Evaluation of process parameters of ultrasonic treatment of bacterial suspensions in a pilot scale water disinfection system

Abstract

In this study, several process parameters that may contribute to the efficiency of ultrasound disinfection are examined on a pilot scale water disinfection system that mimics realistic circumstances as encountered in an industrial environment. The main parameters of sonication are: (i) power; (ii) duration of treatment; (iii) volume of the treated sample. The specific energy (E(s)) is an indicator of the intensity of the ultrasound treatment because it incorporates the transferred power, the duration of sonication and the treated volume. In this study, the importance of this parameter for the disinfection efficiency was assessed through changes in volume of treated water, water flow rate and electrical power of the ultrasonic reactor. In addition, the influences of the initial bacterial concentration on the disinfection efficiency were examined. The disinfection efficiency of the ultrasonic technique was scored on a homogenous and on a mixed bacterial culture suspended in water with two different types of ultrasonic reactors (Telsonic and Bandelin). This study demonstrates that specific energy, treatment time of water with ultrasound and number of passages through the ultrasonic reactor are crucial influential parameters of ultrasonic disinfection of contaminated water in a pilot scale water disinfection system. The promising results obtained in this study on a pilot scale water disinfection system indicate the possible application of ultrasound technology to reduce bacterial contamination in recirculating process water to an acceptable low level. However, the energy demand of the ultrasound equipment is rather high and therefore it may be advantageous to apply ultrasound in combination with another treatment.

Ultrasound enhancement of near-neutral photo-Fenton for effective E. coli inactivation in wastewater

“…6c. Increasing US power results in higher particle breakage [64] and more efficient removal, in the high frequencies [59,60]. In our system, decreasing the power from 20 to 10 W, and consequently, the power-to-volume ratio, decreased the efficiency, although in a non-linear, cost-effective manner; 50% reduction did not result to 50% decrease of the inactivation, but to 33%, although the main target is total inactivation.…”

“…Finally, although literature suggests that modifying the sonication volume has not a significant effect on the efficiency of the sonication process (if the power-to volume ratio is respected) for bacterial inactivation [59,60], in Fig. 4c we observe 2 and 3 log 10 U of difference, respectively.…”

“…The three recirculation rates correspond to 1.87, 3.44 and 4.39 L/h. Hulsmans et al [59] suggest that increasing the flow rate in a US system resulted in higher disinfection rate. However, in our system, changing the recirculation rate causes the faster sequential change from US to photo-Fenton, and therefore, shorter cycles of treatment.…”

“…However, the current set-up employs almost 40 kW/m 3 electrical energy per hour, and compared with other low-frequency sonication applications (e.g. [59] or [65]), the electrical energy required is much higher, in a 4-h scale. The sum drops if a higher amount is treated, but is still economically challenging.…”

Evaluation of Power Ultrasonic Effects on Algae Cells at a Small Pilot Scale

“…The effects of ultrasound are based on the formation and collapse of acoustic cavitation bubbles [7][8][9]. The overall effects of acoustic cavitation on algae cells can be summarized as follows [6,10,11]: (1) High power low frequency ultrasound results in a reduction of algal cell numbers through the mechanical rupture of algal cell walls through cavitation bubble collapse; (2) Low power ultrasound can induce declumping of flocs of algae into single cells, thus making them more susceptible to chemical or sonochemical treatment; (3) Higher frequency ultrasound, although producing less powerful mechanical effects of cavitation collapse, generates more free radicals from the decomposition of water than low frequency ultrasound. Free radicals reduce cell numbers via chemical attack on the cell walls.…”