The organic loading to a trickle filter is expressed as?

The organic loading to a trickle filter is appropriately expressed in pounds of Biochemical Oxygen Demand (BOD) per day per 1,000 cubic feet. This unit of measurement captures the amount of organic material entering the system and allows for an understanding of the filter’s capacity to treat wastewater.

Pounds of BOD per day is a standard measurement for evaluating the organic load because it reflects the total mass of organic material that can exert a demand for oxygen, thereby influencing the treatment process's efficiency. By using a standardized volume measure, such as 1,000 cubic feet, operators can easily compare loading rates across different filters and systems.

Using shorter time intervals, such as hours or months, as seen in some of the other options, would not provide the same clarity regarding daily operational conditions, especially since the microbiological activity and treatment effectiveness may be significantly influenced by daily variations in organic loading. Therefore, expressing this parameter in terms of daily pounds provides a practical and relevant framework for operators managing trickle filters.