All of the following are benefits of closing sand filters periodically EXCEPT:

Closing sand filters periodically can provide various benefits that enhance the overall efficiency and effectiveness of the filtration process.

Improved filtration quality is achieved through the natural cleaning and regeneration of the sand medium. During the closure, accumulated particles and organic matter can be washed away, thus allowing the filter to perform better when reopened. This results in a more efficient removal of contaminants from the wastewater.

Better microbial growth occurs when filters are closed for a time, as this provides a stable environment for beneficial microorganisms to thrive. These microbes play a key role in breaking down organic matter and enhancing the filtration process.

Enhanced nutrient removal is another benefit observed with periodic closure, as the rest period allows for more effective biological processes that reduce nutrients like nitrogen and phosphorus in the treated water. The microbial activity during this time contributes to the breakdown and uptake of these nutrients.

In contrast, a reduction in filtration speed is a negative outcome rather than a benefit. Closing sand filters should not result in decreased efficiency; instead, the goal is to maintain or improve the filtration rate through the maintenance of the system. Therefore, the reduction in filtration speed is not aligned with the advantages intended by periodically closing sand filters.