Ozone use in Groundwater Remediation ENVS522 – Environmental Chemistry Muhammad Said Abdallah Instructor: Dr. Bassam S. Tawabini

Outline Introduction Major Uses of Ozone in Water Treatment Ozone Chemistry Ozone Production Ozone Measurement Major Uses of Ozone in Water Treatment Disinfection Oxidation Ozone-Based Advanced Oxidation Process (AOP) UV/Ozone H2O2/Ozone Bromate Formation during Ozonation of Bromide Waters Summary Outline Department of Geosciences | College of Petroleum Engineering & Geosciences

Introduction Ozone can be broadly classified into two main types: Good Ozone and Bad Ozone. Good Ozone is the natural ozone that is present in the stratosphere of the Earth’s atmosphere. This stratospheric ozone layer helps to filter out and reflect back some of the harmful ultraviolet (UV) radiation that is emitted from the Sun. Bad Ozone originates from man-made sources and is generally found in the troposphere. Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone Chemistry One classical reversible chemical equation that is used to describe the formation of ozone is given as follows: 3 𝑂 2 ⇌2 𝑂 3 This equation states that there may exist an equilibrium between the conversions of an oxygen molecule into an ozone molecule. In accordance to this equation, the formation of ozone takes place in an endothermic reaction. Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone Chemistry (cont.) The other basic chemical equation is given as follows: 𝑂 2 +𝑂⇌ 𝑂 3 According to this equation, the increase in temperature would increase the possibility of having dissociated oxygen molecules (O) in the atmosphere. These dissociated oxygen molecules would then react with the abundant oxygen molecules (O2) present in the atmosphere to form ozone. Contrary to the first equation, this equation describes the formation of ozone as an exothermic process. Department of Geosciences | College of Petroleum Engineering & Geosciences

The basic principle behind the generation of ozone, relies on the dissociation of oxygen molecules into oxygen atoms. Several methods exist that utilize this concept. The methods aim to disassociate oxygen molecules by the use of temperature, electricity, light, and nuclear power, to name a few. Ozone Production Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone Production (Cont.) Temperature: The increase in the temperature would lead to a higher possibility of having dissociated oxygen atoms. This method of generating ozone is scarcely used and is generally not economically feasible. The method involves passing a jet of oxygen air over near molten metal or glowing solids in order to heat the oxygen to the temperature necessary to decompose it. Another form of this method may involve the injection of liquid oxygen into a plasma jet. Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone Production (cont.) Light: Exposure of oxygen molecules to UV radiation at a specific wavelength may in fact help to dissociate the oxygen molecule into oxygen atoms. The reaction then proceeds to form ozone. It is important to note, however, that exposure of ozone to UV radiation at a different wavelength would trigger a reaction between ozone and H2O to form hydrogen peroxide (H2O2) and oxygen. Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone Production (cont.) Nuclear Power: The generation of ozone may also be achieved by the use of alpha or gamma radiation (α- or γ-radiation), for instance. This technique has earned a higher popularity in recent times due to the large-scale construction of several nuclear reactors around the globe that can be utilized for this purpose. Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone Production (cont.) Electricity: Electrolysis may be utilized to a great extent to produce ozone and oxygen. The process works by passing an electric current through an aqueous solution of an acid or base. The electric current would then dislodge oxygen atoms, ions, and radicals and transport them to the negative anode of the electrolysis cell. The oxygen atoms that have collected at the anode may be utilized to form ozone in a separate reaction. Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone Measurement There are two main types of technologies that are utilized to measure the levels of ozone and ozone profiles in the Earth’s atmosphere. Namely, they are ground-based technologies and satellite-based technologies (Hassler, et al., 2014). Ground-based technologies include: Ozonesondes, Dobson/Brewer, Lidar, FTIR, and Microwave. Satellite-based technologies utilize a number of measurement techniques. They are grouped as follows: Solar Occultation Technique, Stellar Occultation Technique, Limb Viewing Technique, Limb-Scatter Technique, and Nadir Viewing Technique. Department of Geosciences | College of Petroleum Engineering & Geosciences

Major Uses of Ozone in Water Treatment Ozone can be used to disinfect water and wastewater by attacking and killing microbial organisms such as bacteria, viruses, and parasites. The efficiency of the disinfection would depend on the type of microbial organism present in the water. Each organism would offer a different relative resistance to the ozone. Department of Geosciences | College of Petroleum Engineering & Geosciences

Major Uses of Ozone in Water Treatment (Cont.) Other applications of ozone may include the oxidation of inorganic and organic compounds into less harmful compounds or into substances that can be easily removed of via other means such as, filtering, settling, or biological processes. Ozone is sometimes, although rarely, used to oxidize inorganic compounds. Note, though, that ozonation is rarely the only method utilized to remove contaminants from wastewater. It is more often than not used in combinations with other treatment methods. Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone-Based Advanced Oxidation Process (AOP) The combination of UV radiation with ozone leads to a reaction that leads to the production of hydrogen peroxide and oxygen. The reaction is triggered by the UV light; hence it is one of photolysis. The reaction is given as: 𝑂 3 + 𝐻 2 𝑂→ 𝐻 2 𝑂 2 + 𝑂 2 The produced hydrogen peroxide may then react with ozone to produce the desired hydroxyl radicals (OHo). Department of Geosciences | College of Petroleum Engineering & Geosciences

Ozone-Based Advanced Oxidation Process (AOP) (Cont.) The combination of hydrogen peroxide with ozone would lead to the formation of hydroxyl radicals if the hydrogen peroxide is present as an anion (HO2-). Intermediate steps take place before the final hydroxyl radical is reached. One of the intermediate steps involves the formation of a hydroperoxyl radical (HO2o) and an ozonide anion (O3o-). This reaction is given as: 𝐻 𝑂 2 − + 𝑂 3 ⟶𝐻 𝑂 2 𝑜 + 𝑂 3 𝑜− These intermediates then enter into a radical chain reaction to form the hydroxyl radical. Department of Geosciences | College of Petroleum Engineering & Geosciences

Bromate Formation during Ozonation of Bromide Waters Ozone would react unfavorably with the bromine ions to form bromate which is a possible carcinogenic. Concentration of bromide in natural water sources varies depending on natural factors such as salt-water intrusions and water intrusion from special geological formations. It may also be affected by human-induced activities such as potassium mining, coal mining, and industrial production of chemicals. Department of Geosciences | College of Petroleum Engineering & Geosciences

Bromate Formation during Ozonation of Bromide Waters The bromate is generated by the oxidation of bromide via the reaction between ozone and the hydroxyl radical. The concentration has to be limited in order to avoid adverse effects to human health. The problem is exacerbated when the water is to be used for drinking purposes. The World Health Organization (WHO) and the European Union (EU), for instance, have set the maximum bromate level at 10 μg/L or 10 ppb. Department of Geosciences | College of Petroleum Engineering & Geosciences

Summary Ozone can be broadly classified into two main types: Good Ozone and Bad Ozone. Ozone Chemistry. Ozone Production: The basic principle behind the generation of ozone, relies on the dissociation of oxygen molecules into oxygen atoms. Methods may use temperature, electricity, light, and nuclear power. Ozone Measurement: There are two main types of technologies that are utilized to measure the levels of ozone and ozone profiles in the Earth’s atmosphere. Namely, they are ground-based technologies and satellite-based technologies Ozone can be used to disinfect water and in the oxidation of inorganic and organic compounds. Ozone-Based Advanced Oxidation Process (AOP): UV/Ozone and H2O2/Ozone. Ozone would react unfavorably with the bromine ions to form bromate which is a possible carcinogenic. Department of Geosciences | College of Petroleum Engineering & Geosciences

Department of Geosciences | College of Petroleum Engineering & Geosciences