Removal of organic compounds from aqueous solutions by electron radiation technique

Abstract

Electron beam water treatment is a new, advanced oxidation technology, which is used for decomposition of organic contaminants in water. Very little has been done to estimate an effect of electron radiation parameters on efficiency of the decomposition. The objective of this thesis is to investigate the influence of accelerating voltage, beam current and electron beam power utilization on the removal rate of the compounds, such as : trichloroethylene, benzene, toluene, chloroform and nitrobenzene.

The thesis describes the experiment concerning low and medium energy electron beam water treatment. The design and construction of the lab scale electron beam water treatment apparatus, which has unique features that enable to decompose water contaminants even for low energy of the beam electrons, are explained. The electron beam is generated in high vacuum, pressure is less than 10^-5 Pa, obtained by the system of rotary, sorption and diffusion pumps. The electron beams then accelerated and injected into water through electron permeable membrane (transparent window). In the setup the treated water is also used as the window coolant. This provides an opportunity to operate at a relatively high power density of the incident beam (more than about 500 W/cm^2). The irradiator can utilize two types of the electron permeable windows: 1.15 um and 25 um titanium foils (measured current transmission at 100 kV is 57% and 25%, respectively), 2. 10 um boron nitride ceramic window (measured current transmission at 100 kV is 95%).

The dependence of relative concentration of the contaminants on radiated and absorbed dose of electron radiation is presented. Additionally, by-products and intermediates distribution depending on the absorbed dose during benzene removal is analyzed. The absorbed dose was calculated on the basis of the measured power loss occurring while the electron beam passes through the transparent window. The obtained results suggest that the relative content of organic contamination decreases exponentially with an increase in the absorbed dose. It has been found that a substantial removal of the investigated contaminants (80-99%) can be obtained for relatively low accelerating voltages range (100-180kV). The use of such low voltage level can result in a significant simplification of X-ray shielding and insulation systems that further would allow to design and build an energy efficient, portable water irradiation apparatus.

The closed water circulation system enables to adjust the dose of electron radiation, not only by the beam power and flow rate of the treated water, but also by varying the total treatment time. In this case, the dose of radiation needed for required removal of a given contaminant can be calculated on the basis of low voltage and low current measurements. The dose can then be converted into a high power commercial system, provided that the power absorbed per unit volume is the same, so that the beam power and flow rate can be adjusted in order to obtain the required decomposition of the contaminant.