Environmental Engineering Test 2 Nddc Scholarship

Modern water treatment utilizes various methods for disinfection. Ozone and iodine (A) are powerful oxidizers; chlorine (B) is the standard chemical approach; and ultraviolet (UV) light (C) disrupts the DNA of microorganisms. Depending on the scale and requirements, any of these methods can be used to ensure water is pathogen-free.

Biochemical treatment, such as the activated sludge process, primarily relies on aerobic oxidation. Microorganisms use dissolved oxygen to 'oxidize' or break down organic pollutants into simpler, harmless substances like carbon dioxide and water. This is the most efficient way to reduce the BOD of sewage before it enters natural water bodies.

While 'disinfection' reduces pathogens to a safe level, sterilisation is the process that kills all forms of microbial life, including bacteria, viruses, and spores. In high-stakes environments or laboratory water preparation, sterilisation is the required standard to ensure the total absence of infective agents.

Fluorosis is a condition resulting from the chronic ingestion of excessive fluoride during the period of tooth development. While low levels of fluoride prevent cavities, high levels lead to dental fluorosis (mottled enamel) or skeletal fluorosis, which causes debilitating bone and joint deformities.

Nitrogen and phosphorus act as fertilizers. When they enter water bodies in high concentrations, they trigger eutrophication, leading to undesirable and rapid plant growth (such as algal blooms). As this excess vegetation dies and decomposes, it depletes the oxygen in the water, often killing fish and ruining the ecosystem.

All the statements provided (A, B, and C) are scientifically accurate descriptions of BOD. It is indeed a characteristic (a property) rather than a physical constituent (like a specific chemical). The 5-day incubation period (BOD5) is the standard measurement window, and the typical values for clean water are correctly stated. Therefore, 'none of these' is the correct choice as no statement is wrong.

Potable (drinking) water should be near neutral on the pH scale. A range of 6.5 to 8.5 is generally recommended to ensure the water is neither too acidic (which can corrode pipes) nor too alkaline (which can cause scaling and a bitter taste). The values in Option B fall perfectly within the safe and palatable window for human consumption.

Mercury is a potent neurotoxin. Health organizations generally establish a safety threshold of about 7 micrograms per 100 c.c. (or 7 μg/dL) of blood. Exceeding this limit indicates significant exposure and increases the risk of damage to the nervous system, kidneys, and developing fetuses.

Fertilizer plants primarily deal with nitrogen and sulfur compounds. Nitrogen oxides (NO2) and Ammonia (NH3) are central to urea and nitrate production, while SO2 and SO3 are involved in sulfuric acid units. Carbon Monoxide (CO) is typically a product of incomplete combustion in engines or specific industrial furnaces, which are not characteristic primary emissions of a standard fertilizer manufacturing process.

The average salinity of ocean water is approximately 3.5% (or 35 parts per thousand). This salt content is mainly composed of sodium chloride, but also includes magnesium, sulfate, and calcium ions. This concentration is high enough to make seawater undrinkable for humans without desalination.