William B. Kerfoot, Kerfoot Technologies, Inc., 766-B Falmouth Road, Mashpee, MA  02649, Tel:  508-539-3002, Fax:  508-539-3566, Email:  wbkerfoot@kerfoottech.com

It is a common misconception that ozone gas has a short half-life.  Dissolved ozone, which reacts with water to release hydroxyl radicals, has a half-life of minutes; whereas ozone in gaseous form has a half-life measured in hours or longer.  W. S. Sease in “Ozone Mass transfer and contact Systems,” stated that at 0°C, the half life of gaseous ozone is 2,000 years.  Ozone-air mixtures placed in sampling VOC vials, checked periodically, showed an initial quick drop (half-life 5-9.5 hours) during which time the gas reacts with other air components (nitrogen and moisture), then a slow half-life of 35 hours commonly exists.  Reducing microbubble size has a profound effect on capacity of bubbles to remain in solution, their reactivity, and in transmission through soils.  Below 100 micron size, stable solutions of nano to microbubbles can be produced in aqueous solutions.  With pulsing at certain frequencies and pressure differentials, the bubble emulsions can be transmitted vertically and laterally for oxidative reactions with target organic compounds, like MTBE.  By controlling bubble size, ozone concentration and air/ozone volume released per pulse, the likelihood of fugitive ozone emissions can be reduced or eliminated while oxidation reactions proceed.  Laboratory tests were conducted to compare microbubble buoyancy versus diameter for various column diameters.  Vertical travel velocities were then compared to columns of sand of differing permeabilities.  The effect of pressure differentials in producing significant vertical and horizontal transport were defined and compared to observed field transport.  The arrival of microbubbles into monitoring wells could be counted and was correlated with the arrival of wavefronts.  The observed rate of removal of MTBE at different release sites from retail gasoline service operations is compared with theoretical mechanics.  Observed half-life (pseudo-first order) attenuation coefficients ranged from 3 to 14 days when mean midway ROI values from nano to microporous diffusors are compared.  The radial spread must be taken into account when comparing efficiencies of removal from site to site.  A modification of Clayton’s equation for ozone reactivity can be used for predictive purposes.

Air Spacing Effectiveness in MtBE Removal from Water, Tested on an Intermediate Scale Laboratory Apparatus

Daniele Lausdei, Golder Associates S.r.l., Via Messina, 25, 00198 Roma, Italy, Tel: +39-06-44250873, Fax: +39-06-44250951, Email: dlausdei@golder.it
Claudio Alimonti, Università di Roma "La Sapienza", Via Eudossiana, 18, O0184 Roma, Italy, Tel: +39-06-44585628, Fax: +39-06-44585618, Email: claudio.alimonti@uniroma1.it

In the last decade the groundwater contamination by MtBE due to fuel spills or leakage from underground storage facilities became a high sensible environmental issue. Among all the in-situ groundwater remediation treatments, aimed to remove MtBE and the other gasoline components, the Air Sparging (AS) has been widely used since it is one of the best established economical and reliable technologies for the remediation of volatile compounds dissolved in groundwater. Nevertheless there are still many uncertainties regarding the airflow distribution in saturated media and the interactions of various physical-chemical processes during AS applications. Thus, the present experimental study was aimed to investigate the effectiveness of AS in dissolved MtBE removal from a saturated media, performing a removal test under confined and controlled conditions in an intermediate scale tank (m 1 x 1 x 1,2). The experimental conditions have been focused to study the stripping process driven by the air injection, since stripping is considered to be the most effective among the removal processes driven by AS, in the short terms of its in situ application. Through data interpretation, several considerations were made to evaluate the effects of geometry, water temperature and bulk water movement on the effectiveness of AS removal from MtBE contaminated water. This study confirmed that in-situ AS has a significant potential in groundwater remediation contaminated by MtBE, showing that the stripping action driven by the air injection give such a strong contribution to the comprehensive removal action of the AS technology. Following this, was also investigated the influence of some factors governing the efficiency of the process of stripping, such as the sparge point screen size and the usage of surfactants to enhance the AS performance.

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