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The prospect of treating wastewater and at the same time producing microalgae biomass is receiving increasing attention. Mechanistic models for microalgae growth in wastewater are currently being developed for new systems design as well as to improve the understanding of the involved biokinetic processes. However, mathematical models able to describe the complexity of microalgal cultures are still not a common practice. The aim of the present study is to present and calibrate a new mechanistic model built in COMSOL MultiphysicsTM platform for the description of microalgae growth. Carbon-limited algal growth, transfer of gases to the atmosphere; and photorespiration, photosynthesis kinetics and photoinhibition are included. The model considers the growth of microalgae as a function of light intensity and temperature, as well as availability of nitrogen and other nutrients. The model was calibrated using experimental data from a case study based on the cultivation of microalgae species in synthetic culture medium. The model was able to reproduce experimental data. Simulations results show the potential of the model to predict microalgae growth and production, nutrient uptake, and the influence of temperature, light intensity and pH on biokinetic processes of microalgae. New mechanistic model to simulate microalgae growth 7E-mail address: joan.garcia@upc.edu (J. García). 9 Abstract 10The prospect of treating wastewater and at the same time producing microalgae biomass 11 is receiving increasing attention. Mechanistic models for microalgae growth in wastewater are 12 currently being developed for new systems design as well as to improve the understanding of 13 the involved biokinetic processes. However, mathematical models able to describe the 14 complexity of microalgal cultures are still not a common practice. The aim of the present study 15 is to present and calibrate a new mechanistic modelbuilt in COMSOL Multiphysics TM 16 platformfor the description of microalgae growth. Carbon-limited algal growth, transfer of gases 17 to the atmosphere;and photorespiration,photosynthesis kinetics and photoinhibitionare included. 18The model considersthe growth of microalgae as a function of light intensity and temperature, 19 as well as availability of nitrogen and other nutrients. The model was calibrated using 20 experimental data froma case study based on the cultivation of microalgae species in 21 syntheticculture medium.The model was able to reproduce experimental data. Simulations 22 results show the potential of the model to predict microalgae growth and production, nutrient 23 uptake, and the influence of temperature, light intensity and pH on biokinetic processes of 24 microalgae. 25

Subsurface flow constructed wetlands (SSFs) constitute a wastewater treatment alternative to small communities due to the low operational cost, reduced energy consumption, and no sewage sludge production. Although much information is available about conventional water quality parameters in SSF constructed wetlands, few data are available regarding specific contaminants. In this paper, we focus on the behavior of three widely used pharmaceuticals (clofibric acid, ibuprofen, and carbamazepine) in two pilot SSF constructed wetlands planted with Phragmites australis and characterized by different water depths (i.e., 0.3 and 0.5 m). These SSFs partially treat the urban wastewater from a housing development (ca. 200 inhabitants). The three pharmaceuticals and bromide were continuously injected into the two SSFs during a period of 150-200 h, and the effluent concentration was simultaneously measured as 6 h composite samples. Their removal efficiency was calculated from the injected concentration, and the hydraulic parameters were evaluated and compared to bromide as tracer. In this regard, the behavior of clofibric acid was similar to that of bromide, and no sorption into the gravel bed occurred. On the other hand, carbamazepine showed a higher sorption than bromide and clofibric acid, which is attributable to its interaction on the gravel bed. Accordingly, the use of clofibric acid as a hydraulic tracer is proposed, taking into account its low residence time. Ibuprofen removal was 81% in the shallow SSF and 48% in the deep one. Differences in removal efficiency could be explained by the less anaerobic environment of the shallow wetland.

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