Effective Disinfection Methods for Waterborne Pathogens

Introduction:

More than 2.2 million deaths are reportedly caused by waterborne disease each year, and more cases of illness, such as diarrhea, gastrointestinal disorders, and systemic illnesses, are reported to occur on a daily basis. Children account for about 1.4 million of these deaths. A variety of infectious agents, including bacteria, viruses, protozoa, and helminths, can cause waterborne infections through ingestion, contact with contaminated water, or transmission through the air or contact with water.

What Are Waterborne Pathogens?

Waterborne pathogens refer to microorganisms that have the potential to cause diseases and illnesses when transmitted through contaminated water sources. These pathogens include various types of bacteria, viruses, parasites, and protozoa that can survive and thrive in water environments which are listed below:

• Bacteria: Waterborne bacterial pathogens include species such as Escherichia coli (E. coli), Salmonella, Vibrio cholerae, and Legionella pneumophila. These bacteria can cause gastrointestinal infections, typhoid fever, cholera, and respiratory illnesses.

• Viruses: Waterborne viruses, such as norovirus, rotavirus, hepatitis A virus, and enteroviruses, are extremely small and can remain infectious in water for extended periods. They are responsible for illnesses such as viral gastroenteritis, hepatitis, and respiratory infections.

• Parasites: Waterborne parasites like Cryptosporidium, Giardia, and Cyclospora are commonly found in contaminated water sources. These parasites are often resistant to traditional disinfection methods and can cause gastrointestinal diseases, including diarrhea and stomach cramps.

• Protozoa: Protozoa, like Naegleria fowleri, are known to thrive in warm freshwater environments, such as lakes and hot springs. They can cause severe brain infections, known as primary amebic meningoencephalitis (PAM), when contaminated water enters the nasal passages.

What Are Different Disinfection Methods for Waterborne Pathogens?

In water treatment procedures, implementing effective disinfection strategies plays a critical role in ensuring the eradication of pathogenic microorganisms responsible for causing waterborne illnesses. Several parameters have been identified to influence the efficacy of disinfection in water treatment. Factors such as water pH, temperature, the type of microorganisms present, the specific disinfection technique employed, disinfectant dose, contact time, and the presence of inorganic and organic material in the water can impact the effectiveness of the disinfection process. Various techniques are commonly employed for disinfection, including both conventional chemical processes and physical methods.

• Physical Methods

  1. Membrane Filtration: This method is a highly effective technique in removing bacteria, suspended particles, and organic materials from drinking water and wastewater. Through the passage of water through a physical barrier, this technique allows the separation of contaminants that are present in the water. Reverse osmosis, microfiltration, ultrafiltration, and nanofiltration are all frequently used technologies. Biofouling and virus penetration pose two significant obstacles to membrane filtration water treatment because they cause the membrane's permeability to decrease as biofouling levels rise.

  2. UV Radiation: Ultraviolet (UV) radiation disinfection utilizes UV light to inactivate waterborne pathogens. When water passes through UV disinfection systems, microorganisms absorb the UV energy, damaging their DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) and preventing replication. Due to the radicals' quick reactions, only a brief contact time is needed for disinfection. Additionally, there is no taste or odor when it is applied.

• Chemical Methods

  1. Chlorination: Chlorination is one of the most commonly used disinfection methods. It involves adding chlorine-based compounds to water, such as chlorine gas or sodium hypochlorite. Chlorine effectively kills or inactivates a wide range of waterborne pathogens by disrupting their cellular structures and metabolic processes. Because chlorine has a slower decay rate than other chemical disinfectants, it can maintain disinfection activity for longer. As a result, it is preferred for use in water reservoirs and systems for distributing drinking water because it prevents the regrowth of microorganisms.

  2. Chlorine Dioxide: Chlorine dioxide is a versatile disinfectant that can be used for primary and residual disinfection. Chlorine dioxide disrupts the transport of nutrients across cell membranes, inhibiting the growth and survival of pathogens. It is effective against various waterborne pathogens and has lower levels of disinfection by-product formation compared to chlorine. ClO2 remains more biocidal than chlorine and chloramines, but it also leads to organoleptic abnormalities in the water that is treated, making it less suitable for purification.

  3. Chloramines: Chloramines are formed by combining chlorine with ammonia. They provide a longer-lasting disinfectant residual compared to free chlorine and help control microbial regrowth in distribution systems. It requires more exposure time to inactivate many waterborne pathogens, including enteric viruses, making it a less effective disinfectant than chlorine.

  4. Ozonation: Ozonation involves the use of ozone, a powerful oxidizing agent, to disinfect water. Ozone is generated by passing oxygen through an electric discharge. It acts by rapidly reacting with microorganisms, destroying their cellular structures. Ozonation is effective against a broad spectrum of waterborne pathogens and can also remove organic compounds and odor-causing substances.

• Emerging Methods

  1. Advanced Oxidation Processes (AOPs): Advanced oxidation processes, including processes like photocatalysis and advanced oxidation with hydrogen peroxide, combine strong oxidants and ultraviolet light to produce reactive oxygen species. These species effectively destroy pathogens and organic contaminants, providing an additional layer of disinfection.

What Are the Limitations of Disinfection Methods?

While disinfection methods are essential for eliminating waterborne pathogens and ensuring the safety of drinking water, it is important to recognize their limitations. Here are some common limitations associated with disinfection methods:

1. Ineffectiveness Against Certain Pathogens: No single disinfection method is universally effective against all types of waterborne pathogens. Some disinfection techniques may be less effective against certain resistant pathogens, such as Cryptosporidium and Giardia, which have protective outer layers that make them more challenging to eliminate.

2. Formation of Disinfection By-Products (DBPs): Chemical disinfection methods, particularly those involving chlorine, can result in the formation of disinfection by-products (DBPs). When chlorine reacts with organic matter in water, such as humic and fulvic acids, it can produce potentially harmful DBPs, including trihalomethanes (THMs) and haloacetic acids (HAAs). Long-term exposure to high levels of DBPs may have adverse health effects.

3. Residual Disinfection Challenges: Some disinfection methods, like UV irradiation and ozone treatment, do not provide a residual disinfectant effect. This means that they do not leave behind a protective residual to prevent microbial regrowth in the distribution system. Additional disinfection measures or careful management of the distribution system may be required to ensure ongoing protection.

4. Interference From Water Quality Parameters: Water quality parameters, such as pH, temperature, turbidity, and the presence of organic and inorganic compounds, can affect the efficacy of disinfection methods. For example, high turbidity levels may reduce the effectiveness of UV irradiation by blocking UV light penetration. At the same time, certain chemicals or metals may interfere with the disinfection process or reduce the effectiveness of disinfectants.

5. Potential for Pathogen Regrowth: In some cases, disinfection methods may effectively eliminate pathogens during the treatment process, but there is a risk of regrowth or recontamination in the distribution system if proper maintenance and monitoring practices are not in place. Biofilms and stagnant water areas can provide environments where pathogens can survive and multiply.

Conclusion:

Water is an unavoidable universal solvent that is required for many different tasks, including drinking, cooking, cleaning, bathing, and irrigating crops. To prevent waterborne diseases, it is crucial to implement effective water treatment and disinfection methods, ensuring that water supplies are free from harmful pathogens. Regular water quality monitoring, proper sewage treatment, and safe water storage and handling are essential in reducing the risk of waterborne diseases and promoting public health and safety.