Environmental Engineering Test 2 Nddc Scholarship

Foaming (persistent bubbles) and priming (water droplets carried into steam) are caused by impurities in the boiler water. Reducing total solids—which includes suspended matter (turbidity) and dissolved substances—is essential. High concentrations of these impurities increase the surface tension of the water, leading to these operational issues.

Dense belts of trees act as natural sound barriers by absorbing and scattering sound waves. Scientific studies suggest that a well-designed 'green belt' can reduce ambient noise levels by approximately 5 to 10 decibels. This is a significant reduction for sensitive areas like hospitals where quiet environments are necessary for recovery.

Statement C is incorrect. The main pollutants from petrol engines are Carbon Monoxide (CO), Nitrogen Oxides (NOx), and hydrocarbons. Sulphur dioxide (SO2) is primarily emitted from the combustion of coal or heavy fuel oils in power plants and ships, as petrol undergoes significant desulfurization during refining.

Radium-226 (Ra-226) is part of the uranium decay series. It is particularly hazardous because it (and its decay products) emits alpha, beta, and gamma radiation. Iodine-131 and Strontium-90 are primarily beta emitters, making Ra-226 far more complex and dangerous regarding both internal and external exposure.

Chemical Oxygen Demand (COD) for raw domestic or municipal sewage typically falls between 90 and 120 mg/litre (though it can vary by region). This value is higher than the BOD because it includes chemically oxidizable matter that bacteria cannot break down. Values in the thousands (Option D) are usually indicative of concentrated industrial wastewater.

Turbidity refers to the cloudiness of water caused by suspended particles. For drinking (potable) water, the standard limit is generally 10 ppm (or 5-10 NTU depending on the scale used). High turbidity can shield microorganisms from disinfection processes like chlorination, making it a health concern.

Temporary hardness is specifically caused by the presence of dissolved calcium and magnesium bicarbonates. It is called 'temporary' because it can be removed by simply boiling the water, which causes the bicarbonates to decompose and precipitate as insoluble carbonates (scale). Chloride and sulphate hardness are considered permanent.

To ensure effective disinfection and provide a residual protection against re-contamination in the distribution system, a dose of approximately 1 mg/litre of chlorine is commonly used in municipal water treatment. The target is usually to have a free residual chlorine level of 0.2 to 0.5 mg/L at the consumer's tap.

An oxidation pond (also known as a stabilization pond) is a large, shallow, man-made body of water designed for the biological treatment of wastewater. In these ponds, a symbiotic relationship exists between algae and aerobic bacteria. Algae produce oxygen through photosynthesis, which the bacteria then use to break down the organic matter in the sewage. While lagoons are similar, 'oxidation pond' is the specific technical term for this biological treatment process.

Sedimentation is the simplest and most cost-effective method for removing large suspended solids. It relies on gravity to allow particles heavier than water to settle at the bottom of a tank over time. It is a universal primary treatment step because it requires no expensive chemicals or complex machinery compared to biological oxidation or filtration.