Grantee Research Project Results

Final Report: Acoustic-Enhanced Ozone Drinking Water Disinfection

EPA Contract Number: 68D99059
Title: Acoustic-Enhanced Ozone Drinking Water Disinfection
Investigators: Mcgrath, Steven F.
Small Business: Montec Associates Inc.
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 1999 through March 1, 2000
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1999) RFA Text |  Recipients Lists
Research Category: SBIR - Water and Wastewater , Watersheds , Small Business Innovation Research (SBIR)

Description:

ResonantSonics? , a novel technology that utilizes a mechanically driven resonator to radiate fluids using high-intensity, low-frequency acoustic energy, was evaluated for its ability to enhance ozone disinfection of drinking water. The device consists of an oscillator coupled to an elastic rod or bar. The oscillator drives the elastic member at a resonant bending mode. The vibrations are then transmitted to the fluid where they can be used to promote mixing and mass transport.

In this study, the acoustic radiation was evaluated for its ability to enhance ozone disinfection of drinking water, specifically in the treatment of resistant spore and cyst forming protozoan forms such as Cryptosporidium and Giardia. A surrogate microbe had to be used in place of the protozoans. B. subtilis var niger ATCC 9372 endospores were chosen as a reasonable approximation to the protozoan cysts.

There are two ways in which the acoustic energy could enhance the disinfecting power of ozone:

1. The acoustic waves themselves could damage or otherwise compromise the spores to make them more susceptible to ozone;
2. The mixing and mass transfer effects could give better contact between bubbles and spores, as well as enhance the transfer of ozone from the gas into the liquid.

Experiments were conducted to evaluate the effect of acoustic energy alone, ozone alone, and ozone in combination with acoustic energy on the ability to deactivate the spores for short periods of radiation. (5 minutes).
A 5 log colony forming unit (CFU/mL) was used as a starting population for each test. The contactor was 35 liters in capacity. The tests were conducted in sodium bicarbonate buffered deionized water. Samples were taken as a function of time over the challenge period and quenched with sodium thiosulfate immediately. They were serially diluted and analyzed by standard plate counting techniques, with checking by fluorescence microscopy. The reduction in population was expressed in terms of exposure (ozone concentration times length of exposure).

Summary/Accomplishments (Outputs/Outcomes):

In tests of one hour duration, the acoustic energy, at both high and low intensity, showed no effect on the viability of spores. The ozone challenges, with and without sonics, were conducted at 0.5, 1,5, and 2 mg/L target dissolved ozone concentrations. Data of each concentration could be plotted on an exposure (concentration x time) curve for a given sonic intensity and they all converged. The data are presented in the table below in terms of a 3 log exposure value, i.e. the exposure necessary to reduce the number of viable endospores to a log 2 level; and in terms of the residual population after 5 minutes. From the initial rise in ozone concentration during an

acoustic level dB re 1µPa	3 log CT	log population @ 5 minutes	relative mass transfer
0 (ozone only)	4.46	2	1
205	4.061	1	1.05
215	4.02	<1	1.46

experiment, a relative mass transfer coefficient was estimated to assess the contribution of mass transport.

The decrease in exposure necessary to reach log 2 population and the 5 minute residual population indicate an enhancement of deactivation, related to increased mass transport.

A further experiment was conducted in a sodium carbonate buffered solution at pH 7.8, fortified with 1000 µg/L Br- ( about 10 x the average US drinking water concentration) at the 0dB and 215 dB levels to assess the amount of bromate that would form under each condition. The chemistry of the solution was such that formation of bromate was favored. The acoustically radiated solution formed 10% more bromate, again indicating that mass transport is likely the mechanism responsible for the observed deactivation enhancement.

Conclusions:

The ResonantSonic? contactor is a mechanically simple technology that enhances the utilization of ozone during liquid contacting. It is an individual component, so it could be incorporated into existing facilities. It may be particularly suited to use in the 3300-10,000 user water treatment facility market because of the size of the units and the modular flexibility of design. Application of the technology is not immune to the formation of disinfection byproducts, however, as evidenced by formation of bromate in a bromide containing water.

Supplemental Keywords:

resonant mixing, in-line ozone contactor, mass transport, disinfection, waste destruction., Sustainable Industry/Business, RFA, Scientific Discipline, Water, Technology for Sustainable Environment, Engineering, Chemistry, Environmental Chemistry, Engineering, Chemistry, & Physics, cleaner production/pollution prevention, Drinking Water, New/Innovative technologies, ozonation, protozoa, treatment, innovative technologies, low frequency acoustics, monitoring, drinking water treatment, water treatment, exposure, Giardia, ozone, innovative technology, cryptosporidium , exposure and effects