Surface water filtration using granular media and membranes: A review

An insight decipher on photocatalytic degradation of microplastics: Mechanism, limitations, and future outlook

Plastic material manufacturing and buildup over the past 50 years has significantly increased pollution levels. Microplastics (MPs) and non-biodegradable residual plastic films have become the two most pressing environmental issues among the numerous types of plastic pollution. These tiny plastic flakes enter water systems from a variety of sources, contaminating the water. Since MPs can be consumed by people and aquatic species and eventually make their way into the food chain, their presence in the environment poses a serious concern. Traditional technologies can remove MPs to some extent, but their functional groups, stable covalent bonds, and hydrophobic nature make them difficult to eliminate completely. The urgent need to develop a sustainable solution to the worldwide contamination caused by MPs has led to the exploration of various techniques. Advanced oxidation processes (AOPs) such as photo-catalytic oxidation, photo-degradation, and electrochemical oxidation have been investigated. Among these, photocatalysis stands out as the most promising method for degrading MPs. Photocatalysis is an environmentally friendly process that utilizes light energy to facilitate a chemical reaction, breaking down MPs into carbon dioxide and water-soluble hydrocarbons under aqueous conditions. In photocatalysis, semiconductors act as photocatalysts by absorbing energy from a light source, becoming excited, and generating reactive oxygen species (ROS). These ROS, including hydroxyl radicals (•OH) and superoxide ions ( [Formula: see text] ), play a crucial role in the degradation of MPs. This extensive review provides a detailed exploration of the mechanisms and processes underlying the photocatalytic removal of MPs, emphasizing its potential as an efficient and environmentally friendly approach to address the issue of plastic pollution.

Removal of thallium by MnOx coated limestone sand filter through regeneration of KMnO4: Combination of physiochemical and biochemical actions

Treatment of industrial thallium(Tl)-containing wastewater is crucial for mitigating environmental risks and health threats associated with this toxic metal. The incorporation of Mn oxides (MnOx) into the filtration system is a promising solution for efficient Tl(I) removal. However, further research is needed to elucidate the underlying mechanism behind MnOx-enhanced filtration and the rules of its stable operation. In this study, limestone, a cost-effective material, was selected as the filter media. Raw water with Mn(II), Tl(I), and other pollutants was prepared after a thorough investigation of actual industrial wastewater conditions. KMnO4 was added to induce the formation of MnO2 on limestone surfaces, while long-term operation led to enrichment of manganese oxidizing microorganisms (MnOM). Results revealed a dual mechanism. Firstly, most Mn(II) were oxidized by KMnO4 to form MnO2 attaching to limestone sands, and both Tl(I) and residual Mn(II) were adsorbed onto the newly formed MnO2. Subsequently, enzymes secreted by MnOM facilitated oxidation of remaining Mn(II), resulting in the generation of biogenic manganese oxides (BioMnOx) with numerous vacancies during long-term operation. The generated BioMnOx not only adsorbed Mn(II) and Tl(I) but also promoted their oxidation process. This approach offers an effective and sustainable method for removing both Mn(II) and Tl(I) from industrial wastewater, thereby addressing the challenges posed by thallium-contaminated effluents.

Comparison of different extraction methods of active ingredients of Chinese medicine and natural products

Like other traditional medicine in the world, Chinese traditional medicine (CTM) has a long history, which is a treasure of the combination of medicine and Chinese classical culture even more than 5000 years. For thousands of years, CTM has made great contributions to the reproduction and health of the Chinese people. It was an efficient therapeutic tool under the guidance of Chinese traditional medical theory, its source is generally natural products, but there are also a small number of it are natural products after some processing methods. In fact, the definition of Chinese medicine (CM) includes both traditional and new CM developed by modern technology. It is well known that the chemical composition of most CM and natural products is very complex, for example, a single herb may contain hundreds of different chemicals, including active ingredients, side effects, and even toxic ingredients. Therefore, the extraction process is particularly crucial for the quality and clinical efficacy of CM and natural products. In this work, a new classification method was proposed to divide the extraction technologies of CM and natural products into 21 kinds in recent years and analyze their status, advantages, and disadvantages. Then put forward a new technical route based on ultra-high-pressure extraction technology for rapid extraction else while removing harmful impurities and making higher utilization of CM and natural products. It is a useful exploration for the extraction industry of medicinal materials and natural products in the world.

Magnetic nanocomposite of maize offal biomass for effective sequestration of Congo red and methyl orange dyes from contaminated water: modeling, kinetics and reusability

The current study aims to use a facile and novel method to remove Congo red (CR) and Methyl Orange (MO) dyes from contaminated water with Maize offal biomass (MOB) and its nanocomposite with magnetic nanoparticles (MOB/MNPs). The MOB and MOB/MNPs were characterized with Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), BET, XRD and point of zero charge (pHPZC). The influence of initial CR and MO levels (20-320 mg/L), adsorbent dosage (1-3 g/L), pH (3-9), co-exiting ions, temperature (25-45 °C) and time (15-180 min) was estimated. The findings demonstrated that MOB/MNPs exhibited excellent adsorption of 114.75 and 29.0 mg/g for CR and MO dyes, respectively while MOB exhibited 81.35 and 23.02 mg/g adsorption for CR and MO dyes, respectively at optimum pH-5, and dose 2 g/L. Initially, there was rapid dye removal which slowed down until equilibrium was reached. The interfering/competing ions in contaminated water and elevated temperature favored the dyes sequestration. The MOB/MNPs exhibited tremendous reusability and stability. The dyes adsorption was spontaneous, and exothermic with enhanced randomness. The adsorption effects were well explained with Freundlich model, pseudo second order and Elovich models. It is concluded that MOB/MNPs showed excellent, eco-friendly, and cost-effective potential to decontaminate the water.

Effect of filtration rates on the performance and head loss development in granular filters during the post-treatment of anaerobic reactor effluent

This study investigated the performance of a granular filtration system (GFS) composed of a rock filter (RF), a rapid sand filter (RSF), and an activated carbon filter (ACF), applied to the post-treatment of an anaerobic reactor effluent. Four filtration rates (FR) were applied to the GFS (in m3·m-2·d-1): 100-60-60, 100-90-90, 200-120-120, and 200-160-160, for RF-RSF-ACF, respectively. A clarified final effluent with low turbidity (~ 10 NTU), solids (~ 6.5 mg TSS.L-1), and organic matter content (~ 40 mg COD.L-1) was obtained when the GFS worked with FR up to 100-90-90 m3·m-2·d-1. For higher FR, the effluent quality was a little poorer. Principal component analysis showed when the RSF operated at 120 or 160 m3·m-2·d-1, it presented an effluent with higher turbidity which did not affect negatively the ACF performance. The hydraulic load limits in the RSF were reached in periods of 45, 30, and 24.5 h for the FR of 60, 120, and 160 m3·m-2·d-1, respectively, and head loss analysis depicted a more distributed solid retention through the sand depth with the lower FR. Thus, the results revealed that the RF-RSF-ACS system is a promising alternative for effluent polishing of anaerobic reactor, especially when the FR is set at 90 m3·m-2·d-1 or even higher.

Membrane processes for environmental remediation of nanomaterials: Potentials and challenges

Nanomaterials have gained huge attention with their wide range of applications. This is mainly driven by their unique properties. Nanomaterials include nanoparticles, nanotubes, nanofibers, and many other nanoscale structures have been widely assessed for improving the performance in different applications. However, with the wide implementation and utilization of nanomaterials, another challenge is being present when these materials end up in the environment, i.e. air, water, and soil. Environmental remediation of nanomaterials has recently gained attention and is concerned with removing nanomaterials from the environment. Membrane filtration processes have been widely considered a very efficient tool for the environmental remediation of different pollutants. Membranes with their different operating principles from size exclusions as in microfiltration, to ionic exclusion as in reverse osmosis, provide an effective tool for the removal of different types of nanomaterials. This work comprehends, summarizes, and critically discusses the different approaches for the environmental remediation of engineered nanomaterials using membrane filtration processes. Microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) have been shown to effectively remove nanomaterials from the air and aqueous environments. In MF, the adsorption of nanomaterials to membrane material was found to be the main removal mechanism. While in UF and NF, the main mechanism was size exclusion. Membrane fouling, hence requiring proper cleaning or replacement was found to be the major challenge for UF and NF processes. While limited adsorption capacity of nanomaterial along with desorption was found to be the main challenges for MF.

Cadmium-treatment efficiency and membrane fouling during electrodialysis of wastewater discharged from zinc smelting

Zinc smelting wastewater contains high concentrations of Cd. Here, the treatment efficiency of Cd using electrodialysis was evaluated. In addition, scale accumulation of ion-exchange membrane (IEM) was analyzed, and fouling control was studied. The results showed that spacers effectively improved the limiting current density but accelerated foulant accumulation. The Cd-treatment efficiency improved to 85.4% without a spacer. Dissolved organic carbon (DOC) and hydrophobic DOC levels in diluted water decreased by 0.65 mg L^-1 and 2.1 mg L^-1, respectively; in contrast, hydrophilic DOC level increased by 1.45 mg L^-1. Some of the hydrophobic DOC in the diluted water was converted to hydrophilic DOC and subsequently to low-molecular-weight (LMW) DOC. DOC level in the concentrated water did not change substantially, but the LMW fraction of the hydrophilic DOC increased. In the cation-exchange membrane, a material composed of calcium sulfate accumulated in the bottom layer, and hydroxides of divalent and trivalent ions accumulated on top of it. In contrast, the anion-exchange membrane was fouled by humic substances. In terms of fouling control, physical and acid cleaning of IEMs was more effective than the reversal operation.

Microscale fluid and particle dynamics in filtration processes in water treatment: A review

The complex filtration processes in water treatment, granular filtration and membrane filtration, often suffer from filter fouling, and the fundamental understanding of microscale fluid and particle dynamics is a key to improving filtration efficiency and stability. In this review, we identify and review several key topics in filtration processes: drag force, fluid velocity profile, intrinsic permeability and hydraulic tortuosity in microscale fluid dynamics, and particle straining, absorption, and accumulation in microscale particle dynamics. The paper also reviews several key experimental and computational techniques for investigating filtration processes at microscale considering their applicability and capability. Then, major findings in previous studies on these key topics are comprehensively reviewed in terms of microscale fluid and particle dynamics. Last, future research is discussed in terms of techniques, scopes and links. The review provides a comprehensive overview of microscale fluid and particle dynamics in filtration processes for water treatment and particle technology communities.

Membrane Fabrication and Modification by Atomic Layer Deposition: Processes and Applications in Water Treatment and Gas Separation

Membrane-based separation processes are part of most water purification plants worldwide. Industrial separation applications, primarily water purification and gas separation, can be improved with novel membranes or modification to existing ones. Atomic layer deposition (ALD) is an emerging technique that is proposed to upgrade certain kinds of membranes independent of their chemistry and morphology. ALD deposits thin, defect-free, angstrom-scale, and uniform coating layers on a substrate's surface by reacting with gaseous precursors. The surface-modifying effects of ALD are described in the present review, followed by a description of various types of inorganic and organic barrier films and how these can be used in combination with ALD. The role of ALD in membrane fabrication and modification is categorized into different membrane-based groups according to the treated medium, i.e., water or gas. In all membrane types, the ALD-based direct deposition of inorganic materials, mainly metal oxides, on the membrane surface can improve antifouling, selectivity, permeability, and hydrophilicity. Therefore, the ALD technique can broaden the applications of membranes to the treatment of emerging contaminants in water and air. Finally, the advancement, limitations, and challenges of ALD-based membrane fabrication and modification are compared to provide a comprehensive guideline for developing next-generation membranes with improved filtration and separation performance.

Multifunctional Heterogeneous Ion-Exchange Membranes for Ion and Microbe Removal in Low-Salinity Water

Here, multifunctional heterogeneous ion-exchange metal nanocomposite membranes were prepared for surface water desalination and bacterial inactivation under low-pressure (0.05 MPa) filtration conditions. Ultrafiltration (UF) heterogeneous ion exchange membranes (IEMs) were modified with different concentrations of AgNO₃ and CuSO₄ solutions using the intermatrix synthesis (IMS) technique to produce metal nanocomposite membranes. Scanning electron microscopy (SEM) images revealed that the metal nanoparticles (MNPs) (Ag and Cu) were uniformly distributed on the surface and the interior of the nanocomposite membranes. With increasing metal precursor solution concentration (0.01 to 0.05 mol·L^-1), the metal content of Ag and Cu nanocomposite membranes increased from 0.020 to 0.084 mg·cm^-2 and from 0.031 to 0.218 m·cm^-2 respectively. Results showed that the hydrodynamic diameter diameters of Ag and Cu nanoparticles (NPs) increased from 62.42 to 121.10 nm and from 54.2 to 125.7 nm respectively, as the metal precursor concentration loaded increased. The leaching of metals from metal nanocomposite membranes was measured in a dead-end filtration system, and the highest leaching concentration levels were 8.72 ppb and 5.32 ppb for Ag and Cu, respectively. The salt rejection studies indicated that ionic selectivity was improved with increasing metal content. Bacterial filtration showed higher antibacterial activity for metal nanocomposite membranes, reaching 3.6 log bacterial inactivation.

Review: Current understanding on biological filtration for the removal of microcystins

Harmful algal blooms (HABs) have become a global problem not only in aquatic habitats but also in public health and safety due to the production of cyanotoxins as their secondary metabolites. Among the various identified cyanotoxin groups, microcystins (MCs) are one of the most prevalent cyanotoxin detected during HABs. Different strategies including advanced physical and chemical treatment processes have been developed to mitigate the threat of cyanotoxins in water utilities, but these have revealed certain limitations in terms of high operational costs, low removal efficacy, and harmful by-products formation. Recently, biological filtration systems (BFS) have gained attention for safe drinking water production as they can treat various natural organic matter (NOM) and emerging contaminants through a highly efficient and environmentally sustainable process. However, limited attention has been given to understand the current research progress, research challenges, and knowledge gaps for the successful implementation of BFS for MC removal. Therefore, in this review, currently identified MC biodegradation pathways and MC-degrading microorganisms with their degradation rates are summarized, which may be pivotal for studying bioaugmented BFS to enhance the MC removal during HABs. Moreover, both laboratory and field studies on BFS for MC removal are reviewed, followed by a discussion of current challenges and future research needs for the practical application of BFS.

Adsorption of recalcitrant contaminants of emerging concern onto activated carbon: A laboratory and pilot-scale study

According to the World Health Organization (WHO), the definition of water quality indicators, including contaminants of emerging concern (CECs), associated with the development of multi-barrier approaches for wastewater treatment, are crucial steps towards direct potable reuse of water. The aims of this study were 1) quantifying twelve CECs (including pharmaceutical, stimulant, and artificial sweetener compounds) in both untreated and treated wastewater samples in a Brazilian wastewater treatment plant (WWTP) using bidimensional liquid chromatography coupled with tandem mass spectrometry, allowing the selection of five marker (i.e., priority) CECs; 2) evaluating the adsorption potential of such selected CECs [caffeine, hydrochlorothiazide, saccharin, sucralose (SUC), and sulfamethoxazole (SMX)] onto coconut-shell granular activated carbon (GAC); and 3) investigating the removal of the same CECs by a multi-barrier system (pilot-scale, 350 L h^-1) treating the effluent of the WWTP and composed of reverse osmosis (RO), photoperoxidation (UV/H₂O₂), and filtration with GAC. Such technologies were tested separately and in binary or ternary combinations. Eleven and eight CECs were detected and quantified on the untreated and treated wastewater samples of the Brazilian WWTP, respectively. For the treated wastewater, the concentrations ranged from 499 ng L^-1 (SMX) to 87,831 ng L^-1 (SUC). The adsorption onto AC data fitted the Sips isotherm model, indicating monolayer chemisorption, which was also suggested by the mean adsorption energy values (>16 kJ mol^-1). SMX and SUC were the most and the least adsorbed CECs (4.33 and 1.21 mg g^-1, respectively). Concerning the pilot-scale treatment plant, the ternary combination (RO + UV/H₂O₂+GAC) removed >99% of the five marker CECs and promoted reductions on water color, turbidity, as well as on nitrogen and phosphorus concentrations. Further studies on water reuse could prioritize the selected marker CECs as quality indicators. While the removal of marker CECs is one of the WHO performance requirements, the RO + UV/H₂O₂+GAC system showed promising results as a first approach to direct potable reuse of water.

Membrane technology as an emergency response against drinking water shortage in scenarios of dam failure

With dam failure events, there can be changes in water quality and difficulties in the operation of water treatment plants (WTPs) since they were not designed for water treatment under severe pollution conditions. To avoid that, it was investigated two strategies based on pre-oxidation, ultrafiltration (UF) and reverse osmosis (RO) integrated into a conventional treatment process (coagulation, flocculation, and sand filtration) or with each other, with the potential to reduce the risks of drinking water shortage and guarantee a safe drinking water supply. The study considered the context of the Velhas river basin (Brazil), where water quality is compromised by high turbidities (500-3000 NTU) and excessive arsenic (∼0.4 mg/L), iron (∼50 mg/L), and manganese (∼3 mg/L) levels. They were only partially removed by conventional treatments (removals: 74 ± 21%) and potability standards were only achieved after the membrane separation processes were considered (As: <0.01 mg/L, Mn: <0.1 mg/L, and Fe: <0.3 mg/L). The high water quality after RO enables its blend with the stream obtained after sand filters and would allow for greater flexibility during the operation of WTPs operation. Despite the susceptibility to fouling and most frequent maintenance, the pre-oxidation-UF-RO system would also guarantee a safe drinking water supply. The decision for the most adequate strategy was then based on a multicriteria analysis. A retrofit of conventional WTPs by their integration with UF-RO was classified as the best strategy for centralized facilities, whereas pre-oxidation-UF-RO better fits the reality of decentralized treatments given the lower costs and deployment time. The methodology based on multicriteria analysis and water treatment technologies, exemplified by membranes in this study, presented satisfactory results for different scenarios of critical treatment.

Treatability Studies on the Optimization of Ozone and Carbon Dosages for the Effective Removal of Contaminants from Secondary Treated Effluent

This study investigates the novel and advanced integrated pilot-scale treatment system of removal of contaminants in the secondary effluent from municipal wastewater. The main intent of this work is to assess the combination of pressure sand filter (PSF), ultrafiltration (UF), ozone (O3), and granular activated carbon (GAC) to treat wastewater and evaluate its suitability for water reuse. The experiments were carried out in a following condition: $\text{PSF}+\text{UF}+\text{O}3+\text{GAC}$ , $\text{PSF}+\text{O}3+\text{GAC}$ , and $\text{PSF}+\text{UF}+\text{GAC}$ . Configuration 1 was found to be more effective when compared to the other two and almost there occurred complete removal of contaminants. Whereas configuration 2 had the lowest removal efficiency of all, and configuration 3 had quite positive results. The influence of process parameters such as ozone dosage, flow rate, and filtration time was optimized. The optimized filtration time was 20 min with the filtration feed flow rate of 300 LPH. The best configuration of this treatment process produced a removal efficiency of about 80 to 90% with the ozone dosage of 8.33 mg/L with a flow rate of 4 l/min, whereas there occurred complete removal by the subsequent action of GAC. Moreover, the biodegradability of wastewaters as measured by the BOD5/COD ratio increased from 0.45 to 0.53. The proposed integrated pilot-scale process was effective in removing contaminants to the required level of discharge in the environment or reuse and it will pave the way to provide significant benefits to wastewater treatment.

Highly Permeable Polylactic Acid Membrane Grafted with Quaternary Ammonium Salt for Effective and Durable Water Disinfection

Given the increasing usage of drinking water purifiers, highly permeable membranes with strong antimicrobial functions are desperately desirable for effective and durable water disinfection. Hereby, we prepared such antimicrobial membranes by chemical grafting of quaternary ammonium salt (QAS) molecules, 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride (TPMMC), onto air plasma pretreated biodegradable polylactic acid (PLA) substrates. The high chemical grafting density promoted very strong and positive zeta potential charge of the resulted PLA-QAS membrane, contributing to effective and broad-spectrum antimicrobial efficiencies (>99.99%) against different microbes, including fungi and conventional and drug-resistant bacteria. The solid grafting of QAS molecules produced a durable antimicrobial performance of the PLA-QAS membrane. In addition, the pleated filter (0.45 m²) of PLA-QAS membrane showed outstanding bacteria rejection properties (>99.99%) and excellent washing durability (up to 20 m³ water) even at very high water filtration rates (up to 4 L/min). The disinfection mechanism was clarified that negatively charged bacteria could be rapidly adsorbed to positively charged PLA-QAS spinnings, followed by devastating cell membrane damage to bacterial debris, leaving a clean environment without significant biofilm and biofouling formation.

The effects of anaerobic reactor post-treatments by rapid filtration systems and conventional techniques

Although anaerobic reactors are an excellent alternative in the treatment of domestic effluents, they have the disadvantage of requiring post-treatment. Many technologies have been studied and, recently, rapid filtration systems have been presented as a viable alternative for post-treatment. This work compared post-treatment techniques for anaerobic upflow sludge blanket (UASB) reactors by rapid filtration systems (double filtration (DF); triple filtration with clinoptilolite (TFc); and triple filtration with activated carbon (TFac)) to conventional systems (facultative pond (FP); biological filter (BF); biological filter with recirculation and decantation (BFD)), verifying their potential for improvement of the final effluent quality. The UASB effluent post-treatments by FP, BF, BFD, DF, TFc, and TFac were evaluated. The removal of turbidity in both BFD and FP post-treatments was below 75%. The DF, TFc, and TFac treatments showed over 99% removal of the same parameters. COD removal in the FP, BF, and BFD post-treatments was over 10%, while in the DF, TFc, and TFac treatments, it was over 80%. The greatest total phosphorus removal was observed in TFc and TFac, whose values were over 99%. The best removal of ammoniacal nitrogen, 99% was observed in the TFc treatment. Regarding Al, Cd, Cr, Cu, Mn, Ni, Pb, and Zn removal, all rapid filtration systems showed better performance when compared to conventional systems. The DF, TFc, and TFac systems showed over 90% removal of most metals evaluated, while the FP and BF treatments presented values below 50% for most metals, and in the BFD system, the removal values were below 80% for most metals. The results indicate that rapid filtration systems were better at removing all evaluated parameters when compared to conventional systems.

Removal of microplastics and nanoplastics from urban waters: Separation and degradation

The omnipresent micro/nanoplastics (MPs/NPs) in urban waters arouse great public concern. To build a MP/NP-free urban water system, enormous efforts have been made to meet this goal via separating and degrading MPs/NPs in urban waters. Herein, we comprehensively review the recent developments in the separation and degradation of MPs/NPs in urban waters. Efficient MP/NP separation techniques, such as adsorption, coagulation/flocculation, flotation, filtration, and magnetic separation are first summarized. The influence of functional materials/reagents, properties of MPs/NPs, and aquatic chemistry on the separation efficiency is analyzed. Then, MP/NP degradation methods, including electrochemical degradation, advanced oxidation processes (AOPs), photodegradation, photocatalytic degradation, and biological degradation are detailed. Also, the effects of critical functional materials/organisms and operational parameters on degradation performance are discussed. At last, the current challenges and prospects in the separation, degradation, and further upcycling of MPs/NPs in urban waters are outlined. This review will potentially guide the development of next-generation technologies for MP/NP pollution control in urban waters.

Filtration with Multiple Species of Particles

Membrane filtration of feed containing multiple species of particles is a common process in the industrial setting. In this work, we propose a model for filtration of a suspension containing multiple particle species (concrete examples of our model are shown in two and three species), each with different affinities for the material of the porous filter membrane. Using the pore shape within the membrane as a design objective, we formulate a number of optimization problems pertaining to effective separation of desired and undesired particles in the special case of two-particle species and we present results showing how properties such as feed composition affect the optimal filter design. In addition, we propose a novel multi-stage filtration strategy, which provides a significant mass yield improvement for the desired particles, and, surprisingly, higher purity of the product as well.

Assessment of a Novel Photocatalytic TiO2-Zirconia Ultrafiltration Membrane and Combination with Solar Photo-Fenton Tertiary Treatment of Urban Wastewater

The objective of this study was to assess the combination of a photocatalytic TiO2-coated ZrO2 UF membrane with solar photo-Fenton treatment at circumneutral pH for the filtration and treatment of urban wastewater treatment plant (UWWTP) effluents. Photocatalytic self-cleaning properties were tested with a UWWTP effluent under irradiation in a solar simulator. Then, both the permeates and retentates from the membrane process were treated using the solar photo-Fenton treatment. The UWWTP effluent was spiked with caffeine (CAF), imidacloprid (IMI), thiacloprid (THI), carbamazepine (CBZ) and diclofenac (DCF) at an initial concentration of 100 µg/L each. Retention on the membrane of Pseudomonas Aeruginosa (P. Aeruginosa), a Gram-negative bacterial strain, was tested with and without irradiation. It was demonstrated that filtration of a certain volume of UWWTP effluent in the dark is possible, and the original conditions can then be recovered after illumination. The photocatalytic membrane significantly reduces the turbidity of the UWWTP effluent, significantly increasing the degradation efficiency of the subsequent solar photo-Fenton treatment. The results showed that the membrane allowed consistent retention of P. Aeruginosa at an order of magnitude of 1 × 103–1 × 104 CFU/mL.

Comparison of Disinfection By-Product Formation and Distribution during Breakpoint Chlorination and Chlorine-Based Disinfection in Drinking Water

Breakpoint chlorination (BC) and disinfection with chlorine-based disinfectant are widely used procedures in drinking water production. Both involve dosing chlorine into the raw water, where it can react with organic compounds, forming disinfection by-products (DBPs) of health concern. However, technological parameters (e.g., contact time, chlorine dosage, and bromide to residual free chlorine ratio) of the two chlorination procedures are different, which can lead to differences in DBP formation. To better understand this, a year-long sampling campaign was carried out at three waterworks in Hungary, where both BC and chlorine disinfection are used. To confirm the results of the field sampling, bench-scale experiments were carried out, investigating the impact of (a) bromide concentration in raw water, (b) residual free chlorine (bromide to residual chlorine ratio), and (c) contact time on DBP formation. The measured DBPs were trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and chlorate. During BC, the DBPs were formed in higher concentration, with the exception of one waterwork having elevated bromide content in the raw water. Bromine substitution factors (BSFs) were significantly higher during disinfection than BC in both field and laboratory experiments. After BC, the chlorate concentration range was 0.15–1.1 mg/L, and 96% of the samples exceeded the European Union (EU) parametric value (0.25 mg/L), whereas disinfection contributed only slightly. Granular activated carbon (GAC) filters used to remove DBPs in waterworks were exhausted after 6–8 months of use, first for those chlorinated THMs, which are generated predominantly during BC. The biological activity of the filters started to increase after 3–6 months of operation. This activity helps to remove the biodegradable compounds, such as disubstituted haloacetic acid (DHAAs) and HANs, even if the adsorption capacity of the GAC filters are low.

Lignocellulosic Biomass-Derived Nanocellulose Crystals as Fillers in Membranes for Water and Wastewater Treatment: A Review

The improvement of membrane applications for wastewater treatment has been a focal point of research in recent times, with a wide variety of efforts being made to enhance the performance, integrity and environmental friendliness of the existing membrane materials. Cellulose nanocrystals (CNCs) are sustainable nanomaterials derived from microorganisms and plants with promising potential in wastewater treatment. Cellulose nanomaterials offer a satisfactory alternative to other environmentally harmful nanomaterials. However, only a few review articles on this important field are available in the open literature, especially in membrane applications for wastewater treatment. This review briefly highlights the circular economy of waste lignocellulosic biomass and the isolation of CNCs from waste lignocellulosic biomass for membrane applications. The surface chemical functionalization technique for the preparation of CNC-based materials with the desired functional groups and properties is outlined. Recent uses of CNC-based materials in membrane applications for wastewater treatment are presented. In addition, the assessment of the environmental impacts of CNCs, cellulose extraction, the production techniques of cellulose products, cellulose product utilization, and their end-of-life disposal are briefly discussed. Furthermore, the challenges and prospects for the development of CNC from waste biomass for application in wastewater treatment are discussed extensively. Finally, this review unraveled some important perceptions on the prospects of CNC-based materials, especially in membrane applications for the treatment of wastewater.

Clog mitigation in a microfluidic array via pulsatile flows

Clogging is a common obstacle encountered during the transport of suspensions and represents a significant energy and material cost across applications, including water purification, irrigation, biopharmaceutical processing, and aquifer recharge. Pulsatile pressure-driven flows can help mitigate clogging when compared to steady flows. Here, we study experimentally the influence of the amplitude of pulsation 0.25P₀ ≤ δP ≤ 1.25P₀, where P₀ is the mean pressure, and of the frequency of pulsation 10^-3 Hz ≤ f ≤ 10^-1 Hz on clog mitigation in a microfluidic array of parallel channels using a dilute suspension of colloidal particles. The array geometry is representative of a classical filter, with parallel pores that clog over time, yielding a filter cake that continues to grow and can interact with other pores. We combine flow rate measurements with direct visualizations at the pore scale to correlate the observed clogging dynamics with the changes in flow rate. We observe that all pulsatile amplitudes at 0.1 Hz yield increased throughput compared to steady flows. The rearrangement of particles when subject to a dynamic shear environment can delay the clogging of a pore or even remove an existing clog. However, this benefit is drastically reduced at 10^-2 Hz and disappears at 10^-3 Hz as the pulsatile timescale becomes too large compared to the timescale associated with the clogging and the growth of the filter cakes in this system. The present study demonstrates that pulsatile flows are a promising method to delay clogging at both the pore and system scale.

Fouling mitigation in reverse osmosis processes with 3D printed sinusoidal spacers

Feed spacers are an essential part of spiral wound modules for reverse osmosis (RO). They create flow channels between membrane sheets and manipulate hydrodynamic conditions to control membrane fouling. In this work, additive manufacturing (Polyjet) was used to print novel sinusoidal spacers with wavy axial filaments connected by perpendicular (ST) or slanted (SL) transverse filaments. When tested with 2 g/L NaCl solution, conventional and SL spacers had similar flux while the ST spacer had about 5-7% lower flux. The pressure losses for ST and SL spacers increased by up to 3 folds depending on the flow condition. In the colloidal silica fouling and biofouling tests, the sinusoidal spacers showed lower membrane permeability decrease of 46% for ST, 41% for SL vs 56% for conventional and 26% for ST, 22% for SL vs 33% for conventional, respectively. Optical coherence tomography images from colloidal silica fouling and confocal images from biofouling tests revealed that fouling patterns were closely associated with the local hydrodynamic conditions. Overall, sinusoidal spacers showed promising results in controlling membrane fouling, but there is potential for further optimizations to reduce channel pressure loss.

Development and appraisal of handwash-wastewater treatment system for water recycling as a resilient response to COVID-19

In this work, results from characterization of handwashing wastewater from selected stations in Kampala City, Uganda, revealed that handwashing wastewater did not meet permissible international standards for wastewater discharge to the environment. The ratio of BOD₅ to COD of ˂ 0.5 implied that handwashing wastewater was not amenable to biological treatment processes. Turbidity of ˃ 50 NTU pointed to the need for a roughing filter prior to slow sand filtration. Subsequently, a handwashing wastewater treatment system consisting of selected particle sizes of silica sand, zeolite, and granular activated carbon as filtration and/or adsorption media was developed and assessed for performance towards amelioration of the physicochemical and biological parameters of the handwashing wastewater. Treated water from the developed wastewater treatment system exhibited a turbidity of 5 NTU, true color of 10 Pt-Co, apparent color of 6 Pt-Co, and TSS of 9 mgL^-1, translating to removal efficiencies of up to 98.5%, 98.1%, 99.7%, and 96.9%, respectively. The residual total coliforms and E. coli of 1395 and 1180 CFU(100 mL)^-1 respectively, were totally eliminated upon disinfection with 0.5 mL NaOCl (3.5% wt/vol) per liter of treated wastewater. The treated water was thus suitable for recycling for handwashing purpose as opposed to letting handwashing wastewater merely go down the drain. This approach provides a resilient response to COVID-19, where communities faced with water scarcity can treat and recycle handwashing wastewater at the point of washing. It thus enables more people to have the opportunity to practice handwashing, abating the high risks of infection, which could otherwise arise.

Modeling of the Suspended Solid Removal of a Granular Media Layer in an Upflow Stormwater Runoff Filtration System

Upflow granular media filtration devices are widely used for stormwater runoff treatment. However, the system performance is not well characterized due to the irregular removal of suspended solid (SS) in the pretreatment (sedimentation) chamber and, hence, its irregular input to the media layer. In this regard, the performance of the granular media layer of an upflow filtration system is investigated herein by the use of various models. Due to the significant variation in the SS concentration of the influent and effluent to and from the media layer, the deep bed filtration model, the k-C* model, and the porous media capture model provide limited descriptions of the system performance. By contrast, the performance is well described using the kinetic model, the modified k-C* model using a specific deposit, and the modified porous media capture model using a specific deposit. The parameters of the latter models are shown to be in good correlation with the filtration velocity, SS removal, and specific deposit. The results suggest that modeling using a specific SS deposit can provide an accurate description of the granular media layer performance under a highly variable influent SS concentration.

Virus pH-Dependent Interactions with Cationically Modified Cellulose and Their Application in Water Filtration

Norovirus and Rotavirus are among the pathogens causing a large number of disease outbreaks due to contaminated water. These viruses are nanoscale particles that are difficult to remove by common filtration approaches which are based on physical size exclusion, and require adsorption-based filtration methods. This study reports the pH-responsive interactions of viruses with cationic-modified nanocellulose and demonstrates a filter material that adsorbs nanoscale viruses and can be regenerated by changing the solution's pH. The bacteria viruses Qbeta and MS2, with diameters below 30 nm but different surface properties, are used to evaluate the pH-dependency of the interactions and the filtration process. Small angle X-ray scattering, cryogenic transmission electron microscopy, and ζ-potential measurements are used to study the interactions and analyze changes in their nanostructure and surface properties of the virus upon adsorption. The virus removal capacity of the cationic cellulose-based aerogel filter is 99.9% for MS2 and 93.6% for Qbeta, at pH = 7.0; and desorption of mostly intact viruses occurs at pH = 3.0. The results contribute to the fundamental understanding of pH-triggered virus-nanocellulose self-assembly and can guide the design of sustainable and environmentally friendly adsorption-based virus filter materials as well as phage and virus-based materials.

Processing Strategies to Obtain Highly Porous Silk Fibroin Structures with Tailored Microstructure and Molecular Characteristics and Their Applicability in Water Remediation

The present work reports on the control of silk fibroin (SF) porous structures performance through various processing methods. The study includes the analysis of two dissolving techniques (CaCl₂/H₂O/EtOH ternary and LiBr/H₂O binary solutions), three regeneration methods (gelation, lyophilization and gas foaming) and one post-processing (EtOH). In all the cases, followed steps lead to SF structures with porosity values above 94% and large surface areas. Also, results about samples microstructure, secondary organization, crystallinity and water behavior, reveal a direct correlation between processing and SF properties. Thanks to the achieved progress, the SF varying porous structures were evaluated for metalloids (As⁵⁺ and As³⁺) and heavy metals (Cr⁶⁺ and Cr³⁺) adsorption, observing a direct relationship between samples processing and ionic species adsorption ability. Thus, it is shown that the control of the properties of SF based porous structures through processing, represents a suitable and ecofriendly approach for the development of bio-based materials for environmental applications.

Combined dual-size foam glass media filtration process with micro-flocculation for simultaneous removal of particulate and dissolved contaminants in urban road runoff

In this study, a combined media filtration process with micro-flocculation (CMF) was developed, to simultaneously treat particulate and dissolved contaminants in urban road runoff. Dual-size foam glass media with stone and sand layers were applied and the efficiency of road runoff treatment was investigated according to filtration and micro-flocculation under various experimental conditions (stone/sand layer ratio, linear velocity, and coagulant types). Moreover, the removal efficiencies of suspended solids (SS), phosphorus, organic carbon, and heavy metals (Zn, Cu, Pb, Cd) by CMF were evaluated. The removal rate of SS was maintained to be above 84.1% for 1 h filtration by the dual-size foam glass, regardless of increasing pressure. The removal of phosphorus by micro-flocculation was more suitable in alum than ferric due to a higher initial floc growth rate and an increased particle size. The performance of the CMF was significantly improved over media filtration only process (MF) in removing both particulate and dissolved contaminants. The removal efficiency of all particulate pollutants by CMF was found to be more than 90%, and notably, the dissolved phosphorus, which was mostly not removed by MF, was also removed by 97.4%. Meanwhile, the backwash efficiency of CMF was half that of MF. Physical removal mechanisms, such as internal diffusion, dominated MF, whereas chemical removal mechanisms, such as adsorption and surface precipitation, dominated CMF. These results show the potential of the CMF process for the treatment of urban road runoff and identify the removal mechanisms of the filtration process that use micro-flocculation with dual-size foam glass.

Performance of Layer-by-Layer-Modified Multibore® Ultrafiltration Capillary Membranes for Salt Retention and Removal of Antibiotic Resistance Genes

Polyether sulfone Multibore^® ultrafiltration membranes were modified using polyelectrolyte multilayers via the layer-by-layer (LbL) technique in order to increase their rejection capabilities towards salts and antibiotic resistance genes. The modified capillary membranes were characterized to exhibit a molecular weight cut-off (at 90% rejection) of 384 Da. The zeta-potential at pH 7 was −40 mV. Laboratory tests using single-fiber modified membrane modules were performed to evaluate the removal of antibiotic resistance genes; the LbL-coated membranes were able to completely retain DNA fragments from 90 to 1500 nt in length. Furthermore, the pure water permeability and the retention of single inorganic salts, MgSO₄, CaCl₂ and NaCl, were measured using a mini-plant testing unit. The modified membranes had a retention of 80% toward MgSO₄ and CaCl₂ salts, and 23% in case of NaCl. The modified membranes were also found to be stable against mechanical backwashing (up to 80 LMH) and chemical regeneration (in acidic conditions and basic/oxidizing conditions).

Biosorption of organic micropollutants onto lignocellulosic-based material

The occurrence of organic micropollutants such as pharmaceutical drugs and hormones in the environment reflects the inefficiency of traditional wastewater treatment technologies. Biosorption is a promising alternative from a technical-economic point of view, so understanding the mechanisms of adsorption in new biosorbents is vital for application and process optimization. Within this context, this study aims to evaluate the mechanisms of adsorption and removal of synthetic and natural hormones by Pinus elliottii bark biosorbent (PS) compared to commercial granular activated carbon (GAC) through kinetic models, isotherm models, and thermodynamic models. The adsorbents were also characterized by morphology, chemical composition, functional groups, and point of zero charge. Characterization of the adsorbents highlights the heterogeneous and fibrous morphology and broader range of functional groups found for PS. Kinetic adjustments showed high accuracy for pseudo-second-order, Elovich, and intraparticle diffusion models, presenting multilinearity and evidencing multi-stage adsorption. The isotherms for PS followed high-affinity models, predominantly chemisorption, while those for GAC followed the Langmuir model, where physisorption predominates. These mechanisms were confirmed by thermodynamic models, which also indicated a higher dependence on temperature in the adsorption process. In the fortified water removal test, PS showed removal values higher than GAC, highlighting the advantages of this adsorbent.

The Influence of Feed and Drinking Water on Terrestrial Animal Research and Study Replicability

For more than 50 years, the research community has made strides to better determine the nutrient requirements for many common laboratory animal species. This work has resulted in high-quality animal feeds that can optimize growth, maintenance, and reproduction in most species. We have a much better understanding of the role that individual nutrients play in physiological responses. Today, diet is often considered as an independent variable in experimental design, and specialized diet formulations for experimental purposes are widely used. In contrast, drinking water provided to laboratory animals has rarely been a consideration in experimental design except in studies of specific water-borne microbial or chemical contaminants. As we advance in the precision of scientific measurements, we are constantly discovering previously unrecognized sources of experimental variability. This is the nature of science. However, science is suffering from a lack of experimental reproducibility or replicability that undermines public trust. The issue of reproducibility/replicability is especially sensitive when laboratory animals are involved since we have the ethical responsibility to assure that laboratory animals are used wisely. One way to reduce problems with reproducibility/replicability is to have a strong understanding of potential sources of inherent variability in the system under study and to provide "…a clear, specific, and complete description of how the reported results were reached [1]." A primary intent of this review is to provide the reader with a high-level overview of some basic elements of laboratory animal nutrition, methods used in the manufacturing of feeds, sources of drinking water, and general methods of water purification. The goal is to provide background on contemporary issues regarding how diet and drinking water might serve as a source of extrinsic variability that can impact animal health, study design, and experimental outcomes and provide suggestions on how to mitigate these effects.

A novel filtration system based on ceramic silver-impregnated pot filter combined with adsorption processes to remove waterborne bacteria

Halving the proportion of the people without sustainable access to safe drinking water and basic sanitation is among the Sustainable Development Goals (SDG). Lack of access to safe drinking water has been associated with the prevalence of waterborne diseases. Due to this reported association, the development of household water treatment devices has been an alternative to improve the quality supply of domestic water. In this study, we aimed to evaluate the performance of a ceramic silver-impregnated pot filter (CSF) system coupled with an adsorption process, composed of silver-impregnated granular activated carbon and zeolite (CSF + GAC-Z), to remove waterborne bacteria Escherichia coli and Salmonella spp. from spiked water. The performance of this system was compared with the conventional CSF system. In this respect, we evaluated six CSF and six CSF + GAC-Z using spiked water with 10³ and 10² CFU/mL of E. coli and Salmonella spp. The mean percentage of removals ranged between 98% and 99.98%. The highest bacterial removal efficiency was recorded by the CSF + GAC-Z (99%) and CSF (99.98%) for E. coli and Salmonella spp., respectively, but no significant statistical differences were found between filtration systems. Our findings suggest that the CSF + GAC-Z system was effective in the removal of waterborne bacteria from spiked water.

The Estimation of Postmortem Serum Urea via the Ultrafiltration of Hemolyzed Blood

Postmortem serum urea has been demonstrated as an objective indicator for the forensic diagnosis of cause of death. However, samples used in postmortem biochemical analysis are always affected by hemolysis. To investigate whether hemolysis affects the biochemical analysis of urea and to explore the feasibility of using ultrafiltration to process hemolyzed blood samples, three different levels of hemolyzed blood samples were used to assess the influence of hemolysis on postmortem biochemical analysis of urea, and two ultrafiltration methods were used to process the hemolyzed blood samples. Bias% was used to assess the interference of hemolysis. Our results showed that heavy hemolysis had a significant influence on the biochemical analysis of urea. Both ultrafiltration methods in the present study could significantly reduce the interference of hemolysis, with the |bias%| of methods A and B decreasing from 69.74% ± 99.14% to 12.18% ± 7.23% and 10.77% ± 8.09%, respectively, compared to the original serum. After regression correction, there was no significant difference between the urea concentration in the ultrafiltrates of the two ultrafiltration methods and that in the original serum, which suggested that the postmortem serum urea concentration could be estimated by the corrected urea concentration in the ultrafiltrate. The current study also provided possible pretreatment methods for postmortem biochemical analysis of other biomarkers in hemolyzed blood samples of forensic practice.

Reuse of ultrafiltered effluents for crop irrigation: On-site flow cytometry unveiled microbial removal patterns across a full-scale tertiary treatment

Reuse of treated wastewater for crop irrigation has been widely adopted to mitigate the effects of water scarcity on agricultural yields and to help preserving the integrity of aquatic ecosystems. This paper presents the outcomes of one-year monitoring of a full-scale agro-industrial wastewater treatment plant designed for water reuse, with a multistage tertiary treatment based on sand filtration, membrane ultrafiltration, storage and on-demand UV disinfection. We aimed to test flow cytometry as a monitoring tool to provide on-site indications on tertiary treatment performances and on the quality of treated wastewater along the treatment scheme. Membrane ultrafiltration retained prokaryotic cells and E. coli (>3 log). During storage of treated effluents, a significant decay of E. coli was observed together with the growth of prokaryotic and eukaryotic cells, and the UV disinfection was effective only against fecal indicators. The microbial quality of the treated effluent was comparable to the control groundwater locally used for irrigation. On-site rapid assessments by flow cytometry allowed unveiling crucial aspects affecting the microbiological quality of ultrafiltration permeate and treated effluent immediately after sampling, including plant operating performances and microbial removal patterns across the treatment train.

Influence of granular activated carbon media properties on natural organic matter and disinfection by-product precursor removal from drinking water

Operational and financial constraints challenge effective removal of natural organic matter (NOM), and specifically disinfection by-product (DBP) precursors, at remote and/or small sites. Granular activated carbon (GAC) is a widely used treatment option for such locations, due to its relatively low maintenance and process operational simplicity. However, its efficacy is highly dependent on the media capacity for the organic matter, which in turn depends on the media characteristics. The influence of GAC media properties on NOM/DBP precursor removal has been studied using a range of established and emerging media using both batch adsorption tests and rapid small-scale column tests. DBP formation propensity (DBPFP) was measured with reference to trihalomethanes (THMs) and haloacetic acids (HAAs). All GAC media showed no selectivity for specific removal of precursors of regulated DBPs; DBP formation was a simple function of residual dissolved organic carbon (DOC) levels. UV₂₅₄ was found to be a good surrogate measurement of DBPFP for an untreated water source having a high DOC. Due to the much-reduced concentration of DBP precursors, the correlation was significantly poorer for the coagulation/flocculation-pretreateed water source. Breakthrough curves generated from the microcolumn trials revealed DOC removal and consequent DBP reduction to correlate reasonably well with the prevalence pores in the 5-10 nm range. A 3-6 fold increase in capacity was recorded for a 0.005-0.045 cm³/g change in 5-10 nm-sized pore volume density. No corresponding correlation was evident with other media pore size ranges.

Removal of methylene blue from aqueous solutions by biochar prepared from the pyrolysis of mixed municipal discarded material

This paper investigates the adsorption of organic compounds in aqueous solution to biochar adsorbent, using methylene blue as an indicator for adsorption. Biochar was produced by the pyrolysis of mixed municipal discarded material in an innovative heat pipe reactor, the pyrolysis temperature was held at 300°C for 12 h. Biochar produced under these conditions was found to have oxygen containing functional groups that are beneficial to the adsorption of methylene blue as well as graphitic structures suggesting potential sites for π-π interactions with methylene blue. Methylene Blue followed the pseudo second order kinetic model with higher R² values than both the pseudo first order kinetic and intraparticle diffusion models. The adsorption also closely fit the Langmuir isotherm rather than the Freundlich model, suggesting monolayer adsorption rather than multilayer adsorption. Maximum adsorption capacity was observed at 7.2 mg/g for initial concentration of 100 mg/l Methylene blue in aqueous solution. The amount of Methylene blue adsorbed increased with increasing initial concentration as expected. The adsorption mechanisms are likely π-π interactions between methylene blue and the graphitic structures in the biochar which are shown to be present in Raman spectroscopy, as well as electrostatic attraction and ionic bonding between negatively charged surface sites on the char and the positive charge on the dissolved methylene blue molecules. The results show that biochar obtained from mixed waste could be employed as a low-cost and effective tool in water treatment for the removal of basic dyes and potentially other organic impurities.

Simultaneous manganese adsorption and biotransformation by Streptomyces violarus strain SBP1 cell-immobilized biochar

Consumption of water containing high proportions of manganese could cause Parkinson's like symptoms and damage the central nervous systems. This study aims to investigate the potential of manganese removal through the development of microbial cell-immobilized biochar. The wood vinegar industry generates a large volume of carbonized wood waste (natural biochar) from the pyrolytic process. This is the first investigation utilizing this low value waste combined with biological treatment for water purification. Raw and hydrogen peroxide-modified biochars were used to immobilize an effective manganese-oxidizing bacterium, Streptomyces violarus strain SBP1 (SBP1). The results demonstrated that the modified biochar had a higher proportion of oxygen-containing functional groups leading to better manganese removal. Manganese adsorption by the modified biochar fitted pseudo-second-order and Langmuir models with the maximum adsorption capacity of 1.15 mg g^-1. The modified biochar with SBP1 provided the highest removal efficiency at 78%. The advanced synchrotron analyses demonstrated that manganese removal by the biochar with SBP1 is due to the synergistic combination of manganese adsorption by biochars and biological oxidation by SBP1.

Analysis of microbial contamination of household water purifiers

Household water purifiers are increasingly used to treat drinking water at the household level, but their influence on the microbiological safety of drinking water has rarely been assessed. In this study, representative purifiers, based on different filtering processes, were analyzed for their impact on effluent water quality. The results showed that purifiers reduced chemical qualities such as turbidity and free chlorine. However, a high level of bacteria (10²-10⁶ CFU/g) was detected at each stage of filtration using a traditional culture-dependent method, whereas quantitative PCR with propidium monoazide (PMA) treatment showed 10⁶-10⁸ copies/L of total viable bacteria in effluent water, indicating elevated microbial contaminants after purifiers. In addition, high-throughput sequencing revealed a diverse microbial community in effluents and membranes. Proteobacteria (22.06-97.42%) was the dominant phylum found in all samples, except for purifier B, in which Melainabacteria was most abundant (65.79%). For waterborne pathogens, Escherichia coli (10⁰-10⁶ copies/g) and Pseudomonas aeruginosa (10⁰-10⁵ copies/g) were frequently detected by qPCR. Sequencing also demonstrated the presence of E. coli (0-6.26%), Mycobacterium mucogenicum (0.01-3.46%), and P. aeruginosa (0-0.16%) in purifiers. These finding suggest that water from commonly used household purifiers still impose microbial risks to human health.

Filtration behaviors and fouling mechanisms of ultrafiltration process with polyacrylamide flocculation for water treatment

This study aims to investigate thermodynamic mechanisms of filtration behaviors of ultrafiltration (UF) process with polyacrylamide (PAM) flocculation for surface water treatment, which has not been investigated previously. It was interestingly found that, filtration of durably mixed sodium alginate (SA) solution corresponded to an extraordinarily high specific filtration resistance (SFR) (3.28 × 10¹⁴ m·kg^-1 without polyacrylamide addition) and a V-shaped profile of SFR characterized by a sharp fall followed by a correspondingly sharp rise along with the increase in PAM addition concentration. Experimental characterizations suggested that, membrane fouling was mainly caused by the gel layer formation rather than the pore clogging and cake/floc formation. Rather than the chemical composition change, the changes of the solution physicochemical properties (pH and zeta potential) and foulant morphology are associated with above-mentioned interesting filtration behaviors. Accordingly, the thermodynamic mechanisms of the filtration behaviors were proposed. It was proposed that, the thermodynamics of polymeric network described by the Flory-Huggins lattice theory were responsible for the extraordinarily high SFR of SA gel layer. Low dosage of PAM addition decreased the negative zeta potential and homogeneity of the gel system, causing the reduced SFR. In contrast, further PAM addition increased the negative zeta potential and homogeneity of the gel system, and then increased the SFR of the gel layer. These results reasonably explained the V-shaped profile of SFR. This study provided significant insights into the effects of PAM addition on ultrafiltration behaviors of alginate solution.