2.3.2. Fresh matter (FM) and dry matter (DM) measurement

FM and DM concentrations [kg/m³] were measured using two different methods for WWTP low biomass streams and high biomass streams (SI 7). For both types of streams standardized daily measurement procedures were used. Low biomass streams were 1.inflow municipal; 2.inflow industrial, 3, 4, 5.grit chambers, 19.centrate, and 18.distribution shaft. Here, FM was determined by using 120 mL to 600 mL of process streams to concentrate approximately 1 g of FM with centrifugation steps at 3200 g, 10 min, 4°C using 50 mL Falcon tubes filled with a 40 mL sample. The resulting pellet was transferred into 2 mL Eppendorf tubes and centrifuged at 6000 g, 10 min, 4°C. The supernatant was discarded, and FM was measured. High biomass streams were 6, 7, 11.nitrification basin, 8, 9, 10.denitrification basins, 12, 13, 14.return sludge, and 15, 16, 17.excess sludge. FM concentration was determined by using 2 mL of process streams in 2 mL Eppendorf tubes or 40 mL of process streams in 50 mL Falcon tubes. The tubes were centrifuged at 3200 g, 10 min, 4°C and, after removal of the supernatant, at 6000 g, 10 min, 4°C. For both types of streams the tubes were dried for 3 days at 50°C and DM was measured. All measurements were done in triplicates. For the low biomass streams FM‐DM conversion factors were determined (Table S7.1). Controls and devices are presented in SI 7.1. In addition, a comparison between Hach TSS values obtained from the WWTP and our values for high biomass streams can be found in Table S7.2.

Furthermore, FM and DM concentrations [kg/m³] were determined for yeast sludge (SI 7.2). The yeast specific growth rate as a change of yeast DM concentration over 48 h was calculated for stage 2a. In the BioP‐Rec module stage 2b, the average yeast DM concentration was used for calculation of P content in DM.