A new approach for modeling flux variation in membrane filtration and experimental verification

Efficient adsorption of lead and copper from water by modification of sand filter with a green plant-based adsorbent: Adsorption kinetics and regeneration

In this study, pomegranate seed waste (PSW) was added into sand filter (SF) to increase removal efficiency of Lead (Pb(II)) and Copper (Cu(II)) from polluted water. The performance of PSW was compared with activated carbon (AC) as a typical adsorbent. Based on the SEM, EDX, FTIR, XRD, BET and proximate analyses, PSW had porous structure with specific surface area of 2.76 m2/g and active compounds which suggested PSW as an appropriate adsorbent for heavy metals (HMs) adsorption. According to the batch experiments, SF without treatment could only remove 46% and 35% of Pb(II) and Cu(II), respectively. These numbers increased to 88% and 75% for Pb(II) and Cu(II) by adding 3 g/kg PSW to the SF, respectively under the optimal conditions of HMs initial concentrations = 100 mg/L, pH = 7 and contact time = 60 min. The adsorption kinetic and isotherm followed the pseudo-first-order and Langmuir models, respectively indicating that mainly physisorption was involved in the HMs adsorption process of PSW. Based on the column experiments (flow rate = 62.5 mL/min), the Pb(II) and Cu(II) removal increased from 14% to 60% and 10%-55%, respectively after 5 pore volumes (40 min) by adding 3 g/kg PSW to the SF. Breakthrough curves matched better with Thomas mode rather than Adam's Bohart proving Langmuir adsorption isotherm. Our finding suggested modification of SF with PSW is a promising approach for efficient removal of HMs from water.

An environmentally friendly approach for industrial wastewater treatment and bio-adsorption of heavy metals using Pistacia soft shell (PSS) through flocculation-adsorption process

In this research, the potential application of Pistacia soft shell (PSS) was investigated as a novel bio-based flocculant for pulp and paper wastewater (PPWW) treatment. In line with this, after characterization of the PSS, the removal efficiencies of chemical oxygen demand (COD), turbidity and heavy metals (Cu2+ and Pb2+) from PPWW were investigated with different dosage of PSS. The results were compared with alum as a reference flocculant. In addition, the effect of pH adjustment on the flocculation-adsorption performance of PSS was studied under acidic and alkaline condition. Zeta potential, BET, FTIR and SEM as well as kinetics and isotherm analyses were conducted for mechanistic understanding. According to the results, PSS treatment could remove COD, turbidity, Cu2+ and Pb2+ up to 67%, 87%, 70% and 74%, respectively which were better than alum: 56%, 85%, 31% and 35%. It was observed that, pH adjustment significantly improved the performance of PSS treatment. Maximum removal efficiencies of 92%, 95%, 97% and 98% were achieved for COD, turbidity, Cu2+ and Pb2+, respectively, under optimal condition of using 2 g/L PSS at pH 9. The mechanism analysis revealed that the high removal efficiency of PSS is related to the dual flocculation-adsorption of bridging and sweeping mechanisms. The results of this study suggested PSS as a promising, sustainable and eco-friendly bio-based flocculant and adsorbent for industrial wastewater treatment.

Could organoclay be used as a promising natural adsorbent for efficient and cost-effective dye wastewater treatment?

There is an urgent need for developing eco-friendly adsorbents for dye wastewater treatment with high efficiency and low cost. Meanwhile, organoclay has received an increasing attention as a natural adsorbent for dye removal. However, no comprehensive investigation has been conducted to evaluate the feasibility of this approach in terms of operation cost and removal efficiency. In this research, we intend to answer this question: could organoclay be used as an efficient and cost-effective approach for dye wastewater treatment? In line with that, after characterization of the Na-bentonite and modified clay by using SEM, EDX, FTIR and XRD, the performance of the organoclay was optimized in terms of AO7 dye removal efficiency and adsorption cost using response surface methods (RSM). Then, the organoclay performance was compared with other typical adsorbents activated carbon and chitosan. The characterization results proved that Na-bentonite was successfully modified by CTAB. According to RSM results, the maximum dye removal of 95% and the minimum adsorption cost of 0.009 $/g were achieved under optimum conditions of: pH: 5, AO7 concentration: 56 mg/L, contact time: 53 min and organoclay dosage: 0.8 g/L. While, in the case of other adsorbents of Na-bentonite, chitosan and activated carbon the maximum removal of 11%, 84% and 92% were achieved with 0.0136, 0.0324 and 0.1011 $/g, respectively. The adsorption kinetics and isotherms analyses revealed that the experimental data fitted well with the pseudo-second-order (R² = 0.993) and Langmuir (R² = 0.988). This study proved that organoclay can be used as a promising adsorbent for dye removal with low cost and high removal efficiency.

New Insights into the Fouling of a Membrane during the Ultrafiltration of Complex Organic-Inorganic Feed Water

This paper presents an analysis of the fouling of a ceramic membrane by a mixture containing high concentrations of humic acid and colloidal silica during cross-flow ultrafiltration under various operating conditions. Two types of feed water were tested: feed water containing humic acid and feed water containing a mixture of humic acid and colloidal silica. The colloidal silica exacerbated the fouling, yielding lower fluxes (109-394 L m^-2 h^-1) compared to the humic acid feed water (205-850 L m^-2 h^-1), while the retentions were higher except for the highest cross-flow rate. For the humic acid feed water, the irreversible resistance prevails under the cross-flow rate of 5 L min^-1. During the filtration of an organic-inorganic mixture, the reversible resistance due to the formation of a colloidal cake layer prevails under all operating conditions with an exception. The exception is the filtration of the organic-inorganic mixture of a 50 mg L^-1 humic acid concentration which resulted in a lower flux than the one of a 150 mg L^-1 humic acid concentration under 150 kPa and a cross-flow rate of 5 L min^-1. Here, the irreversible fouling is unexpectedly overcome. This is unusual and occurs due to the low agglomeration at low concentrations of humic acid under a high cross-flow rate. Under lower transmembrane pressure and a moderate cross-flow rate, fouling can be mitigated, and relatively high fluxes are yielded with high retentions even in the presence of nanoparticles. In this way, colloidal silica influences the minimization of membrane fouling by organic humic acid contributing to the control of in-pore organic fouling.

Development a novel hexagonal airlift flat plate photobioreactor for the improvement of microalgae growth that simultaneously enhance CO2 bio-fixation and wastewater treatment

A novel hexagonal airlift flat plate (HAFP) photobioreactor was designed to improve microalgae growth rate and compared with traditional flat plate (TFP) photobioreactor. The computational fluid dynamics (CFD) simulation was used to determine hydrodynamic parameters and optimal aeration rate in the photobioreactors. Additionally, the capability of the HAFP photobioreactor to enhance microalgae based CO₂ bio-fixation and wastewater treatment were investigated. The results of CFD simulation indicated that the HAFP photobioreactor could improve hydrodynamic parameters of turbulence kinetic energy (TKE), average fluid velocity, dead zone (DZ), and water shear stress (WSS) up to 78 %, 41 %, 44 % and 40 %, respectively, under optimal aeration rate of 0.6 vvm. The proposed HAFP photobioreactor showed a drastic improvement in microalgae growth (up to 61 %). The maximum CO₂ removal of 53.8 % and bio-fixation of 0.85 g L^-1 d^-1 were achieved in the HAFP photobioreactor which were approximately 70 % more than that in the TFP photobioreactor. The results suggested that the HAFP photobioreactor could accelerate nutrients removal and achieve remarkably higher efficiencies of 91 %, 99 %, 97 % and 93 % of ammonia (NH₃), nitrate (NO₃^-), phosphate (PO₄^3-) and chemical oxygen demand (COD) within seven days of cultivation.

A Review on Ion-Exchange Membrane Fouling during the Electrodialysis Process in the Food Industry, Part 1: Types, Effects, Characterization Methods, Fouling Mechanisms and Interactions

Electrodialysis (ED) was first established for water desalination and is still highly recommended in this field for its high water recovery, long lifetime and acceptable electricity consumption. Today, thanks to technological progress in ED processes and the emergence of new ion-exchange membranes (IEMs), ED has been extended to many other applications in the food industry. This expansion of uses has also generated several problems such as IEMs' lifetime limitation due to different ageing phenomena (because of organic and/or mineral compounds). The current commercial IEMs show excellent performance in ED processes; however, organic foulants such as proteins, surfactants, polyphenols or other natural organic matters can adhere on their surface (especially when using anion-exchange membranes: AEMs) forming a colloid layer or can infiltrate the membrane matrix, which leads to the increase in electrical resistance, resulting in higher energy consumption, lower water recovery, loss of membrane permselectivity and current efficiency as well as lifetime limitation. If these aspects are not sufficiently controlled and mastered, the use and the efficiency of ED processes will be limited since, it will no longer be competitive or profitable compared to other separation methods. In this work we reviewed a significant amount of recent scientific publications, research and reviews studying the phenomena of IEM fouling during the ED process in food industry with a special focus on the last decade. We first classified the different types of fouling according to the most commonly used classifications. Then, the fouling effects, the characterization methods and techniques as well as the different fouling mechanisms and interactions as well as their influence on IEM matrix and fixed groups were presented, analyzed, discussed and illustrated.

A pilot-scale sulfur-based sulfidogenic system for the treatment of Cu-laden electroplating wastewater using real domestic sewage as electron donor

Elemental sulfur (S⁰) reduction process has been demonstrated as an attractive and cost-efficient approach for metal-laden wastewater treatment in lab-scale studies. However, the system performance and stability have not been evaluated in pilot- or large-scale wastewater treatment. Especially, the sulfide production rate and microbial community structure may significantly vary from lab-scale system to pilot- or large-scale systems using real domestic sewage as carbon source, which brings questions to this novel technology. In this study, therefore, a pilot-scale sulfur-based sulfidogenic treatment system was newly developed and applied for the treatment of Cu-laden electroplating wastewaters using domestic sewage as carbon source. During the 175-d operation, >99.9% of Cu²⁺ (i.e., 5580 and 1187 mg Cu/L for two types of electroplating wastewaters) was efficiently removed by the biogenic hydrogen sulfide that produced through S⁰ reduction. Relatively high level of sulfide production (200 mg S/L) can be achieved by utilizing organics in raw domestic sewage, which was easily affected by the organic content and pH value of the domestic sewage. The long-term feeding of domestic sewage significantly re-shaped the microbial community in sulfur-reducing bioreactors. Compared to the reported lab-scale bioreactors, higher microbial community diversity was found in our pilot-scale bioreactors. The presence of hydrolytic, fermentative and sulfur-reducing bacteria was the critical factor for system stability. Accordingly, a two-step ecological interaction among fermentative and sulfur-reducing bacteria was newly proposed for sulfide production: biodegradable particulate organic carbon (BPOC) was firstly degraded to dissolved organic carbon (DOC) by the hydrolytic and fermentative bacteria. Then, sulfur-reducing bacteria utilized the total DOC (both DOC degraded from BPOC and the original DOC present in domestic sewage) as electron donor and reduced the S⁰ to sulfide. Afterwards, the sulfide precipitated Cu²⁺ in the post sedimentation tank. Compared with other reported technologies, the sulfur-based treatment system remarkable reduced the total chemical cost by 87.5‒99.6% for the same level of Cu²⁺ removal. Therefore, this pilot-scale study demonstrated that S⁰ reduction process can be a sustainable technology to generate sulfide for the co-treatment of Cu-laden electroplating wastewater and domestic sewage, achieving higher Cu²⁺removal and higher cost-effectiveness than the conventional technologies.

The structural and functional properties of polysaccharide foulants in membrane fouling

Polysaccharide foulant is known to play a crucial role in membrane fouling, however the detailed influential mechanisms and the pertinence to specific structure of polysaccharides, as well as intermolecular interactions among them with and without divalent cation are still indistinct. In this study, seven polysaccharides including agarose, sodium alginate, carrageenan, pectin, starch, sodium carboxymethylcellulose (CMC) and xanthan gum, with different chain and molecular structures, were used as model foulants to investigate the role of structural and functional features of polysaccharides in membrane fouling. Two Hermia's models (classical and mass-transfer models) as well as the resistance-in-series model were used to analyze the fouling mechanism. Results show that the spatial configuration of foulant molecule is significant in membrane fouling which actually controls the resistance of gel layer formed on membrane. Polysaccharides with different properties show distinct fouling mechanisms which are in accordance with the four models described by Hermia respectively. Cations may change the interaction of polysaccharide foulant which further leads to the structural change of the gel layer. It turns out that mass-transfer model is more suitable for interpreting of crossflow filtration data. So far, little has been known about the effects of molecule structure of polysaccharides on membrane fouling. In this paper, we provide a basic database for polysaccharide fouling which will work as a theoretical basis for finding more effective measures to prevent and control membrane fouling.

Simultaneous harvesting and extracellular polymeric substances extrusion of microalgae using surfactant: Promoting surfactant-assisted flocculation through pH adjustment

In this research, the use of four different types of surfactants on biomass harvesting and extracellular polymeric substances (EPS) extrusion of Chlorella sorokiniana sp was investigated. The synergy between cationic surfactants and pH was tested to improve flocculation efficiency through the combined mechanism of charge neutralization, bridging and sweeping. Zeta potential and microscopic images were used to gain mechanistic understanding. The harvesting efficacy correlated positively with the biomass zeta potential and the surfactants alkyl-chain length; i.e., CTAB (88%) > DTAB (66%) > triton X-100 (41%) > SDS (11%). When the pH increased from 8 to 12, the harvesting efficiency was improved 12% and 39% for CTAB and DTAB, respectively. More interestingly, pH adjustment dramatically reduced the optimal dosages of CTAB and DTAB from 400 to 50 and 1000 to 300 mg/L, respectively. All selected surfactants could successfully release high value components of EPS such as protein and polysaccharide.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Particle-scale modelling of fluid velocity distribution near the particles surface in sand filtration

Sand filtration is widely used in drinking water treatment processes, yet the hydraulic fundamentals at particle-scale are not well defined, especially the fluid velocity profile near the sand particles surface. In this study, a numerical model is developed by combining the Lattice Boltzmann (LBM) and the Discrete Element Method (DEM), used to describe the fluid flow over the sand particles surface and the micro-structure details of the sand packed bed respectively. The model is validated by comparing the simulation results with the experimental measurements using two systems, showing that the model can describe the fluid velocity distribution around the particles surface. Critical flow velocity is introduced as the balance between hydrodynamic and adhesive torques acting on sand particle surface. Furthermore, a new concept - effective filter surface (EFS), is defined as the area where the velocity near sand particles surface is less than the critical flow velocity, aiming for indirectly evaluating the performance of sand filtration. It is quantitatively demonstrated that increasing the sand particle size or feed flow velocity results in the decrease of both critical flow velocity and EFS under the given tested conditions. The LBM-DEM model provides a useful tool for understanding the fundamentals of liquid flow distribution and also estimating sand filtration performance under different operation conditions.