Environmental Engineering Test 3 Nddc Scholarship

The most critical concern regarding bacteria in drinking water is the potential for disease. Pathogenic microorganisms like E. coli, Salmonella, and Vibrio cholerae can lead to severe waterborne illnesses such as dysentery, typhoid, and cholera. While some bacteria might influence smell or clarity, the primary goal of making water 'potable' is ensuring it is biologically safe to consume.

Temporary hardness is caused by the presence of dissolved calcium and magnesium bicarbonates. It is called 'temporary' because these minerals can be removed simply by boiling the water, which causes the bicarbonates to decompose and precipitate out as insoluble carbonates. In contrast, permanent hardness (caused by chlorides and sulphates) cannot be removed by boiling.

Turbidity refers to the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye. In drinking water standards, a limit of 10 ppm (parts per million) is often cited as the maximum permissible limit to ensure the water is clear and that disinfection processes (like chlorination) are not hindered by suspended solids.

Leather tanning involves the use of various chemicals, including chromium salts, acids, and tanning agents. Constant exposure and direct contact with these irritating substances make workers highly susceptible to skin diseases such as dermatitis. Protective gear is essential in these environments to prevent chemical burns and chronic skin inflammation.

Statement C is incorrect because the primary pollutants from petrol-driven vehicles are Carbon Monoxide (CO), Nitrogen Oxides (NOx), and hydrocarbons. Sulphur dioxide (SO2) is mainly a byproduct of burning coal or heavy fuel oils in industrial plants and ships; petrol is refined to remove most sulphur before it ever reaches a car's engine.

Chemical Oxygen Demand (COD) measures the amount of oxygen required to chemically oxidize organic and inorganic matter in water. For raw municipal sewage, the typical range is 90-120 mg/litre. This value is usually higher than the Biological Oxygen Demand (BOD) because it includes substances that are not easily broken down by bacteria.

Iron and manganese are typically dissolved in groundwater in their reduced forms. To remove them, the water must first undergo oxidation (via aeration or chemicals) to turn these dissolved metals into solid particles. Once they are insoluble solids, they can be removed through settling (sedimentation) and final filtration.

An oxidation pond (or stabilization pond) is a large, shallow, man-made basin designed to treat wastewater through natural biological processes. Algae in the pond produce oxygen through photosynthesis, which aerobic bacteria then use to break down organic matter in the sewage. This is a highly cost-effective treatment method for smaller communities.

Supersonic aircraft fly at very high altitudes to minimize drag and avoid the turbulence of the lower atmosphere. Consequently, they cruise in the stratosphere. Because this layer has very little vertical mixing, pollutants like nitrogen oxides from the exhaust can remain for long periods, potentially leading to the depletion of the ozone layer.

Occupational safety standards (such as OSHA) generally set the limit for a standard 8-hour workday at 90 decibels. If the noise level is higher, the allowed exposure time must be significantly reduced to prevent permanent noise-induced hearing loss. This is why ear protection is mandatory in high-decibel industrial environments.