired material on the heat transfer surface. Knowledge about the HE fouling dynamics is required to plan mitigation strategies, ensuring a sustainable and safe operation. This paper aims to propose a feature‐based technique to predict the fouling status of the HE based on historical data. Three thermal and two hydraulic features are extracted from the HE. Random forest (RF) is employed to detect the dominant features using the Gini index. These dominant features are used to predict the fouling resistance using a deep neural network based on the Long Short‐Term Memory (LSTM) model. Also, these dominant features provide reliable inferences to reason out the fouling dynamics. A diagnostic flag is derived based on the dominant feature and is used to diagnose the ongoing fouling phenomena, which is vital to formulate mitigation. The proposed technique is investigated on the data acquired from the HEs used in a thermal power plant (Case 1) and petroleum refinery (Case 2). Prediction accuracy of 99% and 97% is observed for Cases 1 and 2, respectively. Experimental results illustrate that RF enables the LSTM to achieve faster training and reliable prediction of fouling.

Dynamic modeling of fouling over multiple biofuel production cycles in a membrane reactor

Abstract In this paper, a novel mathematical model that combines a membrane filtration model, component balances and reaction kinetics models for an intensified separation-reaction process in membrane reactor producing biofuels was developed. A unique feature is that the proposed model can capture the dynamics of membrane fouling as function of both reversible and irreversible fouling; which leads to cyclic behavior. Fouling leads to the decline of the reactor productivity. With an appropriate fouling-model, the operational strategy can be optimized. In the case study of biodiesel production, the developed model was validated with experimental data. The model was in good agreement with the data, where R-squared are 0.96 for the permeate flux and 0.95 for the biodiesel yield. From a further analysis, the efficiency of membrane reaction system in term of productivity can be significantly improved by changing the backwashing frequency under specific operating conditions. As the backwashing frequency increased eight times, the biodiesel yield increased to more than two to three times before the permeate flux dropped under a predetermined limit due to the increase of irreversible membrane fouling.

Evaluation of anti-bacterial adhesion performance of polydopamine cross-linked graphene oxide RO membrane via in situ optical coherence tomography

Biofouling is a critical issue which accounts for >45% of all fouling in reverse osmosis (RO). Because fouling occurs on the surface of the membrane, surface modification has been considered an effective measure for fouling mitigation and for achieving sustainable membrane performance. Herein, we modified a RO membrane using graphene oxide (GO) crosslinked with a thin layer of polydopamine (PDA-GO) to obtain a bactericidal and antibiofouling surface. Optical coherence tomography (OCT) was used as a non-destructive, real-time, in situ monitoring tool to observe the fouling dynamics and to understand material-foulant interaction. In situ three-dimensional (3D) monitoring results showed that the modified membrane was antifouling in nature and exhibited low and fully reversible biofilm formation. In addition, the colony forming unit enumeration and results of confocal laser scanning microscopy reveal that the PDA-GO coated membrane exhibited a high bactericidal effect when compared with pristine, PDA, and GO-coated membrane surfaces. Investigation of bacterial cell morphology further validated that the presence of a GO layer and its functional groups combined with a thin PDA layer resulted in physical and chemical disruption of the bacterial cell wall. The high selectivity of the modified membrane against the monovalent salt validated its potential for desalination and wastewater reclamation.

An Optimization Study on Soot-Blowing of Air Preheaters in Coal-Fired Power Plant Boilers

This paper presents a comprehensive approach for optimization of soot-blowing of air preheaters in a coal-fired power plant boiler. In the method, modeling of the cleanliness factor is firstly proposed to monitor the ash deposition status of the air preheaters. Then, the statistical fitting of the ash fouling status is subsequently obtained to analyze the ash fouling dynamics and assessment of optimized soot-blowing strategies. Soot-blowing strategies are finally developed to optimize the steam consumption and heat transfer efficiency. Our methods can achieve the fouling monitoring and soot-blowing optimization of air preheater (APH) by using the existing monitoring data, not requiring additional special instruments and complex computing systems. The methodology is validated with the actual operating data of a 300 MW coal-fired power plant boiler. The results show the effectiveness of the proposed method. It can be used for the soot-blowing optimization in most coal-fired power plant boiler with air preheaters.

Understanding fouling dynamics on functionalized CNT-based membranes: Mechanisms and reversibility

Herein, we explored resistance to fouling and the bactericidal potential of a functionalized carbon nanotube (CNT)-based polyvinylidene fluoride (PVDF) membrane. Humic acid (HA), a main constituent in natural organic matter was used as an indicator for the estimation of organic fouling, while Escherichia coli was employed as a model bacterium for biofouling investigation. In-situ fouling characterization was performed using a non-destructive optical coherence tomography. Results revealed that a thin CNT layer on the PVDF surface effectively prevented HA molecules from interacting directly with the porous structure of membrane, thereby averting the possibility of pore blockage (irreversible fouling). Moreover, the CNT membranes offered higher permeability, increased HA rejection, and better flux restoration capacity as compared with pristine PVDF membrane. This superior anti-HA-fouling performance of CNT membrane was accredited to the electrostatic repulsions between the CNT layer and HA molecules, both carrying a strong negative charge and high density of hydrophilic functional groups on the CNT surface. Antibacterial results from the ultrastructural examination of cell membrane integrity authenticate the bactericidal potential of CNT membrane toward biofouling causing bacteria. Finally, when tested with real sea water, CNT membrane with less organic and biofouling propensity outperformed commercial PVDF, indicating their suitability for seawater reverse osmosis (SWRO) pretreatment.

Dynamics of pore fouling by colloidal particles at the particle level

Particle filtration occurs whenever particles flow through porous media such as membrane. Progressive capture or deposition of particles inside porous structure often leads to complete, and generally unwanted, fouling of the pores. Previously there has been no experimental work that has determined the particle dynamics of such a process at the pore level, since imaging the particles individually within the pores remains a challenge. Here, we overcome this issue by flowing fluorescently dyed particles through a model membrane, a microfluidic filter, imaged by a confocal microscope. This setup allows us to determine the temporal evolution of pore fouling at the particle level, from the first captured particle up to complete blocking of the pore. We show that from the very beginning of pore fouling the immobile particles inside the pore significantly participate in the capture of other flowing particles. For the first time it is determined how particles deposit inside the pore and form aggregates that eventually merge and block the pore.

Modeling Dynamics of Colloidal Fouling of RO/NF Membranes with A Novel Collision-Attachment Approach.

We report a novel collision-attachment approach for modeling the dynamics of colloidal fouling. The model treats fouling as a two-step process: colloidal particles colliding with a membrane surface followed by their attachment onto the surface. An attachment coefficient is adopted to describe the probability of successful foulant attachment for any given collision event, the value of which can be determined by the classical Boltzmann distribution. Our model shows excellent agreement with experimental data in terms of both the kinetics of flux decline and foulant mass deposition. Modeling results reveal the critical roles of water flux and energy barrier in governing colloidal fouling. Greater water flux or lower energy barrier can lead to a collision-controlled condition, where severe fouling occurs and nearly all collision events lead to successful foulant attachment. On the contrary, fouling is increasingly controlled by the probability of successful attachment at lower water flux and/or greater energy barrier. Our model provides deep insights into the various mechanisms governing the dynamics of colloidal fouling (i.e., concentration polarization, collision, and attachment) and the self-limiting fouling behavior under constant-pressure mode.

Flexible Cleaning Regimes Promote Membrane Permeability

Maintain membrane permeability by selecting an efficient cleaning approach based on critical fouling dynamics and source water characteristics, with further reassessment as needed.

Analysis of high resolution flux data to characterize fouling profiles of membranes with different MWCO under different filtration modes

Abstract The flux data represent the response of a filtration system to interactive progression of multiple fouling mechanisms. Analyses using the classical fouling models of filtration (Hermia’s model and its modified forms) are often used by linearization of the flux data ( dJ / dt ) to identify the effects different fouling mechanisms. However, digitally acquired flux data with very short time intervals (high resolution) exhibit oscillations caused by particle-particle and particle-membrane interactions. As a result, dJ / dt can have both positive and negative values and not suitable for linearization. In this study, high resolution flux data were analyzed and compared in terms of magnitude and frequency of flux oscillations over time using Stockwell transform (S-transform) which is a modified form of the Short Time Fourier Transform (STFT). Flux data sets from filtration runs using membranes with different molecular weight cutoff (MWCO) (5, 10 and 30 kDa) were analyzed to characterize the progression of flux loss under submerged and cross flow filtration conditions. The magnitude and frequency of flux oscillations, and flux loss patterns for each filtration run were unique and allowed identification of the critical times when flux oscillation characteristics changes as a result of changing fouling dynamics under different filtration modes. For the submerged filtration conditions, all membranes exhibited significant flux loss immediately after the start of the filtration run due to cake formation followed by cake compression and penetration of particles into the membrane which resulted in flux oscillations at long filtration times, especially with 10 and 30 kDa membranes. Under cross flow conditions, membranes with smaller MWCO (5 and 10 kDa) did not exhibit significant flux loss over time; however, there were significant flux oscillations in the high resolution flux data indicating temporary blockages which did not have long lasting effects. The spectrograms produced by S-transform of high resolution flux data provided unique fouling signatures of the filtration systems and allowed comparison of the fouling progression for each filtration system.

Inline UV-Vis spectroscopy to monitor and optimize cleaning-in-place (CIP) of whey filtration plants

Cleaning in place (CIP) is a necessary, complex and costly process employed all throughout the food industry. CIP of membrane filtration plants is especially delicate as membranes have limited stability towards temperature and can be permanently damaged or gradually changed by cleaning chemicals used for every day. We investigated the capability of inline UV-Vis spectroscopy to elucidate the dynamics of CIP of membrane filtration plants as a gateway to control and optimize the process. For this investigation aged membranes that had been used for industrial ultrafiltration of whey were transferred to a pilot plant equipped with inline UV-Vis spectroscopy on both the retentate and permeate side. Then the dynamics of multiple fouling and cleaning of these membranes were investigated. The results indicate that the first CIP step, caustic cleaning could be shortened and possibly reduced in concentration. The second step of CIP, enzymatic cleaning, seems to be active even longer than the anticipated time. Challenges, first findings and future steps of full scale inline UV-Vis spectroscopy are discussed. We conclude that inline UV-Vis spectroscopy can be used to optimize the processing time, energy and chemicals needed for cleaning in place of membrane filtration plants.

Performance of ceramic microfiltration membranes for treating carbonated and filtered remelt syrup in sugar refinery

The performance of a ceramic microfiltration membrane with 0.5 μm pore size in clarifying carbonated remelt syrup that was filtered by plate-and-frame filter press was investigated under different operating conditions. In total reflux experiments, using 0.5 μm ceramic membranes for treating carbonated, filtered remelt syrup at 80 °C produced steady-state fluxes of 328.4 and 293.1 L/(m2 h) at a cross-flow velocity of 5 m/s, and transmembrane pressures (TMPs) of 3.0 and 2.5 bar, respectively. Decreasing the temperature to 75 °C yielded a corresponding flux of 271.8 L/(m2 h) at a TMP of 3.0 bar. In concentration experiments, when treating 750 L of syrup, 96.7, 76.9 and 72.0 L/(m2 h) of average fluxes were obtained under three operating conditions mentioned above. All conditions produced high-quality filtered syrup. Research on membrane resistances indicated that TMP significantly affected irreversible cake resistance. The increase in cross-flow velocity decreased cake resistance but insignificantly affected pore blocking resistance. All component resistances were decreased with increasing temperature. Membrane fouling dynamics could be represented through a pseudo-first-order rate equation. Fluxes of fouled membranes were recovered by successive cleaning with de-ionized water, a 1% NaOH + 0.5% NaOCl mixed solution, and a 0.5% HNO3 solution.

A model-based analysis of water transport dynamics and fouling behaviors of osmotic membrane

Water transport performance of forward osmosis (FO) has a crucial significance for successful implementations of the process in water and wastewater reclamation and seawater desalination. But, ascertainment of membrane fouling dynamics associated with simultaneous solute and water transfer still remains as one of the main research subjects for FO’s technological development. This study provides a deep insight to reveal the relations between water transport and membrane fouling propensities in FO by which model-based analysis was performed based on a novel osmotic resistance-in-series model developed for normal and reverse membrane orientations. Model results indicated that for the membrane operated with real seawater, osmotic water flux was mainly dependent on the active layer resistance regardless of orientation mode and osmosis time. Interfacial layer from effective draw interface by active layer/draw bulk interface, [dw−ma/db] seemed to be the main performance-limiting domain in which, as interfacial fouling increased, membrane permeated less water to draw. Predominant mechanisms were designated as homogeneous fouling of equivalent solute distributions and heterogeneous fouling of non-uniform nano-exclusion zones in normal and reverse modes, respectively. More interestingly, it was comprehended for reverse mode that the nature of nano-exclusion zones at the interface dw turned to a feature of uniform solute distributions at the interface ma/db. Very good agreements were found between experimental fluxes and theoretical results based on dimensional and dimensionless structural parameter and total resistances. After all, distinctive fouling behaviors clarified upon the adopted dynamics of transport were strongly verified by consistencies of high accuracy in the model estimations.

Soluble microbial products and suspended solids influence in membrane fouling dynamics and interest of punctual relaxation and/or backwashing

To favor the control of membrane fouling on line by relaxation and backwash sequencing, two major fouling origins are considered: the former is due to retention of large particles on the membrane surface forming a growing deposit that can be controlled by tangential shear stresses, the second is due to the retention of the largest soluble polymers forming a thin layer on the membrane surface including pore blocking and inducing a progressive reduction of the deposit porosity, the influence of this second fouling origin can only be reduced by backwashing. A simple model was developed to represent (i) the accumulation of two types of compounds and its consequences and the evolution with time of the hydraulic resistance of the system and (ii) the role of relaxation and backwashing to reduce the fouling impact. Some simulations were presented according to the values of the three model parameters. Simulations were also compared to experimental data obtained on biological suspensions.

Salt stress in a membrane bioreactor: Dynamics of sludge properties, membrane fouling and remediation through powdered activated carbon dosing

Membrane bioreactors are a well-established technology for wastewater treatment. However, their efficiency is adversely impacted by membrane fouling, primarily inciting very conservative operations of installations that makes them less appealing from an economic perspective. This fouling propensity of the activated sludge is closely related to system disturbances. Therefore, improved insight into the impact of fouling is crucial towards increased membrane performance. In this work, the disturbance of a salt shock was investigated with respect to sludge composition and filterability in two parallel lab-scale membrane bioreactors. Several key sludge parameters (soluble microbial products, sludge-bound extracellular polymeric substances, supramicron particle size distributions (PSD), submicron particle concentrations) were intensively monitored prior to, during, and after a disturbance to investigate its impact as well as the potential governing mechanism. Upon salt addition, the supramicron PSD immediately shifted to smaller floc sizes, and the total fouling rate increased. Following a certain delay, an increase in submicron particles, supernatant proteins, and polysaccharides was observed as well as an increase in the irreversible membrane fouling rate. Recovery from the disturbance was evidenced with a simultaneous decrease in the above mentioned quantities. A similar experiment introducing powdered activated carbon (PAC) addition used for remediation resulted in either no or less significant changes in the above mentioned quantities, signifying its potential as a mitigation strategy.