Glossary

3.3 Ozone and peroxide-based treatments

3 min read•july 19, 2024

Ozone and hydrogen peroxide are powerful oxidants used in advanced water treatment. These chemicals create hydroxyl radicals, which break down tough pollutants like pesticides and pharmaceuticals. Their effectiveness depends on factors like dosage, pH, and water quality.

Advanced oxidation processes using ozone and peroxide offer effective contaminant removal but require careful management. Proper dosing and mixing are crucial for optimal performance. While these methods can significantly improve water quality, considerations include energy use, , and overall environmental impact.

Ozone and Peroxide-Based Advanced Oxidation Processes

Reactions in ozone and peroxide AOPs

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  • Ozone (O3O_3) and hydrogen peroxide (H2O2H_2O_2) are strong oxidants used in advanced oxidation processes (AOPs) with high oxidation potentials of 2.07 V and 1.77 V respectively
  • Ozone and hydrogen peroxide react to generate highly reactive hydroxyl radicals (⋅OH\cdot OH) which have an even higher of 2.80 V and non-selectively oxidize a wide range of organic contaminants (pesticides, pharmaceuticals)
  • Ozone decomposition in water produces hydroxyl radicals initiated by hydroxide ions (OH−OH^-) and propagated by chain reactions involving HO2−HO_2^-, ⋅O2−\cdot O_2^-, and ⋅OH\cdot OH
  • Hydrogen peroxide enhances ozone decomposition and hydroxyl radical generation by reacting with O3O_3 to form ⋅OH\cdot OH (2O3+H2O2→2⋅OH+3O22O_3 + H_2O_2 \rightarrow 2\cdot OH + 3O_2) and with ⋅O2−\cdot O_2^- to form ⋅OH\cdot OH (H2O2+⋅O2−→⋅OH+OH−+O2H_2O_2 + \cdot O_2^- \rightarrow \cdot OH + OH^- + O_2)

Effectiveness of O3/H2O2 vs O3/UV processes

  • Both O3/H2O2O_3/H_2O_2 and O3/UVO_3/UV processes generate hydroxyl radicals for contaminant oxidation
  • O3/H2O2O_3/H_2O_2 process: hydrogen peroxide enhances ozone decomposition and hydroxyl radical formation, effective for a wide range of contaminants (micropollutants, taste and odor compounds), can achieve high removal efficiencies (>90%) with optimized dosages
  • O3/UVO_3/UV process: UV light photolyzes ozone to generate hydroxyl radicals (O3+H2O+hv→2⋅OH+O2O_3 + H_2O + hv \rightarrow 2\cdot OH + O_2), effective for UV-absorbing contaminants and byproduct precursors, can achieve similar removal efficiencies as O3/H2O2O_3/H_2O_2 but may require higher ozone dosages
  • The choice between O3/H2O2O_3/H_2O_2 and O3/UVO_3/UV depends on the target contaminants (pesticides, pharmaceuticals), water quality, and treatment goals, with O3/H2O2O_3/H_2O_2 often preferred for its simplicity and effectiveness for a broader range of contaminants while O3/UVO_3/UV may be advantageous when UV disinfection is also desired or for specific UV-sensitive contaminants

Factors influencing AOP performance

  • Ozone and hydrogen peroxide dosages: higher dosages generally improve contaminant removal but may also increase byproduct formation (bromate), optimal dosages depend on water quality and target contaminants
  • pH: higher pH (>7) favors ozone decomposition and hydroxyl radical formation
  • Water matrix:
    1. Natural organic matter (NOM) and inorganic constituents can scavenge hydroxyl radicals and compete with target contaminants
    2. Bicarbonate and carbonate alkalinity inhibit ozone decomposition and hydroxyl radical formation
    3. Higher NOM and alkalinity may require higher ozone and peroxide dosages
  • Reaction time: longer times (5-20 minutes) allow for more complete contaminant oxidation, typical contact times depend on treatment goals and reactor design
  • Mixing and mass transfer: efficient mixing and ozone mass transfer crucial for maximizing contaminant removal, achieved with diffusers, injectors, and static mixers to improve ozone dissolution and distribution

Economic and environmental aspects

  • Economic considerations include ozone generation and hydrogen peroxide costs as main operating expenses, energy consumption for ozone generation and mixing can be significant, capital costs (, contactors, off-gas destruction systems), overall costs depend on treatment capacity, water quality, and target contaminants
  • Environmental aspects:
    • AOPs effectively remove a wide range of contaminants (pesticides, pharmaceuticals) improving water quality and safety
    • On-site ozone generation eliminates need for chemical storage and transportation
    • Ozone and hydroxyl radicals do not leave residuals in treated water
    • Off-gas from ozone contactors must be properly handled to avoid atmospheric ozone release
    • Byproduct formation (bromate) may be a concern in bromide-containing waters, control strategies include pH adjustment, ammonia addition, or activated carbon treatment
  • Life cycle assessment studies can help evaluate overall environmental impacts considering energy consumption, chemical use, byproduct formation, and comparing with alternative treatment technologies to assess trade-offs between different environmental impact categories

Key Terms to Review (18)

Advanced Oxidation Process (AOP): An Advanced Oxidation Process (AOP) is a set of chemical treatment methods designed to remove organic and inorganic pollutants from water and wastewater through the generation of highly reactive hydroxyl radicals. These radicals can effectively break down contaminants that are otherwise difficult to degrade, making AOPs essential in enhancing the efficiency of conventional treatment methods. AOPs can utilize various oxidants, with ozone and hydrogen peroxide being two prominent agents in these processes, enabling a wide range of applications in advanced wastewater treatment.
Byproduct Formation: Byproduct formation refers to the unintended substances produced during a chemical reaction or treatment process, which can occur alongside the desired products. In the context of ozone and peroxide-based treatments, understanding byproduct formation is crucial since these processes can lead to various chemical species that may affect water quality and treatment efficiency. The identification and management of these byproducts are essential to ensure compliance with environmental regulations and to minimize potential harm to aquatic ecosystems.
Disinfection: Disinfection is the process of eliminating or reducing harmful microorganisms from water, surfaces, and other materials to ensure safety and prevent the spread of disease. This process is crucial in maintaining public health and is often achieved through various chemical and physical methods, including the use of ozone and peroxide-based treatments. Understanding disinfection is vital in designing effective tertiary treatment systems and implementing advanced treatment technologies for water reclamation.
EPA Standards: EPA standards refer to regulations set by the Environmental Protection Agency to protect human health and the environment by ensuring that water quality meets specific criteria. These standards are critical in guiding wastewater treatment processes and technologies, ensuring that treated water is safe for discharge and reuse, and they influence design, application, and cost considerations in advanced treatment systems.
Green Chemistry: Green chemistry is a scientific approach aimed at designing chemical products and processes that minimize or eliminate the use and generation of hazardous substances. This approach emphasizes sustainability and the reduction of environmental impact while promoting efficient resource use. By applying principles of green chemistry, industries can innovate safer alternatives, reduce waste, and enhance efficiency in chemical processes, particularly in treatments involving ozone and peroxide.
Hydrogen Peroxide Dosing Systems: Hydrogen peroxide dosing systems are designed to accurately deliver hydrogen peroxide as a treatment agent in various applications, particularly in wastewater treatment. These systems ensure that the right concentration of hydrogen peroxide is injected into the water, effectively breaking down contaminants and improving water quality. They play a critical role in advanced oxidation processes, often used alongside ozone treatments for enhanced disinfection and removal of organic pollutants.
J. l. means: In the context of ozone and peroxide-based treatments, 'j. l. means' refers to the unit of measurement used to express the intensity of light in photochemical reactions, specifically in processes involving ozone and hydrogen peroxide. This measurement is crucial for determining the effectiveness of these treatments in degrading pollutants and disinfecting water, as it correlates with the energy available for reactions that lead to the breakdown of contaminants.
M. G. F. van der Hoek: M. G. F. van der Hoek is a significant figure in the field of environmental engineering and advanced wastewater treatment, particularly known for research related to the application of ozone and peroxide-based treatments. His work has contributed to understanding how these oxidative processes can effectively remove contaminants and pathogens from water, thus enhancing the quality of treated wastewater.
Micro pollutants: Micro pollutants are trace contaminants that exist in the environment at very low concentrations, often in the range of nanograms to micrograms per liter. They typically include a variety of organic and inorganic substances, such as pharmaceuticals, personal care products, heavy metals, and industrial chemicals. These pollutants pose significant risks to aquatic ecosystems and human health due to their persistent nature and potential for bioaccumulation.
Oxidation Potential: Oxidation potential refers to the tendency of a chemical species to acquire electrons and be reduced, which plays a crucial role in redox reactions. In the context of ozone and peroxide-based treatments, oxidation potential helps determine the effectiveness of these oxidizing agents in breaking down contaminants and pollutants in wastewater. The higher the oxidation potential, the more effective the agent is at oxidizing various substances, which is essential for ensuring clean and safe water.
Ozonation: Ozonation is a water treatment process that uses ozone gas (O₃) to oxidize and break down pollutants, including emerging contaminants and micropollutants. This powerful oxidative technique is effective in disinfecting water and improving overall water quality, which aligns with regulatory drivers and design considerations for advanced treatment processes.
Ozone Generators: Ozone generators are devices that produce ozone gas (O₃) through a process called corona discharge or ultraviolet radiation. This gas is widely used in various applications, particularly for its powerful oxidizing properties, which make it effective in treating water and air by breaking down pollutants, bacteria, and viruses. In wastewater treatment, ozone generators play a crucial role in ozone-based treatments, providing an alternative to traditional disinfection methods by reducing chemical residuals and improving effluent quality.
Pathogens: Pathogens are microorganisms such as bacteria, viruses, fungi, and parasites that can cause disease in humans, animals, and plants. In the context of advanced wastewater treatment, understanding pathogens is crucial as they can be present in untreated wastewater and pose health risks if not properly managed through treatment processes.
Peroxidation: Peroxidation refers to the chemical process where organic compounds undergo oxidation through the action of peroxides, leading to the formation of reactive species. This process is particularly important in wastewater treatment as it helps in breaking down contaminants and organic pollutants, making it a vital component of ozone and peroxide-based treatments. By facilitating oxidation reactions, peroxidation enhances the effectiveness of these treatments in degrading harmful substances in wastewater.
PH Levels: pH levels measure the acidity or alkalinity of a solution on a scale from 0 to 14, with lower values indicating acidity, higher values indicating alkalinity, and a value of 7 considered neutral. Understanding pH levels is essential for various treatment processes as they influence the effectiveness of chemical reactions, microbial activity, and overall water quality.
Reaction Kinetics: Reaction kinetics refers to the study of the rates at which chemical reactions occur and the factors that influence these rates. Understanding reaction kinetics is crucial for optimizing processes in advanced oxidation, where the efficiency and speed of chemical reactions determine the effectiveness of contaminant removal. It also plays a significant role in ozone and peroxide-based treatments, as these processes rely on specific reaction mechanisms to achieve desired outcomes. Additionally, reaction kinetics is essential in hydraulic and process modeling, where it helps predict system behavior and performance under various operational conditions.
Temperature: Temperature is a measure of the average kinetic energy of the particles in a substance, influencing various physical and chemical processes. In wastewater treatment, temperature can affect reaction rates, solubility, and microbial activity, making it a critical factor in optimizing treatment efficiency.
WHO Guidelines: WHO Guidelines refer to the recommendations set forth by the World Health Organization for various public health practices, including water quality and treatment standards. These guidelines serve to promote safe and effective methods for wastewater treatment and disinfection, ensuring that the practices align with international health standards. By following these guidelines, countries can safeguard public health, protect the environment, and enhance the overall quality of water resources.
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