# VOC Removal from Manure Gaseous Emissions with UV Photolysis and UV-TiO\({}_{2}\) Photocatalysis
## 3. Materials and Methods
#### 3.1.2 Photolysis Treatment  
A photoreceptor was designed as a flow-through reaction chamber and used for the treatment of a synthetic odorous VOC air mixture (Figure 6 and a photo in Figure S9 in Supplemental Materials).  
This reaction chamber was capable of testing the effects of several variables, including UV wavelength, light energy dose, relative humidity, temperature, and the presence of a catalyst. UV dose was measured with a radiometer with UV-A, -B, and -C (a.k.a. \"deep\" UV) sensors over the controlled treatment time. An on/off switch was used to precisely control the time of UV light-on operation. The chamber temperature was controlled at 25 \"C for all the experiments, except when the effect of temperature was tested. The synthetic gas mixture was routed from the SGG system to feed the photoreceptor and remained in flow-through mode at a steady-state. The photoreceptor was  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**VOCs**} & **ODT * in Air** & \multicolumn{2}{c}{**Odor Descriptor**} \\ \cline{2-4}  & **(ppbv)**[50] & **Flavornet**[51] & **LRI**[52] \\ \hline Methyl mercaptan & 1.05 & sulfur, gasoline, garlic & rotten cabbage, sulfurous \\ Ethyl mercaptan & 1.07 & N/A & earthy, egg, garlic, onion \\ Dimethyl sulfide & 2.24 & cabbage, sulfur, gasoline & asparagus, cabbage, sulfurous \\ Butyl mercaptan & 1.41 & N/A & diffusive, skunky, sulfurous \\ Acetic acid & 363 & sour & acetic, vinegar \\ Propanoic acid & 35.5 & pungent, rancid, soy & N/A \\ Butyric acid & 3.89 & rancid, cheese, sweat & butter, cheese, musty, oily \\ Isovaleric acid & 2.45 & sweat, acid, rancid & cheese, old hop, old socks, sweaty \\ \(p\)-Cresol & 1.86 & medicine, phenol, smoke & medicinal, phenolic, smoky, tarry \\ \hline \hline \end{tabular}  
* ODT, odor detection threshold, N/A = not available.  
\end{table}
Table 3: Odor characteristics of target odorous VOCs used to prepare a synthetic air mixture.  
Figure 6: A scheme of the lab-scale UV photoreactor (0.57 L) in a temperature-controlled chamber. The system includes a data acquisition system for (1) UV lamp status and electric voltage and current; (2) UV light intensity; and (3) light intensity controlled with distance “x” between the lamp and treated air.  
equipped with two toggle valves so that the photodegradation of static air tests could also be carried out. However, severe VOC adsorption and losses to the reactor surface during initial testing of static air scenarios were observed. Thus, all experiments were completed with dynamic airflows, a more realistic scenario for farm-scale applications. The dynamic airflow configuration was also easier to control per establishing steady-state conditions per the aforementioned sorption and losses. Light penetrated the reaction chamber through a quartz top side. Two sets of six 10 W UV mercury lamps (American UV Co., Lebanon, IN, USA) were used to test the effects of UV wavelength. The first group of lamps had a principal output of characteristic UV bands at 254, 312, and 365 nm, i.e., the typical output of germicidal lamps. The second set of lamps had a significant output in the 185 nm in addition to the 254, 312 and 365 nm bands. These two sets of wavelengths were designated \"UV\({}_{254}\)\" and \"UV\({}_{185+254}\)\" (\"deep\" UV) in this manuscript. The far UV lamps, of fused quartz, emit ultraviolet light with two peaks in the UVC band at 253.7 nm and 185 nm due to the mercury within the lamp, as well as some visible light. Ca. 90% of the UV produced by these lamps is at 253.7 nm, whereas only ca. 10% is at 185 nm [54].