Environmental Engineering Test 3 Nddc Scholarship

Planting dense rows of trees, often called 'green belts,' acts as a natural sound barrier. The leaves, twigs, and branches of trees like neem and coconut absorb and scatter sound waves. While not as absolute as a concrete wall, a well-maintained green belt can effectively lower ambient noise by 5 to 10 decibels, which is a significant reduction for sensitive areas like hospital zones.

Chlorination is a common method for making water safe to drink. A dosage of approximately 1 mg/litre is typically applied in municipal water treatment. This ensures that enough chlorine is present to kill pathogenic bacteria and viruses while leaving a small 'residual' amount to protect the water from re-contamination as it travels through the pipes to the consumer.

Dissolved oxygen (DO) is vital for the survival of aquatic organisms. In a healthy, flowing river, the DO concentration is usually quite low in terms of absolute mass, averaging around 5 ppm (parts per million). If the DO drops significantly below this level (due to pollution or high temperatures), fish and other aquatic life can begin to suffocate and die.

When oil is 'emulsified,' it is broken into such tiny droplets that it won't naturally float to the top for skimming. To remove it, industries use chemical reagents (coagulants) that break the emulsion, causing the oil particles to clump together. These larger clumps then become heavy enough to settle out at the bottom of a treatment tank for easy removal.

Radium-226 (Ra-226) is particularly dangerous because it is an 'all-in-one' emitter. As it decays, it releases alpha particles, beta particles, and gamma rays. While some isotopes only emit one type of radiation, the triple-threat emission of Radium-226 makes it extremely hazardous for both external exposure and internal ingestion, as it can damage tissues in multiple ways.

Peroxyacyl nitrate (PAN) is a secondary pollutant that forms in the atmosphere when nitrogen oxides and hydrocarbons from automobile exhaust react in the presence of sunlight. It is a major component of photochemical smog and is notorious for causing intense eye irritation and respiratory distress in urban environments.

Sedimentation is the most widely used primary treatment method because it is incredibly cost-effective. It simply uses gravity; by letting water sit still in a large tank, heavy suspended solids naturally sink to the bottom over time. It requires no chemicals or electricity, making it the most practical first step in purifying water containing sand, grit, or silt.

Temperature significantly affects the chemical activity of pollutants. For potassium cyanide, a common industrial toxin, a mere 10°C increase in water temperature can double its toxic effect on fish and other aquatic life. This is one reason why 'thermal pollution' from power plant cooling systems is strictly regulated; it makes existing pollutants much more lethal.

Water temperature influences the speed of chemical reactions. As water temperature increases, the 'collision rate' between particles increases, and the water becomes less viscous. This allows the chemical coagulant to work more efficiently and quickly, meaning a smaller amount (decrease) of the chemical is needed to achieve the same level of purification compared to cold water.

The printing industry produces wastewater filled with complex dyes and pigments. Standard biological treatments often fail to remove these colors. Electrolytic decomposition is an advanced method where an electric current is passed through the water to break the chemical bonds of the dyes, effectively 'bleaching' or decolourising the water so it can be safely discharged.