Q1: The coagulant widely used for sewage treatment, is

ANS:B - ferric chloride

Ferric chloride is a chemical compound with the formula FeCl3. It is a dark brown or blackish solid, and in aqueous solutions, it appears yellowish-brown. Ferric chloride is widely used in various industrial and municipal applications, including water and wastewater treatment. In sewage treatment, ferric chloride is utilized as a coagulant. Coagulants are chemicals added to wastewater to facilitate the aggregation of suspended particles, colloids, and other impurities into larger flocs, which can then be more easily removed through sedimentation, filtration, or other separation processes. The mechanism of action of ferric chloride in sewage treatment is similar to other coagulants such as alum. When ferric chloride is added to wastewater, it undergoes hydrolysis, leading to the formation of positively charged ferric hydroxide species. These positively charged species neutralize the negative charges on suspended particles and colloids present in the wastewater. As a result, the particles and colloids begin to coagulate and form larger aggregates or flocs. The formation of larger flocs enhances the efficiency of subsequent separation processes such as sedimentation or filtration. The flocs settle more rapidly due to their increased size and density, allowing for the removal of impurities from the wastewater. Ferric chloride is preferred in some cases due to its high coagulation efficiency and ability to work over a wide range of pH levels. It is effective in treating various types of wastewater, including municipal sewage, industrial effluents, and stormwater runoff. However, it's important to note that while ferric chloride is effective in sewage treatment, it may have certain environmental considerations, particularly in terms of its handling and disposal. Proper dosage and control are essential to ensure effective treatment while minimizing adverse impacts on the environment.