Enhanced biobased carbon materials made from softwood bark via a steam explosion preprocessing step for reactive orange 16 dye adsorption

The growing textile industry produces large volumes of hazardous wastewater containing dyes, which stresses the need for cheap, efficient adsorbing technologies. This study investigates a novel preprocessing method for producing activated carbons from abundantly available softwood bark. The preprocessing involved a continuous steam explosion preconditioning step, chemical activation with ZnCl2, pyrolysis at 600 and 800 °C, and washing. The activated carbons were subsequently characterized by SEM, XPS, Raman and FTIR prior to evaluation for their effectiveness in adsorbing reactive orange 16 and two synthetic dyehouse effluents. Results showed that the steam-exploded carbon, pyrolyzed at 600 °C, obtained the highest BET specific surface area (1308 m2/g), the best Langmuir maximum adsorption of reactive orange 16 (218 mg g-1) and synthetic dyehouse effluents (>70 % removal) of the tested carbons. Finally, steam explosion preconditioning could open up new and potentially more sustainable process routes for producing functionalized active carbons.

Preparation and characterisation of alkali-activated blast furnace slag and Na-jarosite catalysts for catalytic wet peroxide oxidation of bisphenol A

In this study, cost-effective alkali-activated materials made from industrial side streams (blast furnace slag and Na-jarosite) were developed for catalytic applications. The catalytic activity of the prepared materials was examined in catalytic wet peroxide oxidation reactions of a bisphenol A in an aqueous solution. All materials prepared revealed porous structure and characterisation expressed the incorporation of iron to the material via ion exchange in the preparation step. Furthermore, the materials prepared exhibited high specific surface areas (over 200 m2/g) and were mainly mesoporous. Moderate bisphenol A removal percentages (35%-37%) were achieved with the prepared materials during 3 h of oxidation at pH 7-8 and 50°C. Moreover, the activity of catalysts remained after four consecutive cycles (between the cycles the catalysts were regenerated) and the specific surface areas decreased only slightly and no changes in the phase structures were observed. Thus, the prepared blast furnace slag and Na-jarosite-based catalysts exhibited high mechanical stability and showed good potential in the removal of bisphenol A from wastewater through catalytic wet peroxide oxidation.

Combination of peracetic acid dosing with diffused aeration in municipal wastewater treatment

Wastewater aeration is an important unit operation that provides dissolved oxygen for microorganisms in wastewater treatment. In this study, the impact of peracetic acid (PAA) dosing on wastewater aeration was assessed in terms of oxygen transfer, visual observation of bubble size changes, and evolution of dissolved oxygen from PAA (and H2O2) decomposition. Oxygen transfer coefficients improved with PAA concentrations of up to 7 mg/L, which was probably due to the smaller bubbles being formed from the aeration diffuser and evolution of small bubbles from PAA (and H2O2) decomposition. At a PAA concentration higher than 7 mg/L, the accumulation of acetate molecules to the gas-liquid interface of bubbles likely began to counteract the positive impact of bubble size decrease by increasing the mass transfer resistance of oxygen from bubbles to water. Finally, a continuous bench-scale primary effluent aeration experiment demonstrated that at a continuous PAA dosing of 1 mg/L, the air input by a compressor could be decreased by 54%, while keeping the oxygen level constant at approximately 1.5 mg/L. PAA dosing could be combined, for example, with aerated grit removal to enhance the primary effluent aeration together with additional benefits of partial disinfection and odor formation prevention.

Aerosol processing technique for the synthesis of mixed-phase copper on carbon catalyst: insights into CO2adsorption and photocatalytic activity

In this study, spray pyrolysis; an aerosol processing technique was utilized to produce a mixed-phase copper on carbon (Cu/Cu_xO@C) catalyst. The catalyst production was performed via chemical reduction of copper nitrate by a reducing sugar, i.e. glucose, using aqueous solution. The physical and chemical properties of the produced particles was assessed using various characterization techniques. The synthesis temperature had pronounced effect on the final particles. Since CO₂adsorption onto the catalyst is an important step in catalytic CO₂reduction processes, it was studied using thermogravimetric and temperature programmed desorption techniques. Additionally, photocatalytic activity of the particles was evaluated by gas-phase oxidation of acetylene gas which revealed excellent activity under both UV and visible light irradiation indicating the possible use of wider range of the solar spectrum.

Photocatalysis and catalytic wet air oxidation: Degradation and toxicity of bisphenol A containing wastewaters

Bisphenol A (BPA) is a commonly used chemical in consumer products. It is an endocrine disrupter that has potentially significant negative effects on human health. The use and chemical stability of BPA have resulted in the appearance of the chemical in wastewaters. Since the current wastewater treatment technologies are not effective enough to remove BPA, new methods to degrade BPA are required. In this paper, we report the efforts made towards developing a bi-functional catalyst for consecutive catalytic wet air oxidation-photocatalytic water treatment. It was found that 2.5% Pt/Ti_0.8Ce_0.2O₂ is a potential bi-functional catalyst for the consecutive treatment. Concentration and toxicity of BPA were successfully reduced by catalytic wet air oxidation. Although BPA was further reduced by photocatalysis, it was not reflected in further decrease of cell toxicity. Thus wet-air oxidation combined with photocatalysis is a promising approach for the reduction of BPA.