Storage mechanisms in constructed wetlands: Should we modify heterotrophic bacteria modelling? Ana Galvão a, ⁎, Joana Pisoeiro a , Helena Pinheiro b a CERIS, Instituto Superior Técnico, Universidade de Lisboa. Av. Rovisco Pais, 1049-001 Lisboa, Portugal b iBB-Institute for Bioengineering and Biosciences, DBE, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal HIGHLIGHTS • Storage evidence was found in biofilm from constructed wetlands. • Storage decreased with COD mass load increase. • Heterotrophic growth yield and storage yield increased with COD mass load in- crease. • Storage evidence suggests heterotro- phic bacteria modelling could be modified. GRAPHICAL ABSTRACT abstract article info Article history: Received 1 May 2018 Received in revised form 28 November 2018 Accepted 8 December 2018 Available online 10 December 2018 This study investigated the occurrence of storage mechanisms in biofilm from constructed wetlands (CWs) through respirometric studies and calculated the corresponding heterotrophic growth yields. Respirometric tests were performed in biofilm extracted from horizontal sub-surface flow CWs batch loaded with three differ- ent COD mass loads: 7.0., 15.6 and 35.2 g COD/(m 2 ∙day). The bed removal efficiency remained above 96% for all mass loads and COD mass removal rates increased from 6.8 g COD/(m 2 ∙day) for the lowest load to 34.5 g COD/(m 2 ∙day) for the highest load. The percentage of tests with storage evidence decreased from 85% to 10% with increasing mass loads and the responses of the microbial community to the acetate pulse showed an adaptation to the feast-famine conditions, through storage mechanisms, for lower loads, and a metabolic shift to the use of COD for growth for higher loads. Heterotrophic biomass yield values varied from 0.54–0.56 g COD/- g COD for low mass loads to 0.69–0.71 for higher mass loads, indicating that greater substrate availably triggers growth and reduces the occurrence of storage. Storage yield values supported this trend varying between 0.89 and 0.94 with increasing mass loads. Given the significant storage evidence obtained in the present study, it is suggested that a modified modelling architecture, which includes storage mechanisms, should be considered in future simulations of CW systems. © 2018 Elsevier B.V. All rights reserved. Keywords: Constructed wetlands Heterotrophic growth yield Oxygen uptake rate Respirometry Storage mechanisms 1. Introduction Constructed wetlands (CWs) have been recognized as a sustainable wastewater treatment technology being widely used for domestic sew- age treatment. In these systems, the interactions between filling media, Science of the Total Environment 658 (2019) 830–835 ⁎ Corresponding author. E-mail addresses: ana.galvao@tecnico.ulisboa.pt (A. Galvão), joana.m.pisoeiro@tecnico.ulisboa.pt (J. Pisoeiro), helena.pinheiro@tecnico.ulisboa.pt (H. Pinheiro). https://doi.org/10.1016/j.scitotenv.2018.12.120 0048-9697/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv