Marek Gryta

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.

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.

Purification of oily wastewater by hybrid UF/MD.

Investigations on the treatment of oily wastewater by a combination of ultrafiltration (UF) and membrane distillation (MD) as a final purification method have been performed. A tubular UF module equipped with polyvinylidene fluoride (PVDF) membranes and a capillary MD module with polypropylene membranes were tested using a typical bilge water collected from a harbour without pretreatment. The permeate obtained from the UF process generally contains less than 5 ppm of oil. A further purification of the UF permeate by membrane distillation results in a complete removal of oil from wastewater and a very high reduction of the total organic carbon (99.5%) and total dissolved solids (99.9%).

CONCENTRATION OF NaCl SOLUTION BY MEMBRANE DISTILLATION INTEGRATED WITH CRYSTALLIZATION

Concentration of NaCl solutions by direct-contact membrane distillation (DCMD) integrated with salt crystallization has been studied. The salt crystallization was carried out in a batch mode or continuously. The influence of process parameters (flow rates, temperatures, and concentrations) on permeate flux has been investigated. To evaluate the polarization phenomena, a simple model was used. This model showed good agreement with the experimental results. Two types of membrane distillation MD capillary modules, with the membranes arranged in a form of braided capillaries or helically wounded, were tested. The membrane wettability during long-term testing was investigated. A slow decline of the module efficiency was observed since the membranes were partially wetted during the process. The MD process integrated with continuous crystallization yielded an average NaCl production of 100 kg m−2 d−1.

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.

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.

The assessment of microorganism growth in the membrane distillation system

Growth of microorganism in the membrane distillation (MD) system has been evaluated, and their presence on the membrane surface was studied using scanning electron microscopy (SEM) coupled with energy dispersion spectrometry (EDS). The membrane samples were collected from MD modules used for the following applications: concentration of salts and acids, production of demineralized water from tap water, separation of ethanol from fermentation broth in a membrane bioreactor and treatment of saline wastewater containing Pseudomonas and Streptococcus faecalis bacteria and Penicillium and Aspergillus fungi. The MD experiments were performed with polypropylene capillary membranes. SEM examinations of the membranes used for the treatment of saline wastewater indicated a significant amount of S. faecalis bacteria and Aspergillus fungi. The polypropylene membranes used did not reject S. faecalis bacteria, which were detected on the membrane surface on the distillate side. The presence of fungi in the membrane pores was observed only on the feed side. The contamination of the membrane surface by yeast cells was not observed in the case of the membrane bioreactor operated over one year. The running conditions of the MD process (such as elevated temperature, significant salt concentrations and low pH values) inhibited the growth of microorganism in the MD system.

Membrane processes used for potable water quality improvement

Abstract The tap water is often used as water source for different industries, however, the water repurification is required to meet the specification of technology. The effect of application of ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO) and membrane distillation (MD) processes on the quality of treated water was investigated. The removal of suspended solids and colloids obtained by UF process allowed the reduction of SDI15 from 8 to 2. The NF process permitted to achieve the complete removal of dissolved organic carbon and the rejection of hardness between 60% and 87%. The rejection of TDS obtained in the RO system was at a level of 99.7%. The highest quality water (0.8 μS/cm, 0.6 ppm TDS) was produced in the MD installation.

The application of membrane distillation for the concentration of oil-water emulsions

The influence of the oil presence in the feed on the performance of membrane distillation (MD) has been investigated. The capillary membranes made from polypropylene with a maximum pore diameter of 0.62 μm were used in these studies. The concentration of oil in the concentrated feed was in the range of 0–2000 ppm. A decrease of the permeate flux obtained in the process along with the increase of oil concentration in the feed was observed. In the case of solutions containing up to 1000 ppm of oil, its presence in the permeate was not detected. However, at its higher concentration, the oil permeated into the distillate, for example at cF = 2000 ppm, the oil concentration in the distillate amounted to cD=0.6 ppm. The combination of MD with a system for oil separation obtained from the emulsion breaking enables maintenance of the oil content in the feed below 1000 ppm.

The fermentation process integrated with membrane distillation

Abstract Ethanol production in tubular bioreactor integrated with the membrane distillation (MD) system has been investigated. The fermentation of sugar with Saccharomyces cerevisiae proceeds with the formation of by-products, which tends to inhibit the yeast productivity. The removal of by-products from the fermenting broth by MD process increased the efficiency and the rate of sugar conversion to ethanol. The fermentation process carried out in the membrane bioreactor with the yeast concentration of 20 g dm −3 resulted in the productivity of 5.5 g EtOH dm −3 h and the efficiency closed to 95%, after 20 h. The productivity decreased to 2.6 g EtOH dm −3 h with the efficiency below 50% for the fermentation under similar conditions, but without MD. The separation of alcohol by MD enabled to achieve a higher content of ethanol in the permeate than that in the broth. The enrichment coefficient amounted to 2–6 were depended on the ethanol concentration in the feed. The presence of yeast cells in the feed increased the concentration and the temperature polarization, consequently the ethanol flux through the membrane was reduced by ca. 50%. A beneficial effect of carbon dioxide presence in the feed on the ethanol flux was found. The evolution of CO 2 bubbles from the fermenting broth enhanced the turbulence in the boundary layer, hence the ethanol transport through the membrane increased.