Water and its Properties

Water and its Technology

• Water exists over a wide temperature range (0-100°C)
• Water has a high specific heat, meaning it takes a significant amount of energy to change its temperature
• Water has a high latent heat of vaporization, which leads to cooling effects during evaporation
• Water is an excellent solvent, carrying nutrients and pathogens
• Water has high surface tension, allowing it to rise through heights
• Water exhibits anomalous expansion; it expands when freezing, causing ice to float
• Common sources of water are rain, rivers, seas, glaciers, springs, and lakes.
• Rainwater is considered the purest form of water.
• Water contains various physical, chemical, and biological impurities that can cause issues in domestic and industrial settings.
• Total water on Earth is distributed as follows: Oceans (97.5%), Freshwater (2.5%)
  • Freshwater is further divided into: Glaciers (68.7%), Groundwater (30.1%), Freshwater Lakes (67.4%), Atmosphere (9.5%), Other Wetlands (8.5%), Soil Moisture (12.2%), Rivers (1.6%), Plants and Animals (0.8%), Permafrost (0.8%)
• Impurities in water include: Physical (insoluble), Inorganic (clay, sand), Organic (oil globules, organic matter), Colloidal (Fe(OH)3, complex proteins) Chemical (soluble), Anions (Cl-, SO42-, CO32-, HCO3-, NO3-), Cations (Ca2+, Mg2+, Na+, K+, Fe3+, Al3+), Dissolved gases (O2, N2, CO2, H2S, NH3). Biological (microorganisms like algae, fungi, bacteria).
• Water hardness is caused by dissolved salts primarily calcium and magnesium, and other heavy metals.
• Hardness is classified into two types: Temporary and Permanent
  • Temporary hardness is due to bicarbonates of calcium and magnesium, and carbonates of iron and other heavy metals that can be removed by boiling.
  • Permanent hardness is caused by dissolved chlorides and sulfates of calcium and magnesium that can be removed via zeolite, Lime-soda, ion-exchange processes.
• Water hardness impacts both domestic and industrial processes.
  • Domestic issues include soap wastage, fuel wastage, urinary infections, kidney stones, skin dryness, etc.
  • Industrial concerns often include boiler scale, sludge, caustic embrittlement, priming, foaming, and problems in industries like textile, sugar, paper, laundry, and pharma.
• The units of hardness are typically measured as parts per million (ppm) or as calcium carbonate equivalents.
  • 1 ppm is equal to 1 mg/L, 1 part of CaCO3 equivalent in 106 of parts of water, in Clark's degree 1 part of CaCO3 equivalent in 70,000 parts of water and in French degree 1 part of CaCO3 equivalent in 105 parts of water.
• Methods used to measure hardness include complexometric titration using EDTA and Eriochrome Black T (EBT). Other methods include flame photometry.

Dissolved Oxygen (DO)

• Dissolved oxygen is the amount of oxygen dissolved in water.
• The amount of DO in water depends on physical, chemical, and biological activities like temp. and pressure.
• Higher pressure leads to more dissolved oxygen at a given temperature. The amount is also lower when the water temperature increases.
• The measurement of dissolved oxygen often employs Winkler's method.
• DO is important for living organisms' biological activities.
• It influences precipitation and dissolution of inorganic and organic substances.
• DO is crucial for pollutant degradation.
• DO level affects boiler corrosion.

Biochemical Oxygen Demand (BOD)

• BOD measures the amount of oxygen needed for the biological oxidation of organic matter in water over five days at 20°C.
• Higher BOD indicates a greater amount of decomposable organic matter.
• BOD is used as a parameter in designing effluent treatment, particularly for industries like domestic sewage, cow shed sewage, paper mills, and tanneries.
• Various factors like pollutants and temperature affect BOD.

Chemical Oxygen Demand (COD)

• COD measures the oxygen equivalent of any oxidizable impurity in water using strong chemical oxidants.
• COD is typically higher than BOD for a sample of water.
• COD is a useful parameter for designing treatment plants for effluents like cellulose and other non-degradable organic matter, as it doesn't get affected by toxins and microorganisms.
• COD measurement takes hours, while BOD requires several days.

pH

• pH measures the concentration of hydrogen ions in a water sample.
• A lower pH indicates higher acidity.
• A higher pH indicates higher alkalinity.
• Water with pH values below 6.5 or above 8.5 is considered harmful.
• pH is measured using instruments like a pH meter.

Total Dissolved Solids (TDS)

• TDS refers to the total amount of dissolved minerals and solids in water.
• TDS can be determined by evaporating a known amount of water to dryness.
• Higher TDS indicates a higher possibility of higher hardness.
• Desired TDS levels in potable water are below 500 ppm, which is crucial for human consumption.
• TDS is measured using gravimetry, chemical analysis, and conductivity methods.

Alkalinity

• Alkalinity in water is due to dissolved anions like HCO3-, CO32-, and OH-
• Alkalinity is quantified by titrating water against standardized acid solution, such as HCl or H2SO4.
• OH- and HCO3- ions can't coexist as they react creating CO32- and water.
• Alkalinity is calculated typically with indicators like phenolphthalein (pH 10 - 8.3, indicating caustic alkalinity) and methyl orange (pH 3.1 - 4.4, illustrating temporary hardness).