Beyond Conveyance: Assessing the Contribution of Process-Critical Bacteria from Urban Sewer Systems to Wastewater Treatment Plants

The microbial ecosystem within urban sewer systems serves as the primary source of bacteria essential for nitrogen and phosphorus removal in wastewater treatment plants (WWTPs). This aspect remains underexplored in scientific literature. In this study, we quantify the biomass transferred from sewer networks to WWTPs by integrating 16S rRNA sequencing data from Aalborg municipality's sewer catchment with mass balance calculations and biomass production rates across gravity and pressure sewer configurations.

Considering microbial processes within sewer wastewater, biofilms, and sediments under steady-state dry weather flow conditions, gravity sewers generate more biomass loads than pressure systems, yielding values of 1.57 and 0.27 kgCOD m-3 d-1, respectively. A critical component of our sewer model is its capacity to estimate biomass contributions from specific bacterial groups, including polyphosphate accumulating organisms (PAOs).

Applying the model to Aalborg West WWTP, the estimated loads for PAOs Azonexus and Ca. Accumulibacter were 2.10 and 1.80 kg day-1, respectively, closely aligning with values derived from monitoring of influent wastewater at 1.77 and 1.20 kg day-1, respectively. This work establishes a framework for future research into sewer microbial dynamics, providing a means to better understand microbial immigration and informing strategies to manage WWTP microbial communities, optimize nutrient removal, and improve overall WWTP design.