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This study investigates the effect of ultrasounds in conversion of waste frying oil into biodiesel. Many researchers have studied the use of ultrasounds in the biodiesel production from different feedstock; however, there are few studies focused on the biodiesel production from waste frying oil. In this research, ultrasound-assisted transesterification was carried out to convert the waste frying oil into biodiesel directly. The effect of different process parameters such as reaction time (30-90 min), amount of catalyst (0.5 -1% wt. NaOH) and temperature (20-40 ºC) were also analyzed to obtain the higher conversion. A methanol to oil molar ratio of 6:1, 0.5% amount of catalyst and 30 ºC was enough to complete the process in 60 min. The obtained results in this study confirm that that ultrasound-assisted transesterification was a fast and efficient method for biodiesel production from waste frying oil even if reaction temperature is low.

Biomass pretreatment has an important role in the production of cellulosic bioethanol. In this study, the effectiveness of microwave assisted alkaline pretreatment of algae waste was analysed. After pretreatment, the product was hydrolysed using sulphuric acid. The effects of microwave power, irradiating time, solid–liquid ratio and NaOH concentration were examined. Under the best conditions, the fermentable sugars were converted to cellulosic bioethanol using Saccharomyces Cerevisiae with a bioethanol yield of 1.93 ± 0.01 g/g and a fermentation efficiency of 40.4%. The reducing sugars concentration was 30% higher than that obtained from conventional hydrolysis without pretreatment. The obtained results suggest that microwave assisted alkaline pretreatment is effective in improving the production of cellulosic bioethanol of algae waste compared to that without microwave effect. Considering energy consumption, low microwave power and short microwave irradiation time are favourable for this pretreatment.