# VOC Removal from Manure Gaseous Emissions with UV Photolysis and UV-TiO\({}_{2}\) Photocatalysis
## 2 Results and Discussion  
### UV Treatment of Odorous VOCs in Synthetic Mixture  
#### 2.1.1 Effects of UV Light dose, Wavelength, and Catalyst on VOC Conversion  
The effect of light energy dose at 254 nm was evaluated by varying exposure times through variation of flow rates of the synthetic VOC mixture through the reaction chamber (at a relatively low light intensity, i.e., \(I<0.084\) mW cm\({}^{-2}\)). Percent conversion, \(R\) (defined in Equation (1), in Methods), is presented in Figures 1 and 2 for UV\({}_{185+254}\) lamps, and for UV\({}_{254}\) lamps, respectively. The difference between the UV\({}_{254}\) and UV\({}_{185+254}\) lamps is only the grade of quartz used on the outer sleeve. The latter use a pureurtz material that transmits the 185 nm emission, though \(>\)90% of the light is still at 254 nm. The effects of TiO\({}_{2}\) use were compared with and without a catalyst either at 185 + 254 nm (Figure 1A: UV\({}_{185+254}\) + TiO\({}_{2}\) vs. Figure 1B: UV\({}_{185+254}\), no catalyst) and at 254 nm (Figure 2A: UV\({}_{254}\) + TiO\({}_{2}\) vs. Figure 2B: UV\({}_{254}\), no catalyst). Positive \(R\) values indicate VOC removal, whereas negative values indicate the formation of target VOCs, presumably as intermediate byproducts during photodegradation of parent compounds [44]. Supporting data for Figures 1 and 2, including measured gas concentrations, % VOC conversion, and VOC mass removed per unit of UV energy input (ng J\({}^{-1}\)) are presented in Tables S1-S4. Figure 1: Treatment of target odorous VOCs in a synthetic mixture with UV lights of 254 nm and 185 nm outputs. Effects of light energy dosage (at different treatment times) on VOC percent conversion, \(R\): (**A**) UV\({}_{185+254}\) + TiO\({}_{2}\) (treatment mainly via photocatalysis); (**B**) UV\({}_{185+254}\); no catalyst (treatment mainly via photolysis). Experimental conditions: UV intensity at 254, 312 and 395 nm was 1.5, 0.23, and 0.084 mW cm\({}^{-2}\), respectively; 25 mg TiO\({}_{2}\); T = 25 \({}^{\circ}\)C; dry air; sampling conditions: 5 min solid-phase microextraction (SPME) sampling time with CAR/PDMS 85 μm. The light energy dosage is based on the output at 254 nm only. The results obtained for the synthetic VOCs mixture confirmed that it is feasible to control odorous VOCs with both photolysis and photocatalysis. The UV treatment effectiveness (expressed as \(R\), Equation (1)) followed the general order of UV\({}_{185+254}\) + TiO\({}_{2}\) > UV\({}_{254}\) + TiO\({}_{2}\) > UV\({}_{185+254}\), no catalyst > UV\({}_{254}\), no catalyst, i.e., photocatalysis with deep UV being the most effective. Percent conversion increased with light energy dose up to \(\sim\)60 s of treatment time and up to \(\sim\)60 J/L. The linearity of \(R\) and light energy dose (summarized in Table S5) showed correlation coefficients R\({}^{2}\) ranging from 0.79 to 1.0. Improved R\({}^{2}\) (0.89-0.98 in Table S5) was observed when linearity was expressed as VOC mass removed as a function of light energy dose. The reproducibility of treatment effectiveness expressed as the average  
Figure 2: Treatment of target odorous VOCs in a synthetic mixture with UV lights of 254 nm principal output (i.e., no deep UV 185 nm output). Effects of measured light energy dosage (at different treatment times) on VOC percent conversion, R: (**A**) UV\({}_{254}\) + TiO\({}_{2}\) (treatment mainly via photocatalysis); (**B**) UV\({}_{254}\), no catalyst (treatment mainly via photolysis). Experimental conditions: UV intensity at 254 nm, 312 nm and 365 nm was 1.5, 0.230, and 0.084 mW cm\({}^{-2}\), respectively; 25 mg TiO\({}_{2}\); T = 25 \({}^{\circ}\)C; dry air; sampling conditions: 5 min SPME sampling time with CAR/PDMS 85 \(\upmu\)m. The light energy dosage is based on the output at 254 nm only. relative standard deviations (RSDs) ranged from 1.76% to 6.37% for target VOCs (Table S6). A significant (\(p\geq 0.05\)) percent conversion of VOCs (>80%) was achieved when light energy was >60 J L\({}^{-1}\).