Ceramic MF Research Articles

Application of ceramic membranes for seawater reverse osmosis (SWRO) pre-treatment

Low-pressure (microfiltration/ultrafiltration (MF/UF)) membranes are being increasingly used as pre-treatment, prior to seawater reverse osmosis (SWRO). The objective of pre-treatment before reverse osmosis (RO) membranes is to remove undesirable and particulate fouling materials (algae, suspended and colloidal particles). Also, a pre-treatment barrier reduces organics and provides better feed water quality for RO membranes. MF and UF pre-treatment prior to SWRO provides Low Silt Density Index (SDI) values recommended for RO operation. Ceramic membranes are more attractive as they made of more chemically resistant materials, which allow for more stable operation and aggressive backwashing (BW) and cleaning.A pilot plant with a monolith ceramic MF membrane (0.1μm pore size) from METAWATER was used to carry out the study. Red Sea water pumped from a distance of 700 m offshore from Thuwal (Kingdom of Saudi Arabia) was used as feed water. The pilot plant was operated automatically at constant flux of 150 LMH that involved BW, air flushing and forward flushing at the end of filtration cycle. Seawater permeates were used for hydraulic BW, while sodium hypochlorite, citric acid and sodium hydroxide were used for chemical cleaning (CIP) to restore the membrane permeability after use. Filtration cycles of 2.5 h were adopted for initial experiments. Aggressive BW flux of 1,800 LMH for 15 s, air flushing of 4 bars for 10 s and forward flushing of 300 LMH for 40 s were applied for regular membrane hydraulic cleaning. The increase of membrane resistances over time was monitored. Further studies were also performed by using Anopore ceramic membranes AAO100 (pore sizes of 0.1 μm) using a constant pressure bench-scale set-up. The feed water and permeate were analysed using an SDI unit, flow cytometre (FCM) and liquid chromatography with organic carbon detection (LC–OCD).The results showed that ceramic membrane filtration reduced the SDI15 of seawater from 6.1 to 2.1 which conform to the requirement of SDI < 3 needed for SWRO feed. The removal of bacteria corresponded to 3.7 log removal, while turbidity improved from 0.6 NTU (feed) to 0.05 NTU (permeate). However, ceramic membranes showed low recovery after BW and significant increase of trans-membrane pressure (TMP) during operation with the membrane alone, without coagulation. This increase of TMP can be related to the presence of sticky polysaccharide-like material called transparent exopolymers particles (TEP) that are known to be in abundance in seawater and contribute to organic fouling and eventually bio fouling. TEP showed resistance and stickiness on the membrane surface (AAO100) even after aggressive BW. This may be responsible for the low flux recovery observed after BW in both bench-scale and pilot experiments.To improve membrane filtration, coagulation was performed by using iron III chloride. Continuous addition of iron III chloride (4 mg/L Fe) through inline coagulation showed almost complete control of irreversible fouling and reduces reversible fouling after 30 h of operation, based on 2.5 h intervals of filtration cycle. Also, biopolymers removal improved to 51–71%, with improved removal at low pH, while for stabilization of flux, a dose of 1 mg/L Fe3+ was sufficient. Reduction of high molecular weight Natural organic matters (NOM) is essential for controlling or reducing irreversible fouling. Therefore, coagulation is recommended for smooth operation of ceramic membranes and for provision of low-fouling feed water, prior to SWRO membranes.

Optimum operating conditions in hybrid water treatment process of multi-channel ceramic MF and polyethersulfone beads loaded with photocatalyst

The effects of water back-flushing period (FT) and polyethersulfone (PES) beads concentration loaded with titanium dioxide (TiO2) photocatalyst were investigated in a hybrid process of multi-channel ceramic MF and photocatalyst. The space between the outside of the membrane (0.4μm pore size) and the module inside was filled with the PES beads. UV at a wavelength of 352nm was radiated from outside of the acryl module. A quantity of humic acid and kaolin was dissolved in distilled water and utilized here as synthetic water. As a result of FT effect, resistance of membrane fouling (Rf) was decreased when FT decreased from NBF (no back-flushing) to 2 min at BT 10 s. Therefore, the FT 2 min at BT 10 s was the optimal condition to reduce membrane fouling and to maintain high permeate flux in our hybrid process. As a result of photocatalyst PES beads concentration, Rf was minimum at 40 mg/L when photocatalyst beads concentration was changed from 50 to 5 mg/L. The highest treatment efficiency of turbidity was 97.6% at 30 g/L. However, the treatment efficiency of UV254 absorbance, which was the organic matter concentration, decreased from 83.5 to 77.3% when PES beads concentration was changed from 50 to 5 mg/L.

Variability and limits of the unified membrane fouling index: application to the reduction of low-pressure membrane fouling by ozonation and biofiltration

The impacts of ozone (0–8 mg O3 L-1) and filtration with biological activated carbon on membrane fouling by surface waters were investigated using three low-pressure membranes (two ceramics—UF or MF—and one polymeric—UF). The unified membrane fouling index (UMFI) was used to quantify the reversibility and irreversibility of membrane fouling. Minimum UMFI were calculated and repeatability assays were performed in order to evaluate the analytical detection limit and the precision of the method, respectively. The lowest ozone dose tested (1 mg O3 L-1) reduced the total fouling by 44, 63, and 41% for the polymeric membrane, the UF ceramic membrane, and the MF ceramic membrane, respectively. Further increase of the dose led to minor or no improvement, except for the ceramic MF membrane. For the ceramic membranes, a similar trend to that observed for total fouling was observed for hydraulically irreversible fouling. For the polymeric membrane, the hydraulically and chemically irreversible fouling were too low to be measured. Although biofiltration reduced the average dissolved organic carbon and turbidity by 25 and 50%, respectively, no significant fouling reduction was observed. The results indicate that irreversible fouling measurements are highly variable and most of the time below the analytical detection limit.

Effect of Metallic Coagulant Agents on Oily Wastewater Treatment Performance using Mullite Ceramic MF Membranes

In this paper, the effects of in-line coagulation on permeation flux (PF), fouling resistance (FR), and total organic compound (TOC) rejection (R) of synthesized mullite ceramic membranes during treatment of oily wastewater in coagulation – MF hybrid process were investigated. Four coagulant ((ferrous chloride (FeCl2.4H2O), ferrous sulphate (FeSO4.7H2O), aluminum chloride (AlCl3.6H2O) and aluminum sulphate (Al2(SO4)3.18H2O)) plus equal concentration of lime in the form of calcium hydroxide (Ca(OH)2) were evaluated in the coagulation – MF hybrid process at different concentrations (0 ppm, 25 ppm, 50 ppm, and 100 ppm). The results showed that coagulation can affect the membrane filtration by changing characteristics of the oil droplets. Coagulant agents improve the membrane performance at low dosage (25 ppm) for aluminum chloride and mean dosage (50 ppm) for ferrous chloride, ferrous sulphate, and aluminum sulphate. At the best conditions (50 ppm ferrous sulphate), PF increased from 2.22 × 10−5 to 2.76 × 10−5 (m3/m2 s), FR decreased from 4.2 × 1012 to 5.55 × 1011 (m−1), and R increased from 93.8% to 97.1%.

Integration of ceramic membrane and compressed air-assisted solvent extraction (CASX) for metal recovery

In our previous publications, compressed air-assisted solvent extraction process (CASX) was developed and proved to be kinetically efficient process for metal removal. In the current study, CASX with a ceramic MF membrane integrated for separation of spent solvent was employed to remove and recover metal from wastewater. MF was operated either in crossflow mode or dead-end with intermittent flushing mode. Under crossflow mode, three distinct stages of flux vs. TMP (trans-membrane pressure) relationship were observed. In the first stage, flux increases with increasing TMP which is followed by the stage of stable flux with increasing TMP. After reaching a threshold TMP which is dependent of crossflow velocity, flux increases again with increasing TMP. At the last stage, solvent was pushed through membrane pores as indicated by increasing permeate COD. In dead-end with intermittent flushing mode, an intermittent flushing flow (2 min after a 10-min or a 30-min dead-end filtration) was incorporated to reduce membrane fouling by flush out MSAB accumulated on membrane surface. Effects of solvent concentration and composition were also investigated. Solvent concentrations ranging from 0.1 to 1% (w/w) have no adverse effect in terms of membrane fouling. However, solvent composition, i.e. D(2)EHPA/kerosene ratio, shows impact on membrane fouling. The type of metal extractants employed in CASX has significant impact on both membrane fouling and the quality of filtrate due to the differences in their viscosity and water solubility. Separation of MSAB was the limiting process controlling metal removal efficiency, and the removal efficiency of Cd(II) and Cr(VI) followed the same trend as that for COD.

Ceramic membranes from Moroccan natural clay and phosphate for industrial water treatment

Ceramic MF membranes have been made from clays and phosphates, coming from Moroccan ores. Several flat disk filters have been obtained by sintering the mixed materials with starch as organic additive. The resulting filters have been characterized by using mercury porosimetry, air and water permeation, to choose the best fabrication parameters. Resulting optimized membranes have been used to treat dye containing solutions to check the utility of such filters in the waste water treatment for Moroccan textile industry. Results are quite promising, allowing these filters to be used as a previous clarification step in textile water treatment.

Removal of organics and viruses using hybrid ceramic MF system without draining PAC

Ceramic microfiltration combined with powdered activated carbon adsorption (PAC-MF) was tested for organic and microbial control using river water laden with sewerage effluents. The PAC-MF was compactly configured with PAC adsorption and MF filtration zones in one reactor. It was operated with PAC addition of 20 g/L at the beginning without PAC drain. Organic matter was largely removed in the adsorption zone and then additional removal was obtained in the filtration zone. Selective adsorption of hydrophobic organic compounds onto PAC resulted in greater UV 260 removal of 90.3 ± 3.2% than DOC removal of 80.2 ± 8.6%. Efficient organic control of the PAC-MF onsiderably decreased chlorine consumption to less than 0.5 ± 0.08 mg/L, and thus THMFP was brought down to less than 8.8 ± 2.2 μg/L in permeate. Furthermore, adsorption or attraction potential of microorganisms by PAC addition as well as virus capture in the PAC cake layer also assisted ceramic MF to remove viruses to less than detection limit after 60 days of operation. Therefore, the hybrid PAC-MF is a prospective advanced water treatment process that is capable of simultaneous organic and microbial removal by adsorption and filtration mechanisms.

315 セラミックMF膜を用いた水道用膜ろ過システムの確立(II)(水環境保全技術,大気・水保全技術)

Membrane filtration process has been introduced to many small water purification plants to fulfill the growing demands of cryptosporidium-free water, rationalized operation and maintenance, and dealing with polluted water source. Recently, introduction of membrane filtration process is to being considered by larger purification plants. For those cases, it is required not only small footprints or high water recovery, but also capability of on-site chemical cleaning of the process. Authors performed a demonstration experiment using pilot scale plant equipped with monolith ceramic MF membrane for put this process to practical use in larger plants. As a result, it was demonstrated that the plant has been operated stably under a flux of 4m/d, with periodical chemical cleaning about once in five month, and water recovery rate was 99.9%.

セラミックＭＦ膜によるパーシャル分解ペクチンを含有した清澄リンゴジュースの開発

セラミックMF膜を用いWSP入り無菌清澄リンゴ果汁を製造することを目的としてWSPの膜透過を検討し,以下の結果を得た.(1) 原果汁のMF膜処理で清澄果汁にWSPを有効に含有させることはできなかった.WSPのなかで分子量が大きいものが膜で阻止され,これが分子量の小さいものまで膜透過を阻害するものとなるためであることが判明した.(2) 20°C,5分間のペクチナーゼによる酵素反応でWSPのパーシャル分解が可能であり,WSPは約(70∼90)%を残存させることができた.(3) パーシャル分解した果汁のWSPはMF膜ろ過で清澄果汁側へ有効に含有させることができた.WSPのMF膜透過には,クロスフロー線速よりもろ過圧力が大きく影響することが判明し,線速(1∼2)m/sで生ずる圧力損失のみをろ過圧とした操作が有効であった.(4) パーシャル分解果汁から得られた清澄果汁は,分子量(100000∼200000)にピークを有するWSPを(110∼190)mg/L含有し,100日間の常温保存では二次沈殿(おり)が発生しないことが分かった.以上のことから,ペクチン含有清澄リンゴ果汁を膜分離技術で製造するには,酵素による低温・短時間のパーシャル分解が有効であり,この方法によって目的を達成することができた.

Determination of membrane pore size distribution using the fractional rejection of nonionic and charged macromolecules

The objective of this study was to develop a new measurement technique for the determination of pore size distributions (PSDs) of polymeric and ceramic membranes, including NF, UF, and MF membranes. The proposed method uses the fractional rejection (FR) concept of a solute in membrane pores. Experimental measurements were conducted using a high performance liquid chromatography (HPLC) equipped with size exclusion chromatography (SEC) columns and a refractive index (RI) detector. A specially designed membrane filtration unit was also used. Two different macromolecules, including nonionic polyethylene glycols (PEG) and natural organic matter (NOM) with ionizable functional (carboxylic and phenolic) groups, were used as solutes. Membrane PSDs, determined with PEG and NOM, can be defined as absolute and effective membrane PSDs, respectively. Two different types of membranes (flat-sheet polymeric and tubular ceramic) were used in this work. Experimental procedures include three major steps: (1) measurements of relative molecular mass (RMM) distributions of solutes included in the membrane feed and corresponding permeate, (2) the calculation of solute FR, and (3) PSD determination. The main results and advantages of this method are: (1) the PSD of various membranes with different pore sizes can be measured using a relatively easy method without significant limitations of pore size and membrane type; (2) various factors that affect membrane PSD, including pH, ionic strength, ion binding, and hydrodynamics, can also be evaluated; (3) the effective PSD of membranes with negatively-charged surfaces, and which exhibit significant shifts in PSD towards the lower RMM region can also be determined.

Membrane Treatment of Secondary Textile Effluents for Direct Reuse

Post-treatment of secondary textile wastewater was tested at pilot scale on membrane modules (microfiltration MF, nanofiltration NF and reverse osmosis RO) for the direct reuse of polished effluent within the dyeing processes. The main polluting parameters monitored in the post-treatment were: organic compounds (COD), colour, surfactants and salinity (as conductivity). The first treatment scheme was made of ceramic MF followed by NF. Aluminium polychloride was added at high concentrations (of the order of 70 mg Al/L) to avoid MF membrane fouling. The quality of the final permeate, produced by NF fed on the MF permeate, was acceptable for water reuse. Clariflocculation (CF) plus multimedia filtration (MMF) followed by low-pressure RO was also tested. This process performed quite well: the RO module (p = 4 bar) ran for relatively long cycles (up to 80 hours) with 5% reduction of the permeate flow rate at a 10 L m−2 h−1 fluxes. A techno-economical analysis on the experimental data indicate that a high quality effluent (COD &amp;lt; 10 mg/l; conductivity &amp;lt; 40 μS/cm; negligible residual colour), to be recycled in the textile dyeing industry, may be produced at affordable costs (less than 0.25 ECU) from secondary textile wastewater.

Membrane treatment of secondary textile effluents for direct reuse

Post-treatment of secondary textile wastewater was tested at pilot scale on membrane modules (microfiltration MF, nanofiltration NF and reverse osmosis RO) for the direct reuse of polished effluent within the dyeing processes. The main polluting parameters monitored in the post-treatment were: organic compounds (COD), colour, surfactants and salinity (as conductivity).The first treatment scheme was made of ceramic MF followed by NF. Aluminium polychloride was added at high concentrations (of the order of 70 mg Al/L) to avoid MF membrane fouling. The quality of the final permeate, produced by NF fed on the MF permeate, was acceptable for water reuse.Clariflocculation (CF) plus multimedia filtration (MMF) followed by low-pressure RO was also tested. This process performed quite well: the RO module (p = 4 bar) ran for relatively long cycles (up to 80 hours) with 5% reduction of the permeate flow rate at a 10 L m−2 h−1 fluxes.A techno-economical analysis on the experimental data indicate that a high quality effluent (COD < 10 mg/l; conductivity < 40 µS/cm; negligible residual colour), to be recycled in the textile dyeing industry, may be produced at affordable costs (less than 0.25 ECU) from secondary textile wastewater.

Water permeability in ultrafiltration and microfiltration: Viscous and electroviscous effects

The applicability of Darcy's law for explaining the water permeabilities of polymeric UF membranes and ceramic MF membranes was investigated at various temperatures, viscosities, salt concentrations, and trasmembrane pressures. It was found that Darcy's law explains the permeabilities well if the viscosity is corrected for electroviscous effects, temperature, and solute concentration. For polymeric UF membranes the compaction of the membranes needs to be taken into account as well. Ceramic MF membranes do not seem compressible for TMPs up to 80 kPa. Increasing the salt concentration from 30 μM to 0.1 M resulted in increases in water fluxes of 2% to 8% both for MF and UF membranes. This apparent permeability increase was explained by electroviscous effects: increased salt concentrations lead to lower zeta-potentials and thinner double-layers, offering less resistance to water passage. From the apparent permeability change the zeta-potentials of the membranes at pH ≈ 7 were calculated. Realistic zeta-potential values were obtained. Water flux measurements at various salt concentrations are thus a simple method to study zeta-potentials of membranes. The resistance ( R m ) of the UF membranes was independent of temperature in the range 4–20°C, but increased with increasing transmembrane pressure (TMP). The increase could be described by a power law ΔR m ∼TMP 0.8, typical for porous solids. The resistance of the ceramic MF membrane was independent of temperature and independent of TMP.

Treatment of surface water rich in humus — Membrane filtration vs. conventional treatment

The investigated raw water from lake Muskan, Nynäshamn community, has a high color content of mainly humic substances (up to 100 mg Pt/l) and also taste and odor problems, particularly during the algae blooming period. Membrane filtration of this raw water is one of the alternatives suggested for the future drinking water production (6,000 m 3/d) in Nynäshamn community. This paper includes mainly the results of laboratory trials in order to evaluate tested membranes (ceramic MF and UF membranes, polymeric UF and NF membranes) with respect to the need of activated carbon treatment as well as for comparison with corresponding results of laboratory trials with conventional flocculation/sedimentation/filtration and activated carbon treatment. The intention has been to select the most feasible membrane method for trial operation in a pilot plant. The latter stage of this project will be reported in a separate paper.IInitial testing was performed, with and without activated carbon treatment, of nine UF and NF membranes with nominal cut-off values varying between about 180 and 20,000 as well as of four ceramic MF and UF membranes. Further concentration trials in combination with membrane cleaning were done with four selected membranes-two NF membranes and two UF membranes (cut-off 20,000 and about 2,000). The purification parameters used for evaluation were primarily color, TOC (DOC) and COD-Mn. The efficiency of added powdered activated carbon (6 mg/l) in the influent before the membrane filtration was negligible. The removal of color and organic matter was almost complete (undetectable levels) with nanofiltration. Activated carbon treatment of the permeate was required with the UF membranes. However, the adsorption isotherm with the selected quality of activated carbon showed low adsorption capacities. As a conclusion of the overall laboratory trials it was stated that nanofiltration of the raw water from lake Muskan is an interesting alternative for the future drinking water production within Nynäshamn community. It was thus recommended to perform trial operation in a pilot plant for design of a full-scale plant. The costs are at present a little higher with the membrane method compared to conventional treatment including activated carbon, but the drinking water quality is better and more consistent.