## 1 Introduction  
Many industries produce gaseous waste, which contains pollutants that are harmful for humans, animals, and the whole environment [1, 2]. Furthermore, these pollutants cause a variety of problems. Apart from industries, the creation of almost all building construction and indoor furnishing materials requires an enormous amount of chemicals [3, 4]. All of these synthetic materials (from wall paint to nail polish) produce many different volatile organic compounds (VOCs), which act as pollutants. Some of these VOCs, such as benzene, toluene, and their derivatives, are already registered as cancer-causing materials, which are primarily present in our indoor air nowadays [3, 5]. The indoor concentrations of several VOCs are 10 times higher than their concentrations outdoors [6].  
Therefore, it is very important to remove/reduce these VOCs contaminants in order to guarantee a healthier life [7]. Conventional treatment processes have their drawbacks. Hence, there is a dire need to develop sustainable processes, which have the potential to degrade these organic compounds. Amongthe modern treatment processes, the advanced oxidation processes (AOPs), such as the photocatalytic process, have already been investigated by several researchers [8; 9; 10; 11]. This photocatalytic process involves a solid phase catalyst composed of a semiconductor material (TiO\({}_{2}\), Fe\({}_{2}\)O\({}_{3}\)), which is brought into contact with a liquid or gas in the presence of a light source (photon) [12; 13; 14; 15]. The photons that are used to excite the semiconductor material cause the formation of electron-hole pairs, which ultimately leads to the formation of hydroxyl radicals (very reactive species) [14]. These hydroxyl radicals react with and degrade organic compounds. Other processes involve the use of an oxidant (H\({}_{2}\)O\({}_{2}\), O\({}_{3}\), or electrical current) as a source of energy in the presence of catalytic materials [16; 17]. These processes are called Fenton oxidation or electro-Fenton oxidation [18; 19; 20]. All previous studies used an oxidant or continuous energy for oxidation when interacting with pollutants, which means that they all used homogenous processes. The uniform dispersion of the catalyst plays a vital role in permitting better catalytic activity [21]. Many researchers have tried several ways to homogeneously disperse catalysts on the solid supports [22; 23; 24; 25; 26].  
In our previous studies, we demonstrated a heterogeneous photo-Fenton process by incorporating Fe\({}_{2}\)O\({}_{3}\) on zeolite socony mobil (ZSM)-5 [27; 28]. The main idea was to simultaneously utilize the porous adsorption qualities of ZSM-5 and its ability to be a semi-conductor, as well as Fenton's reagent properties of iron. The formed Fe-ZSM-5 was pre-irradiated with UV light and was applied for the removal of VOCs from air for the first time. The process showed a good regeneration ability and a high efficiency in the laboratory at batch scale.  
In the present study, we tried to implement the same idea on a semi pilot scale, with the aim of scaling up the technology for commercial use. For this purpose, (1) the Fe-ZSM-5 zeolite material was coated on the polyethylene tubes; (2) a modular reactor was designed to hold most of the catalyst coated tubes; (3) the modular reactor tubes were irradiated with UV lamps; (4) the reactor design parameters, such as linear velocity, surface loading rate (SLR), and surface retention time (SRT), were measured; and (5) finally, the plant was operated for six cycles so as to test its degradation and recyclability. Since the whole work was done on pilot scale, only the total removal of the VOCs was considered, rather than finding the exact % of adsorption and catalysis, although the used material has both properties.