Ozone is a powerful oxidizing agent used for water disinfection because it effectively destroys microorganisms. While it is true that ozone is not radioactive, this property is unrelated to its ability to act as a disinfectant.

Sullage, also known as greywater, refers to domestic wastewater that does not contain sewage or fecal matter. It typically originates from kitchen sinks, showers, baths, and laundry facilities, distinguishing it from blackwater which contains toilet waste.

Biogas is primarily produced through the anaerobic digestion of organic matter. The resulting gas mixture typically consists of 50-75% methane (CH4), 25-50% carbon dioxide (CO2), and trace amounts of other gases like hydrogen, nitrogen, and hydrogen sulfide. Methane is the primary combustible component that gives biogas its energy value.

Residual chlorine refers to the amount of chlorine that remains in the water after the initial demand of the water has been satisfied. This residual is crucial for providing ongoing protection against microbial contamination during the distribution of water to consumers. It is measured to ensure that the water remains safe for consumption throughout the supply network.

Sewage sludge is the solid, semi-solid, or slurry residual material that is produced as a byproduct during sewage treatment. This organic-rich material can be processed in anaerobic digesters to produce biogas, which consists primarily of methane and carbon dioxide.

Alum, specifically potassium aluminum sulfate, is widely used in water treatment as a coagulant. When added to water, it neutralizes the negative charges on suspended colloidal particles, allowing them to clump together into larger particles called flocs, which can then be easily removed through sedimentation or filtration.

Phenol is a toxic organic compound that is harmful to human health and can impart an unpleasant taste and odor to water. While chlorine, bleaching powder, and potassium permanganate are commonly used for water purification due to their oxidizing or biocidal properties, phenol is not a safe or appropriate disinfectant for potable water supplies.

Treating domestic sewage before discharge is essential to remove harmful pathogens, organic matter, and pollutants, preventing water contamination and eutrophication. In contrast, burning plastic releases toxic fumes, burning leaves contributes to air pollution, and excessive chemical fertilizers lead to soil degradation and water runoff issues. Therefore, sewage treatment is the most effective practice for environmental protection among the options provided.

Turbidity is a measure of the degree to which water or any liquid loses its transparency due to the presence of suspended particulates. It is an important indicator of water quality. Higher turbidity levels indicate more suspended particles, which scatter light and make the liquid appear cloudy or opaque, whereas low turbidity indicates high clarity.

Biogas production involves the anaerobic digestion of organic waste by bacteria, which generates methane. This methane can be captured and burned to drive turbines for electricity generation. Open-air burning is environmentally hazardous and inefficient, while electrolytic cells are not standard methods for processing raw garbage for energy production.