Predicting thermodynamic adhesion energies of membrane fouling in planktonic anammox MBR via backpropagation neural network model.

Predicting thermodynamic adhesion energies was a critical strategy for mitigating membrane fouling. This study utilized a backpropagation (BP) neural network model to predict the thermodynamic adhesion energies associated with membrane fouling in a planktonic anammox MBR. Acid-base (ΔGAB), electrostatic double layer (ΔGEL), and Lifshitz-van der Waals (ΔGLW) energies were selected as output variables, the training dataset was collected by the advanced Derjaguin-Landau-Verwey-Overbeek (XDLVO) method. Optimization results identified "7-10-3″ as the optimal network structure for the BP model. The prediction results demonstrated a high degree of fit between the predicted and experimental values of thermodynamic adhesion energy (R2 ≥ 0.9278), indicating a robust predictive capability of the model in this study. Overall, the study presented a practical BP neural network model for predicting thermodynamic adhesion energies, significantly enhancing the prediction tool for adhesive fouling behavior in anammox MBRs.

Harnessing diurnal dynamics: Deciphering the interplay of light cycles on algal-bacterial membrane bioreactors.

Light profoundly modulates the algal-bacterial membrane bioreactor (algal-bacterial MBR) performance. Yet, its outdoor deployment grapples with the inherent diurnal cycle of sunlight, engendering suboptimal light conditions. The adaptability of such systems to these fluctuating light conditions and their implications for practical outdoor applications remained an under-explored frontier. In response, this study meticulously scrutinized two laboratory-scale algal-bacterial MBRs under varying light regimes: a 24-h continuous and a 12-h cyclic illumination. Over 70 days, continuous illumination was observed to yield superior biomass production and total nitrogen and total phosphorus removal efficiencies compared to its cyclic counterpart. Contrarily, when focusing on membrane fouling, the 12-h cyclic illumination exhibited lower membrane fouling. The spectral analyses coupled with adhesion ability evaluation, traced the enhanced membrane fouling under continuous illumination to the elevated organics and heightened adhesive properties of the flocs. Given the tangible benefits of reduced membrane fouling and the potential harnessing of solar radiation, the 12-h cyclic illumination emerges as an economically astute operational paradigm for algal-bacterial MBRs. The significance of this study is to promote the application of algal-bacterial MBR in sewage treatment and provide robust support for the development of green technology in the future.

Mg2+ addition: Unlocking optimized treatment performance and anti-fouling property in microalgal-bacterial membrane bioreactors.

While microalgal-bacterial membrane bioreactors (microalgal-bacterial MBRs) have risen as an important technique in the realm of sustainable wastewater treatment, the membrane fouling caused by free microalgae is still a significant challenge to cost-effective operation of the microalgal-bacterial MBRs. Addressing this imperative, the current study investigated the influence of magnesium ion (Mg2+) addition on the biological dynamics and membrane fouling characteristics of the laboratory-scale submerged microalgal-bacterial MBRs. The results showed that Mg2+, important in augmenting photosynthetic process, yielded a biomass concentration of 2.92 ± 0.06 g/L and chlorophyll-a/MLSS (mixed liquor suspended solids) of 33.95 ± 1.44 mg/g in the RMg (Mg2+ addition test group). Such augmentation culminated in elevated total nitrogen and phosphorus removal efficiencies, clocking 81.73 % and 80.98 % respectively in RMg. Remarkably, despite the enhanced microalgae activity and concentration in RMg, the TMP growth rate declined by a significant 46.8 % compared to R0. Detailed characterizations attributed reduced membrane fouling of RMg to a synergy of enlarged floc size and reduced EPS contents. This transformation is intrinsically linked to the bridging action of Mg2+ and its role in creating a non-stressed ecological environment for the microalgal-bacterial MBR. In conclusion, the addition of Mg2+ in the microalgal-bacterial MBR appears an efficient approach, improving the efficiency of pollutant treatment and mitigating fouling, which potentially revolutionizes cost-effective applications and propels the broader acceptance of microalgal-bacterial MBRs. It also of great importance to promote the development and application of microalgal-bacterial wastewater treatment technology.

Mitigation of protein fouling by magnesium ions and the related mechanisms in ultrafiltration process.

Although protein is an important membrane foulant in the water body that may be significantly affected by the coexisting common cation magnesium (Mg2+), the effect of Mg2+ on protein fouling is rarely reported. In this context, this study selected bovine serum albumin (BSA) as the model foulant, and investigated its fouling characteristics at different Mg2+ concentrations (0-100 mM). Filtration tests showed that the protein fouling can be significantly mitigated by adding Mg2+, and the specific filtration resistance (SFR) of pure BSA (3.56 × 1014 m kg-1) was at least 5 times that of BSA-Mg2+ solutions (0.5-100 mM). In addition, an optimal Mg2+ concentration exists, which can achieve the lowest BSA SFR. A series of characterizations indicated that the main contributors to the differences in BSA SFR were the changes in BSA adhesion capacity and the thickness and structure of the foulant layer. Basically, the above results were attributed to the hydration repulsion effect of Mg2+, which prevented tight adhesion of foulants to the membrane. Moreover, the lowest BSR SFR at 1 mM Mg2+ was achieved not only by the hydration repulsion effect but also by the particle size compression due to the conformational change of BSA molecules. This combined effect led to the lowest foulant retention on the membrane surface and delivered to the lowest SFR. This study conducts a thorough inspection into the specific effect of Mg2+ on protein fouling and provides a fresh insight into protein fouling control in the UF process.

High propensity of membrane fouling and the underlying mechanisms in a membrane bioreactor during occurrence of sludge bulking.

While sludge bulking often occurring in activated sludge processes generally leads to serious membrane fouling in membrane bioreactors (MBR), the underlying causes are still unclear. In this study, fouling behaviors of a MBR operated at stages of normal and sludge bulking were compared, and the fouling mechanisms of the different behaviors were explored. It was found that, the MBR could be stably operated in normal stage without membrane cleaning for about 60 days, whereas, daily membrane cleaning had to be carried out when operated in sludge bulking stage. The bulking sludge possessed a rather high specific filtration resistance (SFR) of about 1.36×1014 m·kg-1, which is over 5.33 times than that of the normal sludge. A series of characterizations demonstrated that the bulking sludge had rather lower dewaterability, smaller particle size, higher fractal dimension, higher viscosity, abundant filamentous bacteria and different functional groups of extracellular polymer sustains (EPS). It was suggested that microbial community transition was responsible for the occurrence of sludge bulking, further affecting membrane fouling. Based on these characterizations, it was reported that adhesion propensity (indicated by the thermodynamic interaction) of the bulking sludge to the membrane surface is about 3.6 times than that of the normal sludge. It was proposed that, extra force should be provided to offset a chemical potential gap caused by foulant layer structure transition during sludge bulking in order to sustain filtration of the bulking sludge, resulting in extremely high SFR. This study offered deep thermodynamic mechanisms of MBR fouling during occurrence of sludge bulking.

Evaluation of membrane fouling in a microalgal-bacterial membrane photobioreactor: Effects of SRT.

As a novel system, the microalgal-bacterial membrane photobioreactor (MPBR) has better performance than the conventional MBRs in membrane fouling control. Nevertheless, how the operating conditions affect its fouling performance is rarely reported. In this study, a microalgal-bacterial MPBR was set and continuously operated to treat synthetic wastewater. Effects of solids retention time (SRT, 10, 20, and 30 d) on the membrane fouling were investigated. The results showed that the relationship between membrane fouling and SRT was nonlinear and the fastest membrane fouling was observed at SRT 20 d. The predominant fouling mechanism was gel layer formation. X-ray photoelectron spectroscopy results showed a significant difference in the surface composition of the microalgal-bacterial consortia at different SRTs. The biological flocs at SRT of 20 d had the largest floc size, moderate filament abundance, and the highest content of bound EPS and SMP. The highest membrane fouling at SRT 20 d was mainly attributed to the highest concentration of EPS and SMP. Environmental stresses and fierce competition between microalgae and bacteria are considered to be the underlying reasons for the elevated production of EPS and SMP. In brief, optimizing the SRT value to control the balanced growth of microalgae and bacteria and keep them at an appropriate ratio is critical for delaying membrane fouling in microalgal-bacterial MPBR.

Molecular-level insights into the mitigation of magnesium-natural organic matter induced ultrafiltration membrane fouling by high-dose calcium based on DFT calculation.

While magnesium cation (Mg2+) universally coexists with natural organic matter (NOM) in the water environment, influence of Mg2+ on NOM fouling in membrane filtration process is still unclear. This work was therefore performed to investigate effects of Mg2+ on NOM (sodium alginate (SA) as a model substance) fouling and role of Ca2+ in mitigating fouling from Mg2+ in the ultrafiltration (UF) water treatment process. Filtration tests showed two interesting fouling phenomena: (1) membrane fouling caused by combination of Mg2+ and SA maintained at a high value with the increased Mg2+ concentration; (2) the high fouling property of Mg2+ can be significantly improved by the prominent addition of calcium cation (Ca2+). It was found that changes of foulant morphology played essential roles through thermodynamic mechanisms represented by the Flory-Huggins lattice theory. Density functional theory (DFT) calculation showed that the combination of SA and Mg2+ tends to coordinate two terminal carboxyl groups in SA, beneficial to stretching alginate chains and forming a stable gel network at low doses. In addition, intramolecular coordination is difficult to occur between SA and Mg2+ due to the high hydration repulsion radius of Mg2+. Therefore, a dense and thick gel network remained even under high Mg2+concentration. Furthermore, due to the higher binding affinity of Ca2+ over Mg2+, high doses of Ca2+ trigger a transition of the stable SA-Mg2+ gel network to other configurations where flocculation and aggregation occur, thereby reducing the specific filtration resistance. The proposed thermodynamic mechanism satisfactorily explained the above interesting fouling behaviors, facilitating to development of new solutions to control membrane fouling.

Fundamental thermodynamic mechanisms of membrane fouling caused by transparent exopolymer particles (TEP) in water treatment.

While transparent exopolymer particles (TEP) has high fouling potential, its underlying fouling mechanisms have not yet been well revealed. In current work, fouling characteristics of TEP under different Ca2+ concentrations (0 to 1.5 mM) were investigated. TEP quantification and filtration tests showed that TEP contents increased with Ca2+ concentration, while TEP's specific filtration resistance (SFR) under the influence of Ca2+ concentration presented a unimodal pattern. The peak of TEP's SFR reached at Ca2+ concentration of 1 mM when SA concentration was 0.3 g·L-1. A series of characterizations suggested that microstructure transformation of TEP particles was the main contributor to the resistance variations of TEP solution. The optical microscope observation showed that above and below the critical Ca2+ concentration (1 mM when SA concentration is 0.3 g·L-1 in this study), the formed TEP existed in the form of c-TEP (average particle size is 0.24 µm) and p-TEP (average particle size is 1.05 µm), respectively. Thermodynamic analysis showed that the adhesion ability of c-TEP (-249,989 and - 303,692 kT) was more than 19 times than that of p-TEP (-12,905 kT), which would accelerate foulant layer formation. In addition, below the critical value, the increased SFR with Ca2+ concentration could be explained by integrating Flory-Huggins lattice theory with the preferential intermolecular coordination. Above the critical value, the decreased SFR can be attributed to the formation of a "large-size crack structure" cake layer from the p-TEP. This study revealed fundamental mechanisms of membrane fouling caused by TEP, greatly deepening understanding of TEP fouling, and facilitating to development of effective fouling control strategies.

A novel composite membrane for simultaneous separation and catalytic degradation of oil/water emulsion with high performance.

It is of great significance to develop novel membranes with dual-function of simultaneously separating oil/water emulsion and degrading the contained water-miscible toxic organic components. To meet this requirement, a dual-functional Ni nanoparticles (NPs)@Ag/C-carbon nanotubes (CNTs) composite membrane was fabricated via electroless nickel plating strategy in this study. The as-prepared composite membrane possessed superhydrophilicity with water contact angle of 0° and splendid underwater oleophobic property with oil contact angle of 142°. When the membrane was applied for separation of surfactant stabilized oil-in-water emulsion, high permeate flux (about 97 L m-2·h-1 under gravity), oil rejection (about 98.8%) and antifouling property were achieved. Benefitting from the NiNPs@Ag/C-CNTs layer on membrane surface, the composite membrane exhibited high catalytic degradation activity for water-miscible toxic organic pollutant (4-nitrophenol) with addition of NaBH4 in a flow-through mode. Meanwhile, the NiNPs@Ag/C-CNTs composite membrane possessed excellent durability, which was verified by the good structural integrity even under ultrasonic treatment. The cost-efficiency, high separation and degradation performance of the prepared membrane suggested its great potential for treatment of oily wastewater.

A unified thermodynamic mechanism underlying fouling behaviors of soluble microbial products (SMPs) in a membrane bioreactor.

Soluble microbial products (SMPs) are the predominate foulants determining fouling extent in membrane bioreactors (MBRs). However, exact mechanism underlying their typical fouling behaviors remains unrevealed. In this study, the typical fouling behaviors of SMPs during initial operational period of a MBR were characterized. It was found that, although being low content, SMPs rather than sludge particulates preferentially adhered to membrane surface to accumulate a gel layer, and moreover, specific filtration resistance (SFR) of SMPs was approximately 700 times larger than that of the sludge particulates at operational day 3. According to energy balance principle, a unified thermodynamic mechanism underlying these fouling behaviors of SMPs was proposed. Thermodynamic analyses demonstrated that, the attractive interaction energy strength in contact between SMPs and membrane was larger by around 3700 times than that between sludge particulates and membrane, well explaining the extremely high adhesive ability of SMPs over sludge particlulates. Meanwhile, filtration through a SMPs layer was modelled and simulated as a thermodynamic process. Simulation on an agar gel showed that, about 92.6% of SFR was originated from mixing free energy change during filtration. Such a result satisfactorily interpreted the extremely high SFR of SMPs layer over sludge cake layer. The revealed thermodynamic mechanism underlying SMPs fouling behaviors significantly deepened understanding of fouling, and facilitated to development of effective fouling control strategies.

Quality of life in Chinese patients with laryngeal cancer after radiotherapy.

This retrospective study explored the quality of life (QoL) in Chinese patients with laryngeal cancer (LC) after radiotherapy.Fifty-nine eligible patients with Tis-T4 LC were included in this retrospective study. All patients received radiotherapy. Outcomes were measured by the core measure Questionnaire-C30 (QLQ-C30), and the disease-specific Head & Neck cancer module (QLQ-H&N35). All outcomes were assessed before and 3 months after the radiotherapy.Three months after the radiotherapy, all items of QLQ-C30 and QLQ-H&N35 scales changed significantly (P < .05), except the social functioning (P = .09), role activities (P = .81), and global (P = .12) in QLQ-C30 scale and social contacts (P = 1.00), teeth problems (P = .21), trismus (P = 1.00), and feeling ill (P = .07) in QLQ-H&N35 scale, compared with these items before the radiotherapy.The results of this study showed that most items of QoL changed significantly after 3 months of radiotherapy in Chinese patients with LC.

Mechanistic insights into alginate fouling caused by calcium ions based on terahertz time-domain spectra analyses and DFT calculations.

Fouling mechanisms underlying the filtration behaviors of alginate solution caused by calcium addition were investigated by Terahertz time-domain spectroscopy (THz-TDS) and density functional theory (DFT) techniques. Filtration tests showed that specific filtration resistance (SFR) of alginate solution (0.75 g L-1) monotonously increased with calcium addition at a relatively low range of calcium concentration (0-1.0 mM), and SFR (2.61 × 1015 m kg-1) of alginate solution with 1.0 mM calcium addition was extremely high as compared with sludge suspension. Characterizations by X-ray photoelectric spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA) showed that the composition of functional groups, elements and thermal stability of alginate was not apparently affected by calcium concentration. Howbeit, THz-TDS spectra showed that calcium addition caused structural variation of alginate polymer in solution. DTF calculation results showed that initial binding of alginate chains induced by calcium ions preferentially occurred in intermolecular other than intramolecular, and moreover, the two alginate chains bridged by a calcium atom tend to stretch in a tetrahedron structure (cross to each other) other than parallel to each other. According to these results, "chemical potential gap" depicted by Flory-Huggins theory was suggested to be responsible for the filtration behaviors of alginate solution caused by calcium addition. This study provided the mechanistic insights into membrane fouling.

Membrane fouling in a submerged membrane bioreactor: An unified approach to construct topography and to evaluate interaction energy between two randomly rough surfaces.

Quantitatively evaluating interaction energy between two randomly rough surfaces is the prerequisite to quantitatively understand and control membrane fouling in membrane bioreactors (MBRs). In this study, a new unified approach to construct rough topographies and to quantify interaction energy between a randomly rough particle and a randomly rough membrane was proposed. It was found that, natural rough topographies of both foulants and membrane could be well constructed by a modified two-variable Weierstrass-Mandelbrot (WM) function included in fractal theory. Spatial differential relationships between two constructed surfaces were accordingly established. Thereafter, a new approach combining these relationships, surface element integration (SEI) approach and composite Simpson's rule was deduced to calculate the interaction energy between two randomly rough surfaces in a submerged MBR. The obtained results indicate the profound effects of surface morphology on interaction energy and membrane fouling. This study provided a basic approach to investigate membrane fouling and interface behaviors.

Influences of fractal dimension of membrane surface on interfacial interactions related to membrane fouling in a membrane bioreactor.

Influences of fractal dimension (Df) of membrane surface on interfacial interactions related to membrane fouling in a membrane bioreactor were investigated based on thermodynamic methods. It was found that membrane surface had significant fractal features, and its fractal dimension could be characterized by the power spectrum method. The modified Weierstrass-Mandelbrot (WM) function was found to be effective to model the fractal membrane surface, and higher Df corresponded to higher number of fine asperities in the modeled surface. Moreover, the modeled surface roughness exponentially decreased with Df. Interaction calculations according to a novel method showed that the interactions for fractal membrane surface were elongated and weakened as compared with smooth membrane surface. It was interestingly found that the absolute value of total interaction monotonically decreased with Df of membrane surface. As Df is a measure of substance stiffness, this result indicates that softer surface is more susceptible to adhesion by sludge foulant. The results offered new insights into membrane fouling mechanisms and alleviation.

Realization of quantifying interfacial interactions between a randomly rough membrane surface and a foulant particle.

Quantification of interfacial interaction with randomly rough surface is the prerequisite to quantitatively understand and control the interface behaviors such as adhesion, flocculation and membrane fouling. In this study, it was found that membrane surface was randomly rough with obvious fractal characteristics. The randomly rough surface of membrane could be well reconstructed by the fractal geometry represented by a modified Weierstrass-Mandelbrot function. A novel method, which combined composite Simpson's approach, surface element integration method and approximation by computer programming, was developed. By using this method, this study provided the first realization of quantifying interfacial energy between randomly rough surface of membrane and a foulant particle. The calculated interactions with randomly rough surface of membrane were significantly different from those with smooth surface of membrane, indicating the significant effect of surface topography on interactions. This proposed method could be also potentially used to investigate various natural interface environmental phenomena.

Quantification of interfacial interactions between a rough sludge floc and membrane surface in a membrane bioreactor.

Interfacial interactions between foulants and membrane directly determine foulant adhesion and membrane fouling. In this study, surface of sludge foulant particles (flocs) was found to be rough, and could be modeled by a sinusoidal sphere function. A novel method, which combined surface element integration (SEI) method, differential geometry and composite Simpson's rule, was developed to quantify the interfacial interactions between the modeled rough floc surface and membrane surface. Application of the novel method in a membrane bioreactor (MBR) provides broad profiles of quantitative interactions with rough floc surface with separation distance. It is also found that increase in the scaled amplitude of floc surface significantly reduced the interaction strength. Derjaguin's approximation (DA) can be regarded as a special case of the novel method, indicating the extensive application prospect of the novel method. The novel method for interaction calculation was verified to be correct and feasible. Finally, roles of the novel method in membrane fouling research were discussed.

Quantitative evaluation of the interfacial interactions between a randomly rough sludge floc and membrane surface in a membrane bioreactor based on fractal geometry.

In this paper, a new method for quantification of interfacial interactions between a randomly rough particle and membrane surface was proposed. It was found that sludge flocs in a membrane bioreactor were of apparent fractal characteristics, and could be modeled by the modified two-variable Weierstrass-Mandelbrot (WM) function. By combining the surface element integration (SEI) method, differential geometry and composite Simpson's rule, the quantitation method for calculating such interfacial interactions was further developed. The correctness and feasibility of the new method were verified. This method was then applied to evaluate the interfacial interactions between a randomly rough particle and membrane surface. It was found that, randomly rough particle possesses stronger interaction strength than regularly rough particle but weaker strength than smooth particle with membrane surface, indicating significant effects of surface morphology and roughness. The proposed method in this study has broad application prospect in membrane fouling study.

Fractal reconstruction of rough membrane surface related with membrane fouling in a membrane bioreactor.

In this paper, fractal reconstruction of rough membrane surface with a modified Weierstrass-Mandelbrot (WM) function was conducted. The topography of rough membrane surface was measured by an atomic force microscopy (AFM), and the results showed that the membrane surface was isotropous. Accordingly, the fractal dimension and roughness of membrane surface were calculated by the power spectrum method. The rough membrane surface was reconstructed on the MATLAB platform with the parameter values acquired from raw AFM data. The reconstructed membrane was much similar to the real membrane morphology measured by AFM. The parameters (including average roughness and root mean square (RMS) roughness) associated with membrane morphology for the model and real membrane were calculated, and a good match of roughness parameters between the reconstructed surface and real membrane was found, indicating the feasibility of the new developed method. The reconstructed membrane surface can be potentially used for interaction energy evaluation.

A new approach to construct three-dimensional surface morphology of sludge flocs in a membrane bioreactor.

In this paper, a novel approach to construct three-dimensional (3D) surface morphology of sludge flocs in a membrane bioreactor (MBR) was proposed. The new approach combined the static light scattering method for fractal dimension (Df) determination with the modified two-variable Weierstrass-Mandelbrot (WM) function based on fractal geometry and coordinate transformation for spherical surface construction. It was found that the sludge flocs in the MBR showed apparent fractal characteristics. Results showed that the constructed 3D morphology of sludge flocs was very sensitive to Df, and higher Df induced a more compact and smoother surface morphology. With a set of proper parameter data, the constructed 3D surface morphology of sludge flocs could be quite similar to the real floc surface morphology, showing the feasibility of the proposed approach. The proposed solution to floc surface construction could be potentially used in interfacial interaction assessment, giving important implications for membrane fouling research.

Influences of acid-base property of membrane on interfacial interactions related with membrane fouling in a membrane bioreactor based on thermodynamic assessment.

Failure of membrane hydrophobicity in predicting membrane fouling requires a more reliable indicator. In this study, influences of membrane acid base (AB) property on interfacial interactions in two different interaction scenarios in a submerged membrane bioreactor (MBR) were studied according to thermodynamic approaches. It was found that both the polyvinylidene fluoride (PVDF) membrane and foulant samples in the MBR had relatively high electron donor (γ(-)) component and low electron acceptor (γ(+)) component. For both of interaction scenarios, AB interaction was the major component of the total interaction. The results showed that, the total interaction monotonically decreased with membrane γ(-), while was marginally affected by membrane γ(+), suggesting that γ(-) could act as a reliable indicator for membrane fouling prediction. This study suggested that membrane modification for fouling mitigation should orient to improving membrane surface γ(-) component rather than hydrophilicity.