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Radiation technologies for treatment: A global perspective

Countries are studying irradiation systems for disinfection and decontamination of liquid and solid hazardous

I ollution of water, land, and air is a of drinking water and wastewater. by widespread and growing concern of global More recently, it has been used in pilot-scale J.F. Swinwood, proportions. Media reports of diseases and con- studies to break down contaminants in soils and T.D. Waite, tamination caused by the improper treatment and slurries. P. Kruger, and disposal of waste products occur on a regular Ultraviolet irradiation systems have regained S.M. Rao basis. This heightened awareness of potential popularity at wastewater treatment plants as an health hazards from insufficient or inappropriate alternative to chlorine. First used many years waste handling methods has stimulated the ago, these systems have undergone improve- search for effective alternatives. ments that resulted in more robust equipment In many countries, initiatives are being and more reliable operation. seen at the individual, community, city, and state Finally, the possible application of X-rays — levels. whose use is well established for medical diag- Of particular concern are wastes that present nosis and cancer therapy — for the treatment of problems in two areas: those containing poten- wastes has been investigated. However, the tech- tially infectious microorganisms ( nology has not yet been applied for this purpose. sludge, biomedical wastes, wastewater) and those contaminated with toxic chemicals. Basic types of irradiation systems which are currently A history of worldwide activities being used in waste treatment operations, or are being studied for this purpose, include gamma, For irradiation treatment in large-scale ap- electron-beam, ultraviolet, and X-ray. plications, several types of radiation sources are Gamma irradiators, typically installed with generally considered. A review of the state-of- an energy source of radioactive cobalt-60, have the-art of the technology for irradiation treat- been widely used since the early 1960s in the ment of water, wastewater, and sludge by four sterilization of medical products and consumer types of radiation was published by the goods. Their use in the disinfection of sewage American Society of Civil Engineers in 1992.* sludge has been demonstrated on a full-scale It summarizes the development status for the basis at a plant near Munich, Germany; and at a four types of radiation technologies investigated: sterilizer in Arkansas, USA, ultraviolet, radioactive isotopes (primarily for the treatment of wastes. Their use for cobalt-60), linear accelerators or electron-beam degradation of toxics in soils currently is under machines, and X-ray machines. investigation. Irradiation facilities for treatment of water Similarly, electron-beam machines have have been constructed in many countries of the seen decades of use in industrial processes. This world. (See table on page 12.) The first large- technology has been proven effective in the dis- scale plant was the Geiselbullach Gamma Sludge Irradiator, constructed in Germany in 1973. Another commercial application, also in

Ms Swinwood is Senior Market Development Officer at Nordion International Inc., Ontario, Canada; Dr Waite is Professor of Environmental Engineering at the University of Miami, USA; Dr Kruger is Professor of Civil Engineering at *Radiation Treatment of Water, Wastewater and Sludge, Stanford University, USA; and Dr Rao is Head of the Isotope Task Committee on Radiation Energy Treatment, American Division, Bhabha Atomic Research Centre, Bombay, India. Society of Civil Engineers, New York, (1992).

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Above: India's sludge irradiation research facility in Baroda. As shown in the schematic, the facility includes the irradiation cell (1); storage silo (2); irradiation vessel (3); source assembly (4); pump house (5); recirculation lines (6); obnoxious gas exhaust (7); container (8); control console (9); and source coolant system (10). Below: \n Canada, lettuce is being grown in land fertilized with irradiated sludge at the Ontario Agricultural College as part of research activities. (Credits: Bhabha ARC, India; Prof. Thomas Bates, Land Resource Science Dept., Univ. of Guelph, Canada.)

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IAEA BULLETIN, 1/1994 FEATURES

Summary of the average dose to remove 99% of trichtoroethylene from tions in the or injected into tank trucks aqueous solution in the presence and absence of clay as the trucks were being filled up with water. (See tables.) No Clay 3% Clay Reaction byproducts for all of the com- Initial Average dose Initial Average dose pounds studied are highly oxidized in nature. For concentration (kGy) required to concentration (kGy) required to example, and formic acid, at range (micro-M)* remove 99% range (micro-M) remove 99% micro-M concentrations, were the only reaction 0.61 - 0 88 0.57 0 58 - 0.72 0.58 byproducts identified for . The 6 2 - 8.9 0.64 6.2 - 7 2 064 remainder of the parent compound was com- 40-58 1.07 45-59 1.06 pletely mineralized to C02 H20 and HCI. *1 micro-M = 0.131 mg per liter It has been shown, therefore, that high energy electron-beam irradiation is effective and effi- cient in destroying organic chemicals from Summary of the average dose needed to remove 99% of benzene aqueous streams. The examples shown here are from aqueous solution in the presence and absence of clay typical of organic chemicals found in waste streams and at remediation sites for hazardous No Clay 3% Clay waste. Initial Average dose Initial Average dose concentration (kGy) required to concentration (kGy) required to range (micro-M)* remove 99% range (micro-M) remove 99% The Canadian sludge recycling facility: 1.1 -2.1 0.56 1.1-1.3 0.49 Marketing irradiated sludge 17-24 0.72 16-19 0.96 23-87 2.00 25 - 76 1 81 Municipal sewage sludge is the solid matter *1 micro-M = 0.078 mg per liter removed during wastewater treatment processes at plants. Sludge typically con- tains potentially harmful components such as infectious organisms (viruses, bacteria, At the design flow of 0.45 cubic meters per parasites), heavy metals, and chemicals. It also minute, influent streams at the EBRF are contains nitrogen, phosphorus, and other presented to the scanned beam in a falling stream nutrients beneficial to plant growth. approximately 4 millimeters thick. Since the In several countries (Germany, India, Italy) maximum penetration in water is approximately the use of irradiation systems to disinfect liquid 7 millimeters for 1.5 MeV electrons, some sludges prior to application on farm land has electrons pass through the stream. Thus not all of been successfully adopted. In Canada, a 4-year the beam energy is transferred to the water. By trial programme has led to a proposal to create a over-scanning the waste stream to ensure that the Sludge Recycling Facility, incorporating a edges of the stream are irradiated, more energy cobalt-60-sourced sludge irradiator. If approved, is lost. The result is that the efficiency of energy the facility will convert sludge into a dry, soil- transfer is approximately 60% to 85%. Thus, at like product ready for bagging and marketing to 50 mA (75 kW), doses of between 6.5 and 8 kGy horticultural firms. have been recorded. Total power consumption including pumps, chillers, and other auxiliary equipment is about 120 kW. Sludge irradiation systems

Irradiation disinfection of sludge would Removal of toxic and hazardous typically be carried out in a gamma irradiator organic chemicals: Summary of results with a cobalt-60 source. There are more than 160 of these full-scale industrial irradiators operating Numerous studies have been conducted on around the world to sterilize syringes, sutures, organic chemicals that may be of interest in con- surgeons' gowns, heart valves, ointments, talcs, taminated soils treatment, remedia- and a multitude of medical and consumer tion, industrial waste treatment, and hazardous products. waste . Results for two compounds are A sludge irradiation disinfection system summarized below. consists of three main components : The data for the removal efficiency was ob- • a concrete-walled disinfection room which tained at several irradiation doses, at three initial houses the irradiator and cobalt-60; solute concentrations, three different pHs, and in • a product handling mechanism which moves the presence and absence of 3% clay. The solutes the sludge into and out of the room; and were either prepared in concentrated stock solu- • a cobalt-60 energy source for disinfection.

14 IAEA BULLETIN, 1/1994 FEATURES

Schematic of a Sludge disinfection system municipal sludge irradiator

Irradiation room

Product out

Product in

Source rack Roller conveyor

Conveyor to bagging Source storage pool Conveyor from surge hopper

Tilt mechanism to unload tote boxes

The cobalt-60 sources are an important part natural components of sludge-based products of the irradiator. Cobalt-60 is a deliberately make it ideal for use around shrubs and flowers. produced radioactive isotope, the same as is used It can also be integrated into new or existing in the treatment of cancer patients in . lawns. Naturally occurring non-radioactive cobalt-59 is fashioned into pencil-like rods. These "pencils" are bombarded with neutrons in a nuclear reactor Future challenges and opportunities for one or more years, after which time about 10% of the cobalt-59 has been transformed into This article has provided a very brief over- cobalt-60. The pencils are then removed from view of the types of the reactor for further processing and preparation problems for which various radiation techno- for shipment to users of industrial irradiation logies can provide solutions. In some cases, systems. more research and testing is required before the The cobalt-60 emits gamma rays as it decays technology can be used on a commercial basis; to nickel. These gamma rays pass through in other instances the technology is already being sludge, killing microorganisms and parasites. used, or is ready for use, on a full-scale basis. They do not leave any residue in or on the sludge, Looking to the future, ongoing research in and they do not make the sludge "radioactive". scientific centres points the way to new roles for The irradiation process will not change moisture the safe, reliable, and economic application of content, or the levels of nutrients and heavy radiation technologies for waste treatment. metals — its sole function is to eliminate Among these are electron-beam machines to rid pathogenic organisms. flue gases of environmental such as nitrogen oxide and sulphur dioxide; machines using cobalt-60 to sterilize hospital and Irradiated sludge as a fertilizer product laboratory wastes for safe disposal; and the in- creasing use of ultraviolet in place of chlorine Disinfected sludge can be safely recycled for chemicals to disinfect wastewater. use as a fertilizer, soil conditioner, or as an in- As each year passes, citizens in all countries gredient in a wide range of specialty fertilizer are confronted with a growing list of seemingly products. Sludge products compete well with insurmountable environmental problems. To soil amendment and animal manure products meet these challenges, high-technology solu- typically available in the marketplace. tions are being sought which will provide Because it is organically based, sludge answers now, as well as in the future. Radiation products offer long-term soil improvement, un- technology provides a viable alternative in this like chemical fertilizers which provide nutrients ongoing search. d but have few soil-enhancement properties. The

IAEA BULLETIN, 1/1994 15