Nano- and microfibrous composites for water filtration applications

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Nano- and microfibrous composites for water filtration applications • Jaroslav Lev1, Marek Holba1,2,Michal Došek1,3, Libor Kalhotka4, Dušan Kimmer5 • 1 - ASIO, spol. s r.o., Tuřanka 1, 627 00 Brno, Czech Republic, e-mail: lev@asio.cz • 2 - Institute of Botany oftheAcademyof Science ofthe Czech Republic, Department ofExperimentalPhycology and Ecotoxicology, Lidická 25/27, 657 20 Brno, Czech Republic • 3 - Mendel University of Brno, Facultyof Agronomy, Department of Technology and Automobile Transport, Zemědělská 1/1665, 613 00 Brno, Czech Republic • 4 - Mendel University of Brno, Facultyof Agronomy, Department ofAgrochemistry, Soil Science, Microbiology and Plant Nutrition, Zemědělská 1/1665, 613 00 Brno, Czech Republic • 5 - SPUR, a.s.,TomášeBaťi299, 764 22 Zlín, Czech Republic Introduction Composites from electrospun nanofibrous material are recently being developed and verified for the production of newestmicro- and ultrafiltration materials used in water and air treatment (Decostere, 2009). Lower filtration pressure led in the case of air filtration to the faster expansion into full-scale applications. Water filtration needs higher mechanical endurance than air filtration applications, however satisfactory filtration efficiency have been achieved too. There are several more problems that prevent wider use at full-scale plants (Barhate, 2007). The most frequent malfunction is the low endurance of nanofibrous layers to mechanical effects caused by pressure weight and movement of treated wastewater. Filter mechanical endurance is determined by mechanical properties of thebase course material. Proper base course material supporting fine nanostructure from the bottom part is sufficient for single use application. However, long-term applications expect filter backflush regeneration that insists higher demands for base course material, e.g. durability and reliable connection with nanofibrous layers. Our research is focused on the development of nanofibrous structure for bacteria removal by wastewater filtration. Our previous tests verified filtration efficiency of polyurethane nanofibrous structures with polypropylene as base course material in lab-scale (Lev, 2012) and we were able to reach log removal 2-4 CFU/mL. Comparable results were achieved also in similar studies (Decostere, 2009). However, transfer those test into pilot-scale showed problems especially with low mechanical filter endurance. Nanofibrous layers were often cracked and separated from base course. We project a new type of composite material that uses good filtration properties of nanofiber layers and mechanical properties of mikrofiberous structure. This material was verified with model pollution.Siltingprocess was monitored and backwash of ourprojectcompositewastested. • Material and Methods Technology • Electrospinning processfor nanofibers production • Electrospinning machine Spineline (SPUR a.s. Zlín, Czech republic) with nozzle electrodes • Conditions: • air humidity 32% • air temperature 24°C • voltage between electrodes 60-75 kV • distance between electrodes 210 mm Material • composite from polyethylene base and electrospun polyurethane nanofiber layers • Fiber diameter varied between 100 and 400 nm • Nanofibrous layerarea weigt 1.6 g/m2 • pressed at the 120 °C for 20 minutesto create composite from nanofibersand microfibers • Size of sample of material – two sheets 200x100 mm SEM pictureof nanofibrous and microfibrouscompositefiltrationmaterial:magnification 50x and 5000x Schema of electrospinning processwithnozzleelectrodes Compositionoffilter • Testing • Compositesbound into the frame of 200 x 100 mm • Clean water permeability test • Filtrationof artificial wastewater (water with E. coli) • Pumping performance optimized 250 mL/min • Observedpressure increase - effect of filter clogging • Backflushwith distilled water with overpressure up to 40 kPa after 60 minutes • Analyze of filter after test Cracked nanofibrous filter (nanofibers on substrate) after backflush Composite filter from micro and nanofibers Schemeof testing aparaturs • Results& Discussion Flow and pressure variations during test are shown on Figure 1.It presentsthe gradual clogging of the filter material, which confirms the increase of pressure in the system. The pressuredrop after backwashlead to the removal of bacteria on the filter surface. Filter withstand pressure during backwash byclean water to 0.4 bar which is sufficient in practice. Filter visual analyseswereperformed after the test and showed cracked nanofibres layer. Ourtestsshow the direction of substantially increasing mechanical resistance of thenanofiberlayers for liquid filtrationwhichwasreinforcement by microfibers.Optimalization and testing of othercomposite variations are expected in the next steps.It is needed to optimize the thickness of the layers of nanowires, durability tests, etc. prior to full-scale application of the nanofibrous composite material. We assumethat by increasing ofthe mechanical strength of nanofiber structures and functionalization layers bybiocidal substances can pass nanofiber materials from laboratory experiments into practice. • Conclusions Our tests showed sufficient composite endurance ofthemechanical damage even with backflush filtration. Neither damage of the layer coherence nor perforation have been observed at the tested material. The simulation of composite filter regeneration with artificial wastewater enriched by E.coli proved the possibility of thebackflush. Future work will focus on monitoring offilter efficiency, area weightoptimizationofthenanofiberlayer and on the full scalelong-term operational testing with real water. Figure1:Pressure and flow variations References Decostere, B., Daels N., De Vrieze S., Dejans P., Van Camp T., Audenaert W., Hogie J., Westbroek P., De Clerck K., Van Hulle W.H.S. (2009). Performance assessment of electrospun nanofibers for filter applications, Desalination 249, 942–948. Botes, M., Cloete, T.E. (2010). The potential of nanofibers and nanobiocides in water purification. Critical Reviews in Microbiology, 36, 68–81. Barhate, R.S., Ramakrishna, S.,(2007). Nanofibrous filtering media, Filtration problems and solutions from tiny materials. Journal of Membrane Science 296, 1-8. Lev, J., Holba, M., Kalhotka, L., Mikula, P., Kimmer, D., (2012). Experimental study on bacteria removal from artificial and real wastewater by nanofibrous filters, Proc. of Int. Conf. NANOCON 2012 Acknowledgements This study was supported and financed by the Technology Agency of the Czech Republic No. TA01010356.