Waichiro Kawakami

Radiation induced oxidative degradation of polymers—I: Oxidation region in polymer films irradiated in oxygen under pressure

Abstract The γ-ray induced oxidation of polyethylene and ethylene-propylene copolymer films has been studied to obtain technological information on reducing the period in the radiation resistance testing of polymer materials. The polymers were irradiated under pressurized oxygen atmosphere (0.21∼10 atm) at high dose rate (0.5∼1 Mrad/h) in order to accelerate the oxidative degradation. The depth of oxidation region in the film was estimated by the gel fraction measurement. The depth was well agreed with the oxygen penetration region, which was calculated using the observed diffusion coefficient and solubility constant of oxygen in the film and specific rate of the oxygen consumption during irradiation. It was found that the depth of oxidation region was proportional to the square root of [oxygen pressure/does rate] and that the testing period could be reduced by higher dose rate irradiation at higher oxygen pressure.

Decoloration and degradation of an anthraquinone dye aqueous solution in flow system using an electron accelerator

Abstract A study on the decoloration and degradation of a commercial anthraquinone dye (Acid Blue 40) was carried out by electron-beam irradiation. Experiments were done in a flow system using a five-stage, dual-tube bubbling column reactor. The oxygen contents of the gas bubbled into the inner tubes of the columns were varied from 0 to 100%. The inlet dye concentration, the solution feed rate and the dose rate were also varied from 50 to 100 ppm, 1.5 to 101/min and 0.1 to 0.15 Mrad/s, respectively. The degree of decoloration and degradation of aromatic rings increased with the oxygen content and became close to those for pure oxygen bubbling system at about 25% of oxygen content. The amount of degraded aromatic rings was proportional to that of consumed oxygen. The rate expression of the decoloration and degradation of the dye and the oxygen consumption were derived according to a reaction scheme.

The degradation of an azo dye in aqueous solutions by high-intensity electron-beam irradiation

Abstract A study of the degradation of Acid Red 265 (azo dye) in aqueous solutions by high-intensity electron- irradiation was carried out in a flow system. For the oxygen-saturated solutions (oxygen bubbled during irradiation), the change of absorption spectra, the degree of decoloration at 542 nm, the reduction in optical density at 230 nm, the change of pH, and the amount of dissolved oxygen were measured as functions of dose under various conditions (dye concentration, dose rate, solution flow rate, and oxygen flow rate). The decoloration scheme in the flow system by electron beam irradiation was similar to that in the batch system by gamma radiation. Oxygen was not necessary for the destruction of the chromophore but was absolutely essential for the destruction of substituted aromatic rings in the dye molecule. For the purpose of the destruction of the skeleton of the Acid Red 265 molecules, it was necessary to keep the concentration of dissolved oxygen above at about 30 ppm (in mass) in the case of the 60 ppm dye solution.

Radiation-induced decomposition of phenol in flow system

Abstract The radiation-induced decomposition of phenol in aqueous solution was studied in flow system. The reactor used was a five-stage, dual-tube bubbling-column-type and an electron accelerator was used as a radiation source. Products in the oxygenated solution were hydroxy-hydroquinone (1,2,4 - trihydroxybenzene), hydroquinone (1,4 - dihydroxybenzene), pyrocatechol (1,2 - dihydroxybenzene), and trace amounts of phloroglucinol (1,3,5 - trihydroxybenzene) and resorcinol (1,3 - dihydroxybenzene). On the other hand, hydroquinone, pyrocatechol, and small amounts of resorcinol and hydroxyhydroquinone were detected in the deaerated solution. A significant amount of suspended solid was also observed in the deaerated solution. The G -value for phenol reduction in the deaerated solution was 2.6 and was 5–6 times larger than that obtained in the deaerated solution using 60 Co as a radiation source. Calculations were done on the concentration of phenol and products according to the reaction scheme obtained from the batch experiments using 60 Co. The results agreed well with the experimental values of the flow system.

Disinfection of sewage sludge cake by an electron accelerator

Abstract Effects of radiation dose rate, electron energy and oxygen on disinfection of sewage sludge cake were studied to obtain technological information on disinfection by radiation. Sludge films were irradiated with electron beams at different voltages and various dose rates in oxygen-containing and oxygen-free atmospheres. Without oxygen, the surviving fraction of bacteria decreased with increasing irradiation dose, but depended little on the sludge film thickness. No effects of dose rate and energy change were found in the ranges from 20 kGy/h to 65 MGy/h and from 0.5 to 2.0 MeV when the film was thin enough to allow electron beam penetration. Similar results were obtained with γ-ray irradiation. In the oxygen-containing atmosphere, higher disinfection efficiency was obtained with thinner films and lower dose rates.

Inhibition of trihalomethane formation in city water by radiation-ozone treatment and rapid composting of radiation disinfected sewage sludge

Abstract Humic acid and Fulvic acid in natural water are precursors of carcinogenic THM which is formed during chlorine disinfection in city water processing. The radiation-oxidation process in the presence of ozone is effective to remove the precursors. The THM formation was reduced more than the decrease in TOC by the combination treatment. This is mainly due to a change in the chemical structure of the oxidation products. A composting of radiation disinfected sludge cake for agricultural reuse could be achieved within 3 days primary fermentation in a sewage plant. The rapid fermentation with use of radiation is effective to scale down of a fermentor of composting plant and the process reduces a health risk from the workers as well as final users.

Enhanced compositing of radiation disinfected sewage sludge

Abstract Studies on isothermal composting of radiation disinfected sewage sludge and liquid chromatography of water extracts of the products were carried out. The optimum temperature and pH were around 50 °C and 7–8, respectively. The repeated use of products as seeds increased the rate of CO2 evolution. The rate reached a maximum within 10 hours and decreased rapidly, and the CO2 evolution ceased after about 3 days. The conversion of organic carbon to carbon dioxide attained to about 40% for the repeated use of products as seeds at the optimum conditions. As long as seeds in available were used, no remarkable difference was found in the composting of unirradiated and irradiated sludges. The composting process using radiation, however, can be carried out at the optimum conditions and is expected to shorten the composting period, because it is not necessary to keep fermentation temperature higher to reduce pathogen in sludge. Liquid chromatographic studies of the products showed that low molecular components decreased and higher molecular ones increased with fermentation. An index expressing the degree of reduction of easily decomposable organics was presented. The index also showed that the optimum temperature for fermentation was 50 °C, and that the easily decomposable organics disappeared above 30% of the conversion of organic carbon.