Essential Properties of Water and Environmental Cycles

Physical Properties of Water

The boiling and melting points of water are abnormally high relative to other hydrides in its chemical family. This is primarily due to the existence of hydrogen bonds.

Density Behavior

• From 0°C to 4°C, the density of water increases.
• From 5°C to 100°C, the density decreases.

Heat Capacity and Latent Heats

Water exhibits high values for both heat capacity and latent heats of melting and vaporization.

Definitions:

• Specific Heat Capacity (C_c): The amount of heat required to increase the temperature of a unit mass of a substance.
• Latent Heat (C_l): The heat required to change the state of a substance without increasing its temperature.

Key Values:

• Heat of Vaporization: 539.5 cal/g
• Heat of Fusion: 79.7 cal/g

Climate Regulation and Density Anomaly

These high thermal values mean that large bodies of water (aquifers) have a strong stabilizing effect on the climate, acting as thermal regulators.

When water solidifies (turns to ice), it increases its volume. Consequently, the density of solid water (ice) is lower than its density as a liquid. This density anomaly allows ice to float on the surface, which, in turn, permits aquatic life to survive in the deeper water below.

Hard Water Characteristics and Treatment

Hard water is defined as water that contains appreciable amounts of dissolved calcium and magnesium compounds. These compounds react with soap to form a highly insoluble precipitate (soap scum).

Types of Hardness

1. Temporary Hardness: Caused by calcium and magnesium bicarbonates. This type of hardness can be eliminated by heating, which precipitates the bicarbonates.
2. Permanent Hardness: Caused by remaining calcium and magnesium salts (e.g., sulfates or chlorides). To eliminate permanent hardness, a chemical agent, such as sodium carbonate (Na₂CO₃), must be added.

Ion exchangers are also commonly used to remove water hardness.

Biological Characteristics of Water

• Universal Solvent: Water is the best solvent for nutrients, making it the primary transport vehicle for these substances throughout the body.
• Metabolic Medium: All metabolic reactions are performed in the presence of water.
• Cellular Movement: Due to its high surface tension, water facilitates protoplasmic movement within cells, allowing cells to move or change shape.
• Thermoregulation: Water acts as a thermoregulator, preventing the body from experiencing sudden changes in temperature.

Physical Indicators of Water Contamination

These parameters are not contaminants themselves, but rather indicators of potential contamination:

• Color
• Odor (Smell)
• Taste
• Turbidity
• Solids (Total Dissolved Solids, Suspended Solids)
• Temperature
• pH
• Conductivity

Chemical and Microbiological Parameters for Contamination

Biochemical Oxygen Demand (BOD)

BOD is used to estimate the concentration of biodegradable organic matter (MO). It is calculated by measuring the decrease in dissolved oxygen concentration [O₂] in the water sample after a specified incubation period.

Chemical Oxygen Demand (COD)

COD measures the total amount of organic and inorganic matter susceptible to chemical oxidation contained in the water. This measurement uses strong chemical oxidants, typically Potassium Dichromate (K₂Cr₂O₇). The test is performed in an acidic medium, and catalysts are added to prevent interference from halogenated compounds.

Total Organic Carbon (TOC)

TOC (often referred to as COT) is measured using catalytic combustion. The sample is heated to a high temperature, ensuring that all carbon content is converted to carbon dioxide (CO₂).

The Sulfur Cycle

1. Vegetable Proteins
2. Consumption by Animal Life
3. Animal Proteins
4. Production of Waste / Death
5. Organic Sulfurous Matter
6. Decomposition
7. Hydrogen Sulfide (H₂S)
8. Oxidation of Sulfur
9. Sulfates / Sulfites
10. Assimilation by Plant Life (Cycle repeats)