Contaminated soil/groundwater remediation using Permeable Reactive Barrier (PRB) techniques

Soil/water demonstration models made from clear perspex are being developed by FOES USQ to observe the performance of crushed charcoal /biochar PRB for removing organic contaminants. Further development of the project will investigate the potential for biochar PRB enhanced with enzymatic bioremediation technology, specifically developed to treat pesticide and nitrate residues in soils and groundwate

Mesoporous activated carbon-zeolite composite prepared from waste macadamia nut shell and synthetic faujasite

Novel activated carbon-zeolite composite adsorbent was prepared from macadamia shell bio-waste and synthetic zeolite X using hydrothermal treatment. Characterization studies revealed mainly mesoporous structure with 418 m2 g-1 BET surface area with faujasite clusters on the carbon carrier. Sorption capacity for methylene blue model pollutant increased from 85 to 97 mg g-1 with the temperature increase from 25 to 45 oC, and improved with increasing pH. Nonlinear regression analyses found accurate fit to the pseudo-first-order kinetics model and intra-particle diffusion rate controlling mechanism. Excellent fits to the Jovanovic isotherm model indicated monolayer coverage on chiefly homotattic surfaces with variable potential. The thermodynamic analysis confirmed spontaneous and endothermic physisorption process. The spent adsorbent was regenerated with 20% capacity loss over five reuse cycles.Although the adsorbent was developed for ammonia, heavy metal and organic matter removal from water sources, the results also indicate good performance in cationic dye removal from wastewaters

Removal of natural organic matter and ammonia from dam water by enhanced coagulation combined with adsorption on powdered composite nano-adsorbent

Enhanced coagulation and adsorption were investigated in separate and combined processes to alleviate problems created by high levels of NOM (15 mg L-1) and ammonia (2.5 mg L-1 NH4-N) in dam water. Raw water acidification to pH 6.2 with optimised enhanced coagulation in jar tests achieved effective (68%) DOC reduction and satisfactory residual turbidity, aluminium, and colour, however removed only 5% ammonia. Adsorption on the nano-adsorbent (termed ACZ) led to 45% DOC reduction and excellent 58% ammonia removal in 30 minutes. Concurrent enhanced coagulation and complementary adsorption using only 80 mg L-1 alum and 150 mg L-1 ACZ doses showed high performance with 76% ammonia, 90% DOC, and 95% trihalomethanes formation potential (THMFP) reduction in 20 minutes time. Concurrent treatment can be simply implemented utilising readily available rapid mixers and flocculators, and operated on demand. Pre-adsorption and consecutive enhanced coagulation using the same alum and ACZ doses resulted in slightly better DOC but reduced (61%) ammonia removal. The results showed that concurrent treatment could safely resolve a challenging operational problem. ACZ combines the distinct advantages of zeolite and activated carbon in a single product, and may find additional uses in removing taste and odour, heavy metals, and synthetic organic matter from ground and surface waters

Use of macadamia nut shell residues as magnetic nanosorbents

Nanosorbents have been increasingly used for targeted contaminant removal; however, handling and separation of spent sorbents from treated water remains a challenge. To address these drawbacks, a hybrid magnetic nanosorbent was prepared from waste macadamia nut shell and magnetite nanoparticles. The novel nanosorbent had primarily meso- and macroporous structure with 70 m2 g−1 specific surface area. Batch sorption tests using methylene blue model pollutant found sorption capacities increasing from 33 to 42 mg g−1 with temperature in the 25–45 °C range. Nonlinear regression analyses found that process kinetics was accurately described by a fractal-like pseudo first order model. The isotherms showed excellent fits to the Langmuir model and implied monolayer adsorption mechanism. The thermodynamic parameters confirmed that the process was spontaneous, endothermic, and involved physisorption. The point of zero charge was 7.4, which is advantageous in the removal of anionic aquatic pollutants. The ferrimagnetic sorbent had 48 emu g−1 saturation and 0.65 emu g−1 remanence that allowed easy handling and rapid separation by magnetic field. Spent sorbents were effectively regenerated by acidic wash for subsequent reuse over four cycles. The intrinsic characteristics of the magnetite/carbon nanosorbent befit tailored water and wastewater treatment applications

Development of visible light sensitive titania photocatalysts by combined nitrogen and silver doping

In this study we present the effects of non-metal (nitrogen) and metal/non-metal (silver/nitrogen) dopants on titanium dioxide (TiO2) in synthesising visible-light reactive photocatalysts. Nanopowders of TiO2-N and TiO2-N–Ag were synthesised using a simple procedure at room temperature. For nitrogen doping, a dispersion of Degussa P-25 was treated with ammonium hydroxide. The obtained modified catalyst was further treated with silver nitrate powder to facilitate silver-nitrogen co-doping. The produced catalysts were characterised using X-ray diffraction, X-ray photoelectron spectroscopy, and specific surface area measurements. Scanning electron microscopy/energy dispersive X-ray and transmission electron microscopy were adapted to detect changes in the morphology and in the chemical composition of synthesised catalysts. The results show that both the morphology and appearance of catalysts were modified to yield nanopowders of yellowish color and relatively high specific surface area. Methylene blue (MB) dye was used as a model aquatic contaminant in 23 mg/L concentration to study the performance of these novel photocatalysts in an aerobic mixed batch reactor system under white light irradiation. Both nitrogen and nitrogen-silver co-doping lead to visible light sensitivity and the new catalysts showed remarkable activities in the decolorisation of MB

Adsorption and photocatalytic degradation of methylene blue over hydrogen-titanate nanofibres produced by a peroxide method

In this study, Degussa P25 TiO2 was partially dissolved in a mixture of hydrogen peroxide and sodium hydroxide at high pH. The fabrication of nanofibres proceeded by the hydrothermal treatment of the solution at 80°C. This was followed by acid wash in HCl at pH 2 for 60min, which resulted in the formation of hydrogen-titanate nanofibres. The nanofibres were annealed at 550°C for 6h to produce crystalline anatase nanofibres. The nanofibres were characterised for physico-chemical modifications and tested for the adsorption and photocatalytic degradation of methylene blue as a model water pollutant. An average specific surface area of 31.54m2/g, average pore volume of 0.10cm3/g and average pore size of 50Å were recorded. The nanofibres were effective adsorbents of the model pollutant and adsorbents and good photocatalysts under simulated solar light illumination. No reduction in photocatalytic activity was observed over three complete treatment cycles, and the effective separation of nanofibres was achieved by gravity settling resulting in low residual solution turbidity

Co-doped photocatalyst nanomaterials for effective utilisation of solar radiation

Photocatalysis over metal oxide semiconductors is an effective way to reduce or eliminate the impact of aquatic and airborne pollutants. Titania (TiO2) photocatalyst is able to degrade many toxic and recalcitrant compounds under UV light illumination. Since UV light accounts for only about 5% of the solar energy, the more significant visible light fraction (45%) remains unused. Here we report the synthesis of non-metal (nitrogen) and metal/non-metal (silver/nitrogen) co-doped photocatalysts that are reactive both in the UV and visible range. Nitrogen doped and nitrogen/silver co-doped TiO2 nanoparticles were fabricated using a sol-gel production method at a relatively low temperature. The obtained gels were neutralised, washed with pure water, dried in oven, and calcined at 400 °C for 4 hours. Morphology changes were monitored using a scanning electron microscope. The photocatalysts were characterised by X-ray diffraction, X-ray photoelectron spectroscopy, and BET specific surface area. The results showed that spherical particles of anatase structure were produced after annealing at 400°C. The photocatalytic activity of these novel catalysts was investigated using a batch reactor system exposed to artificial solar irradiation. Both nitrogen and silver/nitrogen co-doped materials were effective in the photocatalytic degradation of hexamethyl pararosaniline chloride

Preparation and characterisation of mesoporous photoactive Na-titanate microspheres

Mesoporous Na-titanate microspheres were fabricated by a simple low temperature hydrothermal synthesis. Microspheres were obtained after treating TiO2 (Degussa P-25) with a mixture of sodium hydroxide (NaOH) and hydrogen peroxide (H2O2) at 25 ◦C and 80 ◦C. The as-prepared powders were characterised by X-ray diffraction, N2 adsorption–desorption measurements and scanning electron microscope/energy dispersive X-ray spectroscopy. The as-prepared microspheres were calcined at 550 ◦C to investigate the effect of calcination on morphology and characteristics. Microspheres were tested for the adsorption and photodecomposition of methylene blue (MB) under ultraviolet light. The results revealed that microspheres with average diameter of 700 nm were formed by self-assembly of tiny TiO2 nanoparticles during the reaction at 25 ◦C, whereas spherical aggregation of nanofibres was detected in powders produced at 80 ◦C. Calcination of samples had low impact on morphology, adsorption and photocatalytic degradation of MB. These novel materials are effective adsorbents of MB, and also capable of its photodecolorisation