The Electron Beam – a Future in Water Treatment – Part 4 of 4
Since the Miami-Dade project was dismantled in the late 1990s, research has continued but not as pilot projects. rior research from the 1970s and 1980s demonstrated that high energy electrons can alter the physical properties of wastewater sludge particles, thereby enhancing dewaterability and biodegradability through the action of free radical chemistry (Etzel et al. 1969; Kurucz et al. 1991; Sedlácek et al. 1985; Waite et al. 1997; Wang 1993). This research provided evidence that electron beams can be used to improve sludge quality to expand the ability to produce Class A biosolids for land application. The mechanism is via more consistent inactivation efficiency to eliminate potential human pathogens, a concern that resonates with potable reuse and beneficial reuse of biosolids in areas in contact with people, after NRC (2001) raised issues about resistant microorganisms such as viruses, protozoan cysts, and bacterial spores being applied to land application sites where vegetables are being grown. The main competition is from advanced thermal oxidation or incineration. Some utilities run a pelletizing plant to turn the material into a granular fertilizer product, such as Millorganite or Green Edge. Another final stabilization process could be composting.
However, this previous work showed that the electron beam processing of wastewater or biosolids has demonstrated a potential to completely mineralize organic constituents of concern including pharmaceuticals, personal care products, endocrine disrupting compounds, pesticide residues, petroleum hydrocarbons, nutrients, toxic metals, nanoparticles, and disinfection byproduct precursors. The mechanism is by direct and indirect action of short-lived but powerful oxidants and reducers induced in the matrix including hydroxyl radical, hydrogen radicals, aqueous electrons, superoxides, peroxy radicals, and ozone, without requiring chemical additives (Cooper et al. 1998). Undesirable halo-carbons found in waste-water can be decomposed by electron beams (Cooper et al 1990). Geiringer and Eschweiler (1996) noted that electron beams would be enhanced by ozone in creating OH radicals. Wang (2015) found it was effective for bromate removal. The E-beam process disinfects with electron beam and stabilizes with oxidants, chlorine dioxide and/or ferrate depending on the intended end use. The process can produce a Class A product that is at a neutral or acidic pH range and is also ideal for the Western United States (Reimers, et.al.,2005). Several studies have proposed that e-beam (EB) processing could be a good method to remove nonbiodegradable pharmaceutical products from waste waters, as these are not efﬁciently removed by conventional waste water plant treatments (Getoff, 1996; Kimura et al., 2004; Kurucz et al., 1995). Trojanowicz et al (2017) found the electron beam with AOP reduces contaminants of emerging concern. Slegers and Tilquan (2005) reported the ebeam was effective for removal of metaprolo tartate. A full scale water treatment facility at a textile manufacturing plan uses an accelerator with three beam to eliminate the residuals from a textile manufacturing plant (Kim, et al 2000, Han et al 2005).
The only western hemisphere project proposed was in Mexico. This would be the first electron irradiator in Mexico and would focus on sludge treatment at the sewage water treatment plant located north of Toluca in the State of Mexico. This treatment plant is mainly used for domestic wastewater and produces an approximate volume of 70 ton d-1 liquid sewage sludge. The consideration was a 50 kW power of a 10 Mev electron linear accelerator, an irradiation dose of 5 kGy and a treatment capacity of 346 tons per day (Moreno et al 2002), but it is unclear if the facility was installed. These findings open a window for far greater implementation of electron beams.
For example, given that in 2017, there were 14,748 wastewater treatment plants in the United States (ASCE 2017) treating around 32-40 billion gallons of wastewater per day and generating approximately 5.6-7.0 million dry tons per day of treated sewage sludge. The vast majority of systems (80%) treat less than 1 MGD, but an important fraction (17%) of the wastewater treatment plants in the US treat 1-10 MGD, while over 500 facilities treat between 10-100 MGD and 51 treat over 100 MGD (USEPA 2015). Treatment plants in large US cities such as Miami, Chicago, Dallas, Los Angeles, and Washington D.C. routinely treat between 150-400 MGD. Theoretically, facilities that process more than 100 MGD have the manpower, infrastructure, and budgetary capacity to be able to manage electron beam systems, but to process this amount of flow, the number of accelerators and the electrical power needs would be extremely cumbersome without major innovations in the technology. Opportunities should extend well beyond the treatment of sludge. Many areas of the country are looking at forms of potable reuse. It would appear that the electron beam might be a useful tool as a part of the treatment process for potable reuse given its ability to destroy pathogens and emerging contaminants.
Therefore, the target market given the present state of the technology would most likely be the large-sized facilities that treat 10-100 MGD (n ≈ 500). The costs are high, as are the power demands, but a paper by Meeroff et al (2018) showed that the costs are similar to current treatment technologies, and therefore we should perhaps begin to explore this issue further.