Application of a triblock copolymer additive modified polyvinylidene fluoride membrane for effective oil/water separation.

A hollow fibre membrane was fabricated by blending polyvinylidene fluoride (PVDF) with a triblock copolymer additive polymer that has both hydrophilic and oleophobic surface properties. The novel membrane was characterized and examined for oil/water separation under various system conditions, including different cross-flow rate, feed temperature, trans-membrane pressure, and its rejection and cleaning efficiency, etc. By applying the membrane into the filtration of synthesized oil/water emulsion, the membrane constantly achieved an oil rejection rate of above 99%, with a relatively constant permeate flux varied in the range of 68.9-59.0 l m-2 h-1. More importantly, the fouling of the used membrane can be easily removed by simple water flushing. The membrane also demonstrated a wide adaptability for different types of real oily wastewater, even at very high feed oil concentration (approx. 115 000 mg l-1 in terms of chemical oxygen demand (COM)). Hence, the novel triblock copolymer additive-modified PVDF membrane can have a great prospect in the continuing effort to expand the engineering application of polymeric membranes for oily wastewater treatment.

Enhancing the Antifouling Properties of Poly(vinylidene fluoride) (PVDF) Membrane through a Novel Blending and Surface-Grafting Modification Approach.

In this study, poly(vinylidene fluoride) (PVDF) membrane was modified through a novel approach by first blending an active component (poly(vinylidene fluoride-co-chlorotrifluoroethylene), P(VDF-co-CTFE)) with the PVDF base material, followed by surface grafting of the membrane on the active component to obtain a triblock copolymer functional structure. The prepared membranes were characterized by various analyses, including Fourier-transform infrared, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscope, and filtration tests. It was found that the modified membrane surface showed a much better hydrophilicity (water contact angle of 67.3°) and oleophobicity (oil contact angle of 129.7°). The modification reduced the average surface pore size (from 0.1495 to 0.1072 µm) and thus lowered the pure water flux (from 364.0 to 224.6 L m-2 h-1 at 0.10 MPa of transmembrane pressure), but significantly increased the relative flux recovery (RFR) and the retention efficiency of the modified membrane during the filtration of bovine serum albumin solution and oil/water emulsion. For example, the modified membranes showed 98.6% oil retention (at feed concentration of 0.4 g L-1), 92.7% RFR by simple water flushing after filtration, and a consistently high oil removal of 96% or above during a five-cycle-continuous filtration test, as compared to 30.4% oil retention and 51.8% RFR for unmodified PVDF/P(VDF-co-CTFE) blend membrane.

Surface functionalization of Cu-Ni alloys via grafting of a bactericidal polymer for inhibiting biocorrosion by Desulfovibrio desulfuricans in anaerobic seawater.

A novel surface modification technique was developed to provide a copper nickel alloy (M) surface with bactericidal and anticorrosion properties for inhibiting biocorrosion. 4-(chloromethyl)-phenyl tricholorosilane (CTS) was first coupled to the hydroxylated alloy surface to form a compact silane layer, as well as to confer the surface with chloromethyl functional groups. The latter allowed the coupling of 4-vinylpyridine (4VP) to generate the M-CTS-4VP surface with biocidal functionality. Subsequent surface graft polymerization of 4VP, in the presence of benzoyl peroxide (BPO) initiator, from the M-CTS-4VP surface produced the poly(4-vinylpyridine) (P(4VP)) grafted surface, or the M-CTS-P(4VP) surface. The pyridine nitrogen moieties on the M-CTS-P(4VP) surface were quaternized with hexylbromide to produce a high concentration of quaternary ammonium groups. Each surface functionalization step was ascertained by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurements. The alloy with surface-quaternized pyridinium cation groups (N+) exhibited good bactericidal efficiency in a Desulfovibrio desulfuricans-inoculated seawater-based modified Barr's medium, as indicated by viable cell counts and fluorescence microscopy (FM) images of the surface. The anticorrosion capability of the organic layers was verified by the polarization curve and electrochemical impedance spectroscopy (EIS) measurements. In comparison, the pristine (surface hydroxylated) Cu-Ni alloy was found to be readily susceptible to biocorrosion under the same environment.

Characteristics of a bioflocculant produced by Bacillus mucilaginosus and its use in starch wastewater treatment.

A bioflocculant, MBFA9, was produced from a strain of bioflocculant-producing bacteria isolated from a soil sample and identified as Bacillus mucilaginosus. MBFA9 had a good flocculating capability and could achieve a flocculating rate of 99.6% for kaolin suspension at a dosage of only 0.1 ml/l. The major component of MBFA9 was found to be polysaccharide composed mainly of uronic acid (19.1%), neutral sugar (47.4%) and amino sugar (2.7%). Infrared spectrum analysis showed the presence of carboxyl and hydroxyl groups in the bioflocculant. MBFA9 is nontoxic and can be used in food industries for suspended solids (SS) recovery. When applied to starch wastewater treatment, MBFA9 greatly accelerated the formation of flocs and the settling of organic particles in the presence of Ca(2+) salt. After 5 min of settling, the removal rate of SS and chemical oxygen demand were up to 85.5% and 68.5%, respectively, which is better than traditional chemical flocculants.