DOC-20240520-WA0002..pdf environmental engineering

Experiment

1. How to determine chlorides in
Water and Wastewater.
Experiment No 7

2. Chlorides
•Chloride, in the form of the Cl– ion, is one of the
major negative ions, in saltwater and freshwater. It
originates from the dissociation of salts, such as sodium
chloride or calcium chloride, in water.
• NaCl(s) → Na+ (aq) + Cl– (aq)
• CaCl2(s) → Ca2+(aq) + 2 Cl– (aq)
•These salts, and their resulting chloride ions, originate
from natural minerals, saltwater intrusion into estuaries,
and industrial pollution.

3. Chlorides
•The major taste producing salts in water are sodium chloride and
calcium chloride.
•In some water which is having only 250 mg /L of chloride may
have a detectable salty taste if the cat-ion present in the water is
sodium. On the other hand, a typical salty taste may be absent
even if the water is having very high chloride concentration for
example 1000 mg /L.
•This is because the predominant cation present in the water is
not sodium but either calcium or magnesium may be present.

4. Sources of chloride in water

•The Sources of chloride in water may be natural or
human beings. The natural sources are surrounding
rock or soil or seawater intrusion in coastal areas.
Whereas, various human sources are fertilizers, road
salting, wastewater from industries, animal feeds, septic
tank effluents etc.

5. Environmental Significance
•Chlorides associated with sodium (Sodium Chloride) exert salty
taste when its concentration is more than 250 mg/L. These
impact a salty taste to water.
•Chlorides are generally limited to 250 mg/L in water supplies
intended for public water supply.
•In many areas of the world where water supplies are scarce,
sources containing as much as 2000 mg/L are used for domestic
purposes without the development of adverse effect, once the
human system becomes adapted to the water.

6. Environmental significance
•For hard water treatment water softeners are often used. Most of
these use some form of salt. Water softeners remove calcium and
magnesium from the water by ion exchange with sodium. Sodium
chloride, or table salt, is added to the water softener to provide
the source of sodium ions.
•Although soft water eliminates the problems associated with
calcium and magnesium, it increases the levels of sodium chloride
in the water used and produces a large volume of highly saline
water in the regeneration process (the backwash). This backwash
also contains high levels of calcium and magnesium.

7. Environmental significance
•Chlorides, particularly calcium chloride, have been used to
shorten the setting time of concrete. However, calcium chloride
and (to a lesser extent) sodium chloride have been shown to
produce calcium hydroxide and cause chemical changes in
Portland cement, leading to loss of strength,

as well as attacking
the steel reinforcement present in most concrete.

8. Principle
•The amount of chloride present in water can be easily
determined by titrating the given water sample with silver nitrate
solution.
•The silver nitrate reacts with chloride ion according to 1 ml of
AgNO
3 reacts with 1 ml of chloride.
•The end of titration is indicated by formation of red silver
chromate from excess silver nitrate. The results are expressed in
mg/L of chloride.

9. Theory of determination of chloride in water
•The amount of chloride in water can be simply determined
by titrating the collected water sample with silver nitrate
solution by using potassium chromate indicator. The
reaction is quantitative. The AgNO
3 reacts with chloride
ion in a 1:1 ratio. The result is expressed as ppm.
•When silver nitrate solution is gradually added into the
flask, then silver ions react with chloride ions and forms
silver chloride. It is precipitated in bottom of the flask.
The precipitation is white in color.
Ag
+
(aq) + Cl
–
(aq) → AgCl
(s)
•The end point of the titration takes place when all the
chloride ions reacts and precipitated.

10. Procedure
•Measure the pH of the water sample.
•Take a 25 ml collected water sample into a conical flask.
•Add 2-3 drops potassium chromate (K
2CrO
4) indicator.
The color of the water sample is turn into light yellow.
•Add standard silver nitrate solution (0.0141N) from the
burette and shake well. Titrate until the light yellow color
changes to permanent brownish-red color (bricks-red
color).
•Note the volume of silver nitrate added.
•Repeat the titration.
•Calculate chloride ion concentration

13. How to determine chemical oxygen
demand

Experiment 8

14. Where we are now?

15. Chemical Oxygen Demand (COD)
•The chemical oxygen demand (COD) test is commonly
used to indirectly measure the amount of organic
compounds in water.
•Most applications of COD determine the amount of
organic pollutants found in surface water (e.g. lakes and
rivers), making COD a useful measure of water quality.
•It is expressed in milligrams per liter (mg/L), which
indicates the mass of oxygen consumed per liter of
solution.

17. Chemical Oxygen Demand (COD)
•COD is the measurement of the amount of oxygen in
water consumed for chemical oxidation of pollutants.
•COD determines the quantity of oxygen required to
oxidize the organic matter in water or waste water
sample, under specific conditions of oxidizing agent,
temperature, and time.
•This method covers the determination of COD in
ground and surface waters, domestic and industrial
wastewaters. The applicable range is 3-900 mg/L.

18. Environmental Significance
•COD values are particularly important in the surveys designed to
determine and control the losses to sewer systems.
•The ratio of BOD to COD is useful to assess the amenability of
waste for biological treatment.
•Ratio of BOD to COD greater than or equal to 0.8 indicates that
wastewater highly polluted and amenable to the biological
treatment.
•It is useful to assess strength of wastes, which contain toxins and
biologically resistant organic substances.
•BOD value is always lower than COD value. For domestic and
some industrial wastewater, COD value is about 2.5 times BOD
value.

19. Relationship between BOD and COD
•There are no ratio between COD and BOD which
correspond with all type of wastewater.
•The quality of wastewater is different from a source of
discharge to another and from a region to another.
•However, for example in France, one usually assumes
that, for domestic wastewater, it varies for different
wastewaters, the ratio commonly being 25-75% of
COD.

20. A more simple explanation

21. Why are we talking about COD & BOD?

•If the oxygen levels in our air changed, it would be a big
issue. If they decreased, it would be a problem. Now
imagine if the same thing happened in the water. You might
not think it, but it would also be a big issue.
•There are certain ways that we can impact the oxygen levels
in the water, and that's why we’re testing for oxygen.
•A simple way to think of it is this. When you place organic
chemicals or biological matter into water, it will eventually
break down. Just like composting, or how a fallen tree rots
in the woods.
•Oxygen is necessary for breaking down material. The more
material to break down, the more oxygen needed.
•Additionally, aquatic organisms need oxygen to breathe.

22. Why are we talking about COD & BOD?

•A normal, naturally balanced ecosystem will have a certain amount of
oxygen. There will be a happy equilibrium of oxygen so everything
gets what it needs. The fish, the algae, the decaying matter, it'll all have
just enough oxygen so nothing gets out of control.
•Now imagine there was too much organic matter breaking down. Or
aquatic organisms were reproducing at an alarming rate.
•You guessed it, the oxygen would be out of balance. Something that
would normally need oxygen wouldn't be getting it. For example, we're
talking about the breaking down, or decay of matter, which our storm
water runoff can contribute to.
•When too much organic matter, either from a chemical or biological
source, is added to a system, the natural balance is disturbed, and
things like fish kills occur, or extreme algae blooms. Point is, what we
do, can have a serious impact on a naturally balanced ecosystem.
•So how do we prevent this? We monitor for
COD & BOD.

23. What is chemical oxygen demand (COD)?

•COD comes from, you guessed it, chemical sources. It
is a measurement of the amount of chemical organic
matter being added to a water body.

As Wikipedia put it:
The chemical oxygen demand (COD) test is commonly used to
indirectly measure the amount of organic compounds in water.
Most applications of COD determine the amount of organic
pollutants found in surface water (e.g. lakes and rivers) or
wastewater, making COD a useful measure of water quality. It
is expressed in milligrams per liter (mg/L), which indicates the
mass of oxygen consumed per liter of solution.

24. What is biological oxygen demand (BOD)?

There's a fair amount of natural, organic matter which makes its way to
waterbodies via storm water runoff. Same as chemical sources, biological
sources place a burden on the ecosystem by needing oxygen to breakdown.
This would be things like sewage, plant and animal matter, etc.
Here's what Wikipedia says on the matter
•Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic
biological organisms in a body of water to break down organic material present in a given
water sample at certain temperature over a specific time period. The term also refers to a
chemical procedure for determining this amount. This is not a precise quantitative test,
although it is widely used as an indication of the organic quality of water. The BOD value
is most commonly expressed in milligrams of oxygen consumed per liter of sample during 5
days of incubation at 20 °C.
So, just like COD, this is a methodology of determining a degree of pollution in
your runoff.

25. COD values are greater than BOD
•The COD values include the oxygen demand created by
biodegradable as well as non-biodegradable substances. As
a result, COD values are greater than BOD.
•In comparison with BOD
5, COD measurement has an
advantage in that it requires a short digestion period of
about 3 hours rather than incubation of 5 days period
required for BOD
5 measurement.
•For many types of wastes, it is possible to correlate COD
with BOD. Once the correlation has been established,
COD measurements can be used to good advantage for
treatment-plant control and operation.

26. Biodegradable Pollutants

•Those pollutants which can be broken down into
simpler, harmless, substances in nature in due course of
time (by the action of micro-organisms like certain
bacteria) are called biodegradable pollutants. Domestic
wastes (garbage), agriculture residues, paper, wood,
cloth, leather, wool, vegetable stuff or plants are
biodegradable pollutants.

27. Non-biodegradable pollutants
•Those pollutants which cannot be broken down into
simpler, harmless substances in nature, are called non-
biodegradable pollutants. DDT, plastics, polythene,
bags, insecticides, pesticides, mercury, lead, arsenic,
metal articles like aluminum cans, glass objects, iron
products and silver foils are non-biodegradable
pollutants.

28. Interrelationship between BOD, COD
•Typical values for the ratio of BOD/COD for untreated municipal wastewater are in the range
from 0.3 to 0.8 (see in table 3). If the BOD/COD ratio for untreated wastewater is 0.5 or greater,
the waste is considered to be easily treatable by biological means. If the ratio is below about 0.3,
the waste may have some toxic components.
Type of Waste Water BOD/COD
Untreated 0.3-0.8
After Primary Settling 0.4-0.6
Final Effluent 0.1-0.3

29. Advantages
•COD is the most popular alternative test to BOD for
establishing the concentration of organic matter in wastewater
samples.
•The COD test only takes a few hours to complete, giving it a
major advantage over the 5-day BOD test.
•COD can test wastewater that is too toxic for the BOD test.
•The COD test should be considered an independent measure of
the organic matter in a wastewater sample rather than
a substitute for the BOD test.

30. COD Test Procedures

1.Prior to completing the COD test, a series of known standards are
prepared using KHP (potassium hydrogen phthalate). Most
wastewater samples will fall in the high range, so standards of 100,
250, 500 and 1000 mg/L are typically prepared. COD standards can
also be purchased.
2.A COD reactor/heating (150°C) block are allowed to stabilize.
3.Pre-prepared low-range (3-50 ppm) or high-range (20-1500 ppm)
vials are selected for the COD test based on expected results. Both
ranges can be used if expected results are unknown.
4.One vial is marked as a “blank,” and three or four vials are marked
with known standard levels. Two vials are then marked for the
wastewater sample to make a duplicate run. Note: If multiple
wastewater samples are being run, at least 10% of samples are
duplicated.

31. COD Test Procedures


5.2 mL of liquid are added to each vial. In the case of the
“blank,” 2 mL of DI water are added. If the wastewater sample
is tested at full strength, then 2 mL is added to the
corresponding vial.
6.Each vial is mixed well and placed into the reactor block for
two hours. After two hours, the vials are removed from the
block to a cooling rack for about 15 minutes.
7.The colorimeter is set and calibrated per the specific
instructions for that unit (i.e., proper wavelength, blank and
standards) and each vial is placed in the unit and the COD
concentration read.
8. If the sample was diluted, the corresponding multiplication is
made.

32. Blank Solution
•A Blank solution is one that do not have any chemical
that you are looking for or measuring or detecting.
•the BLANK is all those items EXCEPT your desired
chemical.
Sometimes, a blank MAYBE loosely called a "control"
solution.