Field demonstration of UV/H2O2 on the treatment of groundwater contaminated with HMPA

The UV/H2O2 process was demonstrated on 7 GPM of hexamethylphosphoramide (HMPA) contaminated groundwater in a DuPont plant located in Richmond, VA. The treatment reduced the HMPA in the water from 20 PPM of HMPA to non-detectable levels. The TOC in the water, which was about 13 PPM, was reduced by 90%. This level of organics reduction was found to be necessary to insure that the residual organics would not be similar to HMPA, and perhaps as toxic as HMPA. Prior to the field tests, lab tests were conducted in a 1-liter batch photoreactor with a low pressure mercury lamp, which suggested that the UV/H2O2 process would be feasible in destroying the HMPA and TOC. The addition of iron catalyst to the UV/H2O2 process did not improve the organics removal efficiency. The Fenton process (Fe/H2O2) was also evaluated and found to be effective in removing all the HMPA. However, the Fenton process did not reduce the TOC to desirable levels and also generated large amounts of sludge. The optimum H2O2 dose and UV electricity requirements determined in the field test were 250 PPM and 0.04 KWH/gal, respectively. The carbon adsorption process was also field tested side-by-side with the UV/H2O2 process. Carbon adsorption also achieved the treatment goals. Economic evaluations based on the net present value of the two treatment options showed that the UV/H2O2 process was cost competitive with carbon adsorption. After long debates, plant management opted for the old and simple carbon adsorption process to treat the groundwater. The facts that a) the UV/H2O2 process was a relatively new technology to DuPont and perhaps not as robust as carbon adsorption, and b) that there was not a cost incentive in using UV/H2O2 over carbon adsorption tilted the decision in favor of carbon adsorption. The decision makers suggested, for instance, that if the electricity requirement of the UV/H2O2 process had been half of the determined value, they would have opted for this process. This suggests that there is a need to improve the efficiency of the UV/H2O2 process to make it make it more attractive than conventional treatment methods.