Before snails and filter flies can establish themselves in a trickling filter, which condition must exist?

Before snails and filter flies can establish themselves in a trickling filter, which condition must exist?

• A. Inadequate hydraulic loading and dry areas of media
• B. Overloading the system
• C. Excess moisture in media
• D. Low temperature

Answer: (A)

The key idea is how the media is wetted in a trickling filter. Snails and filter flies tend to establish only when the bed has uneven moisture, with dry pockets created by inadequate hydraulic loading. Those dry areas provide microhabitats that allow these macroinvertebrates to take hold as the system cycles moisture and nutrients through the bed. If the bed were evenly and adequately wetted, or if it were over-wet or kept very cold, conditions wouldn’t favor their establishment as readily. So the best choice points to not enough water distribution across the bed, leaving dry spots for these organisms to colonize.

The key idea is how the media is wetted in a trickling filter. Snails and filter flies tend to establish only when the bed has uneven moisture, with dry pockets created by inadequate hydraulic loading. Those dry areas provide microhabitats that allow these macroinvertebrates to take hold as the system cycles moisture and nutrients through the bed. If the bed were evenly and adequately wetted, or if it were over-wet or kept very cold, conditions wouldn’t favor their establishment as readily.

So the best choice points to not enough water distribution across the bed, leaving dry spots for these organisms to colonize.