Adsorbent made by carbonization of biomass under oxygen-limited conditions has become a promising material for wastewater treatment owing to its cost-effective, simple, and eco-friendly processing method. Ultrasound is considered a green technique to modify carbon materials because it uses water as the solvent. In this study, a comparison of Reactive Black 5 (RB5) adsorption capacity between biochar (BC) generated by pyrolysis of water bamboo (Zizania latifolia) husks at 600 °C and ultrasound-assisted biochar (UBC) produced by pyrolysis at 600 °C assisted by ultrasonic irradiation was performed. UBC showed a greater reaction rate and reached about 80% removal efficiency after 4 h, while it took 24 h for BC to reach that level. Scanning electron microscope (SEM) images indicated that the UBC morphology surface was more porous, with the structure of the combination of denser mesopores enhancing physiochemical properties of UBC. By Brunauer, Emmett, and Teller (BET), the specific surface areas of adsorbent materials were analyzed, and the surface areas of BC and UBC were 56.296 m²/g and 141.213 m²/g, respectively. Moreover, the pore volume of UBC was 0.039 cm³/g, which was higher than that of BC at 0.013 cm³/g. The adsorption isotherms and kinetics revealed the better fits of reactions to Langmuir isotherm and pseudo-second-order kinetic model, indicating the inclination towards monolayer adsorption and chemisorption of RB5 on water bamboo husk-based UBC.

The new technology development for municipal solid waste incineration fly ash treatment and reuse is urgent due to landfill shortage and environmental effect of leached hazardous substances. Chlorine (Cl) is worth considering due to its high levels in fly ash. In this study, a treatment process of ultrasound combined with organic acid was used to eliminate Cl from fly ash to enhance its properties for reuse. Taguchi methodology was implemented to design the experiments by controlling four impact factors and the contribution of each factor was evaluated by the ANOVA analysis of variance. Following two treatment steps within 5 min with a solid/liquid ratio of 1:10 at 165 kHz, 98.8% of Cl was eliminated. Solid/liquid ratio was the most prominent factor that contributed to the Cl removal with more than 90%, according to the ANOVA analysis of variance. Tert-butyl alcohol (tBuOH), an ^•OH radical scavenger, was utilized to examine different effects of ultrasonic cavitation on Cl removal efficiency. A 20 kHz ultrasound was used to explore the influence of multi-frequency ultrasound with different mechanical and sonochemical effects on the fly ash dechlorination. This ultrasonic-assisted organic acid treatment was found to be a time and cost-effective pathway for fly ash Cl removal.

In this study, adsorbent materials from natural feldspar were fabricated for application in +NH4 removal. Raw, pretreated by HCl 3M, and modified feldspar by NaOH and aluminum (Al powder, Al(OH)3, and AlCl3.6H2O) were used. Feldspar was modified under different experimental conditions including without calcination and calcinated at 500ºC and 700ºC. The influence of various operating parameters consisting of material size, adsorption time, +NH4 initial concentration and material dosage were investigated. Adsorbent materials < 0.1 mm in size showed the highest adsorption efficiency. Subsequently materials with size of < 0.1 mm were used for the following studies to investigate the affect of other parameters on +NH4 adsorption process. The highest removal efficiency (31.10%) and removal capacity (21.80 mg/g) were obtained by modified feldspar by NaOH and AlCl3.6H2O with calcination at 700ºC at +NH4 initial concentration of 5 ppm. Results from the scanning electron microscope (SEM) showed the differences on surfaces of adsorption materials. Modified feldspar had a clean surface and more tiny pores compared to those of raw and pretreated feldspar resulting in an increased surface area. Consequently +NH4 adsorbent efficiency and removal capacity were increased. By BET (Brunauer, Emmett and Teller) the specific surface areas of adsorbent materials were analyzed and the surface areas of raw, pretreated and modified feldspar were 0.484 m2/g, 0.988 m2/g and 2.024 m2/g, respectively. +NH4 adsorbent mechanisms of all raw, pretreated, and modified feldspar materials were found to follow the Langmuir adsorption isotherm with the correlation coefficient R2 = 0.989 which described the monolayer type of the adsorption.