Objetivo 3: “Pronosticar la probabilidad con la que un aspirante del área

As the resource consents become increasingly restricts, wastewater is tertiary treated before UV disinfected in some WWTP. For example, alum dosing is occasionally used in PNWWTP depending (see section 3.3.3.1), and membrane filtration is used after the secondary treatment in Fielding WWTP (see section 3.3.3.4). The tertiary treated

wastewater generally has high UVT, low TSS and low E. coli concentration, which favours the use of a traditional UV reactor (including the commercial unit).

In theory, the project prototype might only have the advantage at treating low UVT

wastewater. As mentioned in section 2.6.4, the project prototype has a non-submergible UV lamp configuration, which a significant amount of UV light can be lost due to the reflection. With low UVT wastewater disinfection, the loss of UV light as it pass through the fluid will be significant for the commercial unit. This means that the UV loss due to the reflection in the project prototype might be lower than the loss due to the low UVT wastewater in the commercial unit. However, with high UVT wastewater disinfection, the UV loss in the project prototype might be greater than the loss in the commercial unit. Therefore, the project prototype could only perform better than the commercial unit, when treating low UVT wastewater. In order to confirm this hypothesis and also evaluate the applicability of the project prototype for tertiary treated wastewater disinfection; the project prototype and the commercial unit were compared at the tertiary treatment of PNWWTP and Fielding WWTP.

83 | P a g e 4.3.3.1. PNWWTP tertiary treated wastewater test

Similar to the PNWWTP secondary treated wastewater test, the influent of the installed UV system was used, but the wastewater was alum dosed. Alum is a chemical, which can significantly reduce the concentrations of phosphorus, TSS and even microorganisms in wastewater. The wastewater had a UVT of 55%, TSS of 16 mg/L and an average E. coli concentration of 241.6 MPN /100 mL. The quality of the wastewater was overall improved, compares to secondary treated wastewater (without alum dosing). The UVT of the

wastewater was high, and TSS and E. coli concentration is low, indicating a relatively clear and ideal effluent for UV disinfection. The E. coli log reduction of the reactors in the PNWWTP tertiary treated wastewater test is plot in Figure 4-13.

2.0 1.5 1.0 0.5 0.0 2.0 1.5 1.0 0.5 0.0

watt per flow (W. min/L)

E. c o li lo g r e d u ct io n commercial unit prototype at 500 L/min prototype at 250 L/min

Figure 4-13, E. coli log reduction of the reactors in the PNWWTP tertiary treated wastewater test

It is noticed that the E. coli concentration of the wastewater was low, of which the UV disinfection would likely to be at the tailing region, so the microorganism will be harder to be disinfected (as discussed in section 2.4.3). However, the regressions of the project prototype and the commercial unit are reasonably linear, which suggests that the reactors were not operating at the tailing region.

84 | P a g e While Figure 4-13 indicating that the commercial unit performed better than the project

prototype, the statistical analyses suggest that the regressions of the commercial unit data and the project prototype data are the same. This suggests the project prototype performed worse than or equal to the commercial unit.

In Figure 4-13, the trend lines of the prototype at 500 and 250 L/min have similar slopes, but the trend line of 500 L/min is somewhat lower than the trend line at 250 L/min.

Nevertheless, the statistical analyses suggest that the regressions of the prototype data are similar. This suggests that the project prototype performed similarly at the operated flow rate of 500 and 250 L/min.

4.3.3.2. Fielding WWTP tertiary treated wastewater test The influent of the installed UV system in Fielding WWTP was used. The wastewater had a UVT of 64%, TSS of 7.5 mg/L and an average E. coli concentration of 134.3 MPN /100 mL. The quality of this wastewater was even better than the PNWWTP tertiary treated

wastewater. The E. coli log reduction of the reactors from Fielding WWTP tertiary treated wastewater test is plotted in Figure 4-14. While the reactors were tested up to 4 W. min/L, the E. coli concentration of the effluent (at 4 W. min/L) was too low to be detected, and therefore is not shown in the figure. Again, the reactors were unlikely operating at the tailing region, as the regressions are reasonably linear.

85 | P a g e 2.0 1.5 1.0 0.5 0.0 2.5 2.0 1.5 1.0 0.5 0.0

watt per flow (W. min/L)

E. c o li lo g r e d u ct io n commercial unit prototype at 500 L/min prototype at 250 L/min prototype at 130 L/min

Figure 4-14, E. coli log reduction of the reactors in the Fielding WWTP tertiary treated wastewater test

Figure 4-14 shows the data of the commercial unit and project prototype are overlapping. Also, the statistical analyses agree that the regressions of the reactors are the same. This indicates that the project prototype performed similar to the commercial unit.

Figure 4-14 shows most of the project prototype data at 500, 250 and 130 L/min are overlapping, except for the 250 L/min prototype data at 0.6 W. min/L. Nevertheless, the statistical analyses confirms that the regressions of the prototype data are the same. This suggests that the project prototype performed similarly at the operated flow rate of 500, 250 and 130 L/min.

It is noticed that Figure 4-14 shows that some negative E. coli log reduction data at low watt per flow range, where negative log reduction is insensible. This negative value is due to the variation of wastewater.

4.3.3.3. Summary of the tertiary treated wastewater test The project prototype and commercial unit were compared on the tertiary treated wastewater at the PNWWTP and Fielding WWTP. The wastewater in both tests was

reasonably clear and ideal for a traditional UV reactor disinfection. The results of the tertiary treated wastewater test are summarized in Figure 4-15.

86 | P a g e PNWWTP Fielding WWTP 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 P/ C

Figure 4-15, p/c of the project prototype and commercial unit in the tertiary treated wastewater test

Figure 4-15 shows that the p/c value of Fielding WWTP varied from 0.75 to 1.25 and the p/c value of PNWWTP varied from 0.35 to 0.55. On average, Fielding WWTP has p/c of 0.97 and PNWWTP has p/c of 0.48. This suggests that the project prototype performed similar to the commercial unit at Fielding WWTP, but 2.1 times (p/c of 0.48) worse at PNWWTP. This contradicts the results from the PNWWTP tertiary treated wastewater test, which suggested that the project prototype had no difference in performance from the commercial unit. The results in PNWWTP test were compared based on the overall performance of the reactors, so that the statistical analyses suggest that the performance of the reactors were similar. In contrast, the p/c value compares the performance of the reactors at individual points, where the result in Figure 4-13 does appear to show that the commercial unit was better than the project prototype, at certain points of watt per flow. Overall, the test confirms that the project prototype only has advantage at treating low UVT wastewater, but not high UVT wastewater.