The following article will guide you about the various ways for monitoring wastewater.
Way # 1. Biological Oxygen Demand (BOD):
‘BOD measures the requirement of oxygen by micro-organisms when a sample of water is treated at a temperature of 20°C for an elapsed period of five days’. If we have to determine the biochemical oxygen demand in given water sample then measurement of dissolved oxygen in the sample is required. To measure dissolve oxygen and further Biological oxygen demand, some instruments or apparatus and chemical reagents will be required as follows.
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Apparatus/Instrument:
BOD bottles having capacity of 250-300 ml, foil cap, incubator and titration apparatus are required for measurement of dissolved oxygen.
Reagents:
1. Manganous Sulphate Solution:
To prepare this solution, dissolve 364 gm MnSO4.H2O in water, filter it and make volume up to one liter. The MnSO4 solution should not give a colour with starch when added to an acidified potassium iodide (KI) solution.
2. Alkali-Iodide-Azide Reagents:
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For saturated or less than saturated sample- Dissolve 350 gm KOH and 75 gm KI in distilled water and dilute to 500 ml. Add 5 gm NaNO3 dissolve in 40 ml distilled water. This reagent should not give a colour with starch solution when diluted and acidified.
3. Sulphuric Acid:
H2SO4 concentrate-1 ml is equivalent to about 3 ml alkali iodide Azide reagent.
4. Starch-Soluble:
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Starch powder mixture (2% starch solution).
5. Standard Sodium Thio-Sulphate Titrant:
Dissolve 6.205 gm Na2S2O3.5H2O in distilled water. Add 0.4 gm solid NaOH and dilute to 1000 ml distilled water.
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1. Prepare the required dilution of sample as 10%, 20%, 30%, etc.
2. Add phosphate buffer, magnesium sulphate, calcium chloride and ferric chloride solution to each bottle (1 ml/litre) maintain the pH 7.2.
3. Fill the BOD bottles up to overflow; there should not be any air bubble in the bottle.
4. Keep one bottle of the same sample and same dilution in BOD Incubator at 20°C for 5 days.
5. In second bottle, add 1 ml of MnSo4 and 1 ml of Alkali Azide reagent in the bottle due to this yellow ppt forms. Let the ppt settle down upto the half of the bottle.
6. Add about 2 ml of concentrated sulphuric acid to dissolve the precipitate; solution becomes clear and golden in colour.
7. Take 201 ml of the above sample in 250 ml conical flask add 1 ml of freshly prepared stach indicator (solution become dark blue).
8. Titrate this 201 ml solution with standard sodium thio-sulphate solution; disappearance of colour will be the end-point.
9. Note the burette reading for calculation.
By performing above mentioned steps, we can find out burette reading of sodium thiosulphate in ml. Initial DO in mg/l and Final DO in mg/l.
Calculation:
Now, as per data available we can calculate BOD by using following formula:
BOD mg/l in the given sample = Initial DO – Final DO × Dilution factor
Dilution factor = Final volume of sample/initial volume of sample
While performing experiment to determine BOD, we should keep few points in mind that titration should be done carefully, apparatus should be washed and carefully measure the volume of reagents and sample.
Way # 2. Chemical Oxygen Demand (COD):
Recommended method to determine chemical oxygen demand is open reflux method. Organic matter present in sample is oxidised by a boiling mixture of chromic and sulphuric acids. A sample is refluxed in strongly acid solution with a known excess of potassium dichromate (K2Cr2O7).
After digestion, the residual unreduced K2Cr2O7 is titrated with ferrous ammonium sulphate to determine the amount of K2Cr2O7 consumed and the matter which can be oxidised, is calculated in terms of oxygen equivalent. Keep ratios of reagent weights, volumes, and strengths constant when sample volumes other than 50 ml are used.
Some samples which have very low COD may need to be analysed in replicate to get most reliable data. Results are further enhanced by reacting a maximum quantity of dichromate, provided that some residual dichromate remains. For determining the chemical oxygen demand in given water sample, first of all measurement of dissolved oxygen in the sample is required.
To measure dissolve oxygen and further chemical oxygen demand, some instruments or apparatus and chemical reagents are required.
To perform above activity, apparatus like reflux apparatus, blender and wide-bore pipette and chemical reagents will be required as follows:
1. Standard potassium dichromate solution- Dissolve 12.260 g K2Cr2O7, primary standard grade, previously dried at 150°C for 2 h, in distilled water and dilute to 1000 ml. This reagent undergoes a six-electron reduction reaction, the equivalent concentration is 6 × 0.04167 M or 0.2500 N.
2. Sulphuric acid reagent- To prepare this reagent add Ag2SO4, reagent or technical grade, crystals or powder, to concentrate H2SO4 at the rate of 5.5 g Ag2SO4/kg H2 SO4. Leave it for 1 to 2 day to dissolve.
3. Ferroin indicator solution- Dissolve 1.485 g, 1, 10-phenanthroline monohydrate and 695 mg FeSO4*7H2O in distilled water and make up volume to 100 ml. This indicator solution may be purchased from market as already prepared indicator solutions are available in market.
4. Standard ferrous ammonium sulphate (FAS) titran (0.25 M)- Dissolve 98 g Fe (NH4)2(SO4)2*6H2O in distilled water then add 20 ml concentrate H2SO4, cool, and make up volume up to 1000 ml by adding distilled water.
5. Mercuric sulphate- HgSO4, crystals or powder.
6. Sulphonic acid- Used if the interference of nitrites is to be eliminated.
7. Potassium hydrogen phthalate (KHP) standard- HOOCC6H4COOK- Lightly crush and then dry KHP at 110°C. Dissolve 425 mg in distilled water and make up volume up to 1000 ml. KHP has a theoretical COD of 1.176 mg O2/mg and this solution has a theoretical COD of 500 μg O2/ml. This solution is stable under low temperature. Observe development of visible biological growth if any. Weekly preparation of KHP is satisfactory.
Treatment of Samples with COD of >50 mg O2/l:
Blend sample if required and pipette 50.00 ml into a 500-ml refluxing flask. For samples with a COD of >900 mg O2/l, use a smaller portion diluted to 50.00 ml. Add 1 g HgSO4, along with several glass beads, then very slowly add 5.0 ml sulphuric acid reagent and mix to dissolve HgSO4.
Mixing perform under low temperature to avoid possible loss of volatile materials. Add 25.00 ml 0.0417M K2Cr2O7 solution and mix. Attach flask to condenser and turn on cooling water. Add remaining 70 ml sulphuric acid reagent through open end of condenser. Continue swirling and mixing while adding sulphuric acid reagent.
To prevent foreign material from entering refluxing mixture open end of condenser should cover with a small beaker and reflux for 2 h. Cool and wash down condenser with distilled water. Disconnect reflux condenser and make up volume of mixture up to about twice its volume with distilled water. Cool up to room temperature and titrate excess K2Cr2O7 with FAS, using 2 to 3 drops ferroin indicator.
The quantity of ferroin indicator is not critical; the same volume for all titrations can be used. Take as the end point of the titration the first sharp colour change from blue-green to reddish brown that persists for 1-2 min. Samples containing suspended solids or other components may require additional determinations. The blue-green colour may reappear. In the same manner, reflux and titrate a blank containing the reagents and a volume of distilled water equal to that of sample.
Alternate Procedure for Low-COD Samples:
Extreme care is required in this procedure because even a trace of organic matter on the glassware or from the atmosphere may create gross errors. If increased sensitivity is required then concentrate a larger volume of sample before digesting under reflux. In this process add all reagents to a sample larger than 50 ml and reduce total volume to 150 ml by boiling in the refluxing flask open to the atmosphere without the condenser attached.
Calculate amount of HgSO4 which is to be added on the basis of a weight ratio of 10:1, HgSO4: Cl– by using the amount of CI– present in the original volume of sample. Then carry a blank reagent through the same procedure. In this technique there is no loss of easily digested volatile materials. It has the advantage of concentrating the sample without lose of volatile materials.
Determination of Standard Solution:
Evaluate the quality of reagents by conducting the test on a standard potassium hydrogen phthalate solution.
Way # 3. Estimation of TSS, TVS, TDS, ash Content, Lignin, Cellulose, Hemicellulose:
Total, fixed, and volatile solids in water, solids, and biosolids
Total solids (A) = Total suspended solids (B) + Total dissolve solids (C) (B)
Total Suspended Solids:
Total Solids:
All solids present in water are denoted as total solids. Total solids are measured by evaporating all of the water out of a sample and weighing the solids which remain after evaporation of water.
Dissolved Solids:
Solids which are dissolved in the water and would pass through a filter are known as dissolved solids, examples, salt or sugar dissolved in water.
Suspended Solids:
Solids which are suspended in the water and would be retaining by surface of filter.
Types of Suspended Solids:
There are three types of suspended solids:
1. Settleable solids.
2. Non-settleable solids.
3. Colloidal solids.
Some apparatus like desiccators, drying oven, for operation at 103°C to 105°C, analytical balance, capable of weighing to 0.1 mg, graduated cylinder, beaker, glass funnel, whatman filter paper, conical flask and porcelain dish (crucible), 25 ml to 100 ml capacity and filtration unit will be required for the determination of these suspended solids in a given sample, reagents of good quality are also required.
Procedure:
To get best result, first of all dry the filter paper at 105°C in hot air oven for 1 hour, cool in dessicator and take weight as W1, Pour 50 ml water sample on the filter paper by arranging the paper on a clean conical flask. Now keep the filter paper in hot air oven for 1 hr. at 105°C and then cool the filter paper in dessicator and take weight as W2.
Take all the weights in Mg.
Initial weight of filter paper (W1) = …………………..
Final weight of filter paper (W2) = ………………….
Calculation:
Total suspended solids of sample mg/l = W2-W1 x 1000/ ml of sample.
Where, W1 = initial weight of filter paper (mg)
W2 = Final weight of filter paper (mg)
1000 = To covert the values as TSS in mg/l.
Total Dissolve Solids:
Total Solids:
All type of solids present in water either dissolved or suspended considered as total solids. Total solids are measured by evaporating all of the water out of a sample and weighing the solids which remain after evaporation.
Type of Solids:
There are two types of solids:
1. Dissolved Solids:
Solids which are dissolved in the water and would pass through a filter.
2. Suspended Solids:
Solids which are suspended in the water and would be caught by a filter.
To determine total dissolve solids, apparatus like desiccators, drying oven, for operation at 103 to 105°C, analytical balance, capable of weighing to 0.1 mg, graduated cylinder, beaker, glass funnel, whatman filter paper, conical flask and porcelain dish (crucible), 25 ml to 100 m capacity, filtration unit and good quality reagents.
Procedure:
First of all dry the porcelain dish at 105°C in hot air oven for 1 hr. then cool in dessicator and take weight as W1. Then pass 50 ml water sample from the filter paper by arranging the paper on a clean conical flask and collect the filtered water in pre weighted porcelain dish. Keep the Porcelain Dish (crucible) in hot air oven for 1 hr. at 105°C to evaporate water. The water should evaporate completely. At last cool the Porcelain Dish (crucible) in dessicator and take weight as W2. Take all the weights in mg.
Initial weight of porcelain dish (crucible) (W1) = …………………..
Final weight of porcelain dish (crucible) (W2) = ………………….
Calculation:
Total dissolve solids of the given water sample mg/l = W2 – W1 × 1000/ ml of sample
Where, W1 = Initial weight of porcelain dish (crucible) (mg)
W2 = Final weight of porcelain dish (crucible) (mg)
1000 = To covert the values as TDS in mg/l
Procedure for Estimation of Total Solid:
Preparation of Evaporating Dishes:
If volatile solids are to be measured, treat clean evaporating dishes and watch glasses at 550°C for 1 hour in a muffle furnace. If only total solids are to be measured, heat dishes and watch glasses at 103°C to 105°C for 1 hour in an oven. Cool and store the dried glasswares in desiccators. Weigh each dish and watch glass prior to use (record combined weight as ‘Wdish‘).
Preparation of Samples:
Fluid Samples:
If the sample contains enough moisture to flow readily, stir to homogenise, place a 25 to 50 g sample aliquot on a prepared evaporating dish. If the sample is to be analysed in duplicate, the mass of the two aliquots may not differ by more than 10%. Cover each sample with a watch glass, and weigh to the nearest 0.01 g (record weight as ‘Wsample‘). Spread each sample so that it is evenly distributed over the evaporating dish. Evaporate the samples to dryness on a steam bath.
Solid Samples:
If the sample contains pieces of solid material examples, dewatered sludge, take cores from each piece with a No. 7 cork borer or crush the entire sample coarsely on a clean surface by hand, use rubber gloves for the purpose. Place a 25 to 50 g aliquot of the crushed sample on a prepared evaporating dish. If the sample is to be analysed in duplicate, the mass of the two aliquots may not differ by more than 10%. Cover each sample with a watch glass, and weigh (record weight as ‘Wsample‘).
Spread each sample so that it is evenly distributed over the evaporating dish. Dry the samples at 103°C to 105°C for 12 hours then cool to balance temperature in an individual desiccators containing fresh desiccant, and weigh. Cool the residue in a desiccator to balance the temperature. Weigh the residues. Repeat igniting (30 min), cooling, desiccating, and weighing steps until the weight change is less than 4% or 50 mg, whichever is less. Record the final weight as ‘Wvolatile‘.
