Improved wastewater disinfection by ultrasonic pre-treatment

Abstract

The objective of our work is to evaluate the scientific and economic potential of US application as a pre-treatment step in combination with UV to optimise the disinfection process of wastewaters. Ultrasound application of 20 s at low density of 30 W/l changed the particle size distribution (PSD) of the samples, the mean particle diameter dropped from 70 to 11 microm. Generally it is assumed that bioparticles bigger than 50 microm are difficult to disinfect by UV. We observed that the relevant particle size range >50 microm in samples taken from the primary clarifier was reduced by at least three-quarters by low ultrasound doses. As expected, these changes in PSD notably effect the disinfection efficiency of UV. Whereas UV treatment of secondary clarifier's effluents alone led to a reduction of fecal coliforms by 2.5 log units, pre-treatment by sonication (only 5 s at densities of 50 and 310 W/l) clearly enhanced the disinfection efficiency: reductions of CFU (colony forming unit) concentration now ranged between 3.3 and 3.7 log units. We noticed an influence of the bacteria's morphology on the disinfection efficiency of the combined process (US plus UV). Gram-positive streptococci seem less vulnerable to ultrasound exposure than thinner-walled gram-negative bacteria like the entire group of coliforms. The application of an ultrasound step might be also useful in terms of cost-effectiveness. In our lab-scale tests 30 s of UV treatment alone were required to reduce the number of fecal coliforms by 3.7 log units. When applied in combination, 5 s of ultrasonic followed by only 5 s of UV irradiation had the same result and energy consumption was only 43%.

A radial mode ultrasonic horn for the inactivation of Escherichia coli K12

“…Thus it was proposed that the devices should be compared in a manner consistent with other published studies [19,20,21]. The power input of both devices was measured, where the probe device was connected to a generator that displayed the power input in Watts, and for the radial horn the power input was estimated by a calorific method [22].…”

“…Ultrasonic intensity is defined in units of Watts per square centimetre (W/cm 2 ) of horn working surface [19,20] and power density as Watts per cubic centimetre (W/cm 3 ) of the sonicated volume [20]. In this study, both are presented but only power density can be used for comparative purposes since the output surface area of the radial horn is over 30 times greater than that of the probe.…”

Improved Drinking Water Disinfection with UVC-LEDs for Escherichia Coli and Bacillus Subtilis Utilizing Quartz Tubes as Light Guide

“…Figure 9 gives a summary of the possible interactions with solid particles concerning UVC disinfection according to Blume et al [26]. Thus, the theoretical basic conditions disclose that the highest inactivation rates can be achieved in a medium that has low absorbance and contains only little solid particles.…”

Study of short-wave ultraviolet treatments (UV-C) as a non-thermal preservation process for liquid egg products

“…Several works report the efficiency of UV light into the inactivation of different microorganisms by using either bench top collimated beam apparatus or continuous flow reactors (Sommer, 1998;Lage, 2003), what lead to the approval since November 29 UV disinfection is mainly used in air and water purification, and sewage treatment of food and beverages (Blume and Neis, 2004;Chmiel et al, 2002;Green et al, 1995;Hassen et al, 2000), processing of drinking water (Peldszus et al, 2003;Lehtola et al, 2004), and it is potentially useful for milk and fruit juice production (Koutchma, 2004;Matak, 2005). Chmiel et al (2002) determined the reduction of highly contaminated spent process water of food and beverage industries using the combination of a membrane bioreactor, UV pre-disinfector and UV disinfection apparatus.…”

“…Comparing the thermal treatment, no or hardly any change in taste, odor, pH or conductivity is differentiated in water. And also, UV-C systems may be used as a compatible device with other treatment attempting to obtain a synergistic effect (Blume and Neis, 2004;Koivunen and Heinonen-Tanski, 2005). However UV processing was not completely studied and some effects on food matrix are still not well understood.…”