A prototype of an electroporation system for sterilizing wastewater or drinking water has been developed. In electroporation, applied electric fields cause transient and/or permanent changes in the porosities of living cells. Electroporation at lower field strengths can be exploited to increase the efficiency of chemical disinfection (as in chlorination). Electroporation at higher field strengths is capable of inactivating and even killing bacteria and other pathogens, without use of chemicals. Hence, electroporation is at least a partial alternative to chlorination.
The transient changes that occur in micro-organisms at lower electric-field strengths include significantly increased uptake of ions and molecules. Such increased uptake makes it possible to achieve disinfection at lower doses of chemicals (e.g., chlorine or ozone) than would otherwise be needed. Lower doses translate to lower costs and reduced concentrations of such carcinogenic chemical byproducts as trichloromethane. Higher electric fields cause cell membranes to lose semipermeability and thereby become unable to function as selective osmotic barriers between the cells and the environment. This loss of function is the cause of the cell death at higher electric-field intensities. Experimental evidence does not indicate cell lysis but, rather, combined leaking of cell proteins out of the cells as well as invasion of foreign chemical compounds into the cells.
The concept of electroporation is not new: it has been applied in molecular biology and genetic engineering for decades. However, the laboratory-scale electroporators used heretofore have been built around small (400-microliter) cuvettes, partly because the smallness facilitates the generation of electric fields of sufficient magnitude to cause electroporation. Moreover, most laboratory- scale electroporators have been designed for testing static water. In contrast, the treatment cell in the present system is much larger and features a flow-through geometry, such that electric fields strong enough to effect 99.9- percent disinfection can be applied to water flowing in a pipe.
The figure schematically depicts one version of the prototype system, wherein the output of a high-voltage pulse generator is applied to two electrodes on opposite sides of a flow-through electroporation cell. The pulse amplitude, duration, and repetition period are chosen to obtain the desired degree of disinfection. Most critical is the amplitude, which is chosen in consideration of the interelectrode gap (1 cm in the prototype) to obtain the needed electric-field intensity. The threshold electric-field intensity for transient changes in permeability and reduced-dosage infection is about 0.2 kV/cm; the threshold for inactivation is about 5 kV/cm. In a practical system, the electroporation cell would be equipped with multiple pairs of electrodes along the flow path and the high-voltage pulses applied to the pairs would be synchronized so that any given small volume of water would be subjected to multiple high-voltage pulses on its way through the electroporation cell.
Electroporation sterilization technology is best employed in small point-of-entry (POE) and point-of-use (POU) applications as in homes or other small facilities. In smaller pipe diameters, it can be very cost effective, but the power usage becomes excessive in larger water or wastewater treatment facilities. Bioelectromagnetics, however, has developed an alternative electromagnetic field technology that is very cost effective in large water/wastewater treatment installations.
This work was done by Kenneth J. Schlager of Bioelectromagnetics, Inc. for Johnson Space Center. For further information, contact
Kenneth J. Schlager, President
12825 Elmwood Road
Elm Grove, WI 53122
Phone: (262) 782-2048
Fax: (262) 786-1491
Refer to MSC-23377.