Wastewater Influent Microbial Immigration and Contribution to Resource Consumption in Activated Sludge Using Taxon-Specific Mass-Flow Immigration Model

Wastewater influent microorganisms are part of the total chemical oxygen demand (COD) and affect the activated sludge (AS) microbial community. Precise modeling of AS processes requires accurate quantification of influent microorganisms, which is missing in many AS models (ASMs). In this study, influent microorganisms in COD unit were determined using a fast quantification method based on DNA yield and was compared with conventional respirometry method. The actively growing influent microorganisms were identified. A mass-flow immigration model was developed to quantify the influent-to-AS immigration efficiency ( m i ) of specific taxon i using mass balance and 16S rRNA gene high-throughput sequencing data. The modelled average m was 0.121-0.257 in site 1 (LaPrairie), and 0.050-0.126 in site 2 (Pincourt), which were corrected to 0.111-0.186 and 0.048-0.109 respectively using a constrain of m i ≤ 1. The model was further developed to calculate contributions to organic substrate consumption by specific taxa. Those genera with zero or negative net growth rates were not completely immigration dependent ( m i < 1) and contributed to 2.4% - 5.4% of the substrate consumption. These results suggest that influent microbiome may be important contributors to AS microbiome assembly and system performance (substrate consumption), which may help to improve future AS process modelling and design. Synopsis Influent microbial immigration lacks detailed taxon-specific quantification. This study presents quantitative methods and models for influent biomass, mass-flow immigration model, and resource consumption in activated sludge. Graphic Abstract