Improvement of biological activity by low energy ultrasound assisted bioreactors.

Bioreactors are broadly applied in biotechnology and wastewater treatments. The so-called advanced bioreactor systems should be optimised in a more compact, more efficient and more effective form. One method of optimisation is the improvement of the solid-liquid interface of the sludge flocs and the mass transfer rate of gas and nutrients in the liquid. This could be obtained by the intake of ultrasound in the bioreactor at a frequency of 25 kHz and a power input of 0.3 Wl-1. An increase in the biological activity of the process investigated with alternating ultrasound as well as a decrease without ultrasound were measured.