Maria Tomaszewska

Preparation and properties of flat-sheet membranes from poly(vinylidene fluoride) for membrane distillation

The flat-sheet membranes from poly(vinylidene fluoride) were prepared by the phase inversion process. The effects of the casting solution composition, exposure time prior to coagulation and temperature of the coagulation bath on properties of prepared membranes were investigated. LiCl was used as a modifying agent. The membrane structure was studied by scanning electron microscopy. For all prepared membranes an asymmetric structure, sometimes without a dense skin layer, was observed. The porosity of prepared membranes before the drying process varied from 72–88%. After drying the membranes become hydrophobic. A contact angle of water droplet on the membrane surface was 107°. The nitrogen permeability varied from 12-2,205 m3/m2 d, depending on the preparation conditions. The maximum pore size, LEPW and mechanical properties were also determined. The membrane distillation process of 1–2% aqueous NaCl solution was applied as a final test of membrane performance. The permeate flux up to 233 dm3/m2 d was achieved at the temperature of the feed and permeate of 333 K and 293 K, respectively. A chloride elimination in the permeate higher than 99% was reached.

Heat transport in the membrane distillation process

Investigation of membrane distillation (MD) with a laminar flow of the streams in a module has been performed. The equations describing the heat transfer in MD capillary modules were presented and verified experimentally. The equations were derived for the calculation of the feed and distillate temperature at a layer adjacent to the membrane. The heat transfer correlations were implemented in a physical model of the MD process and the applicability of the model was validated.

Removal of organic matter from water by PAC/UF system

The laboratory-scale ultrafiltration (UF) experiments were conducted to determine the effect of the presence of powdered activated carbon (PAC) on the UF process performance, in terms of flux decline and the possibilities of membranes cleaning during backwashing. Poly(vinylidene fluoride) membranes formed by the phase inversion technique were used in the UF experiments. A model solution was prepared as a mixture of humic acids (HA) and phenol in concentration of 10 and 1 mg l(-1), respectively. Commercial powdered activated carbons CWZ 11 and CWZ 30 (Gryfskand Sp. z o. o., Hajnówka, Poland) were used as the adsorbents. PAC dosage was in the range of 10-100 mg PAC l(-1). The process was carried out in the cross-flow system. It was found that PAC addition to the distilled water leads to a small drop in the permeate flux, regardless of PAC dose and its type. Although PAC particles are too large to block the membrane pores inside, they deposit on the membrane surface and partially can plug the surface pores. The experimental results demonstrate that the backwashing process applied in combined PAC/UF system was especially effective when PAC dosages were <20mg PAC l(-1). However, a similar permeate flux was maintained for all carbon dosages used and reached the value of about 1 m3 m(-2) d(-1). Moreover, no further drop in the permeate flux for PAC addition to the solution containing foulants (HA) was observed. Effectiveness of the removal of HA and phenol from the model solutions was also investigated. In the PAC/UF system HA were removed in about 90%, whereas the complete removal of phenol was achieved for PAC dosage equal to 100 mg l(-1).

Study on the concentration of acids by membrane distillation

Abstract The membrane distillation (MD) process was applied for the concentration of different mineral acids, such as, sulfuric phosphoric, hydrochloric and nitric acids. The MD of a citric acid solution as an example of an organic acid was also investigated. The experiments were carried out keeping the warm feed and cold solution temperatures at 333 and 293 K, respectively. The data obtained indicate that the volume flux of a permeate decreased with an increase of acid concentration in the feed. The reduction of acid content in the permeate, close to 100%, for non-volatile acids was independent of the acid concentration in the feed. The amounts of hydrochloric or nitric acids in the permeate increased with a rise of the acid concentration in the feed, reaching the azeotropic composition. The effect of the polarisation phenomena on the concentration process of sulfuric acid is discussed.

Removal of organic matter by coagulation enhanced with adsorption on PAC

Abstract The removal of humic acids and phenol from model solution by coagulation and adsorption on powdered activated carbon (PAC) was investigated. A PAX XL-69 polyaluminum chloride was applied as a coagulant. The adsorption of humic acids and phenol on activated carbon for single- and bi- component solutions was studied. It was found that coagulation without PAC addition was less effective than the adsorption-coagulation integrated system. Coagulation enhanced with adsorption on activated carbon was more effective when coagulation was preceded by adsorption than when the two processes were carried out simultaneously. The best results were obtained at pH 7. Phenol and color were removed pletely, UV 254 absorbance was reduced by about 99% and COD-Mn was reduced by 81–89%.

Membrane distillation with laminar flow

Direct-contact membrane distillation (MD) process in a plate-and-frame module with laminar flow is investigated. The performance of a MD process is strongly influenced by heat transfer taking place within the membrane modules. The present study is concerned mainly with heat transfer across membranes, and specifically with assessing the applicability of existing heat-transfer coefficient correlations to MD membrane modules.

Physical and chemical characteristics of polymer coatings in CRF formulation

Abstract Investigations on the preparation of controlled-release fertilizer coated with polymers, have been described. The polymer materials used were polysulfone (PSF), cellulose acetate (CA) and polyacrylonitrile (PAN). The polymer coatings were formed on the granular NPK fertilizer by the phase inversion technique. The measurements of thickness and porosity of prepared coating and microphotographic observation of the coating were performed. The thickness of fertilizer coatings, measured by the micrometer screw was in the range from 0.21–1.14 mm — depredating on the polymer type. It was found, that a higher concentration of polymer in film forming solution causes a decrease of the porosity of the obtained coating. The microphotographs of the coatings obtained for this study demonstrate that the prepared coatings in all cases were asymmetric with thin skin layer formed on the top of the coating. The polymer coatings were characterised using Fourier transform infrared spectroscopy (FT-IR). The coatings, formed on the fertilizer, were compared with coatings prepared from the same polymer but without the contact with fertilizer. It was observed that the spectra of pure polymer showed the peaks with lower intensity.

Recovery of hydrochloric acid from metal pickling solutions by membrane distillation

Membrane distillation (MD) was applied for the concentration of solutions containing hydrochloric acid and salts. It was found that under MD conditions through pores of a hydrophobic membrane both water vapor and hydrogen chloride are transported. This effect was utilized for the recovery of HCl from acidic spent solutions. The experiments were performed using model or real metal pickling solutions with different compositions. Two methods of the feed concentration for the acid recovery were proposed. The results of the studies show that MD may be a promising method for HCl recovery from industrial effluent.

Concentration of the extraction fluid from sulfuric acid treatment of phosphogypsum by membrane distillation

An attempt was made to apply membrane distillation for the concentration of the sulfuric acid solution obtained after extraction of apatite phosphogypsum, in order to recover lanthane compounds. The process was carried out step-wise, till the acid concentration of the solution reached 40%. Under such conditions the lantane compounds precipitate after cooling of the solution. The temperature of the feed and the cold solution was kept at 333 K and 293 K respectively. The distillation flux decreased from 215 dm3/m2-d to 80 dm3/m2-d with the increase of acid concentration in the feed from 16% to 44%. The acid rejection coefficient was close to 100%, in all experiments performed. The most effective process was that performed in a flow apparatus, where the membrane sides were reversed and the distillate condensation was carried directly into a stream of cooling water. The content of lantane compounds in the precipitate obtained from the concentrated solution amounted to 25%. The experiments were performed with sulfuric acid solutions and a model solution consisting of 12% sulfuric acid saturated with CaSO4.

Treatment of surface water using hybrid processes —adsorption on PAC and ultrafiltration☆

Abstract Studies were performed to determine the effect of the presence of powdered activated carbon (PAC) on ultrafiltration (UF) process performance. The influence of PAC addition to the feed on permeate flux in terms of flux decline and the possibilities of membrane cleaning during backwashing were investigated. The effectiveness of the removal of organic contaminants from the Miedwie Lake water during UF and hybrid processes of adsorption on PAC-ultrafiltration (PAC/UF) were determined. Fourier transform infrared (FTIR) spectroscopy was applied in order to examine the character of membrane foulants. Polyacrylonitrile (PAN) membranes formed by the phase inversion technique were used in the UF experiments. Commercial PACCWZ 30 was applied as the adsorbent. PAC dosage was equal to 100 mg PAC l−1. The process was carried out in the cross-flow system. The experiments were performed at two different pH values (8.7 and 6.5) of the treated water. It was found that the combination of UF and adsorption on PAC was more effective in organics removal than UF alone. The treatment was more efficient at pH 8.7 than at pH 6.5. At both pH values, no significant effect of PAC addition to the feed on the permeate flux was observed. On the basis of the FTIR spectra, it was found that the foulants of the PAN membrane present in Miedwie Lake water were primarily silicates.