Ion Exchange Trials

Secondary treated wastewater was further treated through the use of ion exchange resin. A 100L volume of wastewater was treated for 20 minutes in a mixing tank with 2L of anionic exchange resin. Ion exchange resin is primarily used for the removal of natural organic matter, a significant ozone scavenger that increases ozone demand.

In the non-spiked ion exchange trials, and following wastewater trials, three ozone dosages, consisting of a low, medium and high dose were calculated. These three doses were determined through analysis of the ozone gas concentration vs ozone gas volume data in previous experiments involving IX water samples. A representative average of all the trials was chosen for the calculation of ozone dosages applied in the following micropollutant trials with IX samples. Three trials with initial ozone gas flows of 60 l/hr were used to create this average (Figure 12). Further analysis of the data from each trial revealed that the flow of ozone gas to the reactor did not remain at the initial

measured flow of 60 l/hr. The ion exchange trials showed a higher, fluctuating gas flow rate in comparison to the other trials. This can be seen in the cumulative gas flow vs time in Figure 13, where the plotted trend lines show a ozone gas flow of 1.1 – 1.4 L/min of ozone gas, compared to the 0.96 – 1.1 L/min ozone gas flow seen in the demineralized water matrix trials. This change in gas flow is compensated for in an adjustment made in the calculated ozone uptake for the average trial used to determine the ozone dosages.

Figure 12: O3 gas concentration vs cumulative ozone gas volume for three similar IX trials plotted against an average of those three trials, ozone gas flow 78 l/hr

Figure 13: Cumulative ozone gas flow vs time, IX trials

Figure 14 shows the representative average plot of the ozone gas concentration vs cumulative ozone gas volume calculated from the three trials, two of which were

completed on April 18th _{and one trial on March 29}th_{. To determine the three dosages, the}

ozone uptake, seen in the period from 0 to 14L in Figure 14, was split into low, medium and high dosages for use in the non-spiked and spiked experiments. During this period, the ozone uptake equaled 40.3mg of ozone, a significant increase from the uptake seen in the demineralized and tap water samples. This increase is expected due to the higher level of treatment for dissolved solids and organic matter the previous two sample waters have undergone, compared to the relatively low level of treatment of the IX treated secondary wastewater sample.

Figure 14: Ozone gas concentration vs. time for IX treated wastewater, average gas curve used for ozone dose determination, ozone gas flow 78 L/hr

With the use of Figure 14 and subsequent calculations, three ozone dosages were determined from the ozone uptake (Table 17). The calculated ozone uptake of 40.3mg was split into three ozone dosages, a low dose of 5.2mg/l, a high dose of 10.3mg/l and high dose of 15.5mg/l.

Ozone Uptake (mg of ozone) Exposure Time (mins) Ozone Dose(mg/l)

Low Dose 13.4 1.5 5.2

Medium Dose 26.9 4 10.3

High Dose 40.3 13 15.5

Table 17: Calculated ozone dosages for the IX samples in the NS trials

Three trials were completed with non-spiked IX treated secondary wastewater matrix using the doses and exposure times described in Table 17. The purpose of these trials was to determine the practical settings for the experimental conditions of the OMP spiked experiments. The ozone gas flow was measured initially as 60l/hr for each individual trial, however the average flow varied from 60 – 90l/hr across the three trials performed.

The variation is gas flow observed in the three low, medium and high ozone dosage trials was due to variation in the measurement of the ozone gas flow, further explained in appendix III. Across all experiments in this research, a target ozone gas flow to the reactor was set at 60l/hr in order to achieve equal conditions between trials. In each experimental trial, an initial ozone gas flow from the generator was manually set to 60l/hr and measured prior to ozonation of the reactor chamber. Throughout the three IX trials measurements of the ozone gas flow into the reactor chamber indicated variations in the flow of ozone gas generated and delivered to the water sample. This variation was accounted for in the calculated ozone dosages for each of the trials by calculating a corrective ‘flow adjustment factor’. This factor is a ratio of the average ozone gas flow for each experiment, to the target flow of 60l/hr. The use of this factor is necessary as the ozone dosage delivered is calculated as a function of flow, and if the flow deviates from the 60l/hr rate, it must be accounted for. In the low dose trial for IX, the average ozone gas flow rate was 69l/hr, the flow adjustment factor for this trial is 1.15. This factor is multiplied by the ozone uptake during the period the reactor chamber is ozonated in order to better reflect the ozone dosage received by the water sample in the trial. This was performed for each of the following trials when the average ozone gas flow deviated significantly from the target ozone gas flow of 60l/hr.

Figure 15: Diss. ozone conc. vs. time, IX, low dose of 5.2mg, exposure time 1.5min, O3 flow rate

69 l/hr

Figure 16: Diss. ozone conc. vs. time, IX, medium dose of 10.3mg, exposure time 4min, O3 flow

Figure 17: Diss. ozone conc. vs. time, IX, medium dose of 15.5mg, exposure time 13min, O3 flow

rate 79 l/hr

Figures 18, 19 and 20 show the dissolved ozone concentrations over time for the low, medium and high ozone dosages, respectively. As the ozone dose applied increases, so does the residual ozone concentration following the end of ozonation of the water matrix. This ozone residual lasts for the shortest amount of time in the low dose (2 minutes), lasts for 10 minutes with the medium dose, and the largest ozone residual time is measured in the high dose (20 minutes).