Authors: Eva Mena Gil and Elena de Vicente Aguilar (EMUASA)
In our daily activities, we generate wastewater that requires proper treatment before being returned to nature. Wastewater disinfection plays an essential role in this process as it aims to eliminate or inactivate the pathogenic microorganisms present in this resource, thus ensuring the protection of human health and the preservation of the environment.
This article explores various approaches to disinfecting wastewater. We will explore different aspects of wastewater disinfection, including different categories such as chemical, thermal, saturation, and physical methods. To select the most suitable method it is necessary to consider various variables, such as the specific characteristics of the wastewater, the desired level of quality after treatment, associated toxicity, the generation of unwanted byproducts, and the costs involved in the process.
Chemical methods: Proven efficiency and new alternatives
Chemical methods have proven to be widely used in water treatment due to their efficacy for eliminate pathogenic microorganisms. The use of chemical disinfectants, such as chlorine and its derivatives, and Peracetic Acid (PAA), has shown to be effective in the inactivation of bacteria, viruses, fungi, and other microorganisms.
Chlorine and its derivatives, such as chlorine gas, sodium hypochlorite, and chloramines, are commonly used disinfectants in over two-thirds of the planet. These disinfectants are chosen due to their low cost, ease of implementation, and residual effect. They act by affecting microorganisms through damage to cell membranes, disruption of their functions, and DNA damage. On the other hand, chlorine dioxide acts through selective oxidation, damaging the enzymatic system or interrupting protein synthesis in microorganisms.
An emerging chemical disinfectant is Peracetic Acid (PAA), which has shown to be a promising alternative to traditional chemical disinfectants. PAA has a high spectrum of efficiency against bacteria, viruses, fungi, biofilms, and antibiotic-resistance genes (Ocampo-Rodríguez et al., 2022). Its action mechanism alters the cell membrane permeability, the oxidation of cellular structures and the release of hydroxyl radicals lethal to bacteria.
When evaluating the use of these compounds as disinfectants, various studies have compared chlorine and its derivatives with peracetic acid. It has been concluded that peracetic acid may show less favourable results regarding contaminant degradation and higher costs than sodium hypochlorite (Luongo et al., 2020). Therefore, when considering water treatment options, it is crucial to consider the efficiency and cost of each method.
The rise of physical methods and the persistence of chemicals
Although efforts have been made to reduce dependence on chemicals through the use of advanced physical treatment methods, such as membrane filtration and UV disinfection (Figure 1), an increase in the use of chemicals has been observed in practice (Gitis & Hankins, 2018). Although cutting-edge technologies have left some conventional methods, chemicals are still indispensable at various stages of water treatment, including disinfection.
Physical methods, such as membrane filtration, UV radiation, ultrasound, and ionizing radiation, also play an important role in wastewater disinfection. These methods involve using physical processes to remove or inactivate pathogenic microorganisms. Membrane filtration allows the retention of larger particles and microorganisms while UV radiation disrupts the reproduction and viability of microorganisms through exposure to a source of ultraviolet light.
Figure 1. Ultraviolet radiation lamps used for water disinfection.
Conclusion
Wastewater disinfection is crucial for protecting human health and preserving the environment. Disinfection methods, both chemical and physical, offer diverse options to eliminate or inactivate pathogenic microorganisms present in wastewater.
When selecting the most appropriate method, it is essential to consider the specific characteristics of the wastewater, the desired level of quality after treatment, associated toxicity, the potential generation of unwanted byproducts, and the costs involved. Understanding and carefully evaluating these aspects will allow us to make informed and efficient decisions in wastewater treatment, ensuring proper management of this vital resource.
Bibliography
Gitis, V., & Hankins, N. (2018). Water treatment chemicals: Trends and challenges. Journal of Water Process Engineering, 25, 34-38. https://doi.org/10.1016/j.jwpe.2018.06.003
Luongo, G., Previtera, L., Ladhari, A., Di Fabio, G., & Zarrelli, A. (2020). Peracetic Acid vs. Sodium Hypochlorite: Degradation and Transformation of Drugs in Wastewater. Molecules, 25(10). https://doi.org/10.3390/molecules25102294
Ocampo-Rodríguez, D. B., Vázquez-Rodríguez, G. A., Martínez-Hernández, S., Iturbe- Acosta, U., & Coronel-Olivares, C. (2022). Desinfección del agua: Una revisión a los tratamientos convencionales y avanzados con cloro y ácido peracético. Ingeniería del Agua, 26(3), 185-204. https://doi.org/10.4995/ia.2022.17651