Removal Of Colloidal Particles Research Articles

Reduction of organic matter and disinfection by products formation at surface water treatment plants in Egypt

ABSTRACT Although the removal of colloidal particles continues to be an important reason for using coagulation, currently a newer approach, the removal of organic matter to reduce the formation of disinfection byproducts (DBPs) such as trihalomethanes (THMs) are suspected carcinogens. Inefficient removal of total organic carbon (TOC) leads to the formation of carcinogenic THMs. This motivates the research efforts to find a way to reduce them in potable water. The first objective of this research is monitoring the water quality (raw and produced) for selected three water treatment plants within Giza Governorate to reveal the most polluted site (high TOC in the raw water and THMs in the treated water) in the study areas. The second objective of this study is enhancing coagulation to reduce TOC and THMs from surface water treating. In this study, two different coagulants aluminum sulfate (alum), and ferric chloride were tested under different conditions of pH and coagulant concentration to determine their effectiveness for removal of TOC, THMs and turbidity. Optimum values for the mentioned conditions were used to achieve the maximum reduction for TOC and THMs in Al-Ayat drinking water treatment plant (DWTP) which recorded the highest concentration of TOC and THMs. Ferric chloride as a coagulant achieved the maximum removal percentage % of TOC, THMs and turbidity as 79%, 82% and 94%, respectively, at ferric chloride dose 100 mg/L, while alum as a coagulant recorded the maximum removal percentage % of TOC, THMs and turbidity as 46%, 52% and 91%, respectively, at alum dose 100 mg/L. The results indicated that ferric chloride as a coagulant has the highest efficiency reduction of TOC, THMs and turbidity if compared to alum with the same dose added.

Precursor-Engineered Volatile Inks Enable Reliable Blade-Coating of Cesium-Formamidinium Perovskites Toward Fully Printed Solar Modules.

Reliable fabrication of large-area perovskite films with antisolvent-free printing techniques requires high-volatility solvents, such as 2-methoxyethanol (2ME), to formulate precursor inks. However, the fabrication of high-quality cesium-formamidinium (Cs-FA) perovskites has been hampered using volatile solvents due to their poor coordination with the perovskite precursors. Here, this issue is resolved by re-formulating a 2ME-based Cs0.05FA0.95PbI3 ink using pre-synthesized single crystals as the precursor instead of the conventional mixture of raw powders. The key to obtaining high-quality Cs-FA films lies in the removal of colloidal particles from the ink and hence the suppression of colloid-induced heterogeneous nucleation, which kinetically facilitates the growth of as-formed crystals toward larger grains and improved film crystallinity. Employing the precursor-engineered volatile ink in the vacuum-free, fully printing processing of solar cells (with carbon electrode), a power conversion efficiency (PCE) of 19.3%, a T80 (80% of initial PCE) of 1000h in ISOS-L-2I (85°C/1Sun) aging test and a substantially reduced bill of materials are obtained. The reliable coating methodology ultimately enables the fabrication of carbon-electrode mini solar modules with a stabilized PCE of 16.2% (average 15.6%) representing the record value among the fully printed counterparts and a key milestone toward meeting the objectives for a scalable photovoltaic technology.

Mechanisms of colloid removal from polydimethylsiloxane (PDMS) surfaces during washing: Implications for enhanced produce decontamination

Microbial contamination of fresh produce poses significant challenges to food safety and public health. Postharvest washing is a common practice in the fresh produce industry to reduce microbial load. This study aimed to elucidate the mechanisms involved in bacterial removal from produce surfaces during washing, using model colloids as bacterial surrogates and polydimethylsiloxane (PDMS) replicas of tomato, lettuce, and spinach as model produce surfaces. Colloids were deposited onto the PDMS surfaces and subsequently washed using different solutions (DI water, NaCl, and surfactants Tween 80 and sodium dodecyl sulfate) at varying concentrations. The PDMS surfaces were then withdrawn from the solutions at two distinct velocities. Colloid removal efficacy and the associated physicochemical interactions between colloids and substrate surfaces under various washing conditions were quantified. The results revealed that colloid removal was controlled by the residual amount of washing solution retained and contact line action. These factors, in turn, were influenced by the sample-withdrawal velocity and physicochemical properties of substrate surfaces, colloids, and washing solutions. Specifically, SDS at 2 mol/m3 combined with a slow withdrawal velocity significantly optimized colloid removal, achieving up to 79.0% efficiency. Conversely, using Tween 80 at 0.08 mol/m3 concentration significantly impeded removal efficiency. Understanding these dynamics to minimize residual solution retention and optimize colloid/bacteria movement with the contact line upon washing can significantly enhance the cleaning efficacy of fresh produce. The findings of this study provide an improved understanding on the key factors governing the retention and removal of colloidal particles (including microorganisms) that can guide the development of effective decontamination strategies.

The Potential of Moringa oleifera Seed in Water Coagulation-Flocculation Technique to Reduce Water Turbidity

Using a safe and easy-to-apply economic flocculant to replace alum is necessary to expand and enhance the water quality in rural regions where traditional water treatment is unavailable. The seed of Moringa oleifera is locally available in large volumes and is feasibly economical. A compatibility and applicability research of the easily accessible local Moringa oleifera seed extract (MOSE) was conducted to examine its potential utilization to lessen various degrees of water turbidity at 30 ± 2 °C. The study concerns the optimum dosage of MOSE to give high turbidity removal efficiency in the water. Experiments were carried out for nine turbidity samples: 5, 10, 15, 30, 50, 70, 100, 200, and 300 NTU. The turbidity removal efficiency of up to 89% was achieved for high initial turbid water 300 NTU. However, for low turbid water, its potential efficiency declined. The results demonstrate that the de-oiled extract is substantially more efficient than the crude extract in agglomerating colloidal particles of low initial turbidity samples and achieved up to 76% removal rate. The results of the ANOVA confirmed that the regression model was significant at (p < 0.05) for residual turbidity after the treatment process. The study also demonstrates that a pseudo-first-order kinetic model matched well the nature of the removal of colloidal particles with MOSE in water to form flocs. The study also indicates that the characteristics of water treated with crude MOSE produce little change in electrical conductivity and salinity. However, the hardness and alkalinity of water decreased significantly depending on the initial hardness and the amount of MOSE applied (p < 0.05).

Machine learning model for the optimization and kinetics of petroleum industry effluent treatment using aluminum sulfate

Small-scale preliminary studies are necessary to determine the feasibility of the machine learning (ML) algorithm and time-evolution kinetics to meet the design specification of the treatment unit. The train and test datasets were obtained from jar test experimentation on the petroleum industry effluent (PIE) sample using aluminum sulfate (AS) as the coagulant. The ML algorithm from scikit-learn was employed to determine the optimum operating condition for the removal of colloidal particles, causing turbidity in the PIE. The predictive capacity of four ML models was compared based on their statistical metrics for clean discharge. The predicted optimum condition corresponds to pH (10), dosage (0.1 g/L), and settling time (30 min) which transcends to residual turbidity ≤ 10 NTU and translates to 95% removal efficiency. The second-order AS-sweep flocculation kinetic showed that at the predicted optimum conditions, modeled rate constant of 1.33 × 10−3 L/g.min and flocculation period of 1.2 min reduced the combination of the monomer, dimmer, and trimmer class colloids from an initial 570 mg/L concentration to the residual counts of 24 mg/L corresponding to residual turbidity ≤ 10 NTU under the mixing regime 14 s−1 ≤ G ≤ 164 s−1 satisfied the EPA standard for clean effluent discharge. It incorporated the selected ML output with time-evolution and aggregation kinetics to define sedimentation tank geometry for cleaner discharge. The findings from the design-driven optimization recommended a flow rate (1000 m3s−1), coefficient of kinematic viscosity (0.841 mm/s), and the required detention time (30–60 min) to define the sedimentation tank geometry.

Enhanced Accumulation of Colloidal Particles in Microgrooved Channels via Diffusiophoresis and Steady-State Electrolyte Flows.

The delivery of colloidal particles in dead-end microstructures is very challenging, since these geometries do not allow net flows of particle-laden fluids; meanwhile, diffusive transport is slow and inefficient. Recently, we introduced a novel particle manipulation strategy, based on diffusiophoresis, whereby the salt concentration gradient between parallel electrolyte streams in a microgrooved channel induces the rapid (i.e., within minutes) and reversible accumulation, retention, and removal of colloidal particles in the microgrooves. In this study, we investigated the effects of salt contrast and groove depth on the accumulation process in silicon microgrooves and determined the experimental conditions that lead to a particle concentration peak of more than four times the concentration in the channel bulk. Also, we achieved an average particle concentration in the grooves of more than twice the concentration in the flowing streams and almost 2 orders of magnitude larger than the average concentration in the grooves in the absence of a salt concentration gradient. Analytical sufficient and necessary conditions for particle accumulation are also derived. Finally, we successfully tested the accumulation process in polydimethylsiloxane microgrooved channels, as they are less expensive to fabricate than silicon microgrooved substrates. The controlled and enhanced accumulation of colloidal particles in dead-end structures by solute concentration gradients has potential applications in soft matter and living systems, such as drug delivery, synthetic biology, and on-chip diagnostics.

New insight into quinones triggered ferrate in-situ synthesized polynuclear Fe-hydroxyl complex for enhancing interfacial adsorption in highly efficient removal of natural organic matter

In this study, the effects of quinone on the formation of in-situ synthesized polynuclear Fe-hydroxide (PnFe-H) from ferrate activation and enhanced degradation of organics were investigated by in-situ UV linear differential absorbance spectra for the first time. Results indicated benzoquinone (BQ) efficiently activated ferrate for the flocculation of humic acid (HA) that the flocculation reactions rate constants in Fe(VI)-0.1 mM BQ was 3.3 times as much as the blank. Interestingly, quenching studies suggested PnFe-H derived from the high-valence iron species which were the active components by BQ activation, was proved the vital factor for removing of HA. According to the analysis of interaction energy, BQ promoted FeOH2+ converted to Fe(OH)2+ and Fe2(OH)24+ which weakened the polar property and increased hydrophobicity of compounds, further benefited for adsorption with lower Lifshitz-van del Waals (LW) and Lewis acid-base (AB) interfacial energy between PnFe-H-contaminant compounds. However, excessive BQ reduced freshly particulate Fe(III) to Fe(II), weakened the PnFe-H flocculation performance which retarded the transformation of iron species. In addition, the effects of HA concentration were also studied due to the existent of functional quinone-like moieties. The contribution of PnFe-H flocculation removal on the total removal (Reflocculation/Retotal) improved from 2.6% to 17.09% with Fe(VI)/HA from 0.1 to 1.12. Fe(VI) sufficient oxidized electron-rich moieties and decreased the aromaticity due to π bond was broken, further cooperated with PnFe-H captured small fragment particles by sweep flocculation that Fe(VI) self-accelerating decay produced more Fe(III). The research elucidated a new insight into of ferrate activation by quinone which could expand our knowledge of activation pathway, further regulate the relationship between oxidation and flocculation for enhancing organic and colloidal particle removal in practical application.

Enhanced coagulation by two-stage alum addition: the role of solution pH, floc breakage and assistant of non-ionic polyacrylamide

ABSTRACT Coagulation process is highly influenced by solution pH, floc breakage, and coagulant aid. In this work, two-stage addition of alum-based coagulants, polyaluminum chloride (PACl) and aluminum sulfate (Al2(SO4)3), was compared to their one-stage addition with the same total dosage. The dose ratio of primary and secondary addition was optimised. The effects of solution pH, floc breakage and dosing timing of coagulant aid of non-ionic polyacrylamide (NPAM) on coagulation efficiency and floc property were investigated. The results showed that two-stage addition of PACl showed less sensitivity with the variation of pH. Compared to PACl, two-stage addition of Al2(SO4)3 was more sensitive to the solution pH, especially when the pH ranged from 7 to 10. For all cases, the presence of floc breakage improved the removal of colloidal particles. The coagulation mechanism of primary coagulant was charge neutralisation, while other mechanism was involved with the secondary addition of coagulant. Compared to one-stage addition, the settling performance of aggregates and particulates removal in two-stage addition was more effective with the variation of dosage or dosing timing of NPAM. The present work provides detailed operating parameters for this coagulation strategy.

Modelling of Escherichia coli removal by a low-cost combined drinking water treatment system

AbstractThis work presents mathematical modelling of Escherichia coli (E.coli) removal by a multi-barrier point-of-use drinking water system. The modelled system is a combination of three treatment stages: filtration by geotextile fabric followed by filtration and disinfection by silver-coated ceramic granular media (SCCGM) then granular activated carbon (GAC) filtration. The presented models accounted for removal mechanisms by each treatment stage. E.coli was modelled as a microbial particle. E.coli inactivation by SCCGM was modelled using the Chick's, Chick-Watson, Collins-Selleck and complete mix system bacterial inactivation kinetic models, which were considered adequately representative for describing the removal. Geotextile removal was modelled using colloidal filtration theory (CFT) for hydrosol deposition in fibrous media. The filtration removal contributions by the SCCGM and GAC were modelled using CFT for removal of colloidal particles by granular media. The model results showed that inactivation by silver in the SCCGM was the main bacterial removal mechanism. Geotextile and GAC also depicted appreciable removals. The theoretical modelling approach used is important for design and optimization of the multi-barrier system and can support future research in terms of material combinations, system costs, etc. Collector diameter, particle size, filtration velocity and contact time were identified as critical parameters for E.coli removal efficiency.

Development of an oscillation-based technology for the removal of colloidal particles from water: CFD modeling and experiments

ABSTRACT Colloidal particles removal from water is a challenge in surface water treatment. Previously, we suggested an original technique for colloidal particles separation from water based on physical flow manipulation by an oscillating device. Laboratory experiments and 2D numerical simulation indicated that this technology enhances colloidal particles grouping and enables their rapid, simultaneous aggregation and sedimentation. The 2D model used in that study was unable to fully elucidate the grouping mechanism, settling pattern, or particle trajectories. Here, we extended the numerical simulation from 2D to 3D and examined the system’s distinctive flow field. The flow field was solved with computational fluid dynamics (CFD) simulations in the commercial ANSYS Fluent code and validated by dye injection experiments. The sedimentation patterns could nicely be explained by the computational results. This explanation was strengthened by two-dimensional population balance model simulations, which showed that particles aggregated in two zones trailing the paddle edges. Additionally, the results indicate significantly higher TKE values and faster upward vertical velocities at the higher oscillating frequency, which explains the different sedimentation patterns and removal efficiencies generated by the different oscillation frequencies. The use of 3D numerical simulations will help to better understand and further optimize this novel technology.

Performance enhancement of ultrafiltration membrane via simple deposition of polymer-based modifiers

Ultrafiltration (UF) membrane is extensively utilized in water treatment for the removal of colloidal particles, dissolved organic matters and microorganisms. These colloidal particles and organic matters are prone to being adsorbed on membrane surface known as membrane fouling, which increases operational costs and lowers down membrane efficiency. In this work, a group of synthesized hydrophilic random copolymers and homopolymer were utilized to enhance PES UF membrane performance by a simple deposition of a thin layer. Despite the increased intrinsic resistance as a result of the thin modification layer, higher pure water permeability and recovery rate were observed for the modified Polyethersulfone (PES) membrane during Bovine Serum Albumin (BSA) fouling test in comparison to the virgin membrane. Moreover, the stability of the adsorbed polymer layers was evaluated by a cyclic fouling test and chemical cleaning endurance assessment. The membrane surface morphology and topography were characterized by field emission scanning electron microscopy (FESEM) and atom force microscope (AFM). The chemical composition before and after clcylic fouling test and chemical cleaning were studied with attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy. The results show that the random copolymer modified membrane exhibited average 26 % rises in water permeability compared with the virgin PES UF membrane when 0.5 wt% BSA solution was used as feed. The stable permeability and flux recovery rate during the cyclic study with chemical cleaning suggest good affinity of the newly synthesized random copolymer with the PES membrane and water. This strategy successfully enhanced the UF membrane anti-fouling performance.

Optimization of aluminium recovery from water treatment sludge using Response Surface Methodology

For decades, water treatment plants in Malaysia have widely employed aluminium-based coagulant for the removal of colloidal particles in surface water. This generates huge amount of by-product, known as sludge that is either reused for land applications or disposed to landfills. As sludge contains high concentration of aluminium, both can pose severe environmental issues. Therefore, this study explored the potential to recover aluminium from water treatment sludge using acid leaching process. The evaluation of aluminium recovery efficiency was conducted in two phases. The first phase used the one factor at a time (OFAT) approach to study the effects of acid concentration, solid to liquid ratio, temperature and heating time. Meanwhile, second phase emphasized on the optimization of aluminium recovery using Response Surface Methodology (RSM). OFAT results indicated that aluminium recovery increased with the rising temperature and heating time. Acid concentration and solid to liquid ratio, however, showed an initial increment followed by reduction of recovery with increasing concentration and ratio. Due to the solidification of sludge when acid concentration exceeded 4 M, this variable was fixed in the optimization study. RSM predicted that aluminium recovery can achieve 70.3% at optimal values of 4 M, 20.9%, 90 °C and 4.4 h of acid concentration, solid to liquid ratio, temperature and heating time, respectively. Experimental validation demonstrated a recovery of 68.8 ± 0.3%. The small discrepancy of 2.2 ± 0.4% between predicted and validated recovery suggests that RSM was a suitable tool in optimizing aluminium recovery conditions for water treatment sludge.

Application of natural coagulants extracted from common beans for wastewater treatment

In this paper, the possibility of applying natural coagulants obtained from common beans for the removal of colloidal particles from wastewater was investigated. Three types of wastewater were used in the experiments: stillage from bioethanol production, wastewater from sugar production, and synthetic turbid water. Natural coagulants were extracted from crushed beans using 0.5 M NaCl. Jar tests were conducted with different doses of coagulant at different pH values. After sedimentation, coagulation activity was determined by turbidity measurements. Results showed that the highest coagulation activity of the natural coagulants from common beans was achieved in stillage, at 98.8% (at pH 9 with applied dose of coagulant of 5 mL/L), while the coagulation activity in the synthetic turbid water was 90.1% (at pH 8 and a dose of 0.4 mL/L). The lowest coagulation activity was achieved in the wastewater from sugar production, at 49.8% (at pH 5.5 and dose of 0.4 mL/L).

Study of ionic charge dependent salt resistant swelling behavior and removal of colloidal particles using reduced gum rosin-poly(acrylamide)-based green flocculant

Present work reports the under pressure preparation of reduced gum rosin and acrylamide-based GrA-cl-poly(AAm) green flocculant. Characterization of the synthesized product was carried out by different techniques such as Fourier transform infrared spectroscopy, X-ray diffraction method and scanning electron microscopy. In addition, several variables such as time, physiological pH, solvent, pressure, monomer, cross-linking agent and initiator were examined to obtain maximum flocculation efficiency and explore the salt resistant swelling of the system. The maximum percentage swelling (P s) at pH 7.0 and pressure 8.0 psi was found to be 578 %. Thermal behavior of the flocculant was investigated and the synthesized sample showed higher thermal stability than the gum rosin. The effect of ionic strength and charges of various cations (Na+, Ba+2, Fe+3, Sn+4) on salt resistant swelling of GrA-cl-poly(AAm) flocculant, in different salt solutions such as sodium chloride, barium chloride, ferric chloride and stannic chloride (NaCl, BaCl2, FeCl3 and SnCl4), was also studied. The synthesized sample was found to show ionic charge and salt concentration related behavior. Further, the removal of colloidal particles from wastewater through flocculation showed that GrA-cl-poly(AAm) exhibited significant flocculation efficiency (95.18 %) at a dose rate of 55 mg at 30 °C and pH 5.0. Flocculant capacity in saline medium was found to be maximum (99 %) at 1 % concentration. Further, increase in saline concentration resulted in decreased flocculant capacity. The kinetics of the aggregation of particles, deflocculation and reflocculation was analyzed through the Smoluchowski classical model based on first-order and second-order kinetics.

Production of a biodegradable flocculant from cotton and evaluation of its performance in coagulation-flocculation of kaolin clay suspension: Optimization through response surface methodology (RSM)

Flocculants are widely used along with coagulant to increase the efficiency of coagulation-flocculation process for removal of colloidal particles from wastewaters. The most widely used flocculants are synthetic which have some problems such as non-biodegradability and release of toxic residual monomers. The main aim of this study is to evaluate the performance of cellulose sulfate (CS), which was synthesized through sulfonation of cotton, as a biodegradable and natural-based flocculant. Reaction time as an important factor in the sulfonation reaction was optimized for obtaining CS with high charge density and suitable fiber size. The sulfate content, charge density (CD) and morphology of each CS were determined to investigate and select the best CS for the flocculation process. A suspension containing kaolin clay was used as a colloidal test solution and coagulation was performed using alum (as a coagulant) and CS (as a flocculant). Optimization was performed using response surface methodology (RSM). The optimization results showed that CS had a good performance in turbidity reduction in coagulation-flocculation treatment and maximum turbidity reduction (98.9%) was obtained at alum dosage of 23.1mg/L, CS dosage of 7.2mg/L and pH 6.2. The results showed that the pH variation had insignificant effect on the CS dosage. Zeta potential measurements and microscopic photos of flocs confirm charge neutralization and bridge formation in flocculation using cellulose sulfate, respectively. Also, the total chemical consumption reduced compared with the use of alum alone. As a consequence, CS can be considered as a suitable alternative for conventional flocculants.

Fault Diagnosis by LAMDA methodology Applied to Drinking Water Plant

Water industry is facing increased pressure to produce higher quality treated water at a lower cost. The coagulation-flocculation unit is a major step in the production of potable water, allowing the removal of colloidal particles and contamination sources. Currently, the coagulant dosing is manual and it is determined by the way of jar test (off-line dosing tests). This test cannot be applied to supervision and diagnostic real-time. In order to obtain a simple model to describe the water treatment plant, a behavior model sets out, from the analysis of raw water characteristics to the entrance of the plant: (1) prediction on-line the amount of optimal coagulant dosage (software sensor) and (2) the determination of the functional states in real time. The innovative aspect of this paper resides in the design of intelligent control techniques of information water treatment plant (fuzzy logic for the classifier and neuronal networks for the software sensor).

Intensive rearing of cod larvae (Gadus morhua) in recirculating aquaculture systems (RAS) implementing a membrane bioreactor (MBR) for enhanced colloidal particle and fine suspended solids removal

Intensive rearing of Atlantic cod larvae (Gadus morhua) was investigated in a conventional recirculating aquaculture system (cRAS) and a membrane modified RAS (mRAS). Cod larvae are sensitive to water quality, and beneficial effects on growth and survival from enhanced removal of colloidal particles, fine suspended solids and nutrient reduction were expected. Membrane bioreactors (MBR) are a potential technology for advanced water treatment in aquaculture. The aim of this project was to assess the effect of an MBR system for enhanced treatment in RAS. A cRAS and mRAS treatment train were operated in parallel. In the mRAS Scheme 8.5% of the recycle stream was filtered through the membrane at any time. The mRAS scheme demonstrated a significantly lower turbidity and number of colloidal particles as compared to the cRAS scheme, as well as significantly lower bacteria concentrations and more stability. Overall a 13% higher cod larvae growth (weight, %) at 40dph and 3.5% higher survival rate at 50dph was measured in the mRAS scheme. Results show there is a great potential of implementing a membrane filtration system in aquaculture recycling systems.

Use of nanoparticular and soluble anionic celluloses in coagulation-flocculation treatment of kaolin suspension

In this work, the effectiveness of a novel, combined coagulation-flocculation treatment based on alum and soluble or nanoparticular anionic derivatives of dialdehyde cellulose, ADAC, was evaluated by studying the removal of colloidal material in a model suspension containing kaolin. Four different ADACs with varying degrees of substitution, size and water solubility were synthesized by periodate oxidation and sulfonation of cellulose. The effects of ADAC dosage, solution pH and temperature on flocculation were studied by measuring residual turbidity of the settled suspension. Moreover, the charge densities, sizes, ζ-potentials and stability of the ADACs in aqueous solutions were studied. The combined treatment was effective in the removal of colloidal particles, as demonstrated by reduced residual turbidity with remarkably lower total chemical consumption compared with coagulation with alum alone. Of the ADACs, samples with lower solubility that contained cellulose nanoparticles performed better than the fully water-soluble sample. Due to the restricted pH tolerance of alum, the combined treatment was effective only at acidic conditions (pH < 5), although the ADACs were found to be stable in a much broader pH range (pH of 3 to about 9). ADACs also retained strong activity at higher temperatures (30–60 °C) and after several days of storage in aqueous solution.

Coagulation–flocculation of colloidal suspensions of kaolinite, bentonite, and alumina by chitosan sulfate

AbstractThis article reports on the removal of colloidal suspensions of kaolinite, bentonite, and alumina using chitosan sulfate (ChS). ChS was synthesized by partial introduction of sulfate groups in the chitosan (Ch) structure. The polyampholyte (chitosan sulfate) shows variable charge depending on the pH of the solution. ChS was characterized by FTIR, 13C‐NMR, elemental analysis, and potentiometric titrations. The ChS coagulation–flocculation capacity for kaolinite, bentonite, and alumina aqueous suspensions was systematically studied. The coagulation–flocculation process was carried out at various pH values and ChS concentrations. The pH range in which the largest ChS removal capacity was observed depended on particle type (4.5–5.5 for kaolinite, 4.5–7.0 for bentonite, and 7.0–8.0 for alumina). The removal of colloidal particles is explained by charge neutralization due to electrostatic interactions between ChS and particles and particle entrapping when the polyelectrolyte precipitates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Removal of colloidal particles in ceramic depth filters based on diatomaceous earth

Safe drinking water is still not accessible to more than 15% of the world’s population. Decentralised water treatment with ceramic filter candles at the point-of-use (POU) level provides a low-cost and single-stage filtration process with which pathogenic microorganisms can be removed. However, the retention performance of such depth filters scatters for microbiological contaminants in literature. The purpose of this study was to gain a better understanding on the removal mechanisms in ceramic depth filters based on the natural material diatomaceous earth (DE). Therefore, we manufactured so-called ceramic filter candles by ram-extrusion process and subjected these filters to a detailed physical characterisation regarding porosity, pore size distribution, specific surface area, flowrate, surface charge and microstructure. Next, we investigated experimentally the removal of colloidal latex (polystyrene) particles having diameters from 100 to 500 nm under various ionic strengths. Such particles were found to be removed due to adsorption of the colloids. Extended DLVO-theory was used to investigate the forces that account for the adsorption suggesting that hydrophobic interactions drag latex particles onto specific adsorption sites of the filter. It is hypothesised that these specific adsorption sites originate from the unique nanostructured surface of the diatomaceous earth. Furthermore, we believe that such latex particles may be suitable to model the removal of microorganisms if the surrogate and the target pathogen have similar characteristics.