6, (15%) (a) Describe the step of the BOD test (b) Describe how to correct seed

Question

6, (15%) (a) Describe the step of the BOD test (b) Describe how to correct seed bacteria in BOD test (c) Derive test L(t) In (-:2--kt for a BOD test. Start your answer by defining L() = BODL_ BOD(). Assume first-order decay of L during (c) Derive In (Y) =-kt for a BOD testin BODtest(ie. L t vs. time. You will have to gues click onplottedda alayR-s ven below plot L(t) (d) BOD test results are given below, plot . time. You will have to guess a value for BOD. Assume BODL is 400 mg- O/L. Find the first order kinetic constant k from the plot. (If you use MS Excel, right click on plotted data points, choose "Add Trendline," check for "Linear," set "O" for "Set Interception," and check for "Display equation" and "Display R-square value.") Show the resulting plot in your answer. Once k is found, calculate BOD and compare it with the initial guess In revalued) Show Incubation time (days) Measured BOD (mg O2/L) 4 201 0 72 102 156 221 (e) If the initial guess of BODL (400 mg/L) were not given, write a short discussion on how you would find BODL

Explanation / Answer

BOD test is a useful parameter to check the water quality. The higher the value of BOD,Greater is the amount of organic matter available to oxygen consuming bacteria. The water with BOD level betwen 3-5ppm is considered fit for drinking.

Steps:

* Water sample is collected and filled in a BOD bottle ( incubation bottle ), carefully enough to avoid air bubbles

* 2ml of manganese sulfate is added using a pipette

* Add 2 mL of alkali-iodide-azide reagent to the bottle

* close the bottle and shake tomix the contents. Brownish clouds appear which indicates presence of oxygen

*Allow the ppt to settle down and add 2ml of conc H2SO4. Shake well

* Keep the bottle undisturbed in an incubator for 5days. After 5 days, titrate 50ml of this solution with 0.025N Na2S2O3 till a pale yellow color is obtained

* Add starch as indicator. Solution turns blue

continue titrations till a clear sol is obtained. The conc of dissolved oxygen can be obtained as no.of ml of titrant that gets used

b) Seed is actually the no.of microorganisms that consume the biodegradable organic matter in samples of BOD. Without proper seed, the results of this test may not be accurate. Polyseed capsules can be used to correct the seed of BOD samples.

I apologise but i am not very sure for the derivation parts

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