# VOC Removal from Manure Gaseous Emissions with UV Photolysis and UV-TiO\({}_{2}\) Photocatalysis
## 1 Introduction  
Public awareness of nuisance odor emissions from livestock facilities is growing. Confined animal feeding operations (CAFOs) are sources of aerial emissions of odorous volatile organiccompounds (VOCs), ammonia (NH\({}_{3}\)), hydrogen sulfide (H\({}_{2}\)S), greenhouse gases (GHGs, e.g., CO\({}_{2}\), CH\({}_{4}\), N\({}_{2}\)O), and particulate matter (PM) including bioaerosols. The VOCs emitted by CAFOs have been characterized extensively. The 2007-2009 National Air Emissions Monitoring Study (NAEMS) was completed in the U.S. and resulted in several publications specifically focused on quantitative odor and VOC emissions from swine barns and dairy operations [1; 2; 3; 4]. Multiple studies presented volatiles speciation and characterized key odorants in emissions from poultry and swine [5; 6] and for VOC emissions from beef and dairy cattle [7; 8; 9; 10]. Livestock odor is a global issue and is of interest to the international community of researchers. [PERSON] et al. [11] reported on NH\({}_{3}\), volatile fatty acids (VFAs), and other odorants near beef feedlots in Canada. Emissions of VOCs from swine and dairy barns in Denmark and Germany were published by [PERSON] et al. [12] and [PERSON] et al. [13]. A close relationship is now well established between VOCs and livestock odor [6; 7; 14; 15; 16; 17; 18]. Research studies on the relationship between VOCs and odor track back to the 1970s, when 10 compounds indicated as \"interesting for the manure odor\" were identified: indole, skatole, phenol, \(p\)-cresol, and carboxylic acids containing two to five carbons [19]. Indoles, VFAs, and methanethiols were determined as key compounds of pig odor [20]. _Odor mitigation research_: Researchers have been working on cost-effective and practical solutions to livestock odor emissions. Odor, VOCs, GHGs, NH\({}_{3}\) and H\({}_{2}\)S mitigation technologies for livestock operations have been reviewed [21]. The main approaches for livestock housing include barriers, biofiltration, chimneys, diet modification, electrostatic precipitation, landscaping, oil sprinkling, manure pit additives and ventilation, scrubbers, siting, and setbacks, urine/feces separation, and UV light [22; 23; 24; 25; 26; 27; 28; 29; 30]. To date, however, these technologies, save for biofilters and scrubbers, have a limited on-farm implementation and performance record in the U.S. due to complex regulatory and socioeconomic factors. Nevertheless, comprehensive solutions to livestock odor that have potential for field adaptation will be needed in the foreseeable future as the global demand for animal-based protein increases in parallel to increasingly stringent air pollution and odor regulations worldwide. _UV and livestock farming_: The treatment of air with UV has many potential benefits for livestock housing. Incoming air could be treated to inactivate airborne pathogens. Air quality inside the barn might be improved, and the pathogen load reduced. Perhaps more obviously, gaseous emissions could also be treated with an \"end-of-the-pipe\"-type system. A potential advantage of UV is that it could easily be synchronized with atmospheric conditions and environmental management at the farm. Another advantage is the minimal impact on ventilation, a key environmental parameter for animal well-being. _Photocatalysis_: There is a growing interest in using photocatalysis for the treatment of odor and gases from livestock operations [31; 32]. Studies have been carried out on odorous VOCs [33; 34; 35]; NH\({}_{3}\) and GHGs [36; 37; 38; 39; 40]. To date, most studies focused on lab-scale treatments except those of [PERSON] et al. [36] and [PERSON] et al. [37], carried out at a swine barn. This idea is based on the use of UV light to mineralize odorants to odorless or less odor-offensive compounds, ultimately converting them into CO\({}_{2}\), H\({}_{2}\)O, and other inorganic compounds with or without a photolysis catalyst present.