Environmental Chemistry

Environmental chemistry is crucial for civil engineers involved in water resources, sanitation, and sustainable design. It deals with chemical processes occurring in the environment and the impacts of human activities.

Water Chemistry

Water is the "universal solvent" and plays a vital role in biological and geological processes.

Water Hardness

Hardness is caused by dissolved minerals, primarily calcium ( $Ca^{2+}$ ) and magnesium ( $Mg^{2+}$ ) ions.

Temporary Hardness: Caused by bicarbonate ( $HCO_3^-$ ). Can be removed by boiling.
Permanent Hardness: Caused by sulfate ( $SO_4^{2-}$ ), chloride ( $Cl^-$ ), or nitrate ( $NO_3^-$ ). Requires chemical treatment (e.g., lime softening, ion exchange).
Hardness is expressed as equivalent $mg/L$ of $CaCO_3$ .

Biochemical Oxygen Demand (BOD)

The amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.

High BOD: Indicates high levels of organic pollution.
COD (Chemical Oxygen Demand): Measures the amount of oxygen required to chemically oxidize organic compounds.

Atmospheric Chemistry

The atmosphere consists of layers: Troposphere (where weather occurs), Stratosphere (Ozone Layer), Mesosphere, Thermosphere.

Ozone Depletion: Caused by Chlorofluorocarbons (CFCs) releasing Chlorine atoms in the stratosphere. $Cl + O_3 \rightarrow ClO + O_2$ $ClO + O \rightarrow Cl + O_2$
Greenhouse Effect: Gases like $CO_2$ , $CH_4$ , and $N_2O$ trap infrared radiation, warming the Earth.
Acid Rain: Caused by $SO_2$ and $NO_x$ emissions reacting with water vapor to form sulfuric and nitric acids. $SO_2 + H_2O \rightarrow H_2SO_3$ $2NO_2 + H_2O \rightarrow HNO_3 + HNO_2$

Solid and Hazardous Waste

Incineration: Burning waste at high temperatures. Reduces volume but produces ash and gases.
Landfills: Engineered sites for waste disposal. Leachate collection and treatment is critical to prevent groundwater contamination.
Bioremediation: Using microorganisms to degrade organic pollutants.

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