IAEA Initiatives in Advancement of Radiation Technologies for Environmental Remediation

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1 IAEA Initiatives in Advancement of Radiation Technologies for Environmental Remediation Sunil Sabharwal*, Agnes Safrany, Joao Alberto Osso Junior, Meera Venkatesh Radioisotope Products and Radiation Technology Section, Division of Physical and Chemical Sciences International Atomic Energy Agency, Vienna, Austria Abstract: A variety of emerging chemicals of concern are discharged into the environment leading to contamination of water resources. These chemicals even at trace levels have the potential to adversely affect the aquatic, animals and human life. Effective and efficient technologies for treatment of such pollutants are therefore needed. Advanced oxidation processes (AOP), involving the in situ generation of oxidants such as the hydroxyl radical ( OH), have emerged as an important class of technologies for accelerating destruction of such organic contaminants. These include the use of photons and energetic sub-atomic particles like electrons (high energy radiation) to generate reactive intermediates OH radicals IAEA has been at the forefront of recognizing the need to develop appropriate technologies to meet the challenges of evolving environmental issues. This paper gives an insight into the current status of the radiation technology with emphasis on IAEA activities, including examples of successes achieved as well as challenges for broader dissemination of radiation processing technology for environmental remediation. Introduction Continued urbanization and industrialization has emerged as a leading factor in enhancing environmental pollution. The recognition that a variety of emerging chemicals of concern that are getting discharged into the environment leading to contamination of water resources have the potential to adversely affect the aquatic, animals and human life even at trace levels has necessitated development of effective and efficient technologies for treatment of such pollutants. Conventional treatment methods such as filtration, adsorption, ion-exchange are unable to effectively remove many of these pollutants. Advanced oxidation processes (AOPs) based on generation of highly oxidative hydroxyl radicals ( OH) that can effectively and efficiently oxidize a variety of organic compounds are emerging as potential treatment strategy. Hydroxyl radical ( OH), has a high standard reduction potential (E⁰( OH/H 2 O) = 2.8 V/SHE) and is among the strongest oxidizing agent known. It can highly react with a wide range of organic compounds, regardless of their concentration (1). Many methods are classified under the broad definition of AOPs, as wet oxidation, ozonation, Fenton process, sonolysis, homogeneous ultraviolet irradiation, and heterogeneous photocatalysis using semiconductors, radiolysis and a number of electric and electrochemical methods. The use of photons (radiation) or high energy electrons to *Corresponding author; address: S.Sabharwal@iaea.org generate reactive intermediates OH radicals have been also been investigated for a long time as high energy radiation is an effective and efficient generator of OH radicals. Radiation technologies have a successful history of innovating new products and processes that are environmental friendly (2). In recent years, exciting new developments have taken place in radiation technologies for directly treating industrial pollutants. The successful demonstrations of radiation technology based processes for simultaneous removal of NO x and SO 2 from flue gases, treatment of textile dye waste waters and radiation hygienization of sewage sludge now offer new opportunities for further expanding the horizons of radiation technology. Researchers have also focused on investigating radiation-initiated degradation of organics to transform various emerging organic pollutants (EOPs) into less harmful substances or reduced to the levels below the permissible concentrations. The development of reliable high power accelerators to meet the requirements of treating enormous throughputs in a cost effective manner and development of mobile electron beam machines for demonstrating the technology under actual process conditions to the end users to evaluate the suitability of process for specific application. Fundamental Aspects of Radiation Technology for Treating Organic Pollutants in Aqueous Effluents Radiation Chemistry Aspects The ionizing radiation sources that are used for radiation processing applications are gamma ray ISSN Science & Technology Network, Inc. J. Adv. Oxid. Technol. Vol. 18, No. 2,

2 emitting source like cobalt-60 ( 60 Co) or high energy electron accelerators capable of generating high energy electron beams. The high energy radiations (gamma rays or electrons) interact with the absorber and produce radiolytic transformations. The gamma radiation interacts with the orbital electrons of absorber mainly through the Compact scattering leading emission of secondary electrons which subsequently cause further radiolytic effects. Charged particles like electrons directly interact with the orbital electrons of the absorber and cause radiolytic transformation. Qualitatively both forms of energy lead to similar chemical effects in the absorber medium. When the absorbing medium is water (which is the predominant solvent for most of polluted effluents), irradiation in absence of oxygen by high energy radiation leads to formation of highly reactive species like hydroxyl radicals, hydrated electrons and H atoms besides molecular products like hydrogen peroxide and hydrogen gas as indicated in the following equation: H 2 O OH(0.28), H (0.06), e - aq(0.28), H 2 O 2 (0.07), H 2 (0.04) (1) where the number indicated in parenthesis represent the number of species formed in µmol per Joule of energy absorbed (G-value) (3). The most important parameter for any irradiation process is the absorbed dose which determines the quantitative effects of the process. The international unit of dose is the gray (Gy), which is defined as the absorption of one joule per kilogram (J/kg). As can be seen from the equation, irradiation of water leads to formation of oxidative species (OH and H 2 O 2 ) as well as reductive species (e - aq and H 2 ). The radical species formed in the medium are highly reactive and react with the organic compounds present in the medium at a very fast rate. When irradiation is carried out in presence of oxygen, the formed reductive radical species namely e - aq and H atoms react with the oxygen leading to the formation of oxidative products like superoxide (O 2 - ), hydroperoxyl radical (HO 2 ) as per the following reactions. H + O 2 HO 2 (2) e - aq + O 2 O 2 - (3) Irradiation under oxygenated or aerated conditions therefore leads predominantly to the formation of oxidative radicals in the process. The oxidative species formed during radiolysis subsequently react with the organic contaminants leading to their oxidation. OH, HO 2, O R (organic contaminant) (4) Choice of Radiation Sources As mentioned above, both gamma radiation sources such as cobalt-60 or high energy electron beam particles can be used in principle for radiation technology applications. While the gamma radiation sources offers the advantages of possessing deeper penetration power and being a simple technology, it has a limitation of low dose rates typically dose rate of few Gy/s and hence have lower through puts. On the other hand, electron beam accelerators can deliver dose rates of the order of 100 kgy/s. The successful operation of over 1600 electron beam accelerators in the industry for various applications over last 50 years has proven their reliability for continuous operations over long periods of time. Keeping in view that generally the environmental applications will require low radiation doses but extremely high throughputs, the use of electron beam accelerators seems a preferable option. In recent years, specifically to meet the demands of such applications as flue gas treatment or waste water treatment, extremely high power accelerators with nearly 400 kw of beam power have been developed and deployed (4). G value of the main oxidizing radical (OH) being 0.28 µmol/j, allows production of 0.28x10-3 mol OH radicals per liter of effluent per kgy of radiation absrobed. A typical electron beam accelerators with power of about 400 kw that can deliver a dose rate of 100 kgy/s, with a flow rate of about 100 litre/s can treat over 10,000 m 3 of waste water a day at 1 kgy absorbed dose. The oritically, such an accelerator effectively produces in-situ about 32 mmol of OH radicals per sec which are enough to interact with and chemically transform ppm levels of organic chemical pollutants present in the effluent. Electron Beam Treatment of Textile Dye Waste Water Textile dye and finishing processes remain the major industrial water users with wastes that are difficult to treat satisfactorily due to low biodegradability. The emergences of new dyes that are brighter and possess enhanced stability under sunlight, water soap etc. have made it even more difficult to treat dye waste water. The large variability of the composition of textile wastewaters further poses a challenge to both the textile industry and the wastewater treatment authorities as most of the traditional methods are inadequate for the removal of dyes (color) present wastewaters. Advanced oxidation method such as ozonation or methods producing OH radicals have been proposed as a potential alternative. High energy radiation based methods have been 274 J. Adv. Oxid. Technol. Vol. 18, No. 2, 2015

3 investigated for long time in laboratory scale experiments (5-8). The first serious attempt to utilize electron beam accelerators was carried out in Korea where an electron accelerator of 1 MeV, 40kW with the dose rate of 40 kgy/s was used in the laboratory experiments with irradiation under flow conditions. The major objectives of this initiative were to investigate the treatment of wastewater from various stages of the existing purification process using electron beam to optimize technology of the electron beam treatment of wastewater. The results of this laboratory investigations showed the electron beam treatment of wastewater immediately before biological treatment may result in appreciable reduction of chemical reagent consumption, in reduction of the treatment time, and in increase in flow rate limit of existing facilities by 30-40% (9). Pilot Studies Based on the initial success of the feasibility of laboratory scale tests, a pilot plant for a large-scale test (flow rate of 1,000 m 3 per day) of wastewater was constructed with the electron accelerator of 1MeV, 40 kw in 1998 with the support of International Atomic Energy Agency (IAEA), Korean Government and M/s EB Tech, Korea. For the uniform irradiation of water, nozzle type injector with the width of 1500mm was introduced. The wastewater is injected under the e- beam irradiation area through the injector to obtain the adequate penetration depth. From the operation data of pilot plant at around 1 kgy, the improvement of biological treatment of wastewater after preliminary electron-beam treatment was established. The results showed that electron-beam treatment did not appreciably affect total biodegradability of pollutants but significantly improved biodegradation process at initial stages. In other words, irradiation at comparatively low doses (several Gray) did not change total amount of biodegradable substance characterized by BOD5, but converted part of it into easier digestible form. This was confirmed by the fact that while the decrease in TOC, COD and BOD5 during biological treatment was close to linear one for non-irradiated wastewater, the electron beam treated wastewater the decrease was faster at the beginning of bio-treatment and slowed down during the process (10). Construction of Industrial Plant The success of the pilot scale operation encouraged the stakeholders namely EB TECH Co., Korean government and the IAEA to further upscale the operations by building an industrial scale plant for treating 10,000 m 3 effluent per day of DDIC wastewater was in 2005 to treat up to 10,000 m 3 of dye effluents per day (11). Based on laboratory and pilot plant experiments with Daegu Dyeing Industrial Complex (DDIC) wastewater, the optimum absorbed dose for electron-beam treatment was chosen to be near 1 kgy, and required electron beam power was determined as 400 kw. For this purpose, an electron accelerator of 1 MeV, 400 kw with three separate irradiators was developed jointly by EB TECH Co. Korea and Russian institute BINP (12). The experience of operating the facility led to following technical conclusions: - amount of chemical reagent required for conventional treatment can be reduced up to 50% - removal efficiency of harmful organic impurities is increased by 30% - retention time in Bio-treatment facility is significantly reduced. Besides the technical effectiveness of the process, the successful application of electron bean technology requires establishing and demonstrating the economics of process vis-a-vis the conventional technologies. The establishment and operation of this industrial plant showed that such a facility can be constructed at a cost of about USD 4M and the operation cost was determined to be USD 0.5M per year. Overall, it was established that the treatment cost would work out to be USD 0.3 per each cubic meter of wastewater. Based on the success of this plant, Tsinghua University in China is presently in the process of setting up of a pilot scale experiment to demonstrate its utility to the Chinese industry (13). IAEA Initiatives in Supporting R&D in Radiation Treatment of Emerging Organic Pollutants: The recognition that huge consumption of pharmaceuticals and personal care products (PPCPs) has emerged as a source for the pollution of water resources due to discharge of emerging organic contaminants (EOCs) such as pharmaceuticals, insecticides, surfactants and endocrine disruptors to the receiving rivers, lakes, groundwater and even drinking water supplies. Scientific as well as public concern about presence of such chemicals is increasing gradually due to their potential impact on aqueous ecosystems and human health. It is well known that physical treatments, such as filtration (including nano-filtration and reverse osmosis) and adsorption merely transfer PPCPs from one phase to another phase, but are unable to decompose them. Biological process in WWTPs, such as activated sludge, are also not originally designed to remove such kind of emerging contaminants, therefore, their utility for treatment is usually limited. J. Adv. Oxid. Technol. Vol. 18, No. 2,

4 Consequently, various techniques are being investigated in recent years to eliminate PPCPs from wastewater and waters. Several studies on the use of radiation chemical methods based on gamma and electron beam irradiation have also been investigated and reported in literature for decomposition of these compounds (14). However, lack of comparative data at pilot scale level (alone or in combination with other methods) has been a major issue in further exploring the utilization of this method for deployment in wastewater treatment. There is a need to study further the radiation effects, reliability and cost on specific group of organic pollutants in cooperation with other stakeholders who are involved in using other technologies. With this in view, IAEA has initiated a Co-ordinated Research Project (CRP) on Radiation treatment of wastewater for reuse with particular focus on wastewaters containing organic pollutants was in 2011 with 16 participating laboratories from around the world including Brazil, China, Hungary, Italy, Japan, Republic of Korea, Portugal, USA. The main objectives of the CRP are: to study the basic radiation induced transformations of EOCs and establish effectiveness, reliability of radiation processing develop appropriate analytical and biological methods for validating the efficacy of the process facilitate deployment of technology to treat wastewater contaminated with low and high concentration of organic compounds Following are brief highlights of the work being done under the project. The detailed studies are presented in detail elsewhere (15). Selected Studies on Radiation Treatment of EOCs and Toxicity Evaluation of the Products Formed Hungary The research group of Prof Tackas and Prof Wojnárovits at Institute of Energy Reseach, Hungary have been studying the fundamental aspects of radiation induced degradation of organic pollutants for many years. Under this project, their studies are focused on investigating phenylurea herbicides that are used for control of weeds in many corps and also on non-cultivated areas such as roads and railways and they act as inhibitors of photosynthesis. These herbicides are highly persistent; they degrade in soils with half-lives of several months resulting in continuous contamination surface waters. Although the degradation of fenuron has been often investigated, little information is available about the elementary reaction steps and also about such technically important characteristics as changes of toxicity or carbon to oxygen ratio in the course of treatment. The radiation induced degradation behaviour of herbicide Fenuron in dilute air saturated aqueous solution was investigated by Tackas et al. (15). Fenuron belongs to the class of phenylurea herbicides, these herbicides have the general formula (substituted) phenyl NH C(O) NR 2. With fenuron R is CH 3 group (1,1-dimethyl-3-phenylurea). While pulse radiolysis technique was used in the study to investigate to characteristics the intermediates and kinetics of elementary reactions, steady-state radiolysis utilising the usual analytical techniques was used to study the products and parameters such as chemical oxygen demand (COD), total organic carbon content (TOC) and toxicity of the resulting solutions. The results indicated that Fenuron was easily degraded by irradiation. The first oxidation steps were observed to be due to the reactions hydroxyl radicals. Hydrated electrons or the superoxide radical anion/perhydroxyl radical pair practically did not contribute to the transformations. The main reaction of OH is addition to the aromatic ring forming hydroxyl-cyclohexadienyl radical. This radical has a wide absorption band in the nm range with maximum at about 350 nm, in aerated solution it is expected to react with dissolved oxygen. Some part of the peroxide radicals thus formed finally transformed to Fenuron molecules hydroxylated in the ring. Based on the decrease of the chemical oxygen demand of the solution with irradiation it was calculated that two electron oxidations resulted upon one OH attack. The studies indicated that the toxicity of solutions after irradiation first increases with the absorbed dose and then decreases. This increase was associated partly with some hydroxylated products formed during irradiation. China The reasrch group at Tsinghua University in China has been exploring the use of radiation technological techniques for elimination of organic contaminants in industrial effluents. Their study under the CRP is focused on radiation induced decomposition of diclofenac (2-(2,6-dichlorophenylamino)phenyl acetic acid) (DCF), one of the most widely used nonsteroidal anti-inflammatory drugs. The irradiation results using an electron beam accelerator have demonstrated that DCF can be removed effective (15). In the initial concentration below 40 mg/l, about 100% removal efficiency was achieved at a low dose of 0.5 kgy, although only about 6.5% DCF was mineralized even at 2 kgy. For the real DCF 276 J. Adv. Oxid. Technol. Vol. 18, No. 2, 2015

5 contaminated surface water, the average removal efficiency of COD Mn, NH 4 + -N and UV 254 was reported 17.4%, 86.2% and 6.9% by biological treatment alone, respectively. For the combined process of EB+ Biological aerated filter (BAF), the removal efficiency was improved to 62.0%, 86.1% and 60.3%, respectively. The removal efficiency was substantially influenced by EB pre-treatment. The toxicity assays illustrated that EB pre-treatment and biological treatment could result in a significant decrease in the toxicity of the DCF contained surface water. Republic of Korea Korea has been at the forefront of utilizing radiation based techniques for environmental remediation. The availability of a mobile electron beam facility with 0.7 MeV energy and 20 kw of power has provided them with a tool that can be utilized to demonstrate the efficacy of the process to the end user under actual process conditions. Under this project, radiation degradation behavior of a total of eleven antibiotics that can be potentially present in the livestock WWTP in Korea was investigated by Lee et.al. (15). Antibiotics like chlortetracycline, oxytetracycline, acetylsalicylic acid, and disinfectants were detected with high concentrations in the influents, whereas sulfamethoxazole, erythromycin, and trimethoprim were not detected during sampling periods. Radiation process such as e-beam was very effective for the degradation of antibiotics in aqueous solution. The antibiotics concentrations decreased with increasing radiation doses and the five target antibiotics were completely degraded. Brazil Ecotoxicity assays are an important tool for ensuring safe discharge of effluents. The possibility of by-products formed during the degradation processes possessing higher toxicity than the original contaminant, necessitates assuring that the products formed after irradiation (or processing) possess lower toxicity before discharging wastewaters. Most of the usual toxicity assays for effluents are based on surviving and other critical biological endpoint. The subject of exploring and establishing appropriate methods for ecotoxicity evaluation has been keenly investigated in Brazil in recent years. Borley et. al. (15) during this research project studied two new possibilities for toxicity evaluation: the embryo assay with Daphnia similis and the shrimp surviving. Ecotoxicity assays revealed H. azteca amphipod and D. similis as the most sensitive applied living-organisms. Electron beam irradiation was applied to aqueous solution of Hydrochoride Fluoxetine, to raw sewage and to the mixture of both. The comparisons of results of irradiated and non irradiated samples showed that 5 kgy was an optimum dose for the waters (even the mixture), accounting for > 80% reduction of acute effects to D.similis, due to the decomposition of fluoxetine (> 90% degradation). When radiation was applied to fluoxetine in the presence of raw sewage (50% of each) the whole toxicity removal was > 90%. F ions were obtained from EB degradation of fluoxetine. Japan Kimura et. al. in Japan have investigated the treatment of pharmaceuticals and antibiotics using activated sludge and ionizing radiation methods in laboratory scale experiments (15). Decomposition of pharmaceuticals and antibiotics in wastewater was first carried out by the activated sludge system in order to decompose biodegradable matter and reduce the TOC value in wastewater. Persistent pharmaceuticals and antibiotics, which were not decomposed by the activated sludge system, were treated by -rays, and their decomposition efficiencies depended on the amount of TOC in wastewater. Oseltamivir, aspirin and ibuprofen at 5 µmol dm -3 in wastewater were decomposed by the activated sludge at reaction time for 4 h. On the other hand, carbamazepine, ketoprofen, mefenamic acid, clofibric acid, and diclofenac were not decomposed completely even after 8 h. In the case of antibiotics, decomposition yield of chlortetracycline was 93% for 8 hours, while those of other antibiotics (sulfamerazine, sulfapyridine, sulfamethazine, sulfamethoxazole, and chloramphenicol) were lower than 10%. Decompositions of these persistent pharmaceuticals and antibiotics at 5 µmol dm -3 in wastewater were investigated by the gamma-ray irradiation. Their results showed that concentrations of carbamazepine decreased exponentially as function of absorbed radiation dose and were less than 0.05 mg dm -3 as a threshold concentration of chronic toxicity of pharmaceuticals up to 1 kgy, while mefenamic acid and ketoprofen were decomposed at 2 kgy. Concentration of sulfapyridine, sulfamerazine, sulfamethazine, and sulfamethoxazole were eliminated at 1 kgy. Chloramphenicol also needed a dose of 1 kgy to be eliminated but decomposed slowly than the others. The rate constants of the reactions of these pharmaceuticals and antibiotics with hydroxyl radicals were estimated by the competition reaction method to be mol -1 dm 3 s -1. The authors have concluded that total running cost for the electron beam treatment system of the pharmaceuticals and antibiotics in real wastewater was estimated to be 35 yen m -3 in Japan. J. Adv. Oxid. Technol. Vol. 18, No. 2,

6 The electron beam treatment is considered to have the potential of integrating to the treatment plants. Conclusions Radiation techniques offer clean, effective and efficient methods for treatment of a wide variety of organic contaminants at extremely high throughputs. The successful operation of an industrial scale facility using an electron beam facility to treat m 3 of effluents has demonstrated the reliability and efficacy of the process and the technology to be a viable AOP for treating waste waters. Development of appropriate equipment like high power accelerators and mobile electron beam accelerators for such applications are expected to make the technology even more cost competitive and enhance its application. The efforts of the IAEA in supporting and coordinating research in this area have resulted in generating interest in the Member States to assess the applicability of using this technology. References (1) Spinks, J.W.T.; Woods, R.J. An introduction to Radiation Chemistry; John Wiley & Sons, Inc.: New York, (2) Silverman, J.J. Chem. Ed. 1981, 58, (3) Pikaev, A.K. Modren Radiation Chemistry. Radiolysis of Gases and Liquids; Nauka: Moscow, (4) Chmielewski, A.G. Radiat. Phys. Chem. 2004, 71, (5) Wojnárovits, L.; Takács, E. Radiation Physics and Chemistry 2008, 77, (6) Rauf, M.A.; Ashraf, S.S.T. Hazardous Materials 2009, 166, (7) Paul, J.; Naik, D.B.; Sabharwal, S. Radiation Physics and Chemistry 2010, 79, (8) Vysotskaya, N.A.; Bortun, L.N.; Ogurtsov, N.A.; Migdalovich, E.A.; Revina, A.A.; Volodko, V.V. International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry 1986, 28, (9) Han, B.; Kim, D.K.; Pikaev, A.K. In Proceedings Radiation Technology for the Conservation of the Environment; Zakopane, Poland, 1997, IAEA, Vienna, pp (10) Han, B.; Ko, J.; Kim, J.; Kim, Y.; Chung, W.; Makarov, I.E.; Ponomarev, A.V.; Pikaev, A.K. Radiat. Phys. Chem. 2002, 64, (11) Han, B.; Kim, J.K.; Kim, Y.; Choi, J.S.; Jeong, K.Y. Radiation Physics Chemistry 2012, 81, (12) Han, B.; Kim, J.; Kim, Y.; Vhoi, J.S.; Makarov, I.E.; Ponomarev, A.V. Water Science and Technology 2005, (13) He, S. Tsinghua University, Beijing , China 2014, Personal Communication. (14) Kimura, A.; Osawa, M.; Taguchi, M. Radiation Physics and Chemistry 2012, 81, (15) Radiation Treatment of Wastewater Containing Pharmaceutical Compounds in Report of the 3rd RCM on Radiation Treatment of Wastewater for Reuse with Particular Focus on Wastewaters Containing Organic Pollutants Budapest, Hungary, Working Material, IAEA, Vienna, naweb.iaea.org/napc/iachem/working_materials/rc report.pdf Received for review November 4, Revised manuscript received February 19, Accepted February 21, J. Adv. Oxid. Technol. Vol. 18, No. 2, 2015