Why might a Water Resource Recovery Facility (WRRF) struggle to meet minimum removal standards of BOD₅ and TSS?

A Water Resource Recovery Facility (WRRF) might struggle to meet minimum removal standards of biochemical oxygen demand (BOD₅) and total suspended solids (TSS) due to influent concentration dilution from inflow and infiltration (I&I). When excessive amounts of stormwater or groundwater enter the wastewater system through leaks, cracks, or improper connections, it dilutes the concentration of the wastewater.

This dilution can pose challenges for the treatment processes because the designed systems, typically optimized for a specific range of influent concentrations, may become less effective. The reduced concentration of organic materials and suspended solids means that the biological treatment processes have fewer substrates available for microbial consumption, which is essential for effectively breaking down BOD₅ and removing TSS. As a result, the facility may not achieve the necessary removal rates required to meet regulatory standards.

In contrast, overloaded treatment capacity could lead to performance issues; however, it does not directly indicate a dilution issue caused by I&I. Inadequate treatment technology or insufficient microbial populations could also impact treatment effectiveness, but the fundamental cause related to dilution due to excessive inflow and infiltration is central to this scenario.