What type of organic loading is an indicator for a high-rate trickling filter?

The correct answer is indicative of the organic loading range typical for high-rate trickling filters. High-rate trickling filters are designed to handle significant amounts of organic matter, specifically in the form of Biochemical Oxygen Demand (BOD). The range of 25-300 LB BOD/D•1000ft3 reflects a higher capacity for treating wastewater effectively, allowing for efficient breakdown of organic material by the microorganisms that colonize the filter media.

This range is characteristic of high-rate systems because they operate with a higher organic load compared to other treatment methods, balancing the need for adequate oxygen supply and the capacity of the microbial community to process the incoming waste. In contrast, the other options present lower organic loading capacities, which are more aligned with conventional or lower-rate systems that cannot handle such elevated levels of BOD without risking overloading the treatment process. Thus, the chosen option clearly identifies the operational parameters that make high-rate trickling filters suitable for heavy organic loads in wastewater treatment.