**6. Economic benefits of using electron beam irradiation for the treatment of municipal sewage sludge**

An important aspect in the implementation of a new technology such as an electron accelerator in a wastewater treatment plant is to anticipate its impact on the operation costs of the facility and on the environment. In a recent investigation, the number of kWh used during the irradiation process of the sewage sludge was considered. Data were obtained from the electrical supply company delivering power to the NEO Beam accelerator facility (Toledo Edison, Toledo, Ohio) on the day of the experiment. Energy consumed by the electron accelerator recorded in **Figure 7** shows a relatively stable plateau in the power consumed at the facility prior to sample irradiation. The dosimetry calibration of the irradiation setup started at 9:30 am with an increase of the beam current from 0 to 46.2 mA in equal time intervals. From 9:30 am until the end of the irradiation procedure, we observed a constant increase in power consumption. However, the graph only shows electricity consumption from 9:30 am until 10:00 am.

**Figure 7.** Average power consumed at the NEO Beam electron facility on the day of the experiment (information pro‐ vided by Toledo Edison, Ohio, USA) [7].

The power consumed at a specific irradiation dose was obtained in terms of the beam current used, and the cost was determined to be \$0.115/kWh. Therefore, at irradiation doses 6.7 and 25.7 kGy, the costs were \$1.10 and \$1.26 per m3 of sludge, respectively. This represents only 15% of increase of the cost when quadrupling the dose of irradiation to achieve the required *Ascaris* ova reduction to a class A biosolids, suggesting that when selecting a higher dose of irradiation of sludge, the increase in cost due to the use of higher beam currents should not be a concern [7]. Similar results were obtained by other authors who estimated the cost of using electron beam and gamma radiation for the disinfection of sludge. However, experiments developed were performed under different considerations. Indeed, a team in Florida reported a cost of \$2.50 per 1000 gallons of sludge for a 1.5 MeV electron irradiation facility running at 160 gallons per minute, while another group compared gamma and electron beam irradiations for a sample of activated sludge and obtained treatment costs of \$4.20/m3 for gamma irradiation and \$2.10/m3 for electron beam irradiation, which are lower compared with \$4.85–\$5.19 when using conventional technology at the Central District Wastewater Treatment Facility in Miami Dade County [12]. Furthermore, a comparison was made between irradiation at dose 6 kGy and incineration of sludge samples and showed a cost of \$60.87/m3 for this latter compared with \$3.12/m3 when using gamma radiation. In both instances, gamma and electron beam irradiations prove to be more economic than incineration [13]. Taken altogether, these observations show that electron beam irradiation of sludge is less energy consuming, with shorter processing times, and a more environmental friendly technology compared to methods such as incineration.
