Sono-degradation of Reactive Blue 19 in aqueous solution and synthetic textile industry wastewater by nanoscale zero-valent aluminum.

Reactive dyes, which are commonly used in the textile industry, are toxic and carcinogenic for the ecosystem and human health. The objective of this study was to investigate the removal of Reactive Blue 19 (RB19) from aqueous solution and synthetic textile industry wastewater using nanoscale zero-valent aluminum (nZVAl), ultrasonic bath (US-40 kHz), and combined US/nZVAl through the consideration of varying experimental parameters such as pH, nZVAl dosage, contact time, and initial RB19 dye concentration. The acidic pH value was an effective parameter to degrade RB19. As the nZVAl dosage and contact time increased, the degradation of RB19 dye from aqueous solution and synthetic textile industry wastewater increased using combined US/nZVAl process. A similar result was obtained for RB19 removal with combined US/nZVAl using 0.10 g dosage at 30 min, whereas it was obtained with nZVAl alone using 0.20 g dosage at 60 min. The sono-degradation process activated the nZVAl surface depending on US cavitation effect and shock waves, and increased RB19 dye uptake capacity with a shorter contact time and lower nZVAl dosage. Increasing the initial dye concentration decreased the removal efficiency for RB19. According to the obtained reusability results, nZVAl particles could be reused for four and two consecutive cycles of combined US/nZVAl and nZVAl alone, respectively.

Metal removal from acid mine lake using ultrasound-assisted modified fly ash at different frequencies.

Acid mine drainage/lakes (AMD/AMLs) have a low pH with high concentrations of metals and sulfate and have been a major environmental problem in the Can Coal Basin, in northwestern Turkey. In this study, metal removal from Hayirtepe AML by using fly ash (FA) and modified fly ash (MFA) was investigated in batch experiments. The effects of various parameters, such as ultrasonic frequency, dose, contact time, pH, and temperature, were examined to determine the optimum conditions for metal removal from AML. This study also focused on the application of ultrasound-assisted modification by using a 20-kHz ultrasonic probe and a 40-kHz ultrasonic bath to increase the FA surface and improve its adsorption capacity for metal removal. FA modification at 20 kHz showed better results than that at 40 kHz because it produced rapid bubble implosion with acoustic cavitation. The FA and MFAs selectivity for metal removal was 98%-99% for Fe, 96%-99% for Al, 94%-97% for Zn, 90%-95% for Co, 88%-94% for Ni, 77%-92% for Cu, and 74%-92% for Mn according to the determined optimum parameters. Scanning electron microscopy coupled with the energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffractometry of the solid residues (SRs) identified gypsum as a new mineral phase from sulfate removal from the AML. Inductively coupled plasma mass spectrometry and SEM/EDX analysis revealed that the metal content of the SRs increased. The adsorption process fitted the pseudo-second order kinetic model. Thermodynamic parameters showed that the process was exothermic and the randomness of the solid/solution interface increased during adsorption. Reuse experiments indicated that the MFAs were reused more effectively for metal removal from AML compared with the FA. This study showed that the use of MFAs with a high adsorption capacity and surface area is economic and efficient for metal removal from AML.

Ultrasound-assisted activation of zero-valent magnesium for nitrate denitrification: identification of reaction by-products and pathways.

Zero-valent magnesium (Mg(0)) was activated by ultrasound (US) in an aim to promote its potential use in water treatment without pH control. In this context, nitrate reduction was studied at batch conditions using various doses of magnesium powder and ultrasound power. While neither ultrasound nor zero-valent magnesium alone was effective for reducing nitrate in water, their combination removed up to 90% of 50 mg/L NO3-N within 60 min. The rate of nitrate reduction by US/Mg(0) enhanced with increasing ultrasonic power and magnesium dose. Nitrogen gas (N2) and nitrite (NO2(-)) were detected as the major reduction by-products, while magnesium hydroxide Mg(OH)2 and hydroxide ions (OH(-)) were identified as the main oxidation products. The results from SEM-EDS measurements revealed that the surface oxide level decreased significantly when the samples of Mg(0) particles were exposed to ultrasonic treatment. The surface passivation of magnesium particles was successfully minimized by mechanical forces of ultrasound, which in turn paved the way to sustain the catalyst activity toward nitrate reduction.

Effect of ultrasonic pretreatment on chlorine dioxide disinfection efficiency.

Ultrasound (US) and chlorine dioxide (ClO(2)) were combined sequentially in an aim to improve wastewater disinfection. Results demonstrated that the combined effect of US and ClO(2) on Escherichia coli (E. coli) and total coliform (TC) inactivation in raw wastewater was synergistic involving high removal of bacteria from the solution. A sequential combination of US (150 or 300 W/L) and ClO(2) (2 mg/L) provided about 3.2-3.5 log reduction in the number E. coli and TC in raw wastewater, while the sum of log reductions by the individual treatments were 1.4-1.9. However, the measured inactivation rate with the combination of ultrasound and ClO(2) in synthetic wastewater or secondary effluent was the same as the sum of the log inactivations with individual treatments. The enhancement attained by combined US and ClO(2) disinfection methods was attributed to the presence of high concentration of particles in raw wastewater and their break up under shock sound waves.

Impacts of water organic load on chlorine dioxide disinfection efficacy.

This study has examined the bactericidal effect of chlorine dioxide in untreated artificial and domestic wastewaters and secondary effluent of various organic loads. Results indicated that the inactivation of Escherichia coli in artificial wastewater was similar with that in real municipal wastewater. Among three waters, the bactericidal effect of chlorine dioxide was lowest in secondary effluent. The bacteria log inactivation increased by up to threefold when the COD concentration of raw wastewater was decreased by half. An unfavorable COD effect was also observed for the disinfection of secondary effluent. To explain the COD effect on bacteria inactivation, chlorine dioxide residuals were measured with time through each disinfection process. Results from statistical analyses have revealed that, in comparison to the correlations using CT values, the inactivation data can be better correlated with the ratio of COD to ClO(2) concentrations. The results of this study would be a useful guide for many municipalities and communities in determining chlorine dioxide dosages for water and wastewater disinfection systems.