- PHYSICAL WATER QUALITY PARAMETERS (click on it)
- CHEMICAL WATER QUALITY PARAMETERS
1.CHLORIDE CONTENT
- Chlorides in water are derived mostly from salt (NaCl, CaCl2 etc.), natural mineral deposits, agricultural and irrigation discharges.
- Note that the salty taste is predominantly by NaCl and the rest doesn’t impart a significant salty taste.
- Presence of chloride in high quantity indicates pollution of water due to sewage or industrial waste.
- Test is conducted in accordance with IS 3025 (Part 32).
- Chlorides are estimated by Mohr’s method (also called Argentometric Method) in which raw water is titrated against standard AgNO3 solution using Potassium Chromate (K2CrO4)as indicator.
- The end point of titration is marked by appearance of brick red colour.
- General Acceptable Limit is 250mg/l and in no case, it should exceed 1000 mg/l for public supply of drinking water owing to highly objectionable taste and in the absence of any alternative source.
2.NITROGEN (BASICS)
- Nitrogen is most abundant in Earth’s environment as N2 gas makes up about 78 percent of the air we breathe.
- Nitrogen is vital element required for the basic processes of life to make proteins, to grow, and to reproduce by all organisms.
- Nitrogen is quite common and generally found in many forms in the environment.
- Inorganic forms consist nitrate (NO3), nitrite (NO2), ammonia (NH3), and nitrogen gas (N2).
- Organic nitrogen is found in the cells of all living things and is a component of proteins, peptides, amino acids etc.
- When plants and animals die, proteins (which contain organic nitrogen) are broken down either naturally or by bacteria to form ammonia (NH3). This process is called "ammonification."
- Then Ammonia is broken down by Nitrosomonas bacteria to form nitrite (NO2), which is furthur broken down by Nitrobacter bacteria to form nitrate (NO3).The conversion of ammonia to nitrate and nitrite is known as "nitrification".
- The nitrates are reduced to gaseous nitrogen by the process of "denitrification". This process is performed by organisms such as fungi and the bacteria Pseudomonas. These organisms break down nitrates to obtain oxygen.
Fig: Nitrogen Cycle
3.NITROGEN CONTENT
Presence of nitrogen in water indicates presence of organic matter as decomposition of organic matter liberates nitrogen in various forms.
It occurs in the following forms –
- Free Ammonia or Ammonia Nitrogen – Indicates recent pollution
- Organic ammonia (Albuminoid Nitrogen) – Indicates quantity of nitrogen before decomposition has started
- Nitrite – Indicates partly decomposed condition
- Nitrate – Indicates old pollution i.e. fully oxidized organic matter
- Free ammonia should not be more than 0.15 mg/l and it can be measured by simply boiling the water and measuring the liberated ammonia by distillation process.
- Organic ammonia should not be more than 0.3 mg/l and it is measured by boiling a sample of already boiled water and adding a strong alkaline solution like KMnO4 and measuring the ammonia gas liberated.
- Free ammonia + Organic ammonia = Kjehldahl Nitrogen
- Nitrite (NO2) is highly dangerous as it is partially oxidized, hence its permissible limit is zero. It is measured by colour matching technique.
- Nitrate (NO3) is not harmful as it is fully oxidized but too much of nitrate affects infants because it causes blue baby disease or Methaemoglobinemia.
- Its concentration should not be more than 45 mg/l. It is also measured by colour matching technique.
4.FLOURIDES
- Member of Halogen family & forms a greenish yellow diatomic gas (F2)
- Upto 1 mg/l, it helps to prevent dental cavities. During process of formation of permanent teeth, it combines chemically with tooth enamel which results in harder, stronger teeth that are more resistant to decay.
- Excess value (greater than 1.5-2 ppm) results in discolouration of teeth called mottling of teeth (infants are affected, not adults). The resulting disease is called FLUOROSIS
- Hence, limit of fluoride is 1-1.5 mg/l.
- Greater than 5 mg/l, it causes deformation of bones called bone fluorosis and other skeletal abnormalities.
- Acceptable Limit is 1-1.5 mg/l
5. METALS
- Metals are of two types i.e. toxic and non toxic
- Measurement of metals is done by atomic absorption spectrophotometry.
- Ca, K, Na, Fe, Mn, Zn are non toxic metals
- Ar, Ba, Cr, Pb, Hg etc are toxic metals
- Acceptable Limit of Zn – 5 mg/l (previously 2 mg/l)
6. SODIUM
- Excess Na concentration causes bad taste and harmful for cardiac and kidney patients
- It is also corrosive to metal surface and in large concentrations, it is toxic for plants
- It is measured by atomic absorption spectrophotometry.
7.IRON AND MANGANESE
- Fe and Mn pose colour problem if present in high concentrations.
- Acceptable limits are 0.3 mg/l and 0.1 mg/l for Fe & Mn respectively.
- Some bacteria use iron and manganese compounds as an energy supplements.
- Iron and manganese poses problem in ground water and bottom layers of lakes but not in surface water
- Fe2+ forms Fe(OH)3↓
- Mn2+ forms MnO2↓
8.COPPER
- Its large quantity affects lungs and other respiratory organs
- CuSO4 greater than 250 mg/l has laxative effect
- Its limit is 0.05 – 1.5 mg/l
9.DISSOLVED GASES
- CH4 is known for its explosive tendency & has a high calorific value (to be discussed in detail in sludge digestion)
- H2S imparts bad taste and odour.
- CO2 indicates biological activity, imparts bad taste and water becomes corrosive at high concentration
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