Prueba de hipótesis

Kim et al. (2009) [357] and Afonso-Olivares et al. (2016) [105] reported fluence90 values of 30,

respectively 23 TrOCs in photolysis and/or UV/H2O2 AOP. A comparison of their reported

values and fluence90 values obtained here is presented for overlapping TrOCs in Table 4.2.

Table 4.2: Comparison between UV fluence90 in different processes.

TrOC

fluence90 (mJ cm-2₎

photolysis photolysis ARP AOP AOP blanc (milli-Q)1 wastewater effluent2 blanc (milli-Q)1 wastewater effluent2 wastewater effluent3 metoprolol 2073 3959 11264 657 - diclofenac 193 123 272 113 60 sulfamethoxazole 323 285 414 314 278 clofibric acid 1028 - 1722 - 601 ketoprofen < 120 38 146 45 57 caffeine 33111 - 1675 - 2369 theophylline n.d. 4496 3704 884 - carbamazepine 1597 5413 402 605 1378 propranolol 6254 2277 1779 515 1082 paracetamol 32396 2852 6748 660 - phenazone 752 328 552 293 - ibuprofen 21873 - 16670 - 1214 gemfibrozil 26727 - 20180 - 830 naproxen 5507 1690 3342 434 252 clenbuterol 1427 2368 746 839 -

1 _{current study: 5 mM SO32- dose for ARP} 2 _{Kim et al. (2009) [357]: 8.2 mg L}-1 _{H2O2 dose for AOP} 3 _{Afonso-Olivares et al. (2016) [105]: 20 mg L}-1 _{H2O2 dose for AOP}

-: not included in study

n.d.: not determined due to no observed removal

In general, the photolysis fluence90 values obtained in our study are in relatively good agreement

with those obtained by Kim et al. (2009) [357], despite differences in water matrix: solutes which show fast removal have low fluence90 values and solutes which are less reactive have a high

fluence90. Still, some differences may be noticed, especially for the slower reacting solutes.

Carbamazepine has a fluence90 in wastewater of 5413 mJ cm-2, while in our study we found 1597

mJ cm-2_{. On the other hand, we found higher fluences}

90 for paracetamol and naproxen compared

to Kim et al. (2009) [357]. These differences may be attributed to the latter study being performed in wastewater effluent with a different set of TrOCs, inorganic constituents and different DOM types, which may influence degradation compared to our study.

Interestingly, fluences90 are, with the exception of carbamazepine and clenbuterol, always higher in

ARP than in AOP, despite the difference in water matrix. This proves that ARP react slower compared to AOP. Kim et al. (2009) [357] applied a H2O2 dose of 8.2 mg L-1, corresponding to a

potential generation of 0.5 mM OH• _{out of H}

2O2, and Afonso-Olivares et al. (2016) [105] dosed

20 mg mg L-1 _H

2O2, corresponding to a maximum of 1.2 mM OH• generated out of H2O2. In our

study, a maximum of 5 mM of 𝑒𝑎𝑞− /𝐻• may be produced as reactive species, thus much higher than

for Kim et al. (2009) [357] and Afonso-Olivares et al. (2016) [105]. The generally higher fluence90

in ARP may be due to the lower effective quantum yield of reducing radicals from sulfite at UV253.7 nm (i.e., production of reactive species per einstein of 253.7 nm photons) being

0.116 𝑚𝑜𝑙_𝑒𝑎𝑞− 𝑒𝑖𝑛𝑠𝑡𝑒𝑖𝑛_{𝑝ℎ𝑜𝑡𝑜𝑛𝑠 253.7 𝑛𝑚}−1 [162], whereas the effective OH• quantum yield in UV_253.7 nm/H2O2 is 1.02 𝑚𝑜𝑙𝑂𝐻• 𝑒𝑖𝑛𝑠𝑡𝑒𝑖𝑛𝑝ℎ𝑜𝑡𝑜𝑛𝑠 253.7 𝑛𝑚−1 [102]. Since the quantum yield in UV/sulfite is

lower, a lower amount of radicals are being produced. Therefore a slower reaction compared to UV/H2O2 can indeed be expected. Note that a higher effective quantum yield may be achieved at

different wavelengths. 𝑆𝑂₃2− shows an absorption peak around 210 nm [166], which indicates a higher effective quantum yield of hydrated electrons may be achieved using a zinc lamp, emitting UV light at 213.9 nm [358].

4. Conclusions

This study focused on TrOC removal in artificially created inorganic and organic water matrices with UV253.7 nm photolysis and the UV/sulfite advanced reduction process. A set of 29 TrOCs was

used, having a large range of physico-chemical structures and properties. Inorganic matrix substances included NaCl and Na2CO3, organic matrices were Nordic Reservoir natural organic

matter, humic acid and alginate. As far as we know, this is the first multi-solute study addressing influences of matrix constituents on removal of TrOCs with reducing radicals. The following conclusions can be drawn.

 In photolytic TrOC degradation, both NaCl and Na2CO3 results, in general, in a lower

TrOC degradation compared to milli-Q, as indicated by higher UV253.7 nm fluences90. This

may be attributed to a higher ionic strength upon addition of inorganics, which can deactivate photolytic generated excited states of TrOCs or by quenching TrOC based radicals formed during photolysis. Exceptions to the general trend are dimethoate, paracetamol and naproxen for both inorganics, and dinoseb and diatrizoic acid for Na2CO3

 Also organic matter, in general, decreases photolytic TrOC degradation. The extent of inhibition follows the order of NR-NOM > HA > alginate, indicating inhibition is dependent on DOM characteristics. Ibuprofen and gemfibrozil are however removed better in presence of NR-NOM, caffeine degradation was higher with HA and dimethoate degradation was benefited by each DOM type, indicating photolytic reactive species produced from DOM (such as 1_O

2 or 3DOM*) can play an important role in TrOC removal.  NaCl generally does not affect TrOC degradation in the UV/sulfite ARP, as opposed to photolysis. A bicarbonate water matrix shows to influence TrOC degradation to a larger degree, with halogenated solutes being removed more easily in presence of bicarbonate. However, except of triazine herbicides, no increased formation of dehalogenation products is observed in presence of inorganics, indicating that it is likely that other transformation products than dehalogenation products are being formed in parallel.

 Dissolved organic matter affects TrOC degradation in the UV/sulfite ARP to different extents. NR-NOM generally increases the TrOC (i.e. parent compound) removal efficiency, however this is accompanied by a lower formation and slower subsequent degradation of reduction products, indicating that different transformation products are formed. It is theorized that presence of Na2SO3 enhances the transfer of photolytic generated reactive

entities from NR-NOM. Humic acid and, to a lesser degree, alginate, decrease TrOC degradation, while reduction product formation and subsequent degradation was not largely affected.

 Regardless of matrix substances, dehalogenation products are still being formed well in ARP conditions compared to photolysis.

 Compared to UV/H2O2 AOP results obtained from literature, fluence90 in the UV/sulfite

ARP is generally higher than in AOP, indicating higher energy inputs are necessary in ARP to achieve the same TrOC removal degree from AOP. This may be due to a lower quantum yield at UV253.7 nm irradiation of reducing radicals from sulfite as opposed to oxidizing

radicals from hydrogen peroxide.

These results indicate that the UV/sulfite ARP may be influenced by different matrix constituents, both positively or negatively. Further research should focus on an in-depth identification and quantification of reduction products, as well as further identifying and understanding the different mechanisms at play. Additionally, in order to make ARPs competitive with AOPs, methods to achieve higher yields of reactive entities should be investigated.

Chapter 5:

Selective removal of trace organic