Variables, Processes, and Rate-Expressions Describing Periphytic Algae-Based Biofilms: Development of the Algae Biofilm Model (ABM)

Algae biofilm reactors are an emerging environmental biotechnology used for the removal of nutrients and other contaminants from stormwater and wastewater. Bioreactor models based on the mechanistic description of algae biofilms are few in number, but a dynamic model based on mechanistic principles (chemical and biochemical) that is capable of describing algae-based biofilm reactor performance is needed for efficient process design and optimization. This paper summarizes variables, processes, and rate expressions for both chemical and biochemical conversions inside an algae biofilm. The development of an additional model component describing metabolic processes of bacteria comprising the algae biofilm, and a comprehensive effort describing the overall model is the subject of future work. Chemical and biochemical processes in the algae biofilm model (ABM) are based on theoretical considerations. Chemical processes include acid-base equilibria reactions incorporated primarily to describe the speciation of ammonia and inorganic carbon in the multispecies algae biofilm perpendicular to the growth medium. Biochemical conversion processes result from three bacteria types: photoautotrophic (or phototrophic), chemoautotrophic, and heterotrophic organisms. The mathematical description of our multispecies algae biofilm is based on the general 1-D biofilm model of Wanner and Gujer (1985) and Wanner and Reichert (1995). The ABM is an extension of the mechanistic algae biofilm models described by Flora et al. (1995) and Wolf et al. (2007). Inorganic carbon in the form of dissolved carbon dioxide and light are assumed to simultaneously limit algae biofilm growth. It is assumed that ions do not undergo chemical or biological transformation, but the ions do not maintain a constant concentration profile across the 1-D biofilm. State variables, processes, and kinetic expressions in the ABM are structured using matrix notation.