Application of charged membranes in water softening: modeling and experiments in the presence of polyelectrolytes

Modulation of Interlayer Nanochannels via the Moderate Heat Treatment of Graphene Oxide Membranes

In response to the phenomenon of interlayer transport channel swelling caused by the hydration of oxygen-containing functional groups on the GO membrane surface, a moderate heat treatment method was employed to controllably reduce the graphene oxide (GO) membrane and prepare a reduced GO composite nanofiltration membrane (mixed cellulose membrane (MCE)/ethylenediamine (EDA)/reduced GO-X (RGO-X)). The associations of different heat treatment temperatures with the hydrophilicity, interlayer structure, permeability and dye/salt rejection properties of GO membranes were systematically explored. The results indicated that the oxygen-containing groups of the GO membrane were partially eliminated after heat treatment, and the hydrophilicity was weakened. This effectively weakened the hydration between the GO membrane and the water molecules and inhibited the swelling of the oxidized graphene membrane. In the dye desalination test, the MCE/EDA/RGO membrane exhibited an ultra-high rejection rate of over 97% for methylene blue (MB) dye molecules. In addition, heat treatment increased the structural defects of the GO membrane and promoted the fast passage of water molecules via the membrane. In pure water flux testing, the water flux of the membrane remained above 46.58 Lm-2h-1bar-1, while the salt rejection rate was relatively low.

Recovery of clindamycin from fermentation wastewater with nanofiltration membranes

Experiments were carried out on clindamycin's separation and recovery from clindamycin fermentation wastewater with nanofiltration (NF) membranes. Four types of flat-sheet NF membranes, DLNF-1, NTR-7250, XCNF-1 and MPF-44, were tested under different dynamic operating conditions. It was found that the operating pressure and solute concentration had great influence on membrane performance while flow rates (or velocities) had little influence on membrane performance. Experiments on SO4(2-) rejection were conducted with such four flat-sheet NF membranes because SO4(2-) had bad influence on microbes in biochemical process following the NF process. The results indicated that DLNF-1 and MPF-44 membranes had higher SO4(2-) rejection among four membranes. Two spiral membranes, MPS-44 (1.4 m2) and DLNF2-30 (0.24 m2), were adopted in a concentrating process for clindamycin's separation and recovery from clindamycin fermentation wastewater under laboratory conditions. After being operated for 60h, clindamycin wastewater was concentrated from 266 to 26L, and the clindamycin was concentrated from 220 to 1940 mg/L, which met the demand of reuse. This research may widen the application of NF membranes in disposal of pharmaceutical wastewater.