Once formed, the hydroxyl radicals aggressively attack pollutant compounds, breaking them down into intermediate substances. These intermediates are further decomposed by the remaining radicals and oxidants until the contaminants are transformed into simpler, inorganic compounds like water, carbon dioxide, and salts.

 

AOP systems are predominantly utilized in tertiary treatment stages of water purification. They are particularly effective at this stage due to their sensitivity to suspended solids and other compounds, known as hydroxyl scavengers. These scavengers can impede the oxidation efficiency by absorbing UV radiation and reacting with hydroxyl radicals, thereby reducing the process's effectiveness in targeting specific pollutants.

 

1. A UV disinfection system can be simply modified into a UV/H2O2 AOP system just by adding H2O2

Modifying a UV disinfection system to function as an Advanced Oxidation Process (AOP) is indeed a complex endeavor, far beyond simply attaching a hydrogen peroxide (H2O2) tank. The underlying principles of UV disinfection and AOPs are fundamentally different, and as such, their system designs reflect these distinctions.

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UV disinfection primarily targets microorganisms by disrupting their DNA with ultraviolet light. In contrast, AOPs utilize a combination of UV light, hydrogen peroxide, and/or ozone to generate highly reactive hydroxyl radicals. These radicals are capable of breaking down organic pollutants into benign substances like water and carbon dioxide.

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Hydrogen peroxide, when introduced into a UV system, presents its own set of challenges. Its low adsorption coefficient for UV light means that achieving effective oxidation requires significantly higher doses of peroxide. Consequently, the UV dosage might also need to be increased. Moreover, precise control over peroxide dosing is crucial to prevent any residual peroxide from remaining in the treated water. If residual peroxide is present, it must be removed before the water can be safely used or discharged, which might necessitate additional treatment steps.

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In summary, while adapting a UV system for AOP is feasible, it demands careful consideration of chemical interactions, system design modifications, and additional treatment processes to ensure effectiveness and safety.

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2. Using ozone in an advanced oxidation process

As previously noted, advanced oxidation systems are distinguished by their ability to generate hydroxyl radicals (•OH) in sufficient quantities to effectively treat contaminants. An ozone system alone, unless specifically designed to enhance the production of these radicals, cannot be classified as an advanced oxidation process.

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Ozone, while a potent oxidant on its own, is not as reactive as the hydroxyl radical and exhibits slower reaction rates. For an ozone-based system to qualify as an AOP, modifications are necessary to boost the formation of •OH radicals. This can be achieved through several methods:

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• Alkaline pH Adjustment: By introducing ozone into an alkaline pH environment, the concentration of hydroxide ions (OH⁻) is increased. This elevated concentration facilitates the generation of hydroxyl radicals, thereby enhancing the oxidation process.

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• UV Light Integration: Incorporating ultraviolet (UV) light into the system can catalyze the breakdown of ozone, leading to the production of hydroxyl radicals. UV light provides the energy needed to dissociate ozone molecules and enhance their reactivity.

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• Hydrogen Peroxide Addition: Adding hydrogen peroxide to the ozone system can also promote the formation of •OH radicals. When hydrogen peroxide reacts with ozone in the presence of UV light or under alkaline conditions, it generates hydroxyl radicals more efficiently.

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In essence, while ozone itself is a strong oxidant, its transformation into an advanced oxidation system requires specific conditions and modifications to optimize the production of hydroxyl radicals and achieve effective treatment results.

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3. Can be used in smaller scale applications also

Advanced Oxidation Processes (AOPs) are notably versatile when it comes to their physical footprint. Unlike some complex treatment processes that demand extensive space for their equipment, AOPs are compact and adaptable. This makes them particularly suitable for applications in smaller settings, such as drinking water treatment for small communities.

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One of the key advantages of AOPs is their ability to be scaled down effectively. Some AOP systems are designed to handle flow rates as low as 25 gallons (approximately 100 liters) per minute or even less. This flexibility allows for the deployment of advanced oxidation technology in a variety of scenarios, from small municipal water systems to specialized industrial applications.

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In summary, AOPs provide a space-efficient solution that can be tailored to meet the needs of both large-scale and small-scale water treatment operations, making them a practical choice for diverse applications.

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4. Does not produce concentrated wastes

One of the significant costs associated with wastewater treatment processes is the disposal of removed solids and concentrated wastes. However, Advanced Oxidation Processes (AOPs) stand out because they do not produce concentrated waste byproducts. Instead, AOPs are designed to break down complex, harmful compounds into simpler, more biodegradable substances that are less problematic to handle.

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AOPs work by effectively degrading pollutants into basic, non-toxic forms, such as carbon dioxide and water, without generating concentrated waste streams. This reduction in residual waste not only simplifies the treatment process but also lowers associated disposal costs.

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While AOP is a powerful and effective solution for wastewater treatment, its operational costs can vary depending on the level of contamination and system design. When tailored to the specific needs of the application, AOP can be a highly efficient and cost-effective choice. Given its advantages and the reduction in waste disposal issues, AOP should be considered as a viable technology for appropriate wastewater treatment scenarios.

 

UV Disinfection System

Ultraviolet (UV) light with a wavelength of 253.7 nanometres is widely used for the disinfection of various microorganisms, including bacteria, viruses, molds, algae, and others that can multiply and proliferate. This specific wavelength is highly effective because it targets and destroys the DNA of these microorganisms, rendering them inactive and incapable of reproduction.

 

The mechanism behind UV disinfection involves the absorption of UV light by the DNA and RNA of microorganisms. This absorption causes the formation of thymine dimers, which are molecular lesions that prevent the microorganisms from replicating and carrying out vital functions. As a result, they are effectively killed or inactivated, ensuring that they cannot continue to grow or spread.