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<br /> <br />Trojan measured the concentration of H 2 O2 using the N,N-diethyl-p-phenylenediamine <br />(DPD)/Peroxidase method based on that described by Bader & Hoigne (Wat. Res., Vol. 22, No. 9, pp. <br />1109-1115). A Hach DR890 colorimeter was used for this method. <br />Prior to collecting samples, the sample ports were flushed to waste to ensure that the collected sample <br />was representative of what was in the adjacent pipe at the time of sampling. The ports were flushed <br />and samples collected at approximately 200 ml/min to minimize the disruption of flow through the UV <br />system. Further, the sampling procedure comprised collecting the influent sample first followed <br />immediately by the effluent sample once the system was at steady state. <br /> <br />5 RESULTS AND DISCUSSION <br />The results of the tracer test are summarized in Figure 3. This test was performed at 0.5 gpm and <br />H 2 O 2 injection was initiated at time zero. Influent and effluent samples were subsequently collected <br />every 5 or 10 minutes and analysed for H 2 O 2 concentration. As Figure 3 demonstrates, the influent <br />H 2 O 2 concentration climbed rapidly and plateaued between about 6.5 to 7.0 mg/L by slightly more <br />than 5 minutes after turning the pump on. The effluent H 2 O 2 concentration did not reach the same <br />level until after 15 minutes and the two sample ports did not reach the same concentrations (i.e., steady <br />state) until about 30 minutes after beginning the test. To be conservative, it was decided to wait for 40 <br />minutes after adjusting the operating conditions before collecting samples for runs performed at 0.5 <br />gpm. The corresponding times to reach steady state for the 1 gpm and 2 gpm tests were 20 minutes <br />and 10 minutes respectively. <br /> <br /> 10