Environmental Engineering Test 3 Nddc Scholarship

Statement D is incorrect because radio waves used for long-distance communication are reflected back to Earth by the ionosphere (located within the thermosphere), not the stratosphere. The stratosphere's primary role is housing the ozone layer, while the ionosphere contains the free electrons and ions necessary to bounce radio signals over the horizon.

Statement B is wrong because cooling and freezing do not typically kill bacteria; they merely inhibit their growth or put them into a dormant state. Many bacteria can survive freezing temperatures and become active again once the water thaws. To effectively kill bacteria, methods like boiling (heat), UV radiation, or chemical disinfection (chlorination) are required.

The troposphere is the lowest layer of the atmosphere and contains about 75-80% of the atmosphere's total mass. Because most human activities (industrial emissions, vehicle exhaust) occur at the surface, and because this layer is where weather and mixing happen, the vast majority of air pollutants remain concentrated here.

In thermal power plants, Electrostatic Precipitators (ESP) are the preferred choice for removing fly ash. They are highly efficient (often >99%) at capturing very fine particles, can handle high-temperature flue gases, and operate with a low pressure drop, making them more suitable for the massive volumes of gas produced compared to filters or mechanical separators.

Pneumoconiosis (specifically 'Black Lung Disease' or Coal Workers' Pneumoconiosis) is caused by the long-term inhalation of coal dust. The dust particles accumulate in the lungs, leading to inflammation, scarring (fibrosis), and eventually severe respiratory impairment. It is a common occupational hazard for miners.

Relative stability is a measure of the ability of an effluent to resist putrefaction (decay). It is mathematically expressed as the ratio of the oxygen available (in the form of dissolved oxygen, nitrites, or nitrates) to the total oxygen required for the complete biochemical stabilization of the organic matter in the sewage.

A gravity-type dust catcher (settling chamber) is the least efficient for very fine (sub-micronic) particles. It relies purely on gravity to pull particles out of the gas stream; while it works for large, heavy grit, smaller particles stay suspended in the air current and pass through easily. Bag filters and ESPs are much better suited for fine dust.

Oxidation ponds (or stabilization ponds) are the most economical choice for treating water with a low BOD. These are large, shallow ponds that use natural processes involving sunlight, algae, and bacteria to stabilize organic waste. They require very little maintenance and no mechanical energy, making them highly cost-effective for dilute wastewater.

These heavy industries primarily produce inorganic pollutants. Electroplating involves heavy metals (cyanide, chromium), blast furnaces produce mineral slag and metallic oxides, and coal mining leads to acid mine drainage (sulfates and dissolved metals). Unlike food processing or sewage, these effluents lack significant organic (carbon-based biological) matter.

Phenol at relatively low concentrations (less than 100 mg/litre) is biodegradable. Therefore, treating it in a biological oxidation pond is an effective way to remove it. Microorganisms in the pond break down the phenol molecules into harmless substances. At much higher concentrations, phenol might be toxic to the bacteria, but at this level, biological treatment is efficient.