Effect of ultrasonic and ozonation pretreatment on methane production potential of raw molasses wastewater

• Ultrasonic pretreatment enhances the methane production during anaerobic digestion.
• Ozonation decolorizes the molasses wastewater after 20 min of treatment.
• Ozonation pretreatment adversely affects methane production.
• Sonication followed by anaerobic digestion, increases the COD removal by 74%.

Ozonation and sonication were applied to baker's yeast wastewater with high molasses content, under various operation conditions, in order to study the effect of them on COD (Chemical Oxygen Demand) removal and on methane enhancement. The ozonation treatment resulted in a significant reduction of the COD content; the COD removal was up to 38% after a reaction time of 5 h. Moreover, a remarkable decolorization was observed, at 20 min of ozonation. The effect of sonication on the physical characteristics of the wastewater was negligible and resulted in an increase of the COD value. The anaerobic experiment was carried out in 18 batch reactors at 37 °C. The most efficient pretreatment method was sonication in a continuous mode, since it presented the highest methane production equal to 441.6 LCH4/kgVS. It was found that this method was also effective on COD removal, when sonication is followed by anaerobic digestion. The ozonation as a pretreatment method affected negatively biomethanation, as it resulted in significant reduction of methane production compared to the samples without pretreatment. The findings of the present study proved that the sonication of molasses wastewater followed by anaerobic digestion is an efficient solution, capable of treating this type of wastewater.