Improving chlorine disinfection of wastewater by ultrasound application

Abstract

The presence of soluble organic material as well as high concentrations of suspended matter in waters and wastewaters affect the efficiency when chlorine is used as disinfection agent. The objective of our work is to explore to which extend ultrasonic treatment can facilitate wastewater disinfection with chlorine in order to bring down doses of ecologically questionable chlorine and to shorten contact times. Sewage treatment plant (STP) effluents with different concentrations of suspended solids are exposed to sonication in combination with chlorine dosage. We observed that enhancement of chlorine efficiency is better for samples with higher concentrations of suspended matter. For samples with a TSS concentration of 50 mg/L chlorination efficiency (2 mg/L) can be doubled from 0.7 to 1.4 log when treated simultaneously with 20 kHz ultrasound for 5 minutes, i.e. levels of indicator organisms can be brought down to numbers that conventionally require far higher doses of chemical disinfectants. As subsequent sonication/chlorination does not have the same significant effect as simultaneous application of these two means, ultrasound does not just have a declumping effect; it seems that ultrasound application provokes a better chlorine dispersion in the aqueous media which improves the fast chemical and bactericidal reaction.

Acoustic Hypochlorite Activation in Simulated Curved Canals

“…It has thus been suggested to use acoustic irrigant activation to improve cleanliness and disinfection of root canal systems prior to root filling (2,3). The synergistic effects of ultrasonic energy and sodium hypochlorite in aqueous solution appear to be especially useful in that context (2,4,5). Currently, passive ultrasonic irrigation (PUI) is probably the most established method to activate a sodium hypochlorite irrigant after root canal instrumentation (6)(7)(8).…”

Sonochemical disinfection of municipal wastewater

“…Nevertheless, there is a drive towards the use of ultrasound in decontamination as an adjunct to other techniques because some microorganisms are becoming resistant to existing disinfection techniques involving biocides, ultraviolet light, and heat treatment. In this view, recent studies have dealt with the use of low frequency ultrasound (in the range 20-40 kHz) alongside ozone [6], ultraviolet irradiation [7], hydrodynamic cavitation [8], electrolysis [9], chlorination [10][11][12], and heterogeneous catalysts (i.e. activated carbon, ceramic, zinc, and titanium dioxide) [13,14], and reported that enhanced disinfection efficiencies could be achieved with the combined treatments.…”

Application of cavitational reactors for water disinfection: Current status and path forward

“…Similarly, when the ultrasonic flow cell is used along with hydrodynamic cavitation and hydrogen peroxide, the rate of disinfection is further enhanced as the intensity of cavitation in the hydrodynamic cavitation set-up is increased by the presence of the ultrasonic flow cell which in turn accelerates the decomposition of the hydrogen peroxide or increases the probability of cell wall rupture, coupled with enhanced H 2 O 2 penetration leading to an increase in the death rate of the microorganisms present in the bore well water. Blume and Neis (2005) investigated the role of ultrasound in intensification of the disinfection process using chlorine. The presence of soluble organic material as well as high concentrations of suspended matter in water and wastewater affects the efficiency when chlorine is used as disinfection agent.…”

“…Use of ultrasound can facilitate wastewater disinfection by way of increasing the mass transfer rates and it can bring down doses of ecologically questionable chlorine and also shorten contact times. In the work of Blume and Neis (2005), sewage treatment plant (STP) effluents with different concentrations of suspended solids were exposed to sonication in combination with chlorine dosage. Blume and Neis (2005) reported that enhancement of chlorine efficiency is better for samples with higher concentrations of suspended matter.…”

“…In the work of Blume and Neis (2005), sewage treatment plant (STP) effluents with different concentrations of suspended solids were exposed to sonication in combination with chlorine dosage. Blume and Neis (2005) reported that enhancement of chlorine efficiency is better for samples with higher concentrations of suspended matter. For samples with a TSS concentration of 50 mg/l chlorination efficiency (2 mg/l) can be doubled from 0.7 to 1.4 log when treated simultaneously with 20 kHz ultrasound for 5 min, i.e.…”