*2.3.1. Water radiolysis*

*Catalyst Application*

**Cu** Alumina Phenol

Silica

Sr115

**Pt, Ru** Carbon black composite Silicatitania

Zirconia

cerium oxide

Cerium oxide Titania

Cerium oxide Titania-cerium oxide

**Table 3.** Summary of reported heterogeneous catalytic WO research [38, 57, 77-100]

**Ru, Ru-Ce** Alumina isopropyl alcohol

Titania-cerium oxide Zirconia-

**Ru oxide** Titania

**Ru, Pt** Zirconia

**Ru, Pt** Titania

**Cu** Alumina

166 Wastewater Treatment Engineering

**Mn** Alumina

**Active Phase Carrier Substrate Reference**

**Cu-Zn-Al oxide** Alumina phenol compounds Pintar et al. 1992 **Cu-Mg-La** Zn aluminate acetic acid Box et.al. 1974,

**Mn-Ce** None polyethylene-glycol Imamura et al.1986 **Mn-Zn-Cr** None industrial wastes Moses et al. 1954 **Cu-Co-Ti-Al** Cement phenol Schmidt et. al. 1990 **Co** None alcohols, amines, etc. Ito et. al. 1989 **Co-Bi** None acetic acid Imamura et. al.1982 **Co-Ce** None ammonia Imamura et. al. 1985 **Fe** Silica chlorophenols Sanger et. al. 1992 **Ru** Cerium oxide alcohols, phenols, etc Imamura et. al. 1988 **Ru-Rh** Alumina wet oxidized sludge Takahasi et. al. 1991 **Pt-Pd** Titania-zirconia industrial wastes Ishii et. al. 1991 **Ru** Titania-zirconia industrial wastes sludge Harada et. al. 1993 **Pt** Alumina phenol Hamoudi et. al. 1998 **Mn** Cerium oxide phenol Hamoudi et. al. 1998 **Ru** Titania phenol Vaidya et. al. 2002

**Ru** Pelletized cerium oxide Zirconia phenol Wang et al. 2008

**Pt, Ru** Cerium oxide, Zr-(Ce-Pr)-O2 phenol Keav et. al. 2010

**Graphene oxide (GO)** None phenol Yang et. al. 2014

phenol acetic acid DMF

Phenol p-cresol

phenol chlorophenols Sandra et. al. 1974 Kim et al. 1991 Mishra et. al. 1993

Levec et. al. 1976

Sandra et. al. 1974 Sanger et. al. 1992

chlorophenols Sanger et. al. 1992

phenol Cybulski et. al. 2004

acetic acid Wang et. al. 2008

acetic acid Lafaye et. al. 2015

phenol Espinosa de los Monteros et. al. 2015

Yu et. al. 2011

In the interaction between ionizing radiation (high-energy electron beam, gamma rays) and water, electronically excited and ionized molecules are formed and the product of it will be primary species such as *⋅*OH, eaq, H*⋅*, and molecular products such as H2, H2O2. In the presence of oxygen in water the reducing species H-atoms and the solvated electrons (eeq) are converted into oxidizing species, perhydroxy radicals (HO2*⋅*) and perhydroxyde radical anions (HO2*⋅*). The last one together with the OH*⋅* radicals are responsible for the degradation of water pollutants.

$$\mathrm{H\_2O} \rightarrow \mathrm{OH} \star \mathrm{\cdot} \mathrm{e\_{aq}}^- + \mathrm{H} \star \mathrm{\cdot} \mathrm{H\_2O\_2}$$

**Figure 3.** Radiolysis of water.

The radiation induced degradation of neutral phenol solution was studied in the past using end-product techniques [101-105]. There are other few works on mechanistic studies on phenol and other aromatic molecules that were carried out by combining end products and transient detections and it was suggested that the transformations were initiated by hydroxyl radical attachment to the ring and reaction of O2 with the radicals produced [106-108].

Pulse radiolysis of 2,6-dichloroaniline in dilute aqueous solution was investigated. It is known that mono- and dichloroanilines are considered to be highly hazardous pollutants in waste‐ water. These compounds are important chemical intermediates of dye and plant protection agent production. In this investigation, the hydroxyl radical formed in water radiolysis was reacted with 2,6-dichloroanliline forming hydroxy-cyclohexadienyl derivative. The irradiation was carried out at room temperature by a 60Co γ-source, built into a panorama irradiator, with 1.5 kGy h-1 dose rate. The hydroxy-cyclohexadienyl radical in the absence of dissolved O2 partly transformed to anilino radical when oxygen was present in the reaction mixture the radical transformed to peroxy radical. According to chemical oxygen demand measurements, the reaction of one OH*⋅* radical induced the incorporation of 0.6 O2 into the products [109].

The irradiation-induced decolorization and degradation of aqueous solutions of azo dyes and some intermediates (anilines, phenols, triazines) were successful with electron beam irradia‐ tion. The experimental methods were the pulse radiolysis and end-product analysis with HPLC-MS. Demonstrating the practical applicability of this method, a continuous irradiation device has been built. The feed was the dye containing water of red color; the effluent was the colorless liquid during contact time of less than 0.1 second with the high energy electron beam (4 MeV) generated by a linear electron accelerator [110].

The other topic is the investigation of the degradation of pharmaceuticals that can be detected in natural waters as emergent pollutants. The radiation-induced degradation of ketoprofen in dilute aqueous solution has been tested. The intermediates and final products of ketoprofen degradation were determined in 0.4 mmol/dm3 solution by pulse radiolysis and gamma radiolysis. UV-Vis spectrophotometry and HPLC separation served for identifying the product compounds [111].

The successful degradation of organic molecules being in small concentration in waters, with high-energy irradiation generating radicals already at room temperature prompted us to combine this method with WO. Recently, this hybrid method was used and compared with the classical WO method. Noticeable conversion was observed in phenol oxidation by irradiation already at room temperature in the presence of high concentration of dissolved oxygen [112].

In one of the recent studies, WAO of highly concentrated emulsified wastewater was con‐ ducted. These kinds of wastewater usually contain all kinds of organic matters such as surfactants, additives, and mineral oils. They are typical, highly concentrated hardly biode‐ gradable organic wastewaters. This oxidation took place in a 2 L high-pressure autoclave in batch mode. The initial COD concentration of the wastewater was 48000 mg/L. After 2 h of oxidation at 220°C with supply of oxygen 1.25 times more than its theoretical value, the COD was reduced by 86.4%. The temperature seemed to be a key influential factor, especially between 180°C and 220°C the COD and TOC removal was evidently increased. They also recognized that with increasing the initial partial pressure of oxygen (pO2), the reaction rate significantly increased [113].
