Thursday, June 30, 2016

How does one take samples for water quality tests from lakes

At Jakkur Lake
Earlier this month, Anjana, Siddharth, Vandana and I from Biome visited the office of ATREE to learn about their work, studying and testing water quality.
Apart from the procedural practices of the sampling process we also observed that the part of the lake that's cordoned off to the public harbours noticeable vegetation. With karundas, lantanas , jatrophas, for low shrubbery to acacias, neem and gulmohar for canopies. Also, water snakes have comfortably lodged in the fisherman zone of the lake. The waders have extricated snail and mollusk shells from the floor of the lake. The accumulation was clearly due to the recent rise in temperatures.
We head out to collect samples from inlets, wetland inflows, center of the lake and at the outflows.

What are we testing?
Parameters that need to be analyzed for water quality in the lab are Nitrates, Phosphates and pH, dissolved oxygen, temperature, conductivity and sometimes turbidity. 
For several measurements special portable measuring devices are available.
pH, dissolved oxygen, temperature, conductivity and turbidity tests can be done insitu
Pictured right: Testing conductivity, temperature and pH

First Step
We take samples at the inlets, outlets and center of lake.
Collect samples at about 0.5m from the surface of water with a measured wooden stick
Label the sample containers and store it in an icebox below 4 C
The samples collected for chemical oxygen demand (COD) analysis should be preserved below pH 2 by addition of concentrated sulfuric acid. 
This procedure should also be followed for samples for ammoniac nitrogen, total oxidized nitrogen and phenol analysis.

To test the BOD of the sample, you need to fix the amount of dissolved oxygen in the sample.

Fill the sample to BOD bottle until it overflows. Put stopper on it. Open the stopper and add 1ml of Manganese Sulfate and 1 ml of Alkali-iodide reagent below the surface of liquid. Mix by inverting several times. Slowly brown/white precipitates will form. Check for air bubbles; remix after precipitate has settled to bottom. If brown precipitates appear, add 1ml of concentrated sulfuric acid above the surface of liquid and invert sample to mix, the precipitate will be dissolved. Take 201 ml of sample from the BOD bottle transfer to conical flask.
Titrate sample against standard sodium thiosulphate solution until dark yellow color changes to light yellow. Add starch indicator solution, blue color will develop. Continue the titration until sample turns from blue to colorless. Note down the final reading of burette.

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