This article throws light upon the four important points to be kept in mind at the time of collection and preservation of industrial sample. The points are: 1. Sample Container 2. Quantity of Sample 3. Labelling of Samples 4. Collection and Utilization of Samples.
Industrial Sample: Point # 1. Sample Container:
Generally Polythene containers of 2 litres capacity can be used for collection of samples.
Industrial Sample: Point # 2. Quantity of Sample:
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For determination of all constituents of the sample, a 5 litre polythene containers should be used but for specific parameters only 2 litres of sample is sufficient for the work.
Industrial Sample: Point # 3. Labelling of Samples:
Prior to use of container, used it should be labeled 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
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(v) Name of sample collector
(vi) Rate of flow of effluent
(vii) Temperature
(viii) Depth below surface and
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(xi) Pressure of the day.
Industrial Sample: Point # 4. Collection and Utilization of Samples:
If effluent is discharged into surface water the two samples-one from upstream and other from down-stream should be collected and analyzed. Hot samples should not be taken. The samples should only be taken when effluent has been sufficiently cooled down.
Grab sample:
The spot snap, instantaneous or grab a sample is a sample collected manually of industrial effluent at a point where flow is homogenous.
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Composite sample:
When grab samples are collected a regular interval of time for a period of say 12 hrs to 24 hrs & mixed then this integrated sample is called composite sample.
Composite samples always yield better results.
BOD & D.O. Samples:
Samples for the determination of dissolved oxygen and Bio-chemical 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 etc. 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 manganese sulphate solution and 2ml 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 Imhoff cane is use. It is inverted glass cane 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 and its value should be determined immediately from the 2 litre sample collected at the sampling station.
If its determination is not possible when 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.