Improvement of active biological sludge quality for anaerobic digestion phase in the wastewater treatment plant by ultrasonic pretreatment

This paper emphasized the influence of the main operating parameters of ultrasonic biological sludge
pretreatment onto disintegration (DD-COD) and solubilizing degree of organic matter content. The
optimal ultrasonic reaction time, energy and amplitude of ultrasonic waves and pH of the sludge
(non-modified pH and pH 8.5) were established taking into account their influence on the solubility
level of COD, an evolution of particles size. Correlations between disintegration degree and dimensional
analysis were performed. Ultrasonic reactor operating to 20 kHz ultrasound frequency was a close
system having cooling water jacket. Experimental tests in different operating conditions (reaction
time 5 – 60 min., ultrasound energy 2000 – 9000 kJ, pH = 6.5/8.5) demonstrated that alkaline ultrasonic
treatment (pH = 8.5, initial homogeneous COD = 72600 mg O2/L) at medium - high ultrasound
energy levels led to highest disintegration degree – DD 12% (comparing with pH = 6.5 – DD ~ 5%).
Still, the process should be managed carefully because of possibility to have important variation of DD
during the ultrasonic treatment