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In spite of the increasing interest received by microalgae as potential alternatives for biofuel production, the technology is still not industrially viable. The utilization of digestate as carbon and nutrients source can enhance microalgal growth reducing costs and environmental impacts. This work assesses microalgal growth utilizing the liquid phase of anaerobic digestate effluent as substrate. The effect of inoculum/substrate ratio on microalgal growth was studied in a laboratory batch experiment conduced in 0.5L flasks. Results suggested that digestate may be an effective substrate for microalgal growth promoting biomass production up to 2.6 gTSS/L. Microalgal growth rate was negatively affected by a self-shading phenomenon, while biomass production was positively correlated with the inoculum and substrate concentrations. Thus, the increasing of both digestate and microalgal initial concentration may reduce the initial growth rate (μ from 0.9 to 0.04 d(-1)) but significantly enhances biomass production (from 0.1 to 2.6 gTSS/L).

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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

Henry's law constant higher than 3 10 -1 Pa m 3 mol -1 (i.e. 4-octylphenol, galaxolide, and tributyl phosphate) were removed by volatilization due to the effect of air stripping. Whereas biodegradation was relevant for removing ibuprofen and caffeine, carbamazepine and tris(2-chloroethyl) phosphate behaved as recalcitrant. The use of microalgae was proved to be relevant for increasing the biodegradation removal efficiency of ibuprofen by 40% and reducing the lag phase of caffeine by 3 days. Moreover, the enantioselective biodegradation of S-ibuprofen suggested a biotic predominant removal process, which was supported by the identification of carboxy-ibuprofen and hydroxy-ibuprofen. The results from microalgae reactors fed with nutrients showed no clear evidences of microalgae uptake of any of the studied microcontaminants.