METHODOLOGY31 Collection of water samples Paper

Published: 2021-09-11 18:30:11
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METHODOLOGY
3.1 Collection of water samples
Based on the contracted laboratory’s request, two bottles of one-liter water samples were collected from the three chosen buildings of the study: Roque Rua?o 3rd floor drinking fountain (near Computer Laboratory), Albertus Magnus 2nd floor drinking fountain (near Food & Technology Laboratory) and the Main Building 1st floor drinking fountain (near Science Computer Laboratory). Based on WHO’s guidelines for drinking water quality, water was collected in polyethylene bottles at a low temperature of less than or equal to 4°C and kept as unexposed to light as possible through the use of a cooler. Gloves were used during the collection of the samples as stated in Environmental Protection Agency’s guide to drinking water sample collection. As EPA’s guidelines had stated, the bottle was rinsed thrice using the water sample itself before being filled one to two inches from the top of each bottle. Then, the collected samples were placed in a cooler filled with ice to preserve a low temperature during the samples’ transport to Mach Union Water Laboratory, Las Pi?as, Metro Manila, Philippines where the analysis for the different physico-chemical parameters was conducted. The water samples were delivered and tested in the laboratory within four hours after collection as advised. The collection and analysis were repeated twice and accomplished in the span of two months, once per month for the comparison of results.
3.2 Physicochemical analysis of water
3.2.1 Determination of pH
In determining the pH level of water samples, electrometric method was used. According to Palmer (1992), the accuracy of pH value is in the range of 0.1 to 0.0001. The samples were stored at 4°C and stable for at least 24 hours. The method used the following: pH meter, glass electrode, reference electrode and temperature-compensating device in the classification of the pH level of each water sample. The samples and standards were brought to 25°C before use. The glass electrode was soaked for several hours in standard solution and was removed after the calibration of the instrument. The water sample was then stirred to guarantee consistency and to minimize carbon dioxide entrainment. As the meter stabilized, pH reading was recorded and control standards was evaluated. The glass electrode was stored in pH 7.0 buffer after the measurements was complete. Lastly, the values from the pH meter was determined directly.
3.2.2 Determination of turbidity
Nephelometry was used in determining the turbidity of water samples. In this process, the water samples were placed in a nephelometer. This device measured direct light intensity to the sample while a sensor was mounted at 90° to record the scattered light transmitted through the samples (Lambrou et al.,2009).
The 90° angle is known as the detection angle which is formed between the centerline of the incident light beam and the centerline of the receiving angle from the angle of 90°. It is often used due to its sensitivity to broad range of particles. Attenuated detection angle is another angle that is at 180° relative to the light beam to measure the attenuation of the light beam due to light scatter and absorption. The one that will be sensitive to light scatter being reflected by the sample with respect to the direction of the incident light source is the backscatter detection angle which is angled at 30° and 40° relative to the incident light beam.
Incident light sources such as incandescent light sources which requires specific temperatures, LED sources which are used for common wavelength in terms of turbidity, and laser light sources which are highly sensitive in any change in the turbidity, are used as light media (Sadar, M., 2004)
3.2.3 Determination of TSS and TDS
According to Fondriest Environmental, Inc. (2014) Total suspended solids (TSS) are particles that are bigger than 2 microns found in bodies of water. Any particle that is smaller than 2 microns (size of the filter) is already a dissolved solid. Most suspended solids are made up of inorganic materials like sediment, sand, silt, plankton, and algae. To determine TSS, gravimetric method was used. According to Baxter (2017), to determine the amount of TSS, filtration and sample size selection is done first. A sample weight between 2.5 and 200 mg dried residue was chosen. Moreover, the filtering apparatus was organized and prepared first before suctioning began. Then, the filter was wet with a small volume of water. Subsequently, the sample was stirred with a magnetic teflon coated stirrer at a moderately high speed to break down the bigger particles. While stirring, wide-bore pipet was used to measure the volume onto the seated glass-fiber filter. The filter was then washed with 3 successive 10-mL volumes of water, to complete drainage between washings, and suction was continued for about 3 minutes after the filtration was complete. Samples with high dissolved solids may require additional washings. Later on, the filter was carefully removed from filtration apparatus and transferred to an aluminum weighing dish as a support. Alternatively, the crucible and filter combination was removed from the crucible adapter if a Gooch crucible is used. It should be dried for at least 1 hour at 103 to 105°C in the drying oven, then it should be cooled in a desiccator to balance temperature and should be weighed immediately. The cycle of drying, cooling, desiccating, and weighing was repeated until a constant weight was obtained or until the weight change was less than 4% of the previous weight or 0.5 mg, whichever is less. It had at least 10% of all samples in duplicate and these duplicated results was within the 5% of their average weight.
According to the Safe Drinking Water Foundation (2017), total dissolved solids (TDS) in water are solids that are not trapped when water is filtered. They are small particles in water with a pore-sized measure of 0.45 micrometers. TDS is the amount of dissolved substances like carbonate, bicarbonate, chloride, sulfate, phosphate, nitrate, calcium, magnesium, sodium, organic ions, and other ions. According to Baird et al. (2017), the first procedure to determine the amount of TDS is the preparation of the glass-fiber filtering disk to be used. The disk was inserted with the wavy side up into filtration apparatus. Suction was applied and the disk washed with three consecutive 20-mL volumes of water. Suction was continued until all water marks were removed. The second procedure is preparation of the evaporating dish to be used. The dish was heated first in the oven in the temperature of 180 +- 2°C for an hour then stored in the desiccator until the dish was needed. Afterwards, the dish was immediately weighed before it was used. The third procedure consists of the filter and sample size selection which is the same with the procedure for TSS mentioned above. Following the filter and sample size selection, the total filtrate (washed) was rendered to an evaporating dish that is already weighed and was evaporated to dryness on a steam bath or in a drying oven. Successive portions were added to the same dish after evaporation as needed. The evaporated sample is then dried in the drying oven at 180 +- 2°C for 1 hour and cooled in a desiccator to balance temperature before being weighed. Just like in the process of determining TSS, the cycle of drying, cooling, desiccating, and weighing is done repetitively until a constant weight was obtained or until weight change was less than 4% of previous weight or 0.5 mg, whichever is less. At least 10% of all samples was analyzed in duplicate and these duplicated results was within 5% of their average weight. To calculate the weight for TDS and TSS, the following formula was used:
TSS/TDS (mg/L) =
Where:
A = weight of filter and the dried residue in mg.
B = weight of the filter
C = sample volume in mL
3.2.4 Determination of color
EPA (2018) stated that if the water is of red or brown color, it may indicate the presence of iron and manganese. Moreover, if the water is blue or green in color, it may be a result of copper pipes or corrosive water. Lastly, if the water is cloudy or foamy, it may be due to turbidity. According to Greenberg (1992), in determining the true color of water, visual comparison method must be used. It is necessary to pre-treat the water through turbidity removal since this is the favorable method for removing the turbidity of water without removing its color and it is also currently accepted method. In this method, the apparatuses used were 50 mL Nessler tubes for colorimetric analyses and pH meter for determining the pH level of the samples. A supply of potassium chloroplatinate was later dissolved by 1.246 g, and a crystallize cobaltous chloride which was also dissolved by 1.00 g in distilled water with 100 mL hydrochloric acid that was then diluted in 1000 mL distilled water. This stock standard has a color of 500 color units. After dissolving the said chemicals, the standards were prepared by diluting stock color standards with distilled water to 50 mL in Nessler tubes. For the main procedure, the sample was placed in another Nessler tube the same as the standards prepared earlier. The sample color was observed carefully and compared to the standards. If the turbidity is present and has not been removed on the sample, it should be considered as an “apparent color” which is the color due to substance solution and suspended matter. The next step was to measure the pH of each sample. Afterwards, the color units were calculated using the formula:
where:
A=estimated color for diluted sample
B=mL sample taken from dilution
The color results are recorded in whole numbers as shown in table 1:
Table 3.1 Conversion of color units to whole numbers
Color Units
Record to Nearest
1-50
1
51-100
5
101-250
10
251-500
20
3.2.5 Determination of chlorine residual
According to Harp (2002), in N-diethyl-p-phenylenediamine (DPD) colorimetric method, digital colorimeter was used to determine chlorine residual. Initially, the water sample was immediately placed into a 10 mL cell also called as a “blank”, since chlorine residual was subjected to evaporation when exposed to sunlight over a long time. The meter cap was first removed to place the blank in the cell holder and put back again over the cell compartment to cover the cell. Excess liquid and fingerprints were necessarily wiped off. After the zero/scroll button was pressed, the blank was removed from the cell holder. Afterwards, another cell was filled again with a 10 mL sample. The use of same sample cells for free and total chlorine analysis without completely rinsing the cells with sample between free and total tests was not allowed. After preparing the second cell, the DPD Free Chlorine Powder Pillow or DPD Free Total Powder Pillow was added to the sample cell. Then, the cell was shaken for about 20 seconds. Shaking dissolved the bubble that might form in sample that has dissolved gases. A pink color indicates that chlorine is present in the sample. The prepared sample was immediately placed into the cell holder and covered properly with the device cap. For free chlorine, the waiting time before pressing the read or enter button was 1 minute while 3 to 6 minutes for total chlorine. However, if the sample temporarily turns yellow after adding the reagent or if the display shows “limit” due to high levels of chlorine, another sample will be diluted and tested. Since a minimal loss of chlorine may occur during dilution, the result must be multiplied by the dilution factor.
3.2.6 Determination of calcium
As specified by Fishman and Downs (1966), a hollow-cathode lamp and reducing flame should be used in determination of calcium. A 4227 angstrom line helps in determining the concentrations of calcium less than 20 mg/L. If concentrations exceed 20 mg/L, dilution must be performed. The lamp current was set at 10 ma (milliampere) while the air pressure at 28 psi (pounds per square inch). Moreover, the fuel of the lamp is acetylene with pressure at 8 psi and 9.0 psi at flowmeter. The flow rate of acetylene was adjusted to achieve maximum absorption. Also, the sample uptake was at least 4 mL per minute. In preparing the calcium chloride stock solution, 1.250 g of calcium carbonate(CaCO3) was suspended and dried at 180° for an hour before being weighed. It was diluted to 1000 mL with distilled water. In terms of the lanthanum chloride hydrochloric(LaCl3-HCL) solution, 58.65 g of lanthanum oxide (La2O3) was dissolved in 250 mL of concentrated HCl and dilute to 500 mL with distilled water. At first, the sample was filtered in a 0.45 micron micro pore membrane filter to avoid clogging the atomizer burner. 1.0 mL of lanthanum chloride – hydrochloric acid (LaCl3-HCL) solution was then added to the 10.0 mL of sample. Then, each sample and standard was atomized by the said instruments and percent absorption was shown. This process was repeated and the two values were averaged. If the concentration of calcium was greater than 20 mg/L, the sample was to be diluted again.
3.2.7 Determination of lead
The United States Environmental Protection Agency (1994) stated that lead can be determined through the use of a Stabilized Temperature Graphic Furnace Atomic Absorption. At first, treatment of an unfiltered acid preserved sample aliquot (?20 mL) was done and placed into a 50 mL polypropylene centrifuge tube. Then, an appropriate volume of nitric acid was added to adjust the acid concentration of the aliquot to estimated 1% (volume/volume) nitric acid solution. Afterwards, the cap of the aliquot of sample was properly closed and mixed. For analysis, there must be an allowance for sample dilution in the data calculation.
3.2.8 Determination of fluoride
According to Bruckner (2018), the method to be used for determining the concentration of fluoride in drinking water is ion chromatography. Ion chromatography is a type of liquid chromatography which is commonly used for water analyses as it can measure major cations and major anions like fluoride through separating them based on their interaction with a resin. The liquid sample or the collected water sample examined with an ion chromatograph was filtered beforehand to ensure that there would be no sediments or other pieces of matter so that the risk of microbial alteration of the sample was lessened. The samples were collected using a sterile syringe rinsed three times with water then filtered with 0.45um or smaller filters. The final container was then rinsed with the filtered sample three times. Afterwards, it was filled and kept cold before used for examination. The minimum sample required is approximately 5mL with no maximum limits. During the process of ion chromatography, the water sample first passed through a guard or barrier type of column to prevent any particles from ruining the machine’s components. Then, it passed through a pressurized chromatographic column where the ions present in the sample were absorbed by the column constituents. Afterwards, an ion extraction liquid, eluent passed through the column making the absorbed ions separate from the column. The concentration of the specific ions or fluoride in this case in the water sample is determined by the retention time.
3.3 Data Analysis
Results of each parameter will be compared to the Philippine National Standards for Drinking Water (PNSDW) and World Health Organization (WHO) Drinking Water Standards, known reference points for the standards of drinking-water safety (DOH, 2017). The parameters that will be tested and each of their standard limits are shown in table 2. Comparisons and discussion will then be based on the amount or characteristic of parameters and if each meets the standard.
Components
Maximum Allowable Level
PNSDW
WHO
pH
6.5 – 8.5
6.5 – 8.5
Turbidity
5 NTU
5 NTU
Color
10 CU
5 CU
TDS
600 mg/L
500 mg/L
TSS

500 mg/L
Chlorine residual
1.5 mg/L
0.2 – 0.5 mg/L
Calcium

75 mg/L
Lead
0.01 mg/L
0.01 mg/L
Fluoride
1.0 mg/L
1.5 mg/L

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