BW30 Membrane Research Articles

Fouling assessment of tertiary palm oil mill effluent (POME) membrane treatment for water reclamation

Abstract In order to minimize the adverse impacts of palm oil mill effluent (POME) towards the environment and to cope with the stress associated with water scarcity, membrane technology has been employed to reclaim water from POME. This study investigated the performance and fouling propensity of membranes in treating tertiary POME with the aim to recycle and reuse the reclaimed water as boiler feed water. Three types of membranes (NF270, BW30, and XLE) were used and their performances were evaluated based on the removal of chemical oxygen demand (COD), color, turbidity, total dissolved solids, phosphorus, and conductivity. All parameters were significantly reduced through XLE and BW30 membrane filtration processes in which the permeate was complied with the boiler feed water standard, except NF270 membrane where the COD value exceeded the allowable limit. High permeation drag of NF270 and rougher surface of XLE membranes resulted in the accumulation of foulant on the membrane surfaces which eventually reduced the permeate flux, whereas BW30 membrane was encountered for lower fouling propensity due to its low permeation rate. Hence, BW30 was deemed as the best candidate for water reclamation due to its low fouling propensity and because the production of permeate complied with boiler feed water standard.

Implications of humic acid, inorganic carbon and speciation on fluoride retention mechanisms in nanofiltration and reverse osmosis

The impact of pH and humic acid (HA) on the retention of fluoride (F) and inorganic carbon (IC) by nanofiltration (NF) and reverse osmosis (RO) membranes was determined. Synthetic waters were prepared using realistic ranges of F, IC and HA for carbonaceous waters found for example in the fluoride rich waters in Tanzania. These waters were filtered using NF270 and BW30 membranes to determine retention mechanisms.IC changes speciation with pH. The dominant species at pH<6, 6–10 and >10 are H2CO3, HCO3− and CO32− respectively. This results in changes in charge and size of the hydrated ion radius. The mechanism for IC retention by the NF270 and BW30 membranes are charge repulsion and size exclusion, respectively. F retention increases with pH. IC influenced F retention at pH>10 where IC exists as divalent CO32− and is retained more easily than the monovalent F−.HA enhances the retention of F by NF/RO membranes under certain conditions. The enhancement effect is more pronounced at neutral than at acidic pH and basic pH. The mechanism for the enhancement is attributed to the change in surface charge of the membranes by adsorption of HA. At high HA concentration the F retention enhancement is annulled by deposit formation on the membrane.The results obtained in this study indicate the complexity of retention in real surface- and ground waters that can alter significantly in pH as well as IC and HA content. The research is situated in the context of developing membrane technologies for autonomous systems in remote locations where water quality is variable and mechanisms of membrane performance are poorly understood.

Investigation of mini pilot scale MBR-NF and MBR-RO integrated systems performance—Preliminary field tests

Recovery of wastewater has become compulsory due to the reasons like lowered discharge limits, pollution of water resources, and increasing water cost depending on the population growth and increasing water use. Even though membrane bioreactor (MBR) processes seem to be an alternative solution providing high quality output water, still, another treatment process after MBR might be essential to be able to use obtained water as irrigation water or process water. In this study, applicability of nanofiltration (NF) and reverse osmosis (RO) methods for reuse of industrial wastewater treated with advanced treatment method at Organized Industrial Zone (OIZ) is investigated. Studies have been implemented with the mini pilot-scale spiral wound NF/RO system installed at OIZ, under applied pressure of 10bar. For this purpose, NF membrane (NF90-2540 DOW Filmtec) and RO membrane (BW30-2540 DOW Filmtec) were used. According to results obtained, NF90 permeate flux is higher than that of BW30 membrane from December to August. The maximum water recovery obtained with NF90 was about 52.5% while BW30 achieved a maximum water recovery of 44.5%. From September to November, NF90 and BW30 membranes showed similar performances in water recovery as a result of membrane fouling/scaling. NF90 membrane performed rejection percentages of analyzed parameters in the range of 80–100% while the rejection efficiencies of BW30 membrane were in the range 83–100%. Moreover, in comparison of permeate water of NF90 and BW30 membranes with the irrigation water standards; product water qualities of these membranes were found to be suitable for irrigation. According to Turkish water quality classification, first class water quality was produced with BW30 and NF90 membranes except chloride concentration for NF90 membrane.

Hybrid precipitation-nanofiltration treatment of effluent pond water from phosphoric acid industry

Wastewater generated from phosphoric acid industry poses a real environmental challenge. This water contains valuable components the utilization of which can contribute to the conservation of natural resources. Water sample from an effluent pond of a phosphoric acid plant was collected and characterized for its physical and chemical properties. The collected samples were subjected to a hybrid process of chemical precipitation followed by nanofiltration. Both sulphate and fluoride ions were separated by precipitation using Ca(OH)2. Silicon exhibited complex behaviour during the precipitation stage.The observed flux using the different tested membranes (NF90, NF270, and BW30) indicated the success of the pre-treatment method in preventing heavy fouling. Very high rejections were obtained using the NF90 and BW30 membranes and, generally, the rejection increased with pressure. As expected, higher flux and lower rejections were observed with NF270 for Si and H3PO4 species. At a pressure of 20bar the rejection increased with feed concentration which can be attributed to Donnan effects. It is concluded that NF270 could be potentially applied to separate PA from the rest of the species present in water. However, the main challenge is the low rejection of Si.

How can osmosis and solute diffusion be coupled for the simultaneous measurement of the solvent and solute permeabilities of membranes?

A novel experimental method and its associated model are proposed for the simultaneous determination of membrane solute and solvent permeabilities, which are essential transport parameters of reverse osmosis models used for process simulation. The method utilizes a single bench-scale batch apparatus consisting of two stirred half-cells containing solutions of different concentrations separated by a membrane across which coupled non-steady-state solute diffusion and solvent osmosis take place countercurrently in the absence of transmembrane pressure difference. Results are presented from days-long determinations of the water and sodium chloride permeabilities of Filmtec BW30 and NF270 membrane samples for initial transmembrane salt concentration differences ranging from 1gL−1 to 35gL−1. When used as input parameters for the simulation of pilot reverse osmosis desalination tests, the osmotic-diffusive salt permeabilities approximated the experimental rejection rates.

Renewable energy powered membrane technology: Fluoride removal in a rural community in northern Tanzania

Water samples from 13 sites in the Oldonyosambu Ward in Northern Tanzania were collected and comprehensively analyzed for fluoride and other components. Local water resources are typically of sodium carbonate (Na-HCO3) type with low calcium (Ca2+) concentrations. Water sources contain excessive fluoride concentrations and are used as the principal water supply for drinking and cooking by the rural communities. The occurrence of fluoride has severe health impacts in the population from babies (pre-natal) to the elderly, resulting in severe dental and skeletal fluorosis in this area.Purification technologies suitable for such situations in very rough rural communities are scarce due to the absence of electricity supply, infrastructure and operational skills. The development of advanced, yet appropriate technologies is hence a novel separation and purification challenge in that somewhat established technologies need to be adapted to new environments. To this effect two types of experiments were conducted:(1)The water with the highest fluoride concentration (Site 4, 17.9mg/L, WHO guideline 1.5mg/L, Tanzanian guideline 4mg/L) was treated with different nanofiltration (NF) and reverse osmosis (RO) membranes in batch-scale experiments. Results show that fluoride and other components including sodium, potassium, calcium, magnesium, carbonate, sulfate, silica, and organic matter were removed reliably from these natural waters by NF/RO.(2)A pilot-scale autonomous membrane system powered directly by solar energy was used to treat the water with the highest fluoride concentration and examine the impact of fluctuating energy on three different membranes (BW30, NF90, NF270). The results demonstrated that the BW30 and NF90 membranes achieved the WHO guideline, while the NF270 membrane bettered the Tanzanian fluoride guideline. The total permeate volume produced with these membranes was 1000, 2444 and 2656L, respectively. The resilience of the system to solar fluctuations was good during the short term tests.The results suggest that such advanced membrane technologies powered directly by renewable energy are an attractive option for addressing the water problems in rural areas. While the technology is well established, the adaptation to villages such as those in the Oldonyosambu Ward is far from achieved. This requires further work in terms of integration, technology adaptation and operation and maintenance schemes.

Factors affecting fluoride and natural organic matter (NOM) removal from natural waters in Tanzania by nanofiltration/reverse osmosis

This study examined the feasibility of nanofiltration (NF) and reverse osmosis (RO) in treating challenging natural tropical waters containing high fluoride and natural organic matter (NOM). A total of 166 water samples were collected from 120 sources within northern Tanzania over a period of 16months. Chemical analysis showed that 81% of the samples have fluoride levels exceeding the WHO drinking guideline of 1.5mg/L. The highest fluoride levels were detected in waters characterized by high ionic strength, high inorganic carbon and on some occasions high total organic carbon (TOC) concentrations.Bench-scale experiments with 22 representative waters (selected based on fluoride concentration, salinity, origin and in some instances organic matter) and 6 NF/RO membranes revealed that ionic strength and recovery affected fluoride retention and permeate flux. This is predominantly due to osmotic pressure and hence the variation of diffusion/convection contributes to fluoride transport. Different membranes had distinct fluoride removal capacities, showing different raw water concentration treatability limits regarding the WHO guideline compliance. BW30, BW30-LE and NF90 membranes had a feed concentration limit of 30–40mg/L at 50% recovery.NOM retention was independent of water matrices but is governed predominantly by size exclusion. NOM was observed to have a positive impact on fluoride removal. Several mechanisms could contribute but further studies are required before a conclusion could be drawn.In summary, NF/RO membranes were proved to remove both fluoride and NOM reliably even from the most challenging Tanzanian waters, increasing the available drinking water sources.

A combined ion exchange–nanofiltration process for water desalination: II. Membrane selection

This paper discusses the performance of NF270, NF90, BW30 and SW30 (Dow/FilmTec) membranes during filtration of single and mixed NaCl and Na2SO4 solutions at different feed concentrations and NaCl to Na2SO4 ratios. The feeds represent the compositions of possible streams after IX treatment in a combined ion exchange (IX)–nanofiltration (NF) process of water desalination. The impact of total feed concentration, the NaCl/Na2SO4 ratio and feed pH on membranes flux and rejection of sulphate and chloride ions were determined. All membranes showed excellent rejection of sulphate ions, while chloride rejection largely varied for NF membranes with changes in feed concentration, composition and pH. A high negative rejection of chloride ions was observed with NF270 membrane during treatment of binary aqueous solution with a high Na2SO4 to NaCl ratio due to the Donnan effect.

Combining reverse osmosis and ion-exchange allows beet distillery condensates to be recycled as fermentable dilution water

Combinations of physical purification processes, i.e. anion-exchange, adsorption, and reverse osmosis were evaluated and compared with single ones for their ability to remove target inhibitory compounds from distillery condensates with the purpose of reusing condensates as fermentation water. Performances of the treatments were evaluated through analyses of residual target compounds and batch and continuous fermentation experiments. Reverse osmosis on BW30 membrane (Dow Chemical) at 25bar transmembrane pressure and volume reduction ratio (VRR)=8 followed by anion-exchange (weak Amberlite FPA 51 resin, Dow) was the most efficient process to decrease all inhibitory target compounds (formic, acetic, propanoic, butanoic acids and 2-phenethyl alcohol) present in a distillery condensate below their detection or quantification limit. Water recovery was 87.5%. Such treated condensate proved convenient for reuse as fermentation water. Fermentation tests run in a multistage device exhibited yeast viability and ethanol production performances (concentration and global productivity) equivalent to the blank for a final ethanol concentration of 80gL−1 close to practical value encountered in distilleries.

The efficiency of various chemical solutions to clean reverse osmosis membranes processing swine wastewater

The increasing use of membrane technology to treat highly charged wastewaters has renewed interest in the development of adequate cleaning strategies. This study investigated the efficiency of various chemicals, including acids, bases, surfactants, chelators, salts, enzymes, and oxidants, to clean two reverse osmosis membranes (BW30 and SW30XLE) filtering one swine wastewater pretreated by aerobic biofiltration and two swine wastewaters pretreated by mechanical solid–liquid separation. Mixes of anionic surfactants and chelators provided optimal cleaning efficiency for all fouled membranes and all effluents. A solution containing 10 mM EDTA (ethylenediamine tetraacetic acid) and 10 mM SDS (sodium dodecyl sulfate) yielded the highest flux recovery after one 20-h fouling cycle with the BW30 membrane and three consecutive fouling–cleaning cycles with the SW30XLE membrane. The EDTA + SDS solution also resulted in the lowest residual protein concentration on membrane surface and the optimal restoration of the initial contact angle of the membranes. Conversely, 75 mM acid citric and 100 mM NaCl solutions were the least efficient to clean the fouled membranes. Most chemical solutions were more efficient to clean the fouling layer generated by the swine wastewater pretreated by aerobic biofiltration than mechanical separation.

Fouling of Reverse Osmosis Membranes Processing Swine Wastewater Pretreated by Mechanical Separation and Aerobic Biofiltration

The development of cleaning strategies for RO membranes processing highly charged wastewaters requires knowledge about foulant composition. The objective of this study was to characterize the fouling layer that formed on RO membranes processing swine wastewater pretreated by a mechanical solid-liquid separator (LF) and aerobic biofiltration (AE). The two LF effluents represented swine wastewater concentrated three (LF1) and four (LF2) times with BW30 (36 bar) and SW30 (60 bar) membranes, respectively. Flux decline was slightly higher with LF2-SW30 (37.1%) than LF1-BW30 (31.8%) after 20 h of filtration. The fouling layer had significantly higher protein concentration on LF2-SW30 than on LF1-BW30, but both had similar microbial content and inorganic composition. The AE effluents were concentrated by a factor of 7 and processed at pH 5.75 (AE1) and 8.07 (AE2) with BW30 membranes. Both AE effluents had higher calcium but lower suspended solids and organics than the LF effluents. They generated significantly higher flux decline and biofouling than LF1. High flux decline was also associated with increased protein attachment for AE1 and inorganic fouling for AE2. A mechanical separator may be adequate to prepare swine wastewater for RO filtration but the aerobic pretreatment would allow for a higher volumetric concentration of the effluent.

Aging of RO Membranes Processing Swine Wastewater

<abstract><title><italic>Abstract.</italic></title> There is an increased interest in the application of reverse osmosis (RO) technology to treat agricultural wastewaters because RO membranes can produce reusable water and recover valuable nutrients. With highly charged wastewater, however, membrane replacement could represent an important fraction of the operating costs. The objective of this project was to study the aging process of spiral-wound RO elements (BW30 and SW30) processing swine wastewater. The membrane elements were subjected to 21 h concentration-filtration (CF) cycles followed by a 1 h chemical cleaning and a weekly 3 d soaking period. The BW30 element experienced a 22% increase in intrinsic membrane resistance (R_m), defined as resistance to water flux through the membrane, after the first four CF cycles with swine wastewater. This rapid increase was mainly caused by irreversible compaction of the membrane under high pressures. The SW30 membrane had a lower compressibility, and R_m only increased by 7% in the first four cycles. After this initial period, small but steady increases in R_m were mainly attributed to the accumulation of foulants on or within the membranes. However, a 40% increase in R_m after 42 CF cycles with the BW30 membrane had little impact on permeate flux during swine wastewater filtration because permeate flux was mainly controlled by fouling and substrate-related resistances. All membrane elements maintained their ionic retention efficiency throughout the experiment, indicating no damage to the integrity of the membrane during the CF and cleaning cycles. Projection based on a total of 42 and 20 CF cycles for the BW30 and SW30 membranes, respectively, suggested that R_m would rapidly increase in the initial 12 CF cycles of swine wastewater filtration, by 29% and 11% for the BW30 and SW30 membranes, respectively, mainly due to compaction. Between cycles 12 and 624, R_m would further increase by 32% and 16% for the BW30 and SW30 membranes, respectively. This number of cycles corresponds to three years of operation using the same operational procedures as those described in this study. With proper care, the membrane elements may not need to be replaced for at least three years. However, these predictions remain to be verified in a commercial setting.

Coupling membrane separation and photocatalytic oxidation processes for the degradation of pharmaceutical pollutants

The coupling of membrane separation and photocatalytic oxidation has been studied for the removal of pharmaceutical pollutants. The retention properties of two different membranes (nanofiltration and reverse osmosis) were assessed. Comparable selectivity on the separation of pharmaceuticals were observed for both membranes, obtaining a permeate stream with concentrations of each pharmaceutical below 0.5 mg L−1 and a rejected flux highly concentrated (in the range of 16–25 mg L−1 and 18–32 mg L−1 of each pharmaceutical for NF-90 and BW-30 membranes, respectively), when an initial stream of six pharmaceuticals was feeding to the membrane system (10 mg L−1 of each pharmaceutical). The abatement of concentrated pharmaceuticals of the rejected stream was evaluated by means of heterogeneous photocatalytic oxidation using TiO2 and Fe2O3/SBA-15 in presence of hydrogen peroxide as photo-Fenton system. Both photocatalytic treatments showed remarkable removals of pharmaceutical compounds, achieving values between 80 and 100%. The nicotine was the most refractory pollutant of all the studied pharmaceuticals. Photo-Fenton treatment seems to be more effective than TiO2 photocatalysis, as high mineralization degree and increased nicotine removal were attested. This work can be considered an interesting approach of coupling membrane separation and heterogeneous photocatalytic technologies for the successful abatement of pharmaceutical compounds in effluents of wastewater treatment plants.

Performances of Reverse Osmosis Membranes for Treatment of Olive Mill Wastewater

AbstractIn the following study, two methods were employed in which olive mill wastewaters were treated by using reverse osmosis membranes (BW30 and XLE). In the first, wastewater was centrifuged and then passed through the reverse osmosis whereas in the second, an ultrafiltration was placed between the centrifuge and the reverse osmosis. The reverse osmosis experiments were conducted under 10, 15, 20, and 25 bar. The chemical oxygen demand (COD) removal efficiencies under 25 bar were found to be 97.5% for both BW30 and XLE membranes. The highest conductivity removal rates obtained under 25 bar for BW30 and XLE membranes were found to be 95.6 and 96.2%, respectively. As for the highest permeation flux values obtained under 25 bar, they were separately determined for BW30 and XLE as 15.3 and 21.2 L m−2 h−1, respectively. The performances of the membranes were also evaluated in terms of their mass transfer coefficients. According to this, all mass transfer coefficients were found to be &lt;1 and also in proximate to one another; this clearly reflects the results as COD and conductivity removals were approximate and there was a lack of any significant difference, whether ultrafiltration was applied or not.

Degradation of Polyamide Nanofiltration and Reverse Osmosis Membranes by Hypochlorite

The degradation of polyamide (PA) nanofiltration and reverse osmosis membranes by chlorine needs to be understood in order to develop chlorine-resistant membranes. Coated and uncoated fully aromatic (FA) and piperazine (PIP) semi-aromatic PA membranes were treated with hypochlorite solution and analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). XPS results showed that in chlorine treated FA PA membranes the ratio of bound chlorine to surface nitrogen was 1:1 whereas it was only 1:6 in the case of PIP PA membranes. Surface oxygen of uncoated FA and PIP membranes increased with increasing hypochlorite concentration whereas it decreased for coated FA membranes. High resolution XPS data support that chlorination increased the number of carboxylic groups on the PA surface, which appear to form by hydrolysis of the amide bonds (C(O)-N). FTIR data indicated the disappearance of the amide II band (1541 cm(-1)) and aromatic amide peak (1609 cm(-1)) in both coated and uncoated chlorinated FA membranes, consistent with the N-chlorination suggested by the XPS results. Furthermore, the surface charge of chlorinated membranes at low pH (<6) became negative, consistent with amide-nitrogen chlorination. Chlorination appeared to both increase and decrease membrane hydrophobicity depending on chlorination exposure conditions, which implied that N-chlorination and hydrolysis may be competing processes. The effects of property changes on the membrane performance were also observed for NF90, BW30, and NF270 membranes.

Adsorption of perfluorinated compounds on thin‐film composite polyamide membranes

AbstractThe adsorption behavior of perfluorinated compounds (PFCs), of various chain lengths and two different functional groups, on widely used thin‐film composite polyamide membranes has been investigated. Three commercially available polyamide membranes and two classes of PFCs were evaluated: Dow‐Filmtech BW30, NF90, and NF270 membranes; perfluorosulfonic and perfluoroalkanoic acid with 5, 7, 9, and 11 carbon atoms. The adsorption of PFCs on the membranes strongly depended on the active skin‐top layer material of the membranes, solution chemistry, and structure of PFCs. The piperazine based NF270 membrane showed higher adsorption of PFCs compared to BW30 and NF90 membranes (FT‐30 type membranes). The BW30 membrane, which has a coating layer of aliphatic carbons and hydroxyl groups on the surface of the polyamide substrate, had less interaction with PFCs than the NF90 polyamide membrane had. The adsorption of PFCs increased with increasing ionic strength, decreasing pH, and in divalent ion solutions. PFCs with longer chain lengths and more hydrophobic functional groups showed more attractive interactions with thin‐film composite membranes and, thus, greater adsorption on the membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

CHEMICAL CLEANING OF REVERSE OSMOSIS MEMBRANE FOULED BY APPLE JUICE

ABSTRACTThe effects of several chemical agents on cleaning of RO BW30 membrane fouled by apple juice were investigated. Resistance removal (RR) and flux recovery (FR) were calculated for all the seven chemical cleaning agents (HCl, HNO3, NH3, NaOH, ethylenediaminetetraacetic acid [EDTA], cetyl three methyl ammonium bromide and sodium dodecyl sulfate[SDS]) which were used at 1% (w/v) concentration. For high cleaning efficiency agents, the effect of chemical factors (pH and concentration) and physical factors (velocity, temperature and time) were studied. SDS showed the highest (about 90%) cleaning efficiency. EDTA and NH3 were also quite effective in reacting with organic foulants. The treatment of fouled membrane by distilled water as cleaning agent showed high cleaning efficiency. Investigations of the chemical and physical factors on membrane cleaning indicate that the cleaning efficiency is dependent on these parameters. Increasing the pH of 1.5% SDS solution up to 11.8 showed the highest cleaning efficiency, i.e., approximately 100%.PRACTICAL APPLICATIONSReverse osmosis (RO) is a very useful technology in fruit juice concentration due to maintaining the taste and fresh juice flavors. In contrast, the conventional processes applied for this concentration, e.g., evaporation, have the disadvantage of adding a cooking taste to the product and lowering itsquality, in addition to the high energy consumption. However, fouling by carbohydrate components is the most important problem associated with the RO application. Finding high efficiency cleaning agents for regeneration of membranes is one of the industrial interests, which is proceeded in this work.

Removal of arsenate [As(V)] and arsenite [As(III)] from water by SWHR and BW-30 reverse osmosis

The removal of arsenate [As(V)] and arsenite [As(III)] from water was investigated by using reverse osmosis (RO) technique with SWHR and BW-30 (FILMTEC) membranes. The effect of pH and concentration of the feed water and operating pressure on the rejection of both arsenic species was examined. The experimental results indicated that rejection for both As(V) and As(III) mostly depended on the membrane type, pH of the feed water and operating pressure. For both membranes, As(V) rejection was maximum at pH above 4.0, while As(III) could be effectively removed from water at pH above 9.1. The rejection for both arsenic species increased with increasing operating pressure. The lowest permeate concentration of As(III) and As(V) was obtained when SWHR membrane was used. Finally, a natural (ground) water sample containing 50μg/L of As(V) and 12μg/L of As(III), respectively was treated by using RO with SWHR membrane. The obtained permeate concentration of total arsenic was compared with WHO and EU standards and permeate fluxes were evaluated by considering the chemical composition of the groundwater sample.

Coupling effects of feed solution pH and ionic strength on the rejection of boron by NF/RO membranes

The coupling effects of solution pH and ionic strength on boron rejection by nanofiltration (NF) and reverse osmosis (RO) membranes were investigated. Two NF membranes (namely NF270 and NF90) and three RO membranes (namely BW30, SW30 and UTC80) were used to provide a full spectrum of NF/RO membranes. The rejection of boron by all five membranes was pH-dependent. The dependency of boron rejection on the feed solution pH became much more substantial as the nominal salt (sodium or calcium) rejection value of the membrane decreased. At pH 11, boron rejections by the NF90 and the NF270 membranes were only 10% and 30% lower than those by the other three RO membranes, respectively. On the other hand, the permeabilities of the two NF membranes investigated here were 3–11 times higher than those of the RO membranes. The reported data suggest a possibility of using NF membranes for the second pass in seawater desalination applications to avoid over-demineralisation of the final product water. The reported results also reveal an intricate interplay among the feed solution pH, ionic strength and their effects on the rejection of boron by NF/RO membranes. At pH 10, which is immediately above the intrinsic pK a value (9.23) of boric acid, as the feed solution ionic strength increased up to 42.5 mM, a considerable increase in boron rejection by both the NF270 and the BW30 membranes was observed. This phenomenon could be attributed to the reduction in the apparent pK a of boric acid as the ionic strength increased, which possibly resulted in the observed increase in boron rejection at pH 10. Results reported here suggest that the rejection of boron in the second pass could be further optimised by increasing the feed solution pH and allowing for a marginally higher salt passage in the first pass.

Treatment of olive mill wastewaters by nanofiltration and reverse osmosis membranes

Treatment of olive mill wastewaters (OMW) by membrane techniques were investigated in this study. For this purpose, OMW was centrifuged, and filtered via UC010 ultrafiltration membrane followed by filtration through NP010, NP030, and NF270 nanofiltration membranes, and XLE and BW30 reverse osmosis membranes. Besides, skipping the ultrafiltration step, the centrifuged OMW was filtered through NP010 and NP030 membranes in order to evaluate the performance of the centrifuging process as a pretreatment option. For the OMW percolated through ultrafiltration membranes, the membrane fluxes reached values of up to 21.2, 5.2, 28.3, 15.5, and 12.6 L m − 2 h − 1 for NP010, NP030, NF270, XLE, and BW30 membranes, respectively. The maximum COD removal efficiencies obtained at 10 bars were 60.1%, 59.4% and 79.2% for NP010, NP030, and NF270 nanofiltration membranes, respectively, while they were 96.3% and 96.2% for XLE and BW30 reverse osmosis membranes, respectively. Besides, conductivity removal efficiencies obtained at 25 bars were 93.2% and 94.8% for XLE and BW30 membranes, respectively. Obtained efficiencies are higher than those obtained in the treatment of OMWs with other treatment methods. Thus, it was concluded that membrane processes are a good alternative for the treatment of OMWs. Additionally, the centrifuging process was found to be a promising pretreatment method.