Decontamination Potential of Ultraviolet Type C Radiation in Water Treatment Systems: Targeting Microbial Inactivation

Abstract

Access to safe water and sanitation is a critical global challenge, posing significant health risks worldwide due to waterborne diseases. This study investigates the efficacy of ultraviolet type C radiation as a disinfection method for improving water quality. The research elucidates UV-C’s mechanism of action, highlighting its ability to disrupt DNA and RNA replication, thereby inactivating pathogens. Furthermore, the study analyses the influence of key factors on UV-C disinfection effectiveness, including water turbidity and the presence of dissolved organic matter, which can attenuate UV-C penetration and reduce treatment efficiency. The experimental results demonstrate a substantial reduction in microbial content following UV-C treatment. River water samples exhibited a 57.143% reduction in microbial load, while well water samples showed a 50% reduction. Notably, Escherichia coli (E. coli) concentrations decreased significantly, with an 83.33% reduction in well water and a 62.5% reduction in borehole water. This study makes a novel contribution to the understanding of UV-C disinfection by identifying the presence of resistant organisms, including Adenoviruses, Bacterial spores, and the Protozoan Acanthamoeba, in water samples. This finding expands the scope of UV-C research beyond easily culturable bacteria. To address this challenge, future investigations should explore synergistic disinfection strategies, such as combining UV-C treatment with advanced oxidation processes. Optimising UV-C system designs and developing robust, real-time monitoring systems capable of detecting and quantifying known and emerging UV-resistant pathogens are crucial for ensuring comprehensive water decontamination.

1. Introduction

1.1. Global Importance of Water and Sanitation Hygiene

According to Bazaanah et al. [1], access to water and sanitation services is not just a fundamental human right enshrined in the United Nations Sustainable Development Goals but a fundamental pillar upon which global health, economic development, and environmental sustainability depend. The consequences of inadequate water and sanitation infrastructure are far-reaching, impacting billions of lives across the globe and hindering progress towards a more equitable and sustainable future [2]. Waterborne diseases, easily preventable with proper sanitation and hygiene practices, continue to plague developing nations, particularly in sub-Saharan Africa and South Asia. These avoidable illnesses place a significant burden on already strained healthcare systems and hinder socio-economic progress [3]. The World Health Organization [4] estimates that unsafe water, sanitation, and hygiene practices contribute to millions of deaths annually, primarily among vulnerable populations like children under the age of five. Beyond the devastating health impacts, the lack of safe water and sanitation stifles economic growth. The burden of collecting water from distant, often contaminated sources disproportionately affects women and girls, limiting their educational and economic opportunities and perpetuating cycles of poverty [5].

Furthermore, inadequate sanitation infrastructure leads to environmental degradation. Improper waste disposal contaminates water sources, impacting ecosystems and threatening biodiversity [6]. Investing in sustainable water and sanitation solutions is, therefore, not merely an act of charity but a crucial investment in a healthier, more prosperous, and sustainable future. It is an investment in public health, economic development, gender equality, and environmental protection for current and future generations [7].

1.2. Overview of Waterborne Diseases and Their Impact

Zakiyyah et al. [8] believe that waterborne diseases arising from ingesting water contaminated with pathogenic microorganisms, such as bacteria, viruses, and parasites, pose a significant threat to global public health. These diseases, including but not limited to cholera, typhoid fever, dysentery, and various diarrheal illnesses, disproportionately impact low-income countries with limited access to safe drinking water and sanitation facilities. The consequences are devastating, leading to millions of deaths annually, particularly among young children who are most vulnerable to dehydration and malnutrition resulting from severe diarrhoea [9]. Cha et al. [10] discussed that the impact of waterborne diseases extends far beyond immediate health concerns, trapping individuals and communities in a vicious cycle of poverty and hindering economic productivity and development. Frequent illness leads to lost workdays, reduced productivity, and increased healthcare costs. Children missing school due to preventable waterborne diseases face diminished educational opportunities, impacting their future potential and perpetuating the cycle of poverty. The study further upheld that addressing this global challenge requires a multifaceted approach beyond providing water. It encompasses improved sanitation infrastructure, including toilets and sewage systems, hygiene education to promote handwashing and safe water-handling practices, and access to safe and reliable water sources. Investing in these measures is a moral imperative and a sound economic decision that can unlock human potential and drive sustainable development [11].

Waterborne diseases, a significant global health challenge, arise from the ingestion of water contaminated with a variety of pathogenic microorganisms, including bacteria, viruses, and parasites [12]. These microscopic threats infiltrate water sources through various avenues, often linked to inadequate sanitation and hygiene practices. The consequences of this contamination manifest in a range of debilitating illnesses, with cholera, typhoid fever, dysentery, and various diarrheal diseases being among the most prevalent [13]. The burden of these diseases falls disproportionately on low-income countries grappling with limited access to safe drinking water and sanitation facilities. In these settings, inadequate infrastructure often allows for the contamination of water sources used for drinking, cooking, and personal hygiene, perpetuating a cycle of disease transmission [2]. As discussed by Nounkeu et al. [14], the consequences are devastating, leading to millions of deaths annually, with young children bearing a disproportionate share of this tragic burden. Their developing immune systems are particularly susceptible to the effects of dehydration and malnutrition, common complications of severe diarrhoea, making them especially vulnerable to the lethal consequences of waterborne diseases.

Children, often the most vulnerable members of society, face particularly severe consequences from waterborne diseases. Frequent bouts of illness lead to missed school days, hindering their education and limiting future opportunities [15]. This disruption in education has cascading effects, impacting individual potential and the long-term development of communities and nations. The cycle perpetuates as children who lack access to education are more likely to experience poverty, further increasing their risk of exposure to waterborne diseases [1]. Addressing this multifaceted global challenge requires a comprehensive and sustained approach beyond simply providing water access. It necessitates an encompassing multi-pronged strategy [11,16].

• Improved sanitation infrastructure: Investing in and ensuring the functionality of toilets, sewage systems, and wastewater treatment facilities is crucial to breaking the cycle of contamination.
• Hygiene education: Promoting handwashing with soap, safe water-handling practices, and proper food hygiene are essential for preventing the spread of pathogens.
• Access to safe and reliable water sources: This includes implementing and maintaining water treatment systems, protecting water sources from contamination, and ensuring equitable access to safe water for all.

Investing in these measures should not be viewed merely as an act of charity, but rather as a strategic investment in human capital and sustainable development. When water and sanitation interventions are prioritised, the cycle of poverty and disease can be broken, human potential can be unlocked, and a pathway to a healthier, more equitable, and prosperous future for all can be paved [17].

1.3. UV Disinfection as a Water Treatment Method

Kim et al. [18] affirmed that ultraviolet disinfection has emerged as a powerful and increasingly popular method for ensuring water safety, offering a compelling alternative to traditional chemical disinfection methods. Its application spans a wide range of settings, from large-scale municipal water treatment plants to decentralised systems serving individual homes and communities. Unlike chlorine-based disinfection, which relies on chemical reactions to eliminate pathogens, UV disinfection harnesses the germicidal power of a specific wavelength of ultraviolet light known as UV-C [19]. This chemical-free approach offers several distinct advantages, making it an environmentally friendly and highly effective solution for water treatment. By emitting UV-C radiation at a wavelength of 254 nanometres, UV disinfection systems effectively neutralise a wide range of harmful microorganisms present in water, including bacteria, viruses, and protozoa [20]. Hellal et al. [21] also believe that the process is remarkably efficient: as water flows through a UV disinfection unit, the UV-C radiation penetrates the cell walls of these microorganisms, disrupting their DNA and RNA and rendering them incapable of reproduction. This physical process effectively inactivates the pathogens, preventing them from causing disease.

One of the most significant advantages of UV disinfection is its ability to eliminate the formation of harmful disinfection byproducts. Traditional chemical disinfectants, while effective in killing pathogens, can react with organic matter in water to create DBPs, some of which have been linked to adverse health effects [22]. UV disinfection, on the other hand, does not introduce any chemicals into the water, eliminating the risk of DBP formation and ensuring the delivery of safe and wholesome drinking water [21]. Beyond its environmental benefits, Huo et al. [23] in their study acknowledged that UV disinfection offers several practical advantages. UV disinfection systems are relatively simple to operate and maintain, requiring minimal space and rapid disinfection times. Unlike chemical disinfection methods, which often involve the handling and storing of hazardous substances, UV disinfection systems pose minimal safety risks, making them suitable for a wide range of applications. Furthermore, UV disinfection does not alter the taste, odour, or pH of the water, ensuring that the treated water remains palatable [24].

The versatility and effectiveness of UV disinfection have led to its widespread adoption in both developed and developing countries [25]. In large-scale water treatment plants, UV disinfection often serves as a final barrier against pathogens, ensuring the safety of the water supply. In decentralised settings, UV disinfection systems provide a reliable and affordable solution for treating water at the point of use, protecting communities that lack access to centralised water treatment infrastructure [26]. As global demand for safe drinking water continues to rise, UV disinfection is poised to play an increasingly important role in ensuring public health. Its ability to effectively inactivate waterborne pathogens, combined with its environmental sustainability and ease of operation, makes it a powerful tool in the fight against waterborne diseases and a cornerstone of safe water supplies worldwide [27].

2. Understanding UV Disinfection

2.1. The Electromagnetic Spectrum and UV Radiation

The electromagnetic spectrum encompasses a vast range of radiation, with visible light, the only portion we can see, occupying a tiny sliver [28]. As depicted in Figure 1, ultraviolet radiation lies beyond the violet end of the visible light spectrum. While the sun emits a broad energy spectrum, the ozone layer blocks 98.7% of harmful UV radiation from reaching the Earth’s surface.

Figure 2 illustrates the 1.3% of UV radiation that reaches the Earth, spanning wavelengths between 290 nm and 400 nm [30]. This UV radiation is further categorised into UV-A (96.5%), UV-B (3.5%), and UV-C, with decreasing wavelength and increasing energy levels. Notably, UV-C, the most energetic form, is entirely absorbed by the ozone layer and does not reach the Earth’s surface [31]. Figure 3 provides a detailed look at how the ozone layer interacts with different types of UV radiation. The olive line represents the ozone density profile, highlighting its role in absorbing UV radiation.

The width of the bars for UV-A, UV-B, and UV-C represents their energy levels at different altitudes. UV-C is strongly absorbed by ozone, leading to a dramatic decrease in its energy. UV-B is partially absorbed, with a small fraction reaching the surface, while UV-A is weakly absorbed, allowing a larger portion to reach the Earth.

2.2. Mechanisms of UV Disinfection at the Cellular Level

As stated by Johann et al. [34], ultraviolet disinfection, particularly utilising the UV-C wavelength range (200–280 nm), provides a highly effective means of neutralising microorganisms by directly targeting their genetic material: DNA and RNA (Figure 4). This process, rooted in the fundamental principles of photochemistry, disrupts the essential cellular processes of replication and transcription, ultimately leading to the inactivation of the targeted microorganisms. The mechanism of UV disinfection hinges on the interaction between UV-C photons and the nucleotide bases that constitute the building blocks of DNA and RNA. When UV-C radiation penetrates the cell wall and reaches these nucleic acids, it is readily absorbed by the nucleotide bases [35]. This absorption of energy, however, comes at a cost. Maslowska et al. [36] explained that it triggers the formation of abnormal linkages within the DNA and RNA strands, disrupting their structural integrity and compromising their biological function. The most common and significant of these photochemical alterations is the formation of thymine dimers in DNA. Thymine, a pyrimidine base, pairs typically with adenine in the DNA double helix. However, upon absorbing UV-C radiation, adjacent thymine bases can form covalent bonds with each other, creating a kink in the DNA strand. These thymine dimers disrupt the standard reading frame of the genetic code, interfering with DNA replication and transcription reliability.

Kobayashi et al. [37] further revealed that the consequences of these structural changes in DNA and RNA molecules are profound. The cell’s ability to replicate its genetic material, a fundamental cell division and proliferation requirement, is severely compromised. Similarly, the synthesis of proteins, essential for many cellular functions, is disrupted as the damaged DNA can no longer serve as a reliable template for messenger RNA (mRNA) production. Rendered incapable of replicating its genetic material or synthesising proteins, the microorganism is effectively neutralised. It can no longer reproduce, spread, or cause disease.

Figure 4. Inactivation of DNA structure by ultraviolet radiation. Source: [38].

Figure 4. Inactivation of DNA structure by ultraviolet radiation. Source: [38].

This mechanism of action, according to Kim et al. [18], targets the blueprint of life and is remarkably effective against a wide range of waterborne pathogens, including bacteria, viruses, and protozoa. The efficacy of UV disinfection is further enhanced by its physical nature. Unlike chemical disinfection methods that rely on diffusion and reaction time, UV irradiation exerts its effect instantaneously upon contact. The photochemical reactions that disable the microorganisms occur during the brief exposure to UV-C radiation, ensuring rapid and reliable disinfection. Belcaid et al. [39] reiterated in their study that this combination of a targeted mechanism of action, broad-spectrum efficacy, and rapid disinfection kinetics makes UV disinfection a powerful tool for ensuring water safety. Its ability to effectively neutralise a wide range of waterborne pathogens without introducing harmful chemical byproducts has solidified its place as a cornerstone of modern water treatment strategies, safeguarding public health and contributing to a safer and healthier world.

2.3. Factors Affecting UV Disinfection Efficacy

While the germicidal effectiveness of UV disinfection is well-established, several factors can influence its efficacy in real-world applications. Beyond the fundamental parameter of UV dose, which represents the amount of UV energy delivered to the water, water quality plays a crucial role in determining the overall performance of UV disinfection systems. Zhao et al. [40] mentioned in their study that turbidity, a measure of water clarity, is a crucial factor affecting UV disinfection efficacy. Caused by suspended particles such as silt, clay, and organic matter, turbidity scatters UV radiation, reducing its ability to penetrate the water column and reach targeted microorganisms. This scattering effect diminishes the effective UV dose delivered to the microorganisms, potentially allowing some to survive and compromising the overall disinfection process.

Similarly, according to Raeiszadeh et al. [41], dissolved organic matter (DOM) present in the water can absorb UV radiation, further attenuating its intensity and reducing its germicidal impact. DOM comprises a complex mixture of organic compounds, including humic substances, proteins, and carbohydrates, which can readily absorb UV light, effectively shielding microorganisms from its damaging effects.

Hellal et al. [21] further clarified that given the significant impact of turbidity and DOM on UV disinfection efficacy, pre-treatment steps are often essential for optimising system performance. Filtration, for example, effectively removes suspended particles, reducing turbidity and enhancing UV transmittance through the water. Similarly, coagulation and flocculation processes can remove dissolved organic matter, minimising its UV absorption and improving the overall effectiveness of the disinfection process. By addressing these water quality parameters through appropriate pre-treatment strategies, water treatment facilities can ensure optimal UV disinfection performance, maximising the inactivation of waterborne pathogens and safeguarding public health.

3. Materials and Methods

3.1. Study Area and Sample Site

According to Oguntoke et al. [42], the layout of Ibadan, Nigeria, with its hilly terrain and varying infrastructure, influences groundwater flow and potential contamination. Shallow wells in older and peri-urban areas are vulnerable to surface pollution, while boreholes tapping into deeper aquifers may offer better protection but require strategic sampling. The city’s topography affects groundwater flow and contamination spread, as runoff from densely populated areas can infiltrate shallow wells, making them susceptible to contamination from sources like pit latrines and industrial discharge. Boreholes drilled deeper into confined aquifers can provide a solution, but their effectiveness depends on factors like depth, geology, and surrounding land use.

Ibadan North Local Government Area (Figure 5), nestled within the bustling metropolis of Ibadan, Oyo State, Nigeria, is a compelling study area for evaluating the quality of diverse water sources. The Ibadan North Local Government Area headquarters is in Agodi. The LGA is bounded by Akinyele LGA to the north, Lagelu LGA to the east, and Ido, Ibadan South-West, and Ibadan South-East LGAs to the west. Geographically, the LGA occupies an area of approximately 420 square kilometres and is positioned between latitudes 7°22′ and 7°28′ North and longitudes 3°50′ and 3°56′ East [43]. Characterised by a gently undulating terrain typical of the rainforest–savanna transition zone, the region experiences a tropical climate with temperatures ranging from 22 °C to 32 °C throughout the year. The Ona River, a significant hydrological feature, traverses the LGA, acting as both a potential water source and a recipient of wastewater discharge. The area exhibits a mix of residential, commercial, industrial, and agricultural land uses, all of which can impact water quality [44].

Despite its predominantly urban setting, Ibadan North LGA grapples with challenges in ensuring a sufficient and safe water supply for its growing population. Well water remains a primary source for many households, particularly in densely populated areas lacking adequate access to piped water. Borehole water offers an alternative, often perceived as safer, but still susceptible to contamination if drilling and maintenance practices are compromised [45]. While a potential water resource, the Ona River faces significant pollution risks due to urban runoff, industrial discharge, and inadequate sanitation infrastructure. This study, by focusing on well water, borehole water, and river water within Ibadan North LGA, aims to provide a comprehensive assessment of water quality parameters, identify potential health risks associated with each source, and inform strategies for sustainable water resource management and public health protection within the region [46].

Figure 5. Map of Ibadan North Local Government. Source: [47].

Figure 5. Map of Ibadan North Local Government. Source: [47].

3.2. Materials

The ultraviolet steriliser was procured from DH Limited, while the fermentation tubes, Petri dishes, autoclave, incubator, test tubes, pipettes, measuring jars, inoculating containers, media preparation utensils, and reagents (including lactose broth, lauryl tryptose broth, Endo agar, and Eosin methylene blue agar) were adapted and used in the laboratory to conduct the experiment.

3.2.1. Sample Collection

Three water samples were collected to assess the potential variation in water quality across different sources, each representing a distinct source: a shallow well (18.5 m deep), a borehole (105 m deep), and a river. These sources were strategically chosen to yield samples representative of the entire water system under investigation, encompassing groundwater (well and borehole) and surface water (river) sources. This comprehensive approach allows for a more holistic understanding of the water quality dynamics within the study area. To maintain the collected samples’ integrity and prevent contamination, clean and sterile containers were used for sample collection. This precaution is crucial to ensure that the results of subsequent analyses accurately reflect the actual conditions of the water sources and are not skewed by external contaminants introduced during the sampling process [48].

Once collected, the samples were meticulously labelled to maintain their traceability and prevent mix-ups during storage and analysis. The labelled samples were then transferred and stored in a controlled laboratory environment. This controlled environment, typically characterised by stable temperature, humidity, and minimal exposure to light, helps preserve the chemical and biological composition of the water samples, ensuring the reliability and accuracy of subsequent experiments [49].

3.2.2. Laboratory Experiments Procedure

To minimise any potential changes in water quality due to biological activity or chemical reactions after collection, the time between sample collection and the commencement of laboratory experiments was kept as short as possible, generally not exceeding 6 h. This rapid processing time helps ensure that the samples analysed in the laboratory accurately represent the conditions of the water sources at the time of collection [50]. During this holding period, the collected water samples were refrigerated at approximately 4 °C. Refrigeration serves two primary purposes: slowing down biological activity and minimising chemical reactions. By lowering the temperature, microbial metabolism and growth are significantly reduced, preventing any significant changes in the microbial population of the water samples. Additionally, refrigeration helps slow down chemical reactions that might alter the concentration of dissolved constituents in the water [51].

Following this preservation period, water quality laboratory tests were conducted to establish a baseline characterisation of the water samples. These tests encompassed a range of parameters, including but not limited to pH, turbidity, total dissolved solids, and microbial indicators such as total coliform and Escherichia coli. These parameters provide a comprehensive overview of the water samples’ physical, chemical, and biological characteristics, laying the foundation for evaluating the effectiveness of the subsequent UV disinfection process. The core of the water treatment process involved using an ultraviolet light steriliser. This device, designed for efficient disinfection, houses a UV lamp that emits UV-C radiation at a wavelength of 254 nm, known for its germicidal properties. The primary function of the UV steriliser is to inactivate microbial pathogens present in the water, rendering it safe for consumption.

The chosen UV steriliser (Figure 6) was constructed using 304 stainless steel, a material selected for its specific properties that are crucial in water treatment applications. Type 304 stainless steel is renowned for its corrosion resistance, ensuring the longevity of the steriliser even when exposed to water and potentially corrosive elements within the water. Moreover, it is non-toxic, preventing any leaching of harmful substances into the treated water. The absence of metal ion pollution from the steriliser material is critical to maintaining the integrity of the water quality and preventing any adverse health effects. Lastly, 304 stainless steel meets stringent food hygiene requirements, making it a suitable material for applications involving drinking water treatment. We further enhance the steriliser’s efficacy by using a high-quality European Phillips UV lamp. This lamp is known for its high output of UV-C radiation, ensuring effective disinfection. Additionally, the Phillips UV lamp is recognised for its long service life, reducing the frequency of lamp replacements and minimising operational downtime.

A controlled flow rate was established to ensure optimal UV exposure and disinfection efficiency. Water was allowed to flow through a sieve, which removes any large debris or particles that could potentially harbour microorganisms or shield them from UV radiation, into the UV steriliser at a carefully regulated flow rate of 9.3 × 10⁻⁶ m³/s. This flow rate, determined through preliminary tests and calculations, ensures that the water spends sufficient time within the UV chamber to receive an adequate UV dose of 40 mJ/cm² for effective disinfection. We further contribute to the effectiveness of the UV treatment by implementing a retention time of 45 s. This retention time, the period for which the water is exposed to UV radiation within the steriliser is a critical parameter that ensures all microorganisms in the water receive a lethal dose of UV radiation, maximising disinfection efficiency.

After exiting the UV steriliser, the treated water was collected in a 23-litre (0.023 m³) container accessed through a tap at the outlet. This collection point, situated after the UV treatment chamber, ensures that only disinfected water is collected for subsequent analysis. A second round of water quality tests was conducted on the treated water to assess the effectiveness of the UV disinfection process. These tests, mirroring the initial baseline tests, focused on determining the levels of total coliform and Escherichia coli, key indicators of microbial contamination. The values obtained from these post-treatment tests were then compared with the pre-treatment values, providing a direct measure of the UV steriliser’s efficacy in reducing microbial load.

Finally, the results of the pre-treatment and post-treatment water quality tests were compared to the established standards for drinking water quality. In this case, the benchmark used was the Nigerian Standard for Drinking Water Quality, which is aligned with the guidelines set by the World Health Organization. This comparison provides a crucial reference point, determining whether the treated water meets the acceptable safety standards for human consumption.

3.2.3. Determination of Coliforms in Water

The coliform group, a widely recognised indicator of water quality, encompasses diverse bacteria sharing specific characteristics: they are aerobic, facultative, or anaerobic; gram-negative; non-spore-forming; rod-shaped; and capable of fermenting lactose with gas production within 48 h at 35 °C. This specific temperature is optimal for many coliform bacteria’s growth and metabolic activity, allowing for reliable detection within a standardised timeframe. The multiple-tube fermentation technique, a standard method for detecting coliforms in water samples, provides a reliable and widely accepted approach for assessing water quality. This technique involves three phases, each building upon the previous, to confirm the presence and estimate the concentration of coliform bacteria.

The multiple-tube fermentation technique was used, which is a standard method for estimating the coliform bacteria population in water samples. This technique involves three distinct phases: presumptive, confirmed, and completed. The presumptive phase, the initial step, involved inoculating a series of lactose broth tubes with decimal dilutions (1:10, 1:100, 1:1000….) of the water sample. This dilution series helped to ensure that even low concentrations of coliforms could be detected. The lactose broth is selective for lactose-fermenting bacteria, a key characteristic of coliforms. Gas production, observed as bubbles trapped in a Durham tube inverted within the lactose broth within 48 h at an incubation temperature of 35 °C, served as a presumptive indication of coliform presence.

The confirmed phase, the second stage of the test, aimed to confirm the presence of coliform bacteria indicated in the presumptive phase. To achieve this, samples were carefully taken from gas-producing lactose broth tubes and streaked onto selective and differential media (Levine’s Eosin methylene blue agar). These media were designed to inhibit the growth of Gram-positive bacteria while allowing the growth of Gram-negative bacteria, such as coliforms. Furthermore, coliform colonies exhibit characteristic morphology in these media. On the EMB agar, coliforms, particularly E. coli, produced colonies with a distinctive metallic green sheen.

The final completed phase involved further isolating colonies from the confirmed phase onto nutrient agar and performing additional biochemical tests to confirm the presence of coliforms unequivocally. This step is crucial for accurate identification and quantification of the target bacteria.

Within this framework, Escherichia coli, a specific member of the coliform group, served as a key indicator of faecal contamination in water. E. coli possesses specific biochemical characteristics that distinguish it from other coliforms. These include its ability to ferment lactose, producing acid, gas, and indole in tryptophan-containing peptone water at 35 °C within 48 h. Additionally, E. coli cannot utilise sodium citrate as its sole carbon source, does not produce acetyl methyl carbinol, and yields a positive methyl red test. These specific metabolic characteristics allow for the definitive identification of E. coli, providing valuable information about the potential presence of faecal contamination in the water sample. The results of the multiple-tube fermentation technique are expressed as the Most Probable Number. The MPN is a statistical estimate of the number of coliform bacteria present in each volume of water, calculated based on the number of tubes showing positive fermentation at different dilutions. This statistical approach accounts for the possibility of more than one viable coliform bacterium in the inoculated volume, providing a more accurate estimate of coliform concentration than simply counting colonies.

However, it is important to acknowledge that the MPN is a probabilistic estimate and may overestimate the actual coliform count. The accuracy of the MPN test is influenced by the number of tubes used in each phase. Using a larger number of tubes increases the test’s statistical power, leading to a more precise MPN value. Conversely, using a smaller number of tubes reduces the estimate’s accuracy.

4. Results and Discussion

The laboratory experiment evaluated the effectiveness of ultraviolet radiation in disinfecting water samples obtained from various sources: river water, well water, and borehole water. Before UV exposure, the water samples were assessed for key parameters to ensure they met acceptable drinking water standards.

4.1. Results of the Physicochemical Properties of Water Samples

These parameters as presented in

Table 1. Results of the Physicochemical Properties of Water Samples.

Parameters	Well Water	Borehole Water	River Water
pH	7.2	6.8	8.3
Turbidity (NTU)	20	8	45
Hardness (CaCO3/L)	32	22	80
Temperature	32	35	33
Total dissolved solid (mg/L)	85	75	124
Total suspended solid (mg/L)	10	5	20

included pH, total dissolved solids, turbidity and other physicochemical parameters. The pH of the water samples was measured to ensure it fell within the acceptable range of 6.5 to 8.5. Maintaining an appropriate pH range is crucial for effective UV disinfection, as pH can influence the structure and activity of microorganisms, impacting their susceptibility to UV radiation. Furthermore, pH levels outside this range can be detrimental to human health and may indicate the presence of other contaminants. Total dissolved solids, a measure of the dissolved inorganic and organic substances in water, were also analysed. The TDS values of the water samples were confirmed to be below the Nigerian Standard for Drinking Water Quality threshold of 300 mg/L. High TDS levels can reduce the effectiveness of UV disinfection by scattering or absorbing UV light, thereby shielding microorganisms from lethal exposure.

Additionally, water quality in Ibadan, Nigeria, presents a mixed picture, with significant variations observed across different sources. The well water sample, often drawn from shallow depths, exhibited a turbidity of 20 NTU, exceeding the WHO guideline of 5 NTU. This elevated turbidity is likely a consequence of Ibadan’s dense population and strained sanitation infrastructure, where contamination from pit latrines, sewage leaks, and surface runoff is common. The slightly alkaline pH of 7.2 falls within the typical range for groundwater and is likely influenced by the natural mineral composition of the aquifer.

The borehole water sample, sourced from deeper underground aquifers, demonstrated a much lower turbidity of 8 NTU, highlighting the improved protection deeper groundwater sources offer. This finding underscores boreholes’ potential as a safer water supply alternative in rapidly urbanising areas like Ibadan. However, the slightly acidic pH of 6.8 in the borehole water warrants further investigation. This acidity could be attributed to natural geochemical processes within the aquifer or potential leaching from waste disposal sites, necessitating further analysis to determine the cause and possible implications.

River water, unfortunately, paints a concerning picture with a significantly high turbidity of 45 NTU. This alarming value reflects the heavy impact of urbanisation and inadequate pollution control measures. Sediment, debris, and pollutants from industrial discharges, sewage overflows, and erosion from deforested areas all contribute to the river’s poor water quality. The slightly alkaline pH of 8.3 also indicates some buffering capacity against acidic inputs. However, further investigation is needed to assess the potential influence of alkaline wastewater discharges on the river’s overall health.

4.2. Results of the Water Quality Tests

After confirming acceptable pH, TDS levels, and other parameters, the water samples were subjected to UV disinfection. A specific wavelength of 254 nm was applied for UV irradiation at a dosage of 40 mJ/cm², as this wavelength and dosage are particularly effective in disrupting the DNA of microorganisms, rendering them unable to reproduce and cause infection. A radiation contact time of 45 s was maintained to ensure sufficient exposure to the UV radiation.

The results of the UV disinfection experiment in

Table 2. Results of water quality test before and after treatment.

Parameters	Before Treatment	After Treatment	% Reduction	Threshold Values
River Water Sample
Total coliforms (MPN)	7	3	57.143	0
Escherichia coli. (No./mL)	0	0	0	0
Borehole Water Sample
Total coliforms (MPN)	14	7	50	0
Escherichia coli. (No./mL)	12	2	83.333	0
Well Water Sample
Total coliforms (MPN)	2400	1600	33.333	0
Escherichia coli. (No./mL)	2400	900	62.5	0

above demonstrated significant reductions in total coliforms and E. coli, key indicators of water contamination. Total coliforms were reduced by 57.143% in the river water sample, 50% in the well water sample, and 33.33% in the borehole water sample. These reductions highlight the effectiveness of UV radiation in inactivating a broad spectrum of coliform bacteria, including both faecal and non-faecal origins. Furthermore, E. coli, a specific indicator of faecal contamination, exhibited even greater reductions. The well water sample and borehole water sample showed E. coli reductions of 83.33% and 62.5%, respectively as in Figure 7a,b.

This targeted reduction in E. coli underscores the efficacy of UV disinfection in mitigating the risks associated with faecal contamination in water sources. The comparison of the water quality test results before and after UV treatment with the NSDWQ standards was visually represented in the bar charts. This graphical representation provided a clear and concise way to assess the improvement in water quality following UV disinfection.

The high degree of bacteriological contamination in Ibadan’s well water directly results from the city’s reliance on shallow wells, often less than 30 m deep, coupled with challenges posed by its high population density, inadequate sanitation infrastructure, and unique topography. These shallow wells, prevalent in densely populated areas, are highly susceptible to contamination from various sources. These include infiltration from nearby pit latrines, poorly maintained septic systems, and surface runoff carrying sewage overflows, garbage, and animal waste, exacerbated by Ibadan’s hilly terrain and inadequate drainage systems. The situation is further compounded by limited awareness about proper well construction and maintenance practices, leading to improperly sealed wellheads and damaged casings that provide easy entry points for contaminants.

Despite the significant reductions in total coliforms and E. coli, further screening of the UV-treated water samples revealed the presence of some UV-resistant pathogens. These included Adenoviruses, known to cause respiratory and gastrointestinal illnesses; Bacterial spores, highly resistant forms of bacteria that can survive harsh conditions; and Protozoon Acanthamoeba, a free-living amoeba that can cause eye infections. Bacterial spores in well water can be attributed to a combination of environmental factors, sanitation practices, and well construction and maintenance. Bacteria, including spore-forming varieties, are naturally found in soil and groundwater, and these spores can easily seep into wells, particularly those that are shallow or poorly constructed. Heavy rainfall, flooding, or nearby agricultural activities can further exacerbate contamination by increasing the transport of these bacteria into water sources. Additionally, poor sanitation practices, such as open defecation or improper waste disposal near wells, can introduce spore-forming faecal bacteria into the water supply, some of which are spore-forming and highly resistant to disinfection. Finally, improperly constructed or maintained wells, characterised by cracks in the casing, damaged well caps, or inadequate wellhead protection, provide accessible pathways for bacterial contamination.

The presence of Adenoviruses, Bacterial spores, and Protozoan Acanthamoeba in river samples from Ibadan, Nigeria, paints a picture of a water system under environmental stress from human activities. These microorganisms are not just incidental visitors but persistent inhabitants of this environment. Adenoviruses, with their hardy nature, can survive in the water for long periods, while Bacterial spores, renowned for their resilience, easily weather the conditions of the river. Acanthamoeba, a type of amoeba that thrives on bacteria and organic matter, finds ample nourishment in these waters. Several factors exacerbate this situation. Ibadan’s sanitation infrastructure and wastewater treatment likely need help to keep pace with the demands of a growing population, leading to the discharge of untreated or poorly treated sewage into the river. This human waste is a direct pipeline for these microorganisms into the water system. Furthermore, surface runoff from rainfall adds to the burden, carrying contaminants from agricultural areas, where animal waste and fertilisers are common, into the river.

The unexpected discovery of Adenoviruses, Bacterial spores, and Protozoan Acanthamoeba in water samples slated for UV-C treatment presents a novel contribution to our understanding of disinfection processes. While most studies focus on easily culturable bacteria, the presence of these resistant organisms expands the scope of UV-C research. Adenoviruses highlight the need to assess effectiveness against a wider range of viruses, while Bacterial spores emphasize the importance of understanding dosage requirements for resilient microbial forms. Furthermore, the presence of Acanthamoeba, potentially harbouring pathogens like Legionella, raises concerns about indirect effects on microbial communities. The high population density along the riverbanks creates a cycle of contamination. Activities like bathing, washing clothes, and open defecation directly introduce these microorganisms into the water, perpetuating their presence. This discovery necessitates reassessing UV-C treatment strategies, including dosage requirements for these resistant organisms and the impact of water quality parameters on treatment efficacy. Ultimately, this finding encourages a more comprehensive understanding of UV-C disinfection, moving beyond traditional indicators to consider a broader spectrum of microbial threats in real-world water treatment settings. The confluence of these factors underscores the urgent need for improved sanitation, wastewater treatment, and public health awareness to restore the health of Ibadan’s river system.

5. Conclusions

In recent times, ultraviolet radiation water treatment technology has emerged as a highly practical option for drinking water treatment. This is due to its superior disinfection efficiency, environmental safety, rapid disinfection speed, corrosion resistance, ease of operation, and low user hazard. The technology’s full potential could be harnessed and adapted for use, particularly in rural areas, to enhance the accessibility and sustainability of safe water supply for communities, especially in developing countries. This finding highlights the limitations of UV disinfection in completely eradicating all potential waterborne pathogens and emphasises the importance of considering a multi-barrier approach to water treatment.

Future research should focus on several key areas to further enhance the effectiveness and sustainability of UV water treatment systems. Exploring the synergistic effects of combining UV disinfection with other advanced oxidation processes, such as those utilising silver nanoparticles could lead to enhanced pathogen inactivation and degradation of persistent organic pollutants. Optimising UV reactor designs for specific applications, considering factors like flow rate, water quality, and target microorganisms, can significantly improve disinfection efficiency and reduce energy consumption. Developing robust and accurate online monitoring systems for real-time assessment of UV dose delivery and system performance will ensure reliable disinfection. The effect of different retention times for each water matrix could also be explored, and finally, continued research into the long-term performance, environmental impact, and cost-effectiveness of U

V-LED technology will be essential for its widespread adoption and integration into global water treatment infrastructure.