# VOC Removal from Manure Gaseous Emissions with UV Photolysis and UV-TiO\({}_{2}\) Photocatalysis
## 1 Introduction
Interestingly, photolysis alone has been recognized as a potentially effective treatment for inactivation of livestock pathogens for addressing biosecurity issues, although it is well understood that pathogen inactivation does not require the complete chemical degradation or the organisms. Inactivation of aerosolized porcine respiratory and reproductive syndrome virus (PRRSV) and bovine viral diarrhea virus (BVDV) with UV\({}_{254}\) was described by a two-stage inactivation model by [PERSON] et al. [41]. In this paper, we focus on chemical rather than biological pollutant mitigation. It should be understood that the photocatalytic degradation of gaseous pollutants is an example of heterogeneous catalysis. From a practical standpoint, the overall process for the classical heterogeneous catalysis can be visualized in five steps as described by [PERSON] [42] (with graphical representation and generic reactions):  
1. Transfer of the reactants to the surface;
2. Adsorption of at least one of the reactants to the catalytic site;Reaction or reactions in the adsorbed phase;
* Desorption of the product(s) from the active site(s);
* Removal of the products from the interface. Photocatalysis requires activation of the catalyst by photon absorption, which can generally be considered as occurring under the scope of Step 3, i.e., the reactions happening while the pollutants are adsorbed. It is clear that the rate of photocatalytic degradation can be increased through better adsorption or through changes that make those adsorbed reactions faster and/or more photochemically efficient. [PERSON] [42] provided a review of these concepts as they are applicable to photocatalysis, a full summary of which is beyond the scope of this paper. However, key results are that the rate of photocatalytic degradation of gas phase materials can be increased through increasing adsorption or by increasing the rate of reactions on the surface. Rational approaches to increase adsorption include increasing the surface area of the catalyst itself or making a composite material with another adsorbent such as activated carbon [43]. The rate or efficiency of the chemical processes can be affected by using a modified catalyst (e.g., doping with nitrogen) [42], but this is beyond the scope of our work, in which we rely on an inexpensive commodity (TiO\({}_{2}\)). Other approaches have been studied, which include the addition of electron acceptors, such as oxygen, ozone, and hydrogen peroxide (these work primarily by providing a very rapid reaction that reduces photon wastage [42]). Again, while useful under certain circumstances, for the practical, low-cost applications being studied here, the ambient conditions must be relied on. The parameters that are practical for examination here relate to light intensity, light wavelength, ambient temperature, and the effect of humidity. _Objectives_ In this paper, we report on a study evaluating the feasibility of direct UV photolysis and UV/TiO\({}_{2}\) photocatalysis to treat synthetic air mixtures of key VOCs associated with livestock odor. As variables, we considered the effects of (i) UV light energy dose and wavelength, (ii) the presence of catalysts (TiO\({}_{2}\)), (iii) relative humidity, and air temperature. Additionally, we demonstrated the feasibility of UV/TiO\({}_{2}\) photocatalysis to treat VOCs and odor of real poultry manure atmosphere. Specially designed flow-through photoreactors were built at Iowa State University (USA), for treating synthetic VOCs gas mixtures in a flowrate scale of hundreds of mL min\({}^{-1}\) and at the Agricultural Research Organization, Israel for real poultry manure atmosphere testing in a flowrate scale of tens of L min\({}^{-1}\). Experimental designs covered all features needed to simulate barn exhaust conditions, e.g., flowing air, short treatment times, and the presence of other gaseous compounds and moisture.