Trace elements analysis in drinking water of Meghalaya by using graphite furnace-atomic absorption spectroscopy

An Analytik Jena AAS Vario 6 graphite furnace spectrometer furnished with PC-controlled 6-piece lamp turret and argon gas supply was used for all of the absorption measurements. The hollow cathode lamps were fitted for specific element that has to be analyzed with their respective wavelength and the slit width was adjusted accordingly. Signal measurement was done in peak area and calibration was in linear mode. The sample injection volume is 20 L. The typical heating program of GF-AAS is drying (injection of the sample into the filter furnace), pyrolysis, atomization, and cleansing. The elements instrumental conditions are given in Table 1 [4]. Conductivity was measured using Conductivity Meter (model 304, Systronics, India). The total nitrate and phosphate was determined by APHA methods. The pH measurements were carried out by a digital pH meter (model 802, Systronics, India) and the turbidity was measured with nephelometer (model 131 Systronics, India). All glassware and containers were soaked in 1.4 mol L−1 nitric acid for at least 24 hours and rinsed three times with water before use.

“It is evident from Table 2 that measurement of pH, turbidity, phosphate, and nitrate gives first hand information of water quality which is a frequently used test in water chemistry. In our analysis, the pH of raw and treated water ranges from 6.5 to 7.3; this is within the limit (Table 4). The pH of water indicates the degree of acidity or alkalinity of water and has a significant influence on the reaction of coagulants with raw water. It is also the most important water quality factor controlling levels of these metals in treated water. The turbidity of raw water is 56.24 and 10.27 NTU for treated water. This is very high compared with the standard methods. Raw water which is low in colour and higher turbidity brings somewhat different demands. The flocculation system must be capable of handling heavy floc and large amount of turbidity-laden floc which settle out and cause operation problems. So removal and disposal must also be given special consideration. The concentration of nitrate in raw and treated water is found to be 0.03 and 0.01 mg/L. Nitrate levels may be important under certain conditions although the relative source contribution from drinking water is expected to be a maximum of about 1-2 mg/L. Numerous papers have focused on the impact of nitrate in drinking water. Nitrate may be reduced to nitrite in the low pH environment of the stomach, reacting with amines and amides to form N-nitroso compounds which have been linked to different types of cancer [3]. The phosphate content in raw and treated water is found to be 0.44 and 0.04 mg/L. However; in low alkaline water, control strategies are sometimes utilized such as adding phosphate to reduce Pb and Cu corrosion and release of Fe from pipes scales. Table 3 presents the result of raw and treated water. The salient features of analysis for each element are given below.”

Table 2

Parameters analyzed in treated and untreated water.

Parameters for water analysis Sample East Khasi Hills West Khasi Hills Jaintia Hills

pH Untreated water 6.80 ± 0.018 6.60 ± 0.031 6.10 ± 0.044
Treated Water 7.50 ± 0.045 7.30 ± 0.028 7.10 ± 0.031
Turbidity NTU Untreated water 64.24 ± 2.14 44.15 ± 5.18 59.80 ± 4.18
Treated Water 10.25 ± 0.45 8.40 ± 0.18 12.16 ± 0.26
Conductivityat 25°C with 0.01 M Untreated water 1.00 ± 0.088 1.20 ± 0.048 0.80 ± 0.018
Treated Water 1.50 ± 0.020 1.80 ± 0.042 1.50 ± 0.025
 (mg/L) Untreated water 0.03 ± 0.001 0.03 ± 0.005 0.04 ± 0.003
Treated Water 0.01 ± 0.006 0.02 ± 0.005 0.02 ± 0.009
 (mg/L) Untreated water 0.55 ± 0.058 0.52 ± 0.018 0.25 ± 0.078
Treated Water 0.09 ± 0.003 0.02 ± 0.002 0.01 ± 0.004

Results are mean ± SD of 25 observations each.

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