Impact of ultrasound application on oxidative desulphurization of diesel fuel and on treatment of resulting wastewater.

The ultrasound-assisted oxidative desulphurization (UAOD) process of diesel fuel has gained growing attention due to the strict regulation of sulphur content in the fuel. The goal of the present study was to investigate the impact of ultrasound (US) application for oxidative desulphurization (ODS) of hydrocarbon fuels and for the subsequent treatment of produced wastewater, since sonochemical processes are a new and interesting area of research with wide application in the field of environmental engineering. For that purpose, the model diesel fuel with initial sulphur concentration of 1220-3976 mg l(-1) was used for ODS and UAOD tests, and hydrogen peroxide/acetic acid was applied as the oxidant/catalyst system, respectively. The comparison of the process performance revealed that US significantly reduced the oxidation reaction time. The conversions of dibenzothiophene during 30 min of ODS and UAOD tests were 36% and 87%, respectively. Moreover, subsequent extraction with acetonitrile resulted in the final sulphur removal of 96.5%. The obtained results clearly indicated that UAOD process is beneficial for effective sulphur removal from the model diesel fuel. Furthermore, subsequent experiments included the application of the sono-Fenton process for resulting wastewater treatment. Monitoring of dibenzothiophene sulphone concentration and total organic carbon during the sono-Fenton treatment of wastewater revealed the decrease of 70-75% and 53-66%, respectively. The hypothesis on the possibility of degradation of dibenzothiophene sulphone by •OH radicals was confirmed by observed generation of benzoic acid and aliphatic carboxylic acids during experiments. Accordingly, the wastewater was purified to a satisfactory degree, enabling the reuse of treated water.

Ultrasound assisted biodesulfurization of liquid fuel using free and immobilized cells of Rhodococcus rhodochrous MTCC 3552: A mechanistic investigation.

This paper attempts to gain mechanistic insight into enhancement effect of sonication on biodesulfurization. The approach has been to fit Haldane kinetics model to dibenzothiophene (DBT) metabolism and analyze trends in model parameters concurrently with simulations of cavitation bubble dynamics. Mechanistic synergy between sonication and biodesulfurization is revealed to be of both physical and chemical nature. Generation of micro-turbulence in medium by sonication leads to fine emulsification and enhancement of DBT transport across organic/aqueous interphase. Microturbulence also enhances transport of substrate and product across cell wall that increases reaction velocity (Vmax). Michaelis constant (Km) and inhibition constant (KI), being intrinsic parameters, remain unaffected by sonication. Radicals produced by transient cavitation oxidize DBT to DBT-sulfoxide and DBT-sulfone (intermediates of metabolism), which contributes enhancement of biodesulfurization. However, high shear generated by ultrasound and cavitation has adverse effect on action of surfactant ß-cyclodextrin for enhancement of interphase transport of DBT.