Collection, Preservation and Tabulation of Industrial Samples

After reading this article you will learn about the collection, preservation and tabulation of industrial samples.

The collection and preservation of industrial sample for analysis work is a very important part and hence it should be done very carefully. The improper care may lead to wrong results. The quantity of the sample, place of taking sample (sampling station), temperature, immediate pH, D.O., BOD., etc. are some of the factors which vary if the sample is not treated for preservation immediately.

The following are some of the important points to be kept in mind at the time of collection and preservation of industrial sample:

1. Sample Containers:

Generally Polythene containers of 2 litres capacity can be used for collection of samples.

2. Quantity of Sample:

For determination of all constituents of the sample, a 5 litre polythene container should be used but for specific parameters only 2 litres of sample is sufficient for the work.

3. Labeling of Samples:

Before the container is used, it should be labelled as follows:

(i) Sample number

(ii) Name or place of sampling station or industry

(iii) Date and time

(iv) Name of the District/City/Village & State

(v) Name of sample collector

(vi) Rate of flow of effluent

(vii) Temperature

(viii) Depth below surface

(ix) Pressure of the day

Collection and Utilization of Samples:

If effluent is discharged into surface water then two samples – one from upstream and other from down-stream should be collected and analysed. Hot samples should not be taken. The samples should only be taken when effluent has been sufficiently cooled down.

Grab Sample:

The spot, snoop, instantaneous or grab sample is a sample collected manually of industrial effluent at a point where flow is homogeneous.

Composite Sample:

When grab samples are collected at a regular interval of time for a period of say 12 hrs. to 24 hrs. and mixed then this integrated sample is called composite sample. Composite samples always yield better results.

B.O.D. and D.O. Samples:

Samples for the determination of dissolved oxygen and Biochemical oxygen demand should be collected in BOD bottles (available in the market) by siphoning to avoid aeration. BOD bottles are 1 litre Pyrex or corning bottles. Special devices such as Displacement sampler or Kemmerer type samples can be used for collecting samples for D.O. and B.O.D.

The bottles should be filled without entrapment of any air should not be disturbed during collection. The effluent can be siphoned through a rubber into the sample bottle. An important point is that tip of the tube should be at the bottom of the bottle and temperature along with pressure should be noted immediately.

If possible D.O. should be determined immediately at the sampling station otherwise its value will be changed. If it is not possible to determine its value immediately then sample can only be preserved if 2 ml. of monogamous sulphate solution and 2 ml. of alkali – iodide – azide are added immediately and sample is kept at 4°C in dark only for 24 hrs.

By calculating dissolved oxygen before & after 5 days at 20°C, the BOD can be calculated & hence there is no need to collect the samples for BOD separately. When sample does not contain any oxygen then it is supplied with oxygen & depletion is calculated as BOD.

Oil Sample:

For analysis of oil in the effluent, about 5 litres of sample is collected in dry and glass stoppered bottles. Sample bottles are filled partially to avoid loss of oil when stopper is used.

Sample for Settleable Solids:

For collection of suspended particles an Imhoft cone is used. It is inverted glass cone of 1 litre capacity where the upper part is graduated in ml.

C. O.D. Sample:

Chemical oxygen demand is the oxygen required of a sample for oxidation of organic and inorganic matter hence it is an important parameter & its value should be determined immediately from the 2 litre sample collected at the sampling station.

If its determination is not possible then add conc. H₂SO₄ until the pH reaches below 2 and analyse it within 7 days if it is kept at room temperature. If the acidified sample is taken in a refrigerator at 4°C then sample can be kept for 24 days.

Sample for Metals:

Composite samples for detection of metals, should be taken in a 2 litre polythene bottle & immediately digested with nitric acid & sulphuric acid as follows:

Take the sample in a evaporating dish. Acidify to methyl range with conc. H₂SO₄ & add 5 ml. conc. HNO₃ & 2 ml 30% H₂O2 to reduce chromate by placing over a water bath or hot plate to about 10 ml. Now transfer this liquid into conical flask with the help of 5 ml. conc HNO₃. Add 10 ml. conc.

H₂SO₄ and a few glass beads. Now evaporate the contents on hot plate till dense fumes of SO₂ just appear in the flask. Cool to room temperature & add 50 ml. distilled water & boil if solids are present & filter through a sintered glass crucible.

Transfer the filtrate with 100 ml. volumetric flask and make it up to the mark by addition of distilled water. Now use this solution for the determination of various metals by using different techniques.

Sample for Biological Examination:

For biological examination, the sample is taken in a dry & pure Pyrex bottle. There should be no gap between stopper and effluent. Any gap of air should be avoided.

When Sample Contains Suspended Matter:

Take the sample in 500 ml. bottle. Add 10 gm. alum & 2 ml. conc. ammonia solution. Stopper & mix thoroughly for about 3 – 4 minutes & keep it for 5 minutes. Take supernatant liquid into BOD bottle & use until it overflows. Stopper it & now use it for D.O. & BOD & other parameters.

When Sample Contains Chlorine Water:

Neutralize the chlorine by taking thio solution & then place the liquid in BOD bottles & use it for D.O. & B.O.D.

When Sample Contains Ferrous Ions:

Take 300 ml. samples in BOD bottle. Add 0.7 ml. conc. H₂SO₄ & add KMnO₄ until it acquires red – violet tinge for about 20 minutes. Add potassium oxalate solution until it discharges. Now add 2 ml. manga-nous sulphate solution (0.1N) & 2ml. alkali – azide reagent (0.1N).

Time between Collection & Analysis of Sample:

As far as possible all samples should be analysed immediately without any delay. If any how sample is to be kept for some-time due to one reason or the other then it should be kept after adding proper reagents at 4°C. The pH, temperature, pressure, oxygen, CO₂ etc. should be determined immediately.

Preservation of Sample:

There are some standards for the preservation of the samples for different constituents.

The recommended methods are given in the following table:

Tabulation of Industrial Samples:

The results should be tabulated as follows:

1. Sample No.

2. Date on which sample taken.

3. Source of sample & Name of industry

4. Sampling station or place

5. Name of collector

A. Physicochemical Characteristics:

1. Colour

2. Odour

3. Temp. °C

4. pH

5. Solids

i) Total, mg/l

ii) Suspended, mg/l

iii) Settleable, ml/l/hr

iv) Dissolved, mg/l

B. Inorganic Pollution (Metallic & metalloids):

1. Copper (as Cu), mg/l

2. Iron (as Fe), mg/l

3. Lead (as Pb), mg/l

4. Manganese (as Mn), mg/l

5. Zinc (as Zn), mg/l

6. Nickel (as Ni), mg/l

7. Mercury (as Hg), mg/l

8. Cadmium (as Cd), mg/l

9. Chromium (trivalent) (as Cr) mg/l

10. Chromium (Hexavalent) (as Cr), mg/l

11. Arsenic (as As), mg/l

12. Antimony (as Sb), mg/l

13. Boron (as B), mg/l.

Non-Metals:

14. Acidity/Alkalinity (as CaCO₃), mg/l

15. Phosphate (as PO₄), mg/l

16. Sulphide (as S), mg/l

17. Sulphite (as SO₃), mg/l

18. Sulphate (as SO₄), mg/l

19. Chloride (as CI), mg/l

20. Fluoride (as F), mg/l

Organic Pollution:

21. Dissolved oxygen, mg/l

22. BOD (5 days at 20°C), mg/l

23. COD, mg/l

24. Total nitrogen kjeldahl, mg/l

25. Nitrite (as Nitrogen), mg/l

26. Nitrate(as Nitrogen), mg/l

27. Total organic carbon, mg/l

28. Ammonical nitrogen, mg/l

29. Oil and grease, mg/l.

Note:

The errors should also be calculated for each parameter & at-least mean of 15 readings should be given in the final table.

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