Grantee Research Project Results

Final Report: Development of a DYNAJET Cavitation System for High-Rate Disinfection of Combined Sewer Overflow

EPA Contract Number: 68D02091
Title: Development of a DYNAJET Cavitation System for High-Rate Disinfection of Combined Sewer Overflow
Investigators: Kalumuck, Kenneth M. , Chahine, Georges L.
Small Business: Dynaflow Inc.
EPA Contact: Richards, April
Phase: I
Project Period: October 1, 2002 through July 31, 2003
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR)

Description:

In this research project, DYNAFLOW, INC., investigated the ability of its DYNAJETS^® cavitating jet technology to kill bacteria representative of those that occur in combined sewer overflows (CSOs) when operated at low to moderate pressures. Experiments were conducted in recirculating flow loops using a variety of cavitating jet configurations and operating conditions. Nonpathogenic strains of Escherichia coli, a gram-negative organism, and Bacillus subtilis, a gram-positive organism, were grown from overnight cultures. These liquids then were introduced into the flow loops and subjected to cavitation for varying periods of time. Destruction of these bacteria was determined from periodic sampling, plating, incubation, and colony-forming unit (CFU) counting. Histories of the bacteria concentration reduction versus time then were obtained. Efficiencies of killing were evaluated based on the energy utilized to achieve a given order of magnitude of bacteria reduction from initial concentrations between 106 and 109 CFU/mL.

Experiments also were conducted in the presence of particulates and organic compounds to demonstrate the ability to kill bacteria under these conditions. Water containing fecal coliforms taken from a stagnant pond was utilized as additional media for disinfection experiments. Flow visualization of the generated cavities with high-speed videos, Plexiglas^® nozzles, and reaction chambers was employed to assure that the desired cavitation was being achieved and to ascertain the hydrodynamic flow field and cavity behavior.

Based on the results, a preliminary set of scaling laws was utilized to estimate the size and requirements of a technology prototype to be developed during Phase II. A conceptual design and a set of design requirements also were developed. There are many potential applications of this technology. Systems incorporating the DYNAJETS^® technology could be deployed for CSO disinfection either at a central location or a point of discharge. The technology is relatively simple and robust, readily applicable to different scales, and easily started and stopped. In addition to CSO disinfection, other potential applications include disinfection for drinking water either for municipal (particularly small) systems or mobile systems that could be employed in emergencies or remote areas, and disinfection of discharge streams such as those from hospitals, pharmaceutical or biotechnology facilities, and research facilities. The technology could easily be implemented at multiple scales such that it could be effectively utilized for both small and large systems.

Summary/Accomplishments (Outputs/Outcomes):

The DYNAJETS^® cavitating jets were found to be capable of substantially reducing the concentrations of both E. coli and B. subtilis. Both classes of DYNAJETS^® cavitating jets investigated (DYNASWIRL^® cavitating swirling jets and STRATOJET^® self-resonating cavitating jets) were found to be capable of achieving bacteria destruction. Repeatable reductions of up to five orders (5 log10) were obtained when starting with concentrations of 108-109 CFU/mL, and reductions as high as six orders (6 log10) were obtained with initial bacteria concentrations of 107 CFU/mL. The DYNAJETS^® bacteria removal was found to be unaffected by the presence of particulates or an organic compound. Fecal coliform levels in water from a stagnant pond were found to be reduced by exposure to the cavitating jets from greater than 23 most probable number (mpn) to less than the detection limit. The relative insensitivity of the performance of the DYNAJETS^® cavitating jets to the presence of particulates and organic compounds indicates great flexibility in the design and implementation of practical systems.

Higher energy-efficient reductions of bacteria were found to occur at moderate pressures of about 60 psi than at higher pressures, although the maximum level of destruction achieved was found to increase with pressure. Energy efficiency was found to vary with the volume of the batch being treated with an optimum that appears to depend on the ratio of batch volume to flow rate and on the quantity of cavitation nuclei. Visualizations of the jet flows show that a large range of cavity characteristics is possible, and that these characteristics depend on the DYNAJETS^® geometry. Scale-up estimates and sizing for a technology prototype show much promise for effective and efficient implementation of the technology.

Conclusions:

The Phase I research project clearly demonstrated the feasibility and great promise of the use of the novel DYNAJETS^® cavitating jet technology for effective and efficient disinfection of water from CSOs and other discharge. In Phase II, a more detailed investigation resulting in optimization scaling experiments and development of a technology prototype will be conducted to lay the groundwork for commercialization and Phase III.

Specific conclusions include:

· E. coli and B. subtilis were found to be effectively killed by the DYNAJETS^® cavitating jets. Repeatable reductions in bacteria count of up to five orders of magnitude (5 log10) were obtained when starting from high concentrations of 108-109 CFU/mL, and reductions as high as six orders (6 log10) were obtained for lower initial bacteria concentrations of 107 CFU/mL.

· Reductions of two to three orders were found to be obtained very rapidly, a finding of particular importance to CSOs in which such reductions often are sufficient.

· The fecal coliform content of water taken from a stagnant pond was found to be reduced by the DYNAJETS^® from greater than 23 mpn to less than 1 mpn (the detection limit) in tests conducted by an outside laboratory.

· The findings of E. coli and fecal coliform destruction strongly indicate the usefulness of this technology for water disinfection in that the presence or absence of E. coli often is utilized as a proxy for potential contamination by other bacteria in assessing water quality. Contamination by E. coli and other fecal coliform bacteria often is present in CSO discharge at a wide range of concentrations.

· The rate of killing of E. coli was found to be unaffected by the presence of particles or organic compounds. This is of particular importance to disinfection of CSOs, because they typically contain particulates and other organic and inorganic matter that can interfere with some alternative means of disinfection.

· Jet flow and cavitation visualizations showed large variation in cavity characteristics that are sensitive to the jet and nearby geometry, which also affect the cavitation collapse intensity.

· The best performance with the least energy consumption was found to occur at moderate pressures of about 60 psi, which is readily obtained with standard commercial pumps. The results indicate that performance was sensitive to pump pressure, with the best performance at moderate pressures.

· Variation of the total volume of liquid treated in the test loop for the same jet flow rate showed an influence on the energy efficiency that was found to have an optimal value and a variation in efficiency of up to a factor of four. This indicates the importance of the design of the system hydrodynamics.

· A conceptual design and sizing was estimated based on the results obtained. Preliminary scaling relations indicate that a technology prototype unit with a production capacity of 25 gpm and a two to three order (2-3 log10) bacteria "knockdown" or concentration reduction would require a central pump operating at about 60 psi with power consumption between 20 and 60 hp.

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this project

Supplemental Keywords:

DynaJets cavitating jet system, bacteria, combined sewer overflow, CSO, Escherichia coli, Bacillus subtilis, colony-forming unit, CFU, water, fecal coliforms, disinfection, most probable number, mpn, particulates, pump pressure, hydrodynamics, wastewater treatment, small business, SBIR., Scientific Discipline, Water, Wastewater, Environmental Chemistry, Wet Weather Flows, Environmental Monitoring, Engineering, Chemistry, & Physics, Environmental Engineering, aqueous impurities, real time analysis, wastewater treatment, water contamination detection, combined sewage outflows, analytical measurement methods, contaminated waters, electrospray mass spectrometry, runoff, urban runoff, analytical chemistry, municipal wastewater, Dynajet cavitation, stormwater, aqueous waste, water quality, wastewater discharges, ultrasonic caviation, combined sewer overflows, real time monitoring, storm drainage, stormwater runoff, electrospray ionization, aqueous waste stream, disinfection, real-time monitoring

SBIR Phase II:

Development of a DynaJet Cavitation System for High-Rate Disinfection of Combined Sewer Overflows  | Final Report