**3.1. Dose mapping: experimental procedure**

Prior to the determination of the dose using different accelerator parameters, the scanned beam on top of the sludge delivery system needed to be mapped in order to verify that all the water coming through the weir length of the sludge delivery system would be exposed to the electron beam. The delivery system consists of a stainless steel box 152 cm (59.8 in) long with two compartments, one for the incoming sludge and the other one to drain the irradiated sludge. The sludge is transferred from one compartment to the other through a weir located in the center of the box. Irradiation takes place at the top of the weir (**Figure 1**).

**Figure 1.** Irradiation dispositive used to irradiate sludge. (a) Overall view of the system, showing the accelerator scan‐ ner (1), the window blower (2), the electron beam shutter (3), the sludge delivery system (4), and the pipes delivering the sludge to the system (5). (b) Simulation of the process using tap water. (1) Lower portion of the accelerator scanner, (2) beam shutter, (3) weir, and (4) incoming water. The depth of the sludge layer at the top of the weir was about 0.3– 0.4 cm. (c) sludge sample (adapted from [7]).

To map the extent of the irradiation zone along the weir, a CTA film was taped to the top of the delivery system just underneath the scanner system of the accelerator and irradiated for 5 s using the following accelerator conditions: E = 3 MeV, I = 15 mA, and S = 100%. After irradiation, the optical absorption at 280 nm was measured along the film using a Genesys 5 spectrophotometer fitted with a driving mechanism to measure film strips. Aerial™ software determined the dose from the absorbance measurements.

#### **3.2. Dose mapping: results and discussion**

**Figure 2** shows a graph of the dose along the top surface of the weir to treat the sludge. The graph shows two features, the extent of the irradiation zone on top of the weir system and the dose uniformity along the weir. The graph shows an effective irradiation length of 127.5 cm which is shorter than the length of the weir itself (152 cm). In order to ensure that all sludge falling over the weir was irradiated, two pieces of aluminum tabs 10 cm long were fastened to each edge of the weir using C-clamps. These tabs shortened the effective weir by a total of 20 cm and allowed for all the sludge falling over the weir to be irradiated by the electron beam given the fact that the scanning angle of the electron beam is 18.5°. The graph also gives information about the uniformity of the electron beam on top of the weir and shows that the dose at the two ends of the weir is about 25% lower than the dose in the idle section of the weir. However, this measurement was taken under static conditions, and in the case of water or sludge, the liquid will not move on a laminar flow fashion and might have been receiving an average dose with variations of up to ± 12.5% assuming that part of the liquid moved on the middle section and another part on the extreme end of the weir. So, then it is reasonable to assume that with the movement of the sludge as well as with its mixing, this might be the maximum difference in dose achieved by the sludge.

**Figure 2.** Dose along the sludge delivery system. The measurements were taken using cellulose triacetate film irradiat‐ ed with 3 MeV electrons, 15 mA of current, 5 s of exposure time and 100% scanning aperture [7].

#### **3.3. Dose measurements: experimental procedure**

The dose delivered to the sludge was determined from temperature measurements made on the sludge before and after irradiation, after calibration in terms of dose with alanine pellets and films. The irradiation of alanine dosimeters produces free radicals that become trapped inside the solid matrix of the dosimeter and can be measured by electron spin resonance (ESR) spectrometry. The trapped radicals are stable over long periods of time, and their concentration can be directly related to the absorbed dose as determined from a calibration curve.

spectrophotometer fitted with a driving mechanism to measure film strips. Aerial™ software

**Figure 2** shows a graph of the dose along the top surface of the weir to treat the sludge. The graph shows two features, the extent of the irradiation zone on top of the weir system and the dose uniformity along the weir. The graph shows an effective irradiation length of 127.5 cm which is shorter than the length of the weir itself (152 cm). In order to ensure that all sludge falling over the weir was irradiated, two pieces of aluminum tabs 10 cm long were fastened to each edge of the weir using C-clamps. These tabs shortened the effective weir by a total of 20 cm and allowed for all the sludge falling over the weir to be irradiated by the electron beam given the fact that the scanning angle of the electron beam is 18.5°. The graph also gives information about the uniformity of the electron beam on top of the weir and shows that the dose at the two ends of the weir is about 25% lower than the dose in the idle section of the weir. However, this measurement was taken under static conditions, and in the case of water or sludge, the liquid will not move on a laminar flow fashion and might have been receiving an average dose with variations of up to ± 12.5% assuming that part of the liquid moved on the middle section and another part on the extreme end of the weir. So, then it is reasonable to assume that with the movement of the sludge as well as with its mixing, this might be the

**Figure 2.** Dose along the sludge delivery system. The measurements were taken using cellulose triacetate film irradiat‐

The dose delivered to the sludge was determined from temperature measurements made on the sludge before and after irradiation, after calibration in terms of dose with alanine pellets

ed with 3 MeV electrons, 15 mA of current, 5 s of exposure time and 100% scanning aperture [7].

determined the dose from the absorbance measurements.

maximum difference in dose achieved by the sludge.

**3.3. Dose measurements: experimental procedure**

**3.2. Dose mapping: results and discussion**

234 Radiation Effects in Materials

For the experiments described in this chapter, a Bruker eScan ESR spectrometer using an insert FL0041 to measure the alanine films and an insert PH0027 to measure the alanine pellets were used to measure the free radicals. In a first experiment, 40 alanine pellets and 40 alanine film strips were randomly selected and irradiated in order to make a calibration curve of the pellets. The pellets would be used to measure the dose in sludge once they were calibrated with the alanine films.

The 40 alanine pellets were divided into ten groups of four and were placed in small plastic bags 1.5 cm long and 0.5 cm wide, and sealed with heat. The bags with the pellets were placed on a piece of cardboard, one at a time, on top of one of the carts that would be conveyed through the electron beam. On the side of the individual bags, four alanine film strips were placed, to measure the dose. The cardboard was irradiated in the cart conveyor system of the NEO Beam facility Dynamitron electron accelerator and irradiated using the following beam parameters: 3 MeV electron energy and 100% scanning angle; the dosimeters were moving under the beam at a constant speed of 20.32 cm/s, and the current changed to give different dose values ranging from 2 to 40 kGy, according to **Table 1**. Once all the dosimeters were irradiated, the alanine films were measured to determine the dose in each run, and with this information and the measurement of the intensity of the ESR signal of the irradiated pellets, a calibration curve was constructed.


**Table 1.** Electron beam current values needed to produce the selected doses for alanine pellets running under the beam at 20.32 cm/s.

A second experiment consisted in irradiating a set of pellets in a pyrex baking dish containing cold tap water at a depth of 1.1 cm (7/16 in). The purpose of this experiment was to simulate the accelerator conditions needed to irradiate the sludge. Four vials per run were used, each containing three alanine pellets. These vials were placed into the baking dish and floated on top of the water. The electron beam parameters were set up such that the electron energy was 3 MeV and five runs were conducted underneath the electron beam. Each run had a constant speed of the samples equal to 23.3 cm/s and the following beam currents: 3.8, 9.6, 19.1, 38.3, and 45.9 mA. After irradiations, the dose from the ESR intensity of each alanine pellet using the Bruker eScan instrument was determined.

The next experiment measured the dose for a sample of water running through the delivery system to irradiate sludge and to relate those measurements to the temperature of the water coming in and going out of the system as measured by a set of thermocouples installed near the sludge delivery system in the influent and effluent pipes. Small sealed plastic bags containing two alanine pellets were introduced into the system through a "Tee" connection into the pipe where the water flowed and sent them through the irradiation zone. At this point, 300 gallons of water was being recirculated through the system at 50 GPM. Two sets of five runs were conducted. Beam conditions for each set were as follows for each run: E = 3 MeV, S = 100%, I = 3.8, 9.6, 19.1, 38.5, and 46.2 mA, respectively. After irradiation, the plastic bags with the alanine pellets were collected in a catch basket that would separate the sealed bags from the water. Some of the bags leaked water when they passed through the water pump that removed the irradiated water from the system. The bags that did not show water leaks were used to measure the dose. Dose measurements were then related to the temperature meas‐ urements from the thermocouples.

Finally, the dose in the sludge was determined from the temperature measurements with the thermocouples, after correcting for the dose measured by the alanine pellets.

#### **3.4. Dose measurements: results and discussion**

As mentioned earlier, the dose absorbed by the sludge was determined from temperature measurements in the sludge after a calibration with alanine pellets was performed. **Figure 3** shows the result of the dose calibration of the pellets when irradiated with alanine films in the cart conveyor system of the NEO Beam facility.

As stated in the experimental section, the pellets were calibrated using alanine films calibrat‐ ed at Risø National Laboratory and then used to calibrate the in-house Bruker eScan spec‐ trometer that measured the doses. After this, the calibrated pellets were used to determine the dose in the experimental setup to irradiate the sludge with the electron accelerator using different beam currents. Thus, the graph in **Figure 4** shows the dose recorded by the pellets run through the irradiation dispositive using water at different beam currents of the electron accelerator.

Elimination of Potential Pathogenic Microorganisms in Sewage Sludge Using Electron Beam Irradiation http://dx.doi.org/10.5772/62705 237

A second experiment consisted in irradiating a set of pellets in a pyrex baking dish containing cold tap water at a depth of 1.1 cm (7/16 in). The purpose of this experiment was to simulate the accelerator conditions needed to irradiate the sludge. Four vials per run were used, each containing three alanine pellets. These vials were placed into the baking dish and floated on top of the water. The electron beam parameters were set up such that the electron energy was 3 MeV and five runs were conducted underneath the electron beam. Each run had a constant speed of the samples equal to 23.3 cm/s and the following beam currents: 3.8, 9.6, 19.1, 38.3, and 45.9 mA. After irradiations, the dose from the ESR intensity of each alanine pellet using

The next experiment measured the dose for a sample of water running through the delivery system to irradiate sludge and to relate those measurements to the temperature of the water coming in and going out of the system as measured by a set of thermocouples installed near the sludge delivery system in the influent and effluent pipes. Small sealed plastic bags containing two alanine pellets were introduced into the system through a "Tee" connection into the pipe where the water flowed and sent them through the irradiation zone. At this point, 300 gallons of water was being recirculated through the system at 50 GPM. Two sets of five runs were conducted. Beam conditions for each set were as follows for each run: E = 3 MeV, S = 100%, I = 3.8, 9.6, 19.1, 38.5, and 46.2 mA, respectively. After irradiation, the plastic bags with the alanine pellets were collected in a catch basket that would separate the sealed bags from the water. Some of the bags leaked water when they passed through the water pump that removed the irradiated water from the system. The bags that did not show water leaks were used to measure the dose. Dose measurements were then related to the temperature meas‐

Finally, the dose in the sludge was determined from the temperature measurements with the

As mentioned earlier, the dose absorbed by the sludge was determined from temperature measurements in the sludge after a calibration with alanine pellets was performed. **Figure 3** shows the result of the dose calibration of the pellets when irradiated with alanine films in the

As stated in the experimental section, the pellets were calibrated using alanine films calibrat‐ ed at Risø National Laboratory and then used to calibrate the in-house Bruker eScan spec‐ trometer that measured the doses. After this, the calibrated pellets were used to determine the dose in the experimental setup to irradiate the sludge with the electron accelerator using different beam currents. Thus, the graph in **Figure 4** shows the dose recorded by the pellets run through the irradiation dispositive using water at different beam currents of the electron

thermocouples, after correcting for the dose measured by the alanine pellets.

the Bruker eScan instrument was determined.

236 Radiation Effects in Materials

urements from the thermocouples.

**3.4. Dose measurements: results and discussion**

cart conveyor system of the NEO Beam facility.

accelerator.

**Figure 3.** Calibration curve for the alanine pellets used to measure dose in this experiment. The dose was measured by alanine films and the response of the pellets as the ratio of the ESR intensity of the alanine to the internal marker of the pellet holder. The eScan instrument performed a trendline analysis on the experimental data obtaining a 4° polynomial as the best fit to the experimental data with a standard error of 0.0076 and an R2 = 0.9989.

**Figure 4.** Doses of electron beam irradiation in water. Doses were measured by alanine pellets as a function of the elec‐ tron beam current of the accelerator. Water was running in the system at a rate of 50 gpm, and the electron energy was 3.0 MeV [7].

At the same time, the increase in temperature of the water running through the sludge delivery system at constant flow rate of 50 gpm and different beam currents was recorded and com‐ pared with the dose given by the alanine pellets. This relationship was later used to determine the dose absorbed by the sludge when irradiated with the electron beam.

The flow rate during the irradiation of the sludge sample was 30 gpm instead of the 50 gpm originally selected for this experiment. In order to keep the doses within the interval selected for this experiment, it was decided to run the experiment at a reduced level of electron beam currents to compensate for this effect. The dose was determined then from temperature increase of the sludge by measuring the temperatures at the input and exit ports of the irradiation setup. **Table 2** presents results of the temperature increments and dose measure‐ ments as a function of the beam currents for the sludge sample running through the delivery system.


**Table 2.** Irradiation conditions used to achieve targeted doses. Sludge samples were flowing at a rate of 30 gpm [7].
