Environmental Engineering Test 2 Nddc Scholarship

In environmental engineering and wastewater treatment, solid particles are classified by size. Particles larger than 75 μm are generally referred to as grit (often consisting of sand, gravel, or heavy organic matter). Dust typically refers to smaller atmospheric particles, and smoke consists of even finer particles (usually less than 1 μm) resulting from incomplete combustion.

While all are harmful, nitrogen oxides (NOx) are often considered the most severe due to their multi-faceted impact. They contribute to the formation of ground-level ozone and photochemical smog, cause acid rain, lead to nutrient pollution (eutrophication) in water bodies, and have direct inflammatory effects on the human respiratory system even at low concentrations.

The primary concern with bacteria in potable water is the risk of disease (pathogenicity). While some bacteria might affect taste or odor, pathogenic bacteria like E. coli, Vibrio cholerae, or Salmonella can cause severe waterborne illnesses such as cholera, dysentery, and typhoid fever. Ensuring water is 'potable' specifically means it is safe from these disease-causing microorganisms.

Radioactive waste management involves various specialized techniques depending on the state and activity level of the waste. Liquid wastes may undergo evaporation or chemical precipitation (A) or ion exchange (B) to concentrate the radioactive isotopes. Solidification (C), often called 'vitrification' or 'cementation,' involves fixing waste in a solid mass to prevent leaching before long-term storage or deep-sea/underground disposal.

Bacteria play a triple role in biological treatment. They secrete sticky polysaccharides that help in flocculation (A), they metabolize organic carbon for energy, releasing CO2 (B), and specialized nitrifying bacteria convert toxic ammonia into nitrites and nitrates (C). Together, these processes effectively remove organic and nutrient pollutants from the water.

[Image showing incomplete combustion in an engine producing Carbon Monoxide]
Carbon Monoxide (CO) is the main primary pollutant in automobile exhaust resulting from the incomplete combustion of fossil fuels. While modern catalytic converters reduce its volume, it remains a major urban air quality concern due to its toxicity and its ability to bind to hemoglobin in the blood, reducing oxygen transport.

Occupational health and safety standards (like OSHA) generally set the Permissible Exposure Limit (PEL) for noise at 90 decibels (dB) for an 8-hour workday. If the noise level increases, the allowable exposure time decreases significantly (e.g., 95 dB is allowed for only 4 hours). This limit is designed to prevent permanent noise-induced hearing loss.

Leather tanning involves the extensive use of chemicals, particularly chromium salts, acids, and organic solvents. Direct contact with these substances frequently leads to dermatitis (skin inflammation) and chemical burns. While some respiratory issues can occur from fumes, skin diseases are the most prevalent occupational hazard in this specific industry due to the handling of treated hides.

Statement D is incorrect because it reverses the wavelengths. The greenhouse effect occurs because the atmosphere allows short-wavelength solar radiation (visible light) to enter, but traps long-wavelength infrared radiation (heat) emitted from the Earth's surface. Statement A is true because COD measures both biodegradable and non-biodegradable matter, unlike BOD.

PAN is a secondary pollutant found in photochemical smog, which is heavily associated with automobile exhaust. While cars don't emit PAN directly, they release nitrogen oxides and hydrocarbons which react in the presence of sunlight to form PAN. It is a powerful eye irritant and is toxic to plants.