Environmental Engineering Test 2 Nddc Scholarship

In an anaerobic sludge digestion tank, complex organic matter is broken down by bacteria in the absence of oxygen. The primary byproduct is 'biogas,' which consists mostly of methane (CH4), usually around 60–70%, along with carbon dioxide (CO2). Methane is the principal gas and is often captured and used as a renewable energy source to heat the digester or generate electricity.

In environmental toxicology, 'pollutant metals' usually refers to heavy metals that are toxic even at low concentrations, such as Mercury, Lead, and Arsenic. While Aluminium can be toxic in very specific acidic soil conditions, it is the third most abundant element in the Earth's crust and is not generally classified as a primary heavy metal pollutant in the same category as the others.

A skimming tank is specifically designed to remove oil, grease, and fatty substances that float on the surface of the sewage. Air is often blown into the bottom of the tank to help these 'light' impurities rise to the top, where they can be mechanicaly scraped or 'skimmed' off before the water moves to primary sedimentation.

The threshold of human hearing is scientifically defined as 0 decibels (dB), but in a practically quiet environment, a sound of 1 decibel represents the absolute weakest sound a healthy human ear can detect. As a reference, a whisper is about 30 dB, and normal conversation is around 60 dB.

Fats, carbohydrates, and proteins are all organic compounds derived from living organisms. Salts of metals (such as nitrates, phosphates, or heavy metal salts) are inorganic chemical substances. These can enter water through industrial discharge or agricultural runoff and are major contributors to chemical water pollution.

An Imhoff tank is a specialized two-story tank for sewage treatment where sedimentation and anaerobic digestion occur simultaneously. Like other anaerobic processes, the decomposition of organic solids in the lower compartment produces methane (CH4) as the main sludge gas, which escapes through gas vents.

While air quality standards vary, 5 ppm is often cited as the maximum permissible concentration for short-term exposure in industrial settings. In general ambient air, the target is much lower (often <0.1 ppm), but 5 ppm represents the limit above which SO2 becomes highly irritating to the respiratory tract and detrimental to health.

Raw sewage is often slightly acidic or neutral. After the oxidation process (biological treatment), the breakdown of organic matter typically results in a stable, slightly alkaline effluent. A pH of 7.3 is characteristic of well-treated, oxidized sewage, indicating that it is safe for discharge into natural water bodies.