Q1: In trickling filter, B.O.D. is reduced to

ANS:C - 60 to 80%

the typical reduction in Biological Oxygen Demand (B.O.D.) ranges from 60 to 80%, not 40 to 60% as previously stated. Trickling filters are biological treatment systems used in wastewater treatment plants. In these filters, wastewater is distributed over a medium, such as rocks or synthetic materials, creating a large surface area for microbial growth. Microorganisms attach to the medium and form a biofilm where they metabolize organic pollutants present in the wastewater. The microbial activity in the biofilm consumes oxygen, which leads to the breakdown of organic matter, including B.O.D. The extent of B.O.D. reduction depends on various factors such as the design of the trickling filter, the characteristics of the wastewater, and operational parameters. In well-designed and operated trickling filters, it's common to achieve B.O.D. reductions ranging from 60 to 80%. This means that the concentration of organic pollutants, as indicated by B.O.D., is reduced by 60 to 80% as the wastewater passes through the trickling filter. The effectiveness of trickling filters in reducing B.O.D. makes them valuable components of wastewater treatment systems, contributing to the overall purification of wastewater before it is discharged into the environment.