ES 203: Water and Wastewater Engineering
Prof. Anurag Garg
Environmental Science & Engineering Department, IIT Bombay
2024-25
Water Quality Parameters
Total Dissolved Solids (TDS)
• TDS results from the solvent action of water on solids and liquids.
• These may be organic or inorganic in nature.
• Such solids may produce aesthetically displeasing colour, tastes and
odour.
• TDS in natural waters are mainly due to primary and secondary ions:
– Primary: sodium, calcium, magnesium, bicarbonate, sulfate and chloride
– Secondary: iron, strontium, potassium, carbonate, nitrate, fluoride, boron and silica
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Alkalinity
• It is a measure of the buffering capacity of the water.
• The alkalinity constituents result from
– the dissolution of mineral substances,
– microbial decomposition of organic materials,
– wastewater discharges containing detergents, fertilizers and insecticides.
• Higher alkalinity impart bitter taste to water.
• Total alkalinity = CO32- + HCO3- + OH- - H+ (All ions are expressed
in mg/l as CaCO3)
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Problem
• A 200 ml sample of water with an initial pH of 10.6 is titrated
with 0.02 N H2SO4. The sample reaches pH 8.3 after an
addition of 8.8 ml of the acid and an additional 5.5 ml is
required to bring the sample to pH 4.5. Identify the species of
alkalinity present and determine the concentrations (mg/l) of
each.
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Hardness
• Hardness is a term used to express the properties of highly mineralized
water.
• Hardness in water is derived largely from contact with the soil and rock
formation.
• This is due to the presence of multivalent metallic cations (such as
Ca2+, Mg2+, Fe2+, Mn2+, Sr2+).
• Desirable hardness should be between 75 – 115 mg/L as CaCO3.
• Hardness causes
✓ Greater soap consumption,
✓ Scaling of boilers,
✓ Corrosion of pipes
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Types of Hardness
Hardness
(Due to cations
Ca2+, Mg2+ etc)
Temporary or Permanent or
carbonate Non-carbonate
(CO32-, HCO-3) (SO42-, Cl-, NO3-)
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Problem
• A sample of water from a surface stream is analyzed for the common ions
with the following results:
Ca2+ = 98 mg/l, Cl- = 89 mg/l, HCO3- = 317 mg/l,
Mg2+ = 22 mg/l, Na+ = 71 mg/l, SO42- = 125 mg/l
✓ What is the percent error in the cation anion balance
✓ Draw a bar diagram for the water.
✓ Determine hardness of water.
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Nitrogen
• Nitrogen is found in proteins, chlorophyll and many other biological compounds.
• Its principal forms in the water are:
✓ Free ammonia
✓ organic nitrogen
✓ Nitrites
✓ Nitrates
• Presence of high nitrates may cause blue baby disease in infants.
Forms of Nitrogen Permissible limit (mg/l)
Free NH3 0.15
Organic N 0.3
Nitrites Nil
Nitrates 45 9
Fluoride
• Fluoride is mainly originated from sedimentary or igneous rocks.
• F concentration below 1 mg/l may cause dental cavities in children.
• Higher F concentrations > 1.5 mg/l cause discoloration of teeth (also
called mottling).
Chloride
• Chlorides are generally present in water in the form of salt.
• These may be originated from the leaching of marine sedimentary
deposits, pollution from sea water, brine or industrial and domestic
wastes etc.
• Cl- concentrations above 250 mg/l are objectionable.
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Dissolved Gases
• O2, CO2, H2S and CH4 may be found in dissolved state in water.
• H2S even in smaller concentrations gives bad taste and odour.
• Presence of CO2 indicates biological activity.
• Deficit of O2 in the sample indicates the presence of organic matter.
Metals
• Sources of metals in natural waters include dissolution from natural
deposits and discharges of domestic, industrial or agricultural
wastewaters.
• Fe and Mn may cause colour problems even at very low concentrations.
• Pb, Ba, As, Cd, Hg and Cr are considered poisonous and a very small
quantity of these metals may cause serious health hazards.
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Permissible Limits of Metals in Potable Water
Metal Max. permissible conc. (mg/l)
Fe 0.3
Mn 0.05
Cu 0.05
Pb 0.05
As 0.05
Se 0.05
Cd 0.01
Cr 0.05
Ag 0.05
Zn 5.0
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Organics
• Biodegradable
❖ Those organics that can be utilized for food by micro-organisms aerobically or
anaerobically within a reasonable length of time.
❖ Examples are starch, fat, protein, alcohol, acid, aldehydes and ester.
• Non-biodegradable
❖ Organics those can not be degraded biologically.
❖ Examples: lignin, phenols, pesticides and chlorinated hydrocarbons
• BOD, COD and TOC are used as lumped parameters for measuring organics in water or
wastewater
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