Impact of Ultrasound Treatment on the Biofilm Structure and Performance of a Membrane Biofilm Reactor for Tertiary Hydrogen Driven Denitrification of Wastewater

This study aimed to investigate the impact of the ultrasound treatment on autotrophic denitrification of low organic carbon content wastewater with a biofilm growing on hydrogen diffusing membrane. Ultrasound treatment significantly affected thickness of the biofilm. When no mixing or ultrasound treatment was applied to the system, biofilm thickness averaged 813+/− 254 μm due to accumulation of solids on the biofilm surface. Ultrasound treatment resulted in the reduction of biofilm thickness to 335+/−104 μm. In contrast, the biofilm density, expressed as total solids per liter of biofilm volume exhibited an increasing trend when ultrasound treatment was introduced. No significant changes in carbohydrates and EPS content within biofilm was observed, however overall cell viability dropped significantly from 31+/−1% to only 15+/−1% with ultrasound treatment. Ultrasound treatment proved to be successful in improving denitrification efficiency. Rates for operation without any shear force were on the average 60% lower than those obtained with ultrasound treatment.