Raka Mukherjee

Adsorptive removal of phenolic compounds using cellulose acetate phthalate–alumina nanoparticle mixed matrix membrane

Mixed matrix membranes (MMMs) were prepared using alumina nanoparticles and cellulose acetate phthalate (CAP) by varying concentration of nanoparticles in the range of 10 to 25wt%. The membranes were characterized by scanning electron micrograph, porosity, permeability, molecular weight cut off, contact angle, surface zeta potential, mechanical strength. Addition of nanoparticles increased the porosity, permeability of the membrane up to 20wt% of alumina. pH at point of zero charge of the membrane was 5.4. Zeta potential of the membrane became more negative up to 20wt% of nanoparticles. Adsorption of phenolic derivatives, catechol, paranitrophenol, phenol, orthochloro phenol, metanitrophenol, by MMMs were investigated. Variation of rejection and permeate flux profiles were studied for different solutes as a function of various operating conditions, namely, solution pH, solute concentration in feed and transmembrane pressure drop. Difference in rejection of phenolic derivatives is consequence of interplay of surface charge and adsorption by alumina. Adsorption isotherm was fitted for different solutes and effects of pH were investigated. Catechol showed the maximum rejection 91% at solution pH 9. Addition of electrolyte reduced the rejection of solutes. Transmembrane pressure drop has insignificant effects on solute rejection. Competitive adsorption reduced the rejection of individual solute.

Nanostructured polyaniline incorporated ultrafiltration membrane for desalination of brackish water

A novel salt rejecting ultrafiltration (UF) membrane was prepared by a facile, scalable route involving in situ incorporation of negatively charged polyaniline (PANI) nanoparticles within polysulfone (PSF). The incorporated PANI acts as a porogen and charge inducing agent, improving the porosity, permeability, hydrophilicity as well as the surface charge, leading to an enhancement of the permeate flux and improvement of the salt rejection capability. Specifically, 2 wt% PANI loading leads to a 25 times increase in the molecular weight cut-off (from 0.2 to 4.8 kDa). Also, there is improvement in porosity (from 20% to 64%), and a 2-fold increase in permeability (from 8 × 10−12 to 16 × 10−12 m3 m−2 Pa−1 s−1). Surface hydrophilicity (reduction of the contact angle from 82° to 69°) was enhanced as well. All of these effects ultimately lead to a 2.5 times enhancement in the permeate flux (from 21 l m−2 h−1 to 38 l m−2 h−1 at 690 kPa transmembrane pressure, TMP and 20 l h−1 cross flow rate, CFR). This reflects the change in membrane behavior from nanofiltration (NF) to UF. An increase in zeta potential (from −4 mV to −28 mV at pH 7) results in salt rejection between 40–53%, equivalent to the NF performance. Developed UF membranes match the desalination performance of NF membranes showing a higher flux and lower energy requirement. Advantageously, these membranes are also found to be fouling resistant during salt solution filtration, requiring no extensive regeneration. Desalination performance of these membranes is also demonstrated using artificially synthesized seawater. These UF membranes may be exploited as a pretreatment for inlet load reduction to reverse osmosis or for the production of industrial process water. It is believed these charged membranes lay the foundation for the development of next generation desalination membranes possessing high flux and fouling resistant characteristics.

A socio-economic study along with impact assessment for laterite based technology demonstration for arsenic mitigation

Arsenic contamination mitigation technologies have been adsorption-based, but the most widely-used and traditionally available adsorbents suffered inherent limitations, including cost infeasibility and problems associated with regeneration and disposal of the spent adsorbent. The present technology is based on indigenously developed activated laterite prepared from the naturally and abundantly available material, and can hence easily be scaled up for community usage and large scale implementation. The total arsenic removal capacity is 32.5mg/g, which is the highest among all naturally occurring arsenic adsorbents. A major issue in earlier adsorbents was that during regeneration, the adsorbed arsenic would be released back into the environment (leaching), and would eventually contaminate the groundwater again. But the adsorbent in this filter does not require regeneration during its five-year lifespan and does not leach upon disposal. An attempt is made to test and demonstrate the practical implementation of the technology - its effectiveness and viability in three community (primary schools - one in Malda and two in north 24 Parganas, West Bengal, India) and 20 household filters, catering to over 5000 people in different areas of West Bengal exposed to high arsenic contamination of groundwater (ranging from 0.05 to 0.5mg/l). The work also focuses on the social impact of the real life technological solution on the lives on the affected people in the worst hit arsenic affected communities, perhaps the greatest public health risk emergency of the decade.