The objective of this work was to develop and validate an updated process model and open-source process simulator for intensive microalgae-based wastewater treatment, with a focus on tertiary phosphorus removal/recovery. To this end, the original PPM was expanded into the Phototrophic-Mixotrophic Process Model (PM 2 ) using lumped pathway metabolic modeling to account for heterotrophic growth of microalgae on glucose and acetate (as well as photoautotrophic metabolism). To verify pathway relevance for modeling mixed communities of microalgae, 11 microalgae metabolic reconstruction data sets (across seven microalgal species) were analyzed to confirm the presence of relevant enzymes. The updated process model, PM , was incorporated into QSDsan -an open-source tool in Python for the quantitative sustainable design (QSD) of sanitation and resource recovery systems -for flexible process modeling, rapid and reproducible simulation, and transparent implementation. Model calibration and validation was supported with data from a 568 m 3 •d -1 microalgae-based tertiary wastewater treatment process, the EcoRecover system. A network of sensors enabled online monitoring of the system (45 days, 5-minute data interval, 12,950 data points), which was supplemented with on-site analyses of grab and composite samples for data reconciliation and bench-scale batch experiments run on-site in the greenhouse. Ultimately, the process model developed in this study will support the design and optimization of microalgae-based tertiary phosphorus removal/recovery systems to improve effluent quality and process reliability, advancing the use of microalgal technologies in the wastewater treatment industry.