AbstractFor commercial-scale production of microalgae, in the recent years, biofilm bioreactors have been proven to solve some of major technical problems in this field. Among different approaches, porous substrate photobioreactor (PSBR) is one of the most promising bioreactor types. However, before the actual construction of such a system and application, various design parameters need to be determined. For this purpose, mathematical modeling is considered to be an efficient tool. In the present study, a model for estimating design parameters of PSBRs is proposed. The proposed model estimates the effects of different design parameters on the productivity of PSBR systems based on (1) global solar irradiance data, (2) geographical location of the simulated system, and (3) empirical functions describing the relationship between light intensity on the module surface and module productivity, derived from experimental data. In the present study, to demonstrate the capacity of the proposed model, production of Halochlorella rubescens using a PSBR (Twin-Layer technology) was modeled for various scenarios. Also, simulated production of astaxanthin using Haematococcus pluvialis was performed. The results demonstrated the ability of the proposed model to estimate various design parameters for PSBR systems under various conditions. Based on the prediction made by the proposed model, these parameters can be individually optimized for different geographical locations and/or applications.