What is one consequence of organic and inorganic solids settling out in sewer systems?

Settling of organic and inorganic solids in sewer systems often leads to increased maintenance costs. When solids accumulate in the system, they can cause blockages and reduce the effective flow of wastewater. This situation necessitates more frequent cleaning and maintenance to ensure that the sewer system functions properly. As the buildup of solids continues, it can lead to more serious issues such as backups or overflows, which require more intensive and costly interventions to resolve. The need to maintain operational efficiency in the system ultimately contributes to these increased costs.

While the other options might seem appealing, they do not accurately reflect the typical impact of solids settling in sewer systems. For instance, lower energy consumption and enhanced treatment efficiency would generally be associated with well-functioning systems rather than the accumulation of solids, and reduced sewer volume is not a typical result of solid settling, as the volume would usually remain the same despite the solids present in the system.