ANTIMICROBIAL EFFICACY OF SOLAR DISINFECTION OF SELECTED DRINKING WELL WATER IN BENIN CITY, NIGERIA

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INTRODUCTION
Water is an essential component upon which living systems and the human body depends. Moreover, the quality and potability of water is of immense importance for the optimal functioning of the human body. The WHO recommends that drinking water from any source including wells most be free from microbial pathogens for it to be considered safe for consumption. Due to pollution of drinking water with common sources of contaminants, potable water has become a rare commodity and of public health concern (Kuruf et al., 2010). A quick review of literature reveals that most sources of drinking water in Nigeria are polluted with both solid and liquid contaminants. Microbial pathogens especially coliforms are frequently isolated from various water sources including well water which exceeds WHO recommendation (Obafemi et al., 2018).
However, well water serve as a very cheap source of community water supply in most African and Asian countries. Well water is classified as ground water and as such, the type and level of contamination in these water sources largely depends on the edaphic, topographic and anthropological characterization of the of the location which influences and contribute to quality of the water (Palamuleni and Akoth, 2015).
Anthropogenic activities have been largely implicated with the pollution of most water bodies. Human activities such as the indiscriminate disposal of inorganic and microbial matter on land surface or through direct injection of pollutants into water bodies (Sur et al., 2006). In addition, ground water sources such as well water are largely contaminated by the practice of poor hygiene in most rural areas. Practices such as the indiscriminate use of contaminated fetching barrels or buckets to draw-up water from deep wells, coughing, sneezing and chatting while fetching water have being identified as potential sources of well water contamination (Obafemi et al., 2018). Such contaminated well water adversely impacts the health and wellbeing of people who ingests them without proper treatment (Obire et al., 2008).
Various forms of treatment are employed all around the world to improve on the potability of drinking water. At the community and household level, common water treatment methods such as; boiling, use of alum, de-coloration, chlorination and filtration abounds. In Nigeria, boiling is the commonest method employed in household water treatment because it is relatively fast, efficient and comparatively cost-effective. However, with the current increase in cost of burning fuel, most people are now seeking more cost-effective ways of treating domestic water. One of such low-cost alternatives is the use of the solar radiation. Solar Disinfection (SODIS) has been identified as a relatively cheap method of purifying water against pathogens (Burch and Thomas, 1998). This water treatment method is a very simple process involving the use of the sun's radiation to hamper the growth and destroy pathogenic microorganisms present in water. The use of sun's radiation, which is universally available for all to use, is a free gift of nature. Being free of charge, is the basis of its being a low-cost and sustainable form of water treatment (Odeyemi et al., 1988). Disinfection of water using the sun's rays has been carried out historically since the Egyptian times. The London-based scientists, Downes and Blunt in the late 1870s where the first to build an experimental setup to study the process which was reported in scientific literature thereafter for the first time (Byrne et al., 2011). Solar Disinfection also known as SODIS is best used for treating small quantities of drinking water with an un-universally agreed recommendation of two (2) litres per person per day and for small family use; approximately 10-15 litres per family per day (Wegelin et al., 1994). The process of solar disinfection of water, is a relatively simple, cheap, efficient, useful, renewable and environmentally friendly process.
The process employs the combination of the sun's heating potential and its ultraviolet (UV) radiation to sufficiently inactivate and destroy pathogenic microorganisms present in a water sample (Burgess, 2002). Consequently, this study was conducted to evaluate the antimicrobial efficacy of solar disinfection of selected drinking well water in Benin City, Nigeria.

STUDY AREA
This study was conducted in Benin City located in the south-south geopolitical zone of Nigeria. Benin City is bounded by latitudes 06° 06' N, 06° 30' N and longitudes 05° 30' E, 005° 45' E and the capital of Edo State. Benin City falls within the tropical equatorial zone dominated by dry season (November -March) and wet seasons (April -October).
The average maximum and minimum temperatures are 34°C and 17°C in February and December respectively, with an average annual variation of 4°C. The City is underlain by sedimentary formation. Its ground water aquifer for wells ranges from 28.4 m3 hr-1 at Iyanomo (south), 125m 3 hr-1 at Uselu (central) to 208m 3 hr-1 at Ogba (northern) with a draw down ranging from 4.8m at Iyanomo, 1.8m at Uselu to 6.7m at Ogba (Short and Stauble, 1967). Samples were collected from the six (6)

SAMPLE COLLECTION
A total of thirty (30) wells was randomly sampled from the six (6) local government areas (LGAs), based on accessibility and communal usage, with five (5) samples from each. Thirty (30) transparent 1L polyethylene terephthalate (PET) bottles were purchased from a local dealer, washed with hypo bleach, soaked overnight in Brine, rinsed with distilled water and stored in sterile polyethylene bags for later use. Well water samples were collected using the prepared PET bottles tied with a strong string to a piece of pre-sterilized metal weighing 500g. The bottle cap was aseptically removed and the weighted bottle lowered into the well to a depth of about 1-2 meters. The bottle was brought up to the surface and covered with a screw cap when no air bubbles were seen inside (Aboh et al., 2015).
The collected samples were immediately labelled, wrapped with black polyethylene bag to prevent photocatalytic reactions and placed in ice-packed containers and sent to the laboratory for analysis.

LABORATORY ANALYSIS
The collected samples were taken to the laboratory for analysis with emphasis on the bacteriological quality of the water samples. Standard microbiological and biochemical test procedures were performed to enumerate, isolate, characterize and identify the isolates to genus level (Cheesbrough, 2000;. Antibiotic susceptibility of the isolate to common antibiotics using Kirby-Bauer disc diffusion method was also carried-out. (Bauer et al., 1996) (Feng et al., 2014). Using the McCradys probability tables, the MPN of coliforms in the 100 ml well water sample was estimated (Mercy et al., 1998). These procedures were performed before (pre) and after (post) exposure to SODIS.

PROCEDURE FOR SOLAR DISINFECTION (SODIS)
Using the Google Weather Forecast App, a very sunny day for the study was picked with a forecasted clear sky, high temperature, low humidity and very low chance of precipitation. A total of thirty (30) transparent PET bottles was employed, of which, five (5) contained well water samples from each LGA. Of these; the content of two (2) bottles were used as "control" following the processes described above. The remaining three (3) bottles were used for SODIS procedure. Of these three (3) bottles, two (2) bottles were designated "Test-bottles" and the last one designated "Tempbottle". The contents of the Test-bottles were used for SODIS laboratory analysis, while the Temp-bottles were used to determine the temperature of the exposed water during SODIS with the help of a thermometer. Test samples were drawn from the test-bottles before and after exposure to SODIS. During the period of exposure, the solar radiance intensity (Average Peak Radiation Intensity (W/m2)) was measured using radiation sensors. During SODIS, the bottles were placed on the roof of the laboratory (made of old, rusted, brown-colored aluminum roofing sheets) from 8am-4pm (8hrs) on the day of the study. Evaluation of the antimicrobial efficacy of solar disinfection (SODIS) of the sampled drinking well water was ascertained by assessing variation in the MPN value, re-occurrence of identified isolates and the isolates antibiotic susceptibility before (pre) and after (post) exposure to solar disinfection (SODIS).

STATISTICAL ANALYSIS
Various statistical analysis was carried out to analyses the resulting data using Statistical package SPSS Version 22.0 and Microsoft Excel version 2015. Results are expressed in percentages, frequencies and graphical representation. (Ogbeibu, et al., 2015). Table 1 shows the mean temperature and average peak radiation intensity on SODIS bottles on the study day. The highest temperature reading was observed at midday with mean value of 56 o C. The average peak radiation intensity recorded was 653.0W/m 2 .  A similar result was reported by Erah et al., (2002) who studied the "The Quality of Groundwater in Benin City: A baseline study on inorganic chemicals and microbial contaminants of health importance in boreholes and open wells".

MICROBIAL ISOLATES DISTRIBUTION
In this study, the researchers observed that Okhoro District in Benin City had very high levels of microbial contamination in their open wells. Coincidently, this district is within the Egor LGA. One possible reason for this high microbial prevalence may be due to relatively shallower nature of the wells in this LGA. It was observed that only

Ikpoba-Okha (Fecal streptococci) and Ovia South-West (Escherichia coli)
LGAs had only one fecal indicator each as opposed to all other LGAs that had both. The high number of heterotrophic bacterial count observed in the study area indicates that the groundwater in that area may be densely contaminated (Nwankwo et al., 2019). LGA=Local Government Area other vegetative forms of fungi which helps build resistance to radiations and adverse environmental conditions (Shuryak, 2019). The overall percentage elimination of the isolates identified in this study was recorded as 42.11%.

OCCURRENCE OF ISOLATE BEFORE AND AFTER SODIS
While the percentage elimination of fecal indicators identified was 50%.  LGA. This assertion is corroborated by Rajasekaran and Abinaya (2014) who posited that anthropogenic sources, such as seepages from domestic sewages and livestock wastes can also affect the quality of shallow groundwater sources in many parts of the world.  Table 5 shows the Most Probable Number (MPN) count of the isolates per 100ml before and after exposure to SODIS.

MICROBIAL POPULATION BEFORE AND AFTER EXPOSURE TO SODIS
It was observed that SODIS was very efficacious with a percentage reduction of above 95% for all identified isolate.
It was also observed that SODIS is slightly more bactericidal as compared to its being fungicidal. However, it was observed in this study that SODIS did not completely eliminate coliforms as it recorded 97.30% reduction. As a result, the disinfection process did not meet the WHO standard of zero (0) coliforms per drinking water sample. A similar result was observed by Ojo et al. (2011) who reported that coliforms in his study area (Ibadan, a relatively close by state to Edo State) were high in all the examined wells with values above the WHO standard.  Figure 2 shows the antibiotic susceptibility pattern of the isolates before and after SODIS. The figure shows that Staphylococcus sp. and Escherichia coli exhibited low antibiotic susceptibility before and after exposure to SODIS.

ANTIBIOTIC SUSCEPTIBILITY PATTERN OF ISOLATES BEFORE AND AFTER SODIS
Thus, SODIS did not alter the antibiotic susceptibility pattern of these isolates. However, Micrococcus sp., Serratia sp., Bacillus sp. and Citrobacter sp. showed a remarkable increase in antibiotic susceptibility after exposure to SODIS.
However, this result could not be attributed with certainty to the effect of SODIS since this result was not observed for all the isolates tested.