Shape stable poly(vinyl alcohol) hydrogels with immobilized metal hexacyanoferrates for cesium removal from waters.

The metal hexacyanoferrates with transition metal ions to replace ferric ions in the face center cubic structure of Prussian blue (PB) crystals are candidate adsorbents for radioactive cesium ions in waters. This study for the first time synthesized the shape stable poly(vinyl alcohol) (PVA) hydrogels with immobilized metal hexacynoferrate (PB analogue) that can be stored at dry and can efficiently adsorb cesium ions from waters after rewetting. A total of eight PB analogue particles in two families M3[Fe(III)(CN)6]2 (MFe(III)) or M4[Fe(II)(CN)6]2 (MFe(II)) with M=Zn, Ni, Cu, or Co were synthesized and were immobilized in the PVA hydrogels following boric acid and sulfate crosslinking. The produced PVA-PB analogue hydrogels are all stable in shape after dry and rewet, and the rewet hydrogels can adsorb cesium ions from waters at much higher rates. As predicted by the diffusion-reaction model, the apparent reaction constants for cesium ion adsorption are 4.2×10-4 1/s, 3.4×10-4 1/s, 3.9×10-4 1/s, 4.1×10-4 1/s, 4.1×10-4 1/s, 3.8×10-4 1/s, 1.1×10-3 1/s, and 9.6×10-4 1/s, for ZnFe(III), ZnFe(II), NiFe(III), NiFe(II), CuFe(III), CuFe(II), CoFe(III), and CoFe(II), respectively. The corresponding maximum adsorption capacities based on Langmuir isotherm model at 25 °C are 232.6 mg/g, 389.0 mg/g, 193.9 mg/g, 256.8 mg/g, 388.2 mg/g, 395.1 mg/g, 297.3 mg/g, and 391.2 mg/g, respectively. The use of PVA-CoFe(III) is the candidate for enhanced Cs removal from waters comparing the use of other PB analogues as adsorbent.

Shape stable poly(vinyl alcohol) hydrogels with immobilized activated sludge at repeated dry-rewet cycles.

The poly(vinyl alcohol) (PVA) hydrogels can be used as a non-toxic and inexpensive immobilization matrix for microbial cells with capability of degrading organic or inorganic pollutants in wastewaters. This study for the first time produced the PVA hydrogels with immobilized cells by two-stage crosslinking which have high shape stability at dry-rewet cycles and, when recovered after sequentially three 24-hr cultivations, reveal high bioactivity in wastewater treatment. The [B(OH)3][SO42-] cores inside the PVA-boric acid-sulfate hydrogels are proposed to support the immobilized cells with sufficient structure flexibility and strength to maintain hydrogel structural integrity and of sufficient recalcitrance to biological attack. Conversely, neither the PVA-boric acid hydrogels nor the PVA-borate hydrogels can be applied as organic pollutant degraders with dry storage capability. The PVA-boric acid-sulfate hydrogels are proposed as ideal matrix that can be produced and stored in dry, massive quantity and then applied latter at the same or different sites.

Poly(vinyl alcohol) and alginate cross-linked matrix with immobilized Prussian blue and ion exchange resin for cesium removal from waters.

Cesium (Cs) removal from contaminated water bodies is an emerging issue after the disaster at the Fukushima Daiichi Nuclear Power Plant. The Prussian blue (PB) is an effective Cs adsorbent but will release hexacyanoferrate fragments from the adsorbent matrix during adsorption. Alginate is an affordable biopolymer for PB particles immobilization. This study synthesized poly(vinyl alcohol) (PVA) and alginate cross-linked matrix for immobilization of PB nano-sized particles and a surface-modified styrene-ethyl styrene divinyl benzene resin and tested their swelling stability and Cs adsorption performance in fresh water and in seawater. The PVA-alginate granules have high structural stability in both fresh water and seawater, with the Cs adsorption capability higher for the former than the latter. The adopted resin effectively remove released PB fragments from the tested granules. The transport and reaction parameters for the granules and for the sand filter bed were estimated.

Lutein recovery from Chlorella sp. ESP-6 with coagulants.

Production of algal lutein included cell cultivation, biomass harvesting, cell wall disruption, and subsequent purification if needed. This work cultivated Chlorella sp. ESP-6 cells in photobioreactor to a biomass content of 1.1 gl(-1) and then the freezing-grinding, ultrasonic treatment (20 and 42kHz) and microwave treatment were used to disrupt the cell walls for recover intracellular lutein. The grinding recovered more lutein than ultrasound or microwave pretreatment. Single coagulation using >30 mgl(-1) chitosan or dual-conditioning using 10 mg l(-1) polyaluminum chloride and 10 mgl(-1) chitosan effectively enhance sedimentation and membrane filtration efficiency of algal suspensions. However, the presence of coagulants lowers the lutein yield from algal biomass in the subsequent 20 kHz ultrasound treatment and purification process. Simulation results revealed affine adsorption of lutein onto chitosan molecules via hydroxyl-amine interaction. The possible drawback by pre-treatment stage should be considered together with the subsequent recovery stage in whole process assessment.

Coagulation-membrane filtration of Chlorella vulgaris.

Filtration-based separation of Chlorella vulgaris, a species with excellent potential for CO(2) capture and lipid production, was investigated using a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane. Coagulation using polyaluminum chloride (PACl) attained maximum turbidity removal at 200 mg L(-1) as Al(2)O(3). The membrane filtration flux at 1 bar increased as the PACl dose increased, regardless of overdosing in the coagulation stage. The filtered cake at the end of filtration tests peaked in solid content at 10 mg L(-1) as Al(2)O(3), reaching 34% w/w, roughly two times that of the original suspension. Differential scanning calorimetry (DSC) tests demonstrate that the cake with minimum water-solid binding strength produced the driest filter cake. Coagulation using 10 mg L(-1) PACl as Al(2)O(3), followed by PTFE membrane filtration at 1 bar, is an effective process for harvesting C. vulgaris from algal froth.