Advanced Water Quality Assessment: Bridging the Gap between Simple Testing Procedures and Sophisticated Analytical Techniques
While simple, small-scale laboratory testing procedures can provide a preliminary estimate of water quality, they are limited in their accuracy and comprehensiveness. For instance, the 12-analysis approach, although suitable for describing contaminated water sources, falls short in providing a detailed and quantitative assessment of water quality. In contrast, advanced analytical instruments such as UV spectrophotometers and High-Performance Liquid Chromatography (HPLC) systems, coupled with computerized data processing and electronic processing systems, offer unparalleled precision and sensitivity in detecting and quantifying a wide range of water pollutants.
These sophisticated analytical techniques enable the detection of trace levels of contaminants, including heavy metals, pesticides, and industrial pollutants, which may not be detectable through simple testing procedures. Furthermore, advanced analytical instruments can provide detailed information on the chemical composition and physical properties of water, allowing for a more comprehensive understanding of water quality. By bridging the gap between simple testing procedures and advanced analytical techniques, water quality professionals can ensure more accurate and reliable assessments of water quality, ultimately informing effective management and treatment strategies to protect public health and the environment.
List of tests:
- Total residual chlorine
- Chlorides
- Total Hardness
- Calcium
- Magnesium
- Alkalinity
- Free Carbon dioxide
- Sulphites
- Sulphates
- Dissolved Oxygen
- Chemical Oxygen Demand
- Biochemical Oxygen Demand
Testing procedures
Total Residual Chlorine Determination: A Critical Analysis of Sampling and Analytical Methodologies
The accurate determination of total residual chlorine (TRC) in effluent samples is a crucial aspect of water quality monitoring. However, the residual chlorine content is prone to decrease after sample collection, particularly in hot weather conditions, highlighting the importance of on-site testing. When dealing with samples containing suspended matter, it is essential to allow a portion to settle for 15 minutes and test the supernatant to ensure accurate results.
The iodometric method is a widely employed technique for TRC determination, based on the principle that chlorine liberates iodine from potassium iodide, which is subsequently titrated against a standardized sodium thiosulphate solution. This method is suitable for detecting residual chlorine concentrations between 1 and 10 mg/L. However, it is susceptible to interferences from nitrites, ferric, and manganic compounds, which can lead to inaccurate results. To mitigate these interferences, titration should be performed within a pH range of 4.5 to 8.0, and the results should be reported with a clear indication of whether the titration was conducted in acid solution or not. By acknowledging the limitations and nuances of the iodometric method, water quality professionals can ensure more accurate and reliable TRC determinations.
Reagents
- Dil Sulphuric acid - 4N
- Potassium iodide solution – 10 percent w/v
- Acetic acid – glacial.
- Std potassium hydrogen iodate sol – 0.005N dissolve 0.1625g of potassium hydrogen iodate dried at 105oC in water and make it to 1 lit.
- Std sodium thiosulphate sol – 0.005N dissolve 1.241g of sodium thiosulphate in freshly boiled and cooled water and makeup to 1 lit add 5 ml of chloroform or 0.4g sodium hydroxide per liter as a preservative.
- Starch indicator – triturate 5g of starch and 0.01g of mercuric iodide with 30ml of cold water and slowly pour it with stirring into 1 lit of boiling water. Boil for 3 min allow the solution to cool and decant the supernatant clear liquid.
Determination of Total Chlorine in Water Samples
Procedure:
- Sample Preparation: Take 500ml of the water sample.
- Alkalinity Adjustment: If the total alkalinity of the sample exceeds 400mg/L, add sufficient dilute Sulphuric acid (H2SO4) to reduce the alkalinity to 400mg/L.
- Addition of Reagents: Add 5 ml of potassium iodide (KI) solution and 5 ml of acetic acid (CH3COOH) to the sample. Mix well.
- Titration: Immediately titrate the sample with standardized sodium thiosulphate (Na2S2O3) solution until the color of iodine is nearly discharged.
- Addition of Starch Indicator: Add 2 ml of starch indicator solution to the sample.
- Final Titration: Continue the titration with sodium thiosulphate solution until the blue color disappears for at least 30 seconds.
- Calculation: Calculate the total chlorine content of the sample using the volume of sodium thiosulphate solution used.
Total residual chlorine, mg/l = 0.1773×1000×v/500
Where v = volume in ml of std sodium thiosulphate sol required for the titration.
Total Residual Chlorine Calculator
Total Residual Chlorine (mg/L):
Note:
- The starch indicator solution should be prepared fresh daily.- The sodium thiosulphate solution should be standardized before use.- The titration should be performed in a well-ventilated area, away from direct sunlight.- The result should be expressed in mg/L (milligrams per liter) of total chlorine.
Analysis of particle size of suspended solids:
The particle size of suspended solids is determined by wet screening of the freshly drawn sample through the specified sieve. Since the suspended solids in the sample are likely to coalesce keeping, the test should be carried out on the spot. Leaves, twigs and other wind-blown debris, which are extraneous to the sample, should be removed.
Apparatus :
- Sieve: 850micron sieve
- Enameled pail: of a diameter slightly bigger than that of the sieve
Hold the sieve in one hand and with the other pour gently on the mesh surface of the sieve one litre of well-mixed sample. Pour the sample so that it covers the entire mesh surface. If necessary create a vibration while sieving the sample by a gentle rocking motion of the hand holding the sieve. Fill the enameled pail with fresh water. Then having the screen on opposite sides with the two hands brings it to the surface of the water in the enameled pail and wet screen by jigging(up and down motion). Take care to see that while jigging the sieve is dipped in the water only to half its depth and there is no overflow from the mesh through the sides as suspended solids would be washed out without passing through the screen. If necessary wash the material on the screen with a fine jet of water from a wash bottle until all lodged particles are loosened.
The suspended matter shall be considered passing through the sieve only if no residue is left on it.
Precautions
- Conduct the test on the spot to prevent coalescence of suspended solids.
- Ensure the sieves are clean and free of contaminants before use.
- Handle the sample and suspended solids carefully to avoid loss or contamination.
Estimation and determination of Phenolic compounds:
Isolation of Phenols:
Apparatus :
- Distillation apparatus: all glass assembly with 1-litre distillation flask and preferably, Graham condenser.
- Separating funnel: with ground glass stoppers
- Copper sulphate solution= 10 percent w/v
- Phosphoric acid= 1:10 v/v
- Methyl orange indicator= dissolve 0.01 g of methyl orange in 100 ml of water
- Sodium chloride
- Chloroform
- Sodium hydroxide solution= approximately 1N
To 500 ml of the sample add 5.0ml of copper sulfate solution and acidify to pH less than 4.0 with phosphoric acid, using methyl orange as an indicator. Omit this treatment in the case of samples preserved by the addition of copper sulfate and phosphoric acid. Transfer to the distillation apparatus and distill until about 450ml of the distillate is collected. Stop distillation and when boiling ceases add 50 ml of water to the distillation flask. Continue the distillation operation until a total of 500 ml has been collected.
Acidify the distillate with 1 ml of phosphoric acid and add 5 ml of copper sulfate solution. Transfer to a separating funnel and add 150 grams of sodium chloride. Extract thrice with chloroform, using 50ml of chloroform for each extraction. Take care that all the sodium chloride goes into the solution during the first extraction. Combine the chloroform extracts and discard the aqueous layer. Extract the phenols from the chloroform portion with two successive 75 ml quantities of sodium hydroxide solution. Dilute the combined alkaline extracts to 250 ml with water. Heat in a water bath until the chloroform is driven off completely and dilute with water to 500ml.
Acidify the distillate with 1 ml of phosphoric acid and add 5 ml of copper sulfate solution. Transfer to a separating funnel and add 150 grams of sodium chloride. Extract thrice with chloroform, using 50ml of chloroform for each extraction. Take care that all the sodium chloride goes into the solution during the first extraction. Combine the chloroform extracts and discard the aqueous layer. Extract the phenols from the chloroform portion with two successive 75 ml quantities of sodium hydroxide solution. Dilute the combined alkaline extracts to 250 ml with water. Heat in a water bath until the chloroform is driven off completely and dilute with water to 500ml.
Note: when phenol concentration in the sample is known to be high, distill a smaller volume, but collect about 450 ml of distillate by adding water to the sample in the distillation flask towards the end and continuing the distillation as above, preferably using a smaller capacity flask for distillation when the volume taken is small.