Purification and Concentration of Caustic Mercerization Wastewater by Membrane Processes and Evaporation for Reuse

A membrane-based treatment strategy was developed for purifying the highly alkaline textile mercerization wastewater. 0.2-μm MF and 100 kDa UF membranes were evaluated as pretreatment alternatives before 10 kDa UF and 200 Da NF membranes. Turbidity was almost totally removed by both pretreatment options, while UF (100 kDa) showed higher COD retention than MF. In total recycle mode of filtration, fouling of both UF and MF membranes were 80% reversible by physical and almost totally reversible (≥ 97%) by chemical cleaning. In the second stage filtrations applied to the pretreated wastewater samples, NF could yield high (97-98%) COD retentions and low permeate COD concentrations (≤ 22 mg/L), while 10 kDa UF could only reduce the COD concentration to 150 mg/L. While no NaOH was lost in the MF+UF process, the use of NF as second stage resulted in 12-17% NaOH retention. The permeate flux in all second stage processes were stable, implying that the majority of the feed components that would cause fouling had been removed in the pretreatment stages. Permeate of the MF+NF sequence was concentrated by evaporation with no foaming problems, showing that the hybrid process can be applied to recycle a purified and concentrated caustic stream to the mercerization process.     

Reducing pollution from the deliming–bating operation in a tannery. Wastewater reuse by microfiltration membranes

This paper presents experimental results from the implementation of two measures aimed at reducing the nitrogen concentration in a tannery wastewater. Specifically, this research has focused on the wastewater from the deliming/bating operations. The proposed measures are the replacement of ammonium salts by carbon dioxide in the deliming process and the reuse of wastewater and chemicals after membrane filtration of the deliming/bating liquor. The experimental study covered different wastewater pretreatment alternatives and experiments with two membranes (with different separation properties): one in the range of microfiltration (MF) and one in the range of the ultrafiltration (UF). Results of the pretreatment study indicated that neither settling nor protein precipitation were feasible. Only a security filtration prior to membrane filtration was recommended. The tested MF membrane was selected due to the higher flux (around 25 L/(m² h)) in comparison with the UF membrane. The MF permeate was successfully reused in the deliming/bating process. The delimed leather quality was excellent according to both visual and organoleptic inspection from process technicians and phenolphthalein test, confirming the technical feasibility of the proposal. Globally, the implementation of the above mentioned two measures resulted in 53% total nitrogen reduction.     

Enhancement of Oily Wastewater Treatment by Ceramic Microfiltration Membranes using Powder Activated Carbon

Results of a hybrid microfiltration‐powdered activated carbon (MF‐PAC) system for the treatment of synthetic oily wastewaters with mullite and mullite‐alumina (50 % alumina content) ceramic membranes are presented. The experiments were conducted to determine the effects of the presence of PAC on MF process performance in terms of flux decline, membrane fouling, and total organic carbon (TOC) rejection. The experimental results demonstrate that PAC addition at low concentration (200–400 ppm) increases permeate flux by 19.6 % for mullite and 61 % for mullite‐alumina MF membranes. However, high PAC concentration (1200 ppm) decreases the permeate flux by 22 % for mullite and 25 % for mullite‐alumina MF membranes. Also, TOC rejection increases from 93.8 to 97.4 % for mullite and from 89.6 to 92.4 % for mullite‐alumina MF membranes.     

Treatment of oily wastewater using low cost ceramic membrane: Comparative assessment of pore blocking and artificial neural network models

This work addresses the performance and modeling of the separation of oil-in-water (o/w) emulsions using low cost ceramic membrane that was prepared from inorganic precursors such as kaolin, quartz, feldspar, sodium carbonate, boric acid and sodium metasilicate. Synthetic o/w emulsions constituting 125 and 250 mg/L oil concentrations were subjected to microfiltration (MF) using this membrane in batch mode of operation with varying trans-membrane pressure differentials (ΔP) ranging from 68.95 to 275.8 kPa. The membrane exhibited 98.8% oil rejection efficiency and 5.36 × 10⁻⁶ m³/m² s permeate flux after 60 min of experimental run at 68.95 kPa trans-membrane pressure and 250 mg/L initial oil concentration. These experimental investigations confirmed the applicability of the prepared membrane in the treatment of o/w emulsions to yield permeate streams that can meet stricter environmental legislations (<10 mg/L). Subsequently, the experimental flux data has been subjected to modeling study using both conventional pore blocking models as well as back propagation-based multi-layer feed forward artificial neural network (ANN) model. Amongst several pore blocking models, the cake filtration model has been evaluated to be the best to represent the fouling phenomena. ANN has been found to perform better than the cake filtration model for the permeate flux prediction with marginally lower error values.     

Stainless steel membrane UF coupled with NF process for the recovery of sodium hydroxide from alkaline wastewater in chitin processing

The recovery of sodium hydroxide from alkali wastewater in chitin processing was investigated using stainless steel ultrafiltration membrane (SSM) and HDS-04 nanofiltration (NF) membranes with membrane area of 0.35 m² and 1.4 m², respectively. Flux behaviors were observed with respect to filtration time, volumetric concentration ratio (VCR), operating pressure, temperature, and cleaning. As the VCR increased, the permeate flux declined while almost the same concentration of NaOH was permeable. The SSM and NF operations end with a concentrated protein solution that needed a small amount of waste acid for neutralization and easy spray drying and the permeate of the NaOH solution can be reused. Concentrations of NaOH that govern reusability of permeate were measured to be independent on VCR. The most suitable VCRs for SSM and NF in terms of maintaining relatively good membrane productivity and high rejection of protein and chemical oxygen demand (COD) were approximately 50. At a VCR of 50, the total rejections of protein, COD and suspended solid (SS) were 82.5%, 94% and 100%, respectively, while total NaOH recovery was 96% with SSM average flux 270 LMH and NF average flux 25 LMH. SSM filtration was essential for the pretreatment of the alkali wastewater before it was fed into the NF system.     

Application of an ozonation–adsorption–ultrafiltration system for surface water treatment

Investigations are presented on the effect of the preliminary ozonation on ultrafiltration (UF) and powdered activated carbon (PAC) /UF process performance, especially on permeate flux decline and the effectiveness of model organics removal. Flat membranes from regenerated cellulose were used. A model solution was prepared as a mixture of humic acids and phenol. PAC dosage was equal to 100 mg/l⁻¹. The ozone dosages were in the range of 1–3 mg O₃ l⁻¹ (0.2–0.6 mg O₃/mg TOC). It was found that the most advantageous configuration was preliminary ozonation with an ozone dosage of 0.4 mgO₃/mg TOC–UF. The permeate flux reached a value equal to the pure water flux value. Moreover, a very high effectiveness of model organics removal was obtained: TOC was reduced by about 96% and UV₂₅₄ absorbance was removed completely. When PAC was added to the feed containing humic acids without ozonation, a drop in a permeate flux was observed compared to UF. Similarly, the addition of PAC to feed treated with ozone resulted in a significant drop in the permeate flux in comparison with pure water flux, regardless of ozone dosage applied.     

Application of Taguchi method in optimization of desalination by vacuum membrane distillation

This research focuses on desalination via vacuum membrane distillation (VMD). In order to enhance the performance of VMD in desalination and to get more flux, effects of operating parameters on the yield of distillate water were studied. Four parameters at three levels were selected: temperature (35, 45, and 55 °C), vacuum pressure (30, 80, and 130 mbar), flow rate (15, 30, and 60 mL/s) and concentration (50, 100, and 150 g/L). Taguchi method was used to plan a minimum number of experiments. The optimal levels thus determined for the four factors were: temperature 55 °C, vacuum pressure 30 mbar, flow rate 30 mL/s and concentration 50 g/L. The results show that increasing temperature and decreasing vacuum pressure improve permeate flux. However, the permeate flux increases with increasing flow rate initially and then reaches to a maximum value at 30 mL/s and then decreases with increasing the flow rate.     

Critical flux analyses on differently pretreated olive vegetation waste water streams: Some case studies

One of the main disadvantages of batch membrane processes is the increase of the pollutant concentration in the feedstock throughout the operation. Operating the plant at constant process conditions leads in many cases to weaker performances and, moreover, to heavy fouling on the membranes. Critical flux-based methods are one of the most used approaches to overcome fouling problems. Within critical flux conditions, only reversible fouling can occur, which can be periodically soft-cleaned.This work studies the relationship between particle size distributions in the feed stream and critical flux values when different pretreatment processes are applied to an olive vegetation waste water stream. The considered pretreatment processes were: coagulation (with aluminum hydroxide and aluminum sulphate), aerobic biodigestion (by means of fungi) and photocatalytic organic matter reduction (by means of nanometric titanium dioxide anatase powders irradiated by UV light). The study was carried out at pilot plant scale (100 L batch capacity).These results were compared with performances and effects on the critical flux value for MF, UF and NF membranes. The different pretreatment on the same waste water stream shifts differently the particle size distribution mainly by organic matter degradation, and this influences heavily the critical flux value and thus the filtration outcome.Finally, the purification of the olive vegetation waste water stream can be performed with a MF, UF, NF and RO membrane system in series, being very careful in choosing the correct operating conditions to avoid the quick formation of an unsustainable fouling.     

A pilot scale study of reverse osmosis for the purification of condensate arising from distillery stillage concentration plant

Reverse osmosis (RO) is an interesting process to eliminate small organic solutes (carboxylic acids and alcohols) from distillery condensates before recycling them into the fermentation step. This work investigates the influence of transmembrane pressure, pH and volume reduction factor (VRF) on the efficiency of reverse osmosis treatment of condensate from distillery stillage concentration at pilot scale using three pre-selected membranes (CPA2 and ESPA2 from Hydranautics, BW30 from DOW). Performances were assessed according to permeate flux, solutes rejection and abatement of fermentation inhibition. Transmembrane pressure increase leads to an increase of these three parameters with a plateau for rejections and abatement at 20 bar; however, in order to comply with membranes manufacturer's recommendations and to limit or delay polarization and fouling, it was decided to keep the permeate flux below a value of 30 L h⁻¹ m⁻². This corresponded to a maximum pressure of 10 bar for CPA2 and ESPA2 membranes and 25 bar for BW30 membrane. pH increase leads to a diminution of permeate flux and an increase of carboxylic acids rejection whatever the membrane; nevertheless, no abatement of fermentation inhibition is observed. Increasing VRF provokes a decrease of the permeate flux. Although local rejections are stable, the mean rejection assessed with the raw condensate (feed) and the mean permeate decreases. However, the fermentation inhibition remains under 10% up to a VRF of 8. BW30 membrane exhibits the highest rejections and inhibition abatement. On the basis of the pilot scale results with the BW30 membrane, a preliminary estimation of the membrane area is proposed for an industrial plant with 100 m³ h⁻¹ of condensate flow rate and the optimized parameters (pressure 25 bar, no pH modification, VRF 4 and 8).     

Influence of operation parameters on the separation of mixtures by pervaporation and vapor permeation with inorganic membranes. Part 1: Dehydration of solvents

The separation performance of two different commercially available tubular inorganic membranes was studied for solvent dehydration. The separation layers consisted of A-type zeolite and microporous silica. The membrane characteristics were determined as function of operating conditions such as feed composition, temperature, and permeate pressure in pervaporation and vapor permeation. Among different membranes of the same batch, flux and selectivity were reproducible within 10%. The partial flux of water as the preferentially permeating component increases linearly with the water vapor pressure difference between feed and permeate and depends only marginally (viscosity influence) upon the properties of the organic component. The flux of the organic (retained) component is low and can best be described by assuming a substance and membrane specific permeance (flux over partial pressure difference) that is independent of composition. At very low water concentration in the feed one would expect a strong increase in permeability of the retained component through non-zeolite pores and larger silica pores as predicted by pure component measurements. However, this effect was not observed in mixtures within the concentration range studied here. A temperature rise improves flux rates exponentially while selectivity remains high. Thus, higher module cost in comparison to polymeric membranes can be compensated by reduced membrane area if a higher operating temperature can be chosen. Flux and selectivity decline as a function of permeate pressure with decreasing driving force. In vapor permeation with inorganic membranes superheating of the vaporous feed improves their performance while for polymeric materials a steep flux decline is observed. High flux and selectivity are obtained in the separation of water from alcohols. The normalized flux values of the A-type zeolite membrane are roughly 10 kg/m² h bar with a mixture selectivity of 2000 for methanol, 4000 for ethanol and 8000 for n-butanol. The average permeance of the amorphous silica membrane lies above 12 kg/m² h bar with mixture selectivity of 50 for methanol, 500 for ethanol and 2000 for n-butanol. The separation mechanism is mainly based on adsorption and diffusion enhanced by shape selectivity and size exclusion in some cases. The transport characteristics could be described with a simple transport model based on normalized permeate fluxes. With regard to the operation stability of the membranes, no deterioration of the performance was observed for the A-type zeolite in solvent dehydration or in separation of water from reaction mixtures. The silica membrane showed an initial conditioning effect involving a rearrangement of Si-OH groups with an increase in selectivity and decrease in flux of about 30%. After a few hours the performance stabilized and remained constant during further operation.     

Application of ultrafiltration hybrid membrane processes for reuse of secondary effluent

This study evaluates the factors affecting pretreatment conditions for hybrid UF membrane processes for reuse of secondary effluent from the sewage treatment plant. The experimental results obtained from the ultrafiltration (UF) membrane process showed that the particles of the size range between 0.2 and 1.2 μm caused a significant impact on membrane fouling in all cases even with or without the coagulation process. As pretreatment of UF membrane process, the coagulation significantly improved the permeate flux. Optimal flux improvement was seen at an alum dose of 50 mg/L. In addition, it was found that the permeate flux was least declined under the coagulation condition of charge neutralization (pH 5.0). Also, the powdered activated carbon (PAC) adsorption enhanced the permeate flux. Application of the direct filtration as a pretreatment of UF membrane process was also very effective in reducing the UF membrane fouling.     

Separation of casein from whey proteins by dynamic filtration

It has been proven that functional properties of milk proteins can improve the quality and nutritional value of foods. This paper investigates the separation of whey proteins from casein micelles using a Multi Shaft Disk (MSD) module and a rotating disk dynamic filtration module. The MSD module was equipped with 6 ceramic membranes of 0.2 µm pores. PVDF and Nylon membranes of 0.2 µm pores were tested in the rotating disk module. Permeate flux with the MSD module increased with TMP and rotation speed, reaching a maximum of 132 L h^− 1 m^− 2 at 1931 rpm. α-Lactalbumin (α-La) and β-Lactoglobulin (β-Lg) transmissions also increased with rotation speed, ranging from 25% at 1044 rpm to 40% at 1931 rpm . With a Nylon membrane, the rotating disk module yielded lower permeate fluxes than the MSD module, while when equipped with a PVDF membrane it provided higher permeate fluxes than the MSD, but casein micelles rejection was lower. α-La and β-Lg transmissions were higher with the rotating disk module, using Nylon and PVDF membranes, than for the MSD. From this comparison, it can be concluded that the MSD module gave the best compromise between high permeate flux, high α-La and β-Lg transmissions and high casein micelles rejection.     

Study on a new air-gap membrane distillation module for desalination

A new air-gap membrane distillation (AGMD) module for desalination with internal latent-heat-recovery which consisted of parallel hollow fiber membranes and heat exchange hollow fibers was successfully developed. The influences of feed flow rate, feed temperature and feed initial concentration on AGMD process were investigated. The vapor pressure polarization coefficient (η) was introduced to measure the reduction in the effective driving force for mass transfer with regard to the driving force imposed. Among all AGMD experiments, the maximum water vapor permeate flux (J_D) of 5.30 kg/m² h and the gained output ratio (GOR) of 5.70 were obtained. A theoretical model based on the mass and energy balances of the hot feed side was established to calculate the temperature and the local water vapor permeate flux distributions along the hollow fiber membrane, which showed that the temperature drop and local water vapor permeate flux drop were much larger at the upper part than those at the lower part of the membrane module in the hot feed side.     

Investigation of two ultrafiltration membranes for treatment of olive oil mill wastewater

In this study, a promising treatment method is given for the olive oil mill wastewater (OMWW). Although the same steps of this method have been used in different studies before, flow scheme is novel. The membrane filtration of pretreated OMWW was investigated by using two ultrafiltration membranes in this study. Pretreatment steps were pH adjustment (pH = 2) and cartridge filter filtration, and pH adjustment (pH = 6) and cartridge filter filtration. Each step of cartridge filter filtration was batch process and effluent from the filter was recycled back to OMWW tank. Pretreated OMWW was sent to feed vessel of experimental set-up. Recovery of olive oil in the OMWW was realized collecting it from the top of pretreated OMWW. Ultrafiltration membranes used were JW and MW membranes supplied by Osmonics. The effects of main operating parameters (transmembrane pressure, feed flow rate, pH and membrane type) on the permeate flux and membrane fouling were examined. The effectiveness of the different membranes and operating conditions was evaluated using retention coefficients calculated from COD and TOC of experimental studies. The highest permeate flux (25.9 l/m² h) was obtained using MW membrane under operational conditions of Qf = 200 l/h flow rate and TMP = 4 bar, while the highest removals were obtained at Qf = 100 l/h flow rate and TMP = 1 bar. COD, TOC, SS, oil and grease concentrations of MW membrane effluent were 6400 mg/l, 2592 mg/l, 320 mg/l, and 270 mg/l, respectively.     

Membrane choice for wastewater treatment using external cross flow tubular membrane filtration

Systematic investigations of activated sludge separation were conducted using membrane filtration. To accomplish this, different organic tubular membranes with different separation limits and diameters were examined. Furthermore, from the results obtained in the initial tests, an appropriate membrane was chosen for a long-term test. The investigations determined that for biomass separation by the tubular membranes in the tested system, neither the membrane material nor the separation limit within a range of 1 μm to 20,000 Da had a significant influence on the filtration characteristics. It was recognized that the application of a tubular membrane with a diameter of less than 8 mm is problematic, because high flow velocities were needed to prevent blockage of the membrane. When the flow velocity was in the range of 1 to 4 m/s, a linear relation between flux and velocity was found. This showed the potential for controlling the membrane filtration process and externally influencing the permeate rate. An average retention of TOC was about 75%. The retention of TOC was not significantly influenced by the nominal pore sizes of the membranes (except for the membrane WFNX 0505) which were tested here. The ultrafiltration membrane WFS 0120 (Stork) was prominent in the long-term test due to its very high flux, germfree permeate with a MWCO (molecular weight cut-off) of 100,000 Da, and was not blocked with a diameter of 14.4 mm, also at lower flow velocities. The results of the long-term test supported the hypothesis that a meaningful application of such a module concept is possible in a filtration plant for the preparation of samples or for the rejection of the biomass in small sewage treatment plants.     

Electrokinetic property of ZrO2/cordierite composite MF membrane and its influence on the permeate flux

ZrO₂/cordierite composite microfiltration (MF) membrane was prepared by the combination of extrusion and slip casting techniques. The electrokinetic properties of as-prepared membrane were characterized by streaming potential measurements operated in tangential microfiltration mode. The influences of pH, electrolyte species and concentrations of filtered solutions on the electrokinetic properties and permeate flux were investigated. Results show that the streaming potentials are dependent on the pH, types of the electrolyte and concentrations of filtered solutions. The isoelectric point (IEP) of membranes moved from 4.2 to 5.4 with different types of 10^− 3 M electrolyte solutions. The change of ionic concentration of NaCl solution does not alter the IEP of the membranes, but does make the streaming potential tend to be zero at high salt concentration. The specific adsorption of Ca²⁺ and SO₄²⁻ ions in CaCl₂ and Na₂SO₄ solutions onto the pore wall can alter the IEP and the net charge sign of the membrane. The as-prepared ZrO₂/cordierite membrane shows a maximal permeate volume flux near the IEP.     

Removal of boric acid,monoborate and boron complexes with polyols by reverse osmosis membranes

The effects of reverse osmosis (RO) membrane type on the rejection efficiency of boric acid, monoborate and boron complexes with d-mannitol, sodium d-gluconate and N-methyl d-glucamine was revealed. The membranes examined included: XLE, TW-30, BW-30 and SW-30, supplied by DOW™ FILMTEC™. The mass transport coefficients: permeability and reflection coefficient were determined for each species in boric acid–polyol aqueous system. The influence of the membrane type upon these coefficients was evaluated and quantitative, comparative analysis of the efficacy of boron rejection at varying permeate flux, the feedwater boron content, the alcohol/boron molar ratio and the pH was conducted. It was found that boron rejection in the above systems was determined by the extent of boric acid transport, even when boric acid constituted only a minor component of the feedwater. At high permeate flux the effectiveness in boric acid rejection decreased in the following descending membrane order: SW-30 > BW-30 > TW-30 > XLE. The results presented here enable the selection of the best membrane, the most suitable operating conditions for boron separation by RO in the presence or absence of polyols, and for quantitative prediction of the efficiency of boron removal with various RO membranes.     

Spheroidization of low-cost alumina powders for the preparation of high-flux flat-sheet ceramic membranes

Two kinds of low-cost alumina powders with irregular morphology were pretreated by spheroidization and the two spherical powders were used to prepare high-flux flat-sheet support and microfiltration (MF) membrane with high separation accuracy, respectively. It was found that the spheroidization pretreatment not only unified the morphology of alumina powder particles into spherical shape, but also narrowed the particle size distribution of the powders, which both were conducive to optimizing the performance of the as-prepared ceramic membranes. After sintering at 1350 °C, the open porosity, bending strength, average pore diameter and pure water permeability of alumina flat-sheet support from spheroidized alumina coarse powder were 44.3%, 36.3 MPa, 3.3 μm and 3240 L/h m² bar, respectively. The slurry derived from spheroidized alumina fine powder was dip-coated on the flat-sheet support to prepare MF membrane. The crack-free MF membrane with a thickness of 23.5 μm had a pore diameter of 0.12 μm and pure water permeability of 850 L/h m² bar. Additionally, the elaborated MF membrane was used to clarify aqueous suspension of carbon black with the maximum rejection rate of up to 99.7%, exhibiting excellent cleaning performance at the same time by completely restore the virgin permeate flux after backwash.     

Continuous and efficient removal of THMs from river water using MF membrane combined with high dose of PAC

A combination of microfiltration (MF) membrane with a high concentration (40 g/L of the reactor) of powdered activated carbon (PAC) efficiently and continuously removed trihalomethanes (THMs) and total organic carbon (TOC) from river water for a period of two months. Without PAC, the membrane reactor was able to remove less than 18% of THMs and less than 5% of TOC; with PAC, 65 to 95% of THMs and TOC were removed. Even though the THMs concentration in the influent was steadily increasing (reaching 50 μg/L), THMs concentration in the effluents from the reactors with PAC were consistently below 15 μg/L. While the MF membranes alone could not remove organics, PAC and microbial activity in the biofilm deposited on the PAC particles assured long term and continuous removal of THMs. No additional PAC was added into or removed from the reactors during the filtration period. Operational parameters such as the backwashing of the membrane, interval of the filtration cycle and biological pretreatment of the river water had a small effect on the extent of THMs removal, but they increased the filtration time prior to membrane cleaning and improved the overall performance of the reactors.     

Concentration of biologically active compounds extracted from Sideritis ssp. L. by nanofiltration

In the present study experimental results on the nanofiltration of ethanolic extracts from Sideritis ssp. L. are reported, regarding polyphenols and flavonoids concentration and solvent reuse. Three membranes, resistant to organic solvents, have been used: Starmem™ 240 (polyimide), Duramem™ 300 and Duramem™ 500 (both of them modified polyimide). The dependence of the membrane rejection on its MWCO is presented. The separation of flavonoids from phenols with lower molecular weight is found possible at MWCO > 400 Da. A decrease of the flux is observed at permeate to feed volume ratio of about 0.58, thus indicating the existence of a critical concentration, independent of the feed volume and MWCO of the membranes used. The membrane behaviour during nanofiltration has been characterised by ESEM and ATR-FTIR.Concentrations of active compounds up to 3-4 times higher have been obtained in the retentates. The extracts concentrated by nanofiltration preserve their high antioxidant activity. Further dilution of the retentates displays a logarithmic concentration dependence of the radical scavenging activity. The experiments have proved the possibility for permeate use for extraction instead of ethanol, thus essentially reducing the volume of the solvent.