Impact of algal organic matter released from Microcystis aeruginosa and Chlorella sp. on the fouling of a ceramic microfiltration membrane.

Algal blooms lead to the secretion of algal organic matter (AOM) from different algal species into water treatment systems, and there is very limited information regarding the impact of AOM from different species on the fouling of ceramic microfiltration (MF) membranes. The impact of soluble AOM released from Microcystis aeruginosa and Chlorella sp. separately and together in feedwater on the fouling of a tubular ceramic microfiltration membrane (alumina, 0.1 µm) was studied at lab scale. Multi-cycle MF tests operated in constant pressure mode showed that the AOM (3 mg DOC L(-1)) extracted from the cultures of the two algae in early log phase of growth (12 days) resulted in less flux decline compared with the AOM from stationary phase (35 days), due to the latter containing significantly greater amounts of high fouling potential components (protein and humic-like substances). The AOM released from Chlorella sp. at stationary phase led to considerably greater flux decline and irreversible fouling resistance compared with that from M. aeruginosa. The mixture of the AOM (1:1, 3 mg DOC L(-1)) from the two algal species showed more similar flux decline and irreversible fouling resistance to the AOM from M. aeruginosa than Chlorella sp. This was due to the characteristics of the AOM mixture being more similar to those for M. aeruginosa than Chlorella sp. The extent of the flux decline for the AOM mixture after conventional coagulation with aluminium chlorohydrate or alum was reduced by 70%.

Degradation of dimethyl sulfoxide through fluidized-bed Fenton process.

Dimethyl sulfoxide (DMSO), one of the most widely used solvent, was subjected to fluidized-bed Fenton oxidation in this study. Fenton oxidation is considered one of the cheapest advanced oxidation processes due to high availability of Fenton's reagents Fe(2+) and H2O2, wherein, Fe(2+) catalyzes hydroxyl radical production from H2O2. Fluidized-bed Fenton process is a modified approach which is also used to address the production of large amount of iron oxide sludge in conventional Fenton process. Parametric study is included in this research using initial conditions of pH 2-7, 0.5-7.25 mM Fe(2+), 5-87.5mM H2O2, and 5-50mM DMSO. Fluidized-bed Fenton oxidation of 5mM DMSO using 68.97 g/L SiO2 carrier at initial conditions of pH 3, 5mM Fe(2+), and 32.5mM H2O2 resulted to 95.22% DMSO degradation, 34.38% TOC removal and 0.304 mM sulfate/mM DMSO0 production in 2h. The study shows that the intermediate product which was most difficult to oxidize and contributed most to the residual TOC was methanesulfonate.

Barium recovery by crystallization in a fluidized-bed reactor: effects of pH, Ba/P molar ratio and seed.

The effects of process conditions, including upward velocity inside the column, the amount of added seed and seed size, the pH value of the precipitant or the phosphate stream and the Ba/P molar ratio in a fluidized-bed reactor (FBR) were studied with a view to producing BaHPO4 crystals of significant size and maximize the removal of barium. XRD were used to identify the products that were collected from the FBR. Experimental results show that an upward velocity of 48 cmmin(-1) produced the largest BaHPO4 crystals with a size of around 0.84-1.0mm. The addition of seed crystals has no effect on barium removal. The use of a seed of a size in the ranges unseeded<0.149-0.29 mm<0.149 mm<0.29-0.42 mm produced increasing amounts of increasingly large crystals. The largest BaHPO4 crystals were obtained at pH 8.4-8.8 with a Ba/P molar ratio of 1.0. In the homogeneous and heterogeneous processes, around 98% of barium was removed at pH 8.4-8.6 and [Ba]/[P]=1.0. The XRD results show that a significant amount of barium phosphate (Ba3(PO4)2) was obtained at pH 11. The compounds BaHPO4 and BaO were present at a pH of below 10.

Feasibility studies on arsenic removal from aqueous solutions by electrodialysis.

The effectiveness of electrodialysis (ED) in removing inorganic arsenic (As) from aqueous solution was investigated. A tailor-made ED stack was used to perform current-voltage and optimization experiments in a recirculating batch mode. Samples were pre-oxidized with NaClO using 1:2 sample to oxidant weight ratio (RS:O) to transform 100% of As(III) to As(V) in 180 seconds. A high feed water conductivity of 1500 µS/cm and a low feed water conductivity of 800µS/cm had limiting currents of 595 mA and 525 mA, respectively. Optimum experimental conditions that provided maximum As separation were applied potential (E) of 12 V, feed flow rate (Q) of 0.033 L/s, feed concentration (C) of 662.0 µg L(-1), and operating time (t) of 45 min, the most significant ones were applied potential, feed concentration and operating time. Model confirmation experiments showed a good agreement with experimental results with only 0.031% error. The total As in the diluate stream was 4.0 µg L(-1), consisting of an average of 3.0 µg L(-1) As(V) and 1.0 µg L(-1) As(III).

Photocatalytic degradation of acetaminophen in modified TiO2 under visible irradiation.

This study investigated the photocatalytic degradation of acetaminophen (ACT) in synthetic titanium dioxide (TiO2) solution under a visible light (λ >440 nm). The TiO2 photocatalyst used in this study was synthesized via sol-gel method and doped with potassium aluminum sulfate (KAl(SO4)2) and sodium aluminate (NaAlO2). The influence of some parameters on the degradation of acetaminophen was examined, such as initial pH, photocatalyst dosage, and initial ACT concentration. The optimal operational conditions were also determined. Results showed that synthetic TiO2 catalysts presented mainly as anatase phase and no rutile phase was observed. The results of photocatalytic degradation showed that LED alone degraded negligible amount of ACT but with the presence of TiO2/KAl(SO4)2, 95% removal of 0.10-mM acetaminophen in 540-min irradiation time was achieved. The synthetic TiO2/KAl(SO4)2 presented better photocatalytic degradation of acetaminophen than commercially available Degussa P-25. The weak crystallinity of synthesized TiO2/NaAlO2 photocatalyst showed low photocatalytic degradation than TiO2/KAl(SO4)2. The optimal operational conditions were obtained in pH 6.9 with a dose of 1.0 g/L TiO2/KAl(SO4)2 at 30 °C. Kinetic study illustrated that photocatalytic degradation of acetaminophen fits well in the pseudo-first order model. Competitive reactions from intermediates affected the degradation rate of ACT, and were more obvious as the initial ACT concentration increased.

Adsorption of Mn2+ from aqueous solution using Fe and Mn oxide-coated sand.

The adsorption of Mn2+ onto immobilized Mn-oxide and Fe-oxide adsorbent such as manganese oxide-coated sandl (MOCS1), manganese oxide-coated sand2 (MOCS2), iron oxide-coated sand2 (IOCS2), and manganese and iron oxide-coated sand (MIOCS) was investigated. The effects of pH (5.5 to 8.0) and temperature (25 to 45 degrees C) on the equilibrium capacity were examined. Equilibrium studies showed that there is a good fit with both Freundlich and Langmuir isotherm, which indicates surface heterogeneity and monolayer adsorption of the adsorbents. Kinetic data showed high correlation with the pseudo second-order model, which signifies a chemisorption-controlled mechanism. The activation energies, activation parameters (deltaG, deltaH, deltaS), and thermodynamic parameters (deltaG0, deltaH0, deltaS0) confirmed that adsorption with MIOCS was endothermic and more spontaneous at higher temperature while an opposite trend was observed for the other adsorbents. Thermodynamic studies showed that adsorption involved formation of activated complex, where MOCS 1 and MIOCS follow a physical-chemical mechanism, while MOCS2 and IOCS2 follows purely chemical mechanism.

Photocatalytic degradation of paraquat using nano-sized Cu-TiO2/SBA-15 under UV and visible light.

Photocatalytic degradation of paraquat using mesoporous-assembled Cu-TiO2/SBA15 under UV and visible light was investigated. The catalyst was synthesized by impregnation of Cu-TiO2 colloids onto SBA-15. The colloids of Cu-TiO2 were prepared via sol-gel method while the mesoporous support was prepared using hydrothermal technique. The catalyst was characterized using X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV diffuse reflectance spectroscopy, Zeta potential and X-ray adsorption spectroscopy. Results from characterizations showed that Cu doped TiO2 had a small crystalline size and was well-dispersed on SBA-15. The inclusion of SBA-15 significantly enhanced the photocatalytic activity of the catalyst. Among the three types of undoped catalyst in this study (P25, TiO2, TiO2/SBA-15), TiO2/SBA-15 yielded the highest degradation of paraquat for all pH under UV illumination. Meanwhile 2 wt.% Cu-TiO2/SBA-15 yielded the highest activity under visible light.