ecological engineering 35 ( 2 0 0 9 ) 1005–1010 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ecoleng Effect of plant and artificial aeration on solids accumulation and biological activities in constructed wetlands F. Chazarenc a,b,* , V. Gagnon a , Y. Comeau b , J. Brisson a a Institut de Recherche en Biologie Végétale, Département de Sciences biologiques, Université de Montréal, 4101 rue Sherbrooke Est, Montreal, Québec, Canada H1X 2B2 b Department of Civil, Geological and Mining Engineering, Ecole Polytechnique 2900, Edouard-Montpetit, Montreal, Québec, Canada H3T 1J4 article info Article history: Received 16 January 2008 Received in revised form 1 July 2008 Accepted 11 July 2008 Keywords: Water treatment Typha angustifolia Phragmites australis Mesocosms Microbial activity Sulphide abstract In constructed wetlands, solids accumulation may have two consequences with opposing effects on treatment efficiency: it decreases the longevity by reducing void space and it enhances biological activity by favoring biofilm development. The goal of our study was to estimate the effect of plants (presence and species) and artificial aeration on solids accumu- lation (volatile and inorganic). The horizontal and vertical distribution of solids was sampled using solids traps in 12 constructed wetland mesocosms (5 years old). Microbial density and activity were estimated in the biological fraction of the sampled solids. The effect of plant presence reduced accumulated solids by 26% and sulphide content by 50% sulphide content. There was more solids accumulation in Typha angustifolia units than in Phragmites australis. Also, T. angustifolia generated more biological activities at the surface and close to the inlet while conditions were more homogeneous throughout P. australis units. Aeration (1) stimu- lated biofilm development at the inlet of planted beds, (2) seemed to reduce mineral matter accumulation and (3) generated the same pattern of activities in planted beds enabling to reach a total nitrogen removal rate of up to 0.65 g N m -2 d -1 . © 2008 Elsevier B.V. All rights reserved. 1. Introduction In constructed wetland systems (CWs) for wastewater treat- ment, solids accumulation may have two consequences with opposing effects on treatment efficiency: it decreases the longevity by reducing void space and it enhances biological activity by favoring biofilm development. The goal of our study was first to estimate the effect of plant (presence and species) and artificial aeration on solids accumulation (volatile and inorganic), and then to measure the accumulated solids com- position and biological activities. ∗ Corresponding author. Current address: École des Mines de Nantes, Département Systèmes Energétiques et Environnement, 4 rue Alfred Kastler, BP 20722, F-44307 Nantes Cedex 3, France. Tel.: +33 2 51 85 86 93; fax: +33 2 51 85 82 99. E-mail address: florent.chazarenc@emn.fr (F. Chazarenc). In horizontal flow CWs, solids accumulation has been rec- ognized as a major factor decreasing CW longevity (Cooper et al., 2005). The origin of solids accumulated in void space of CWs is attributed to a fraction of TSS and VSS contained in the influent (Tanner and Sukias, 1995; Tanner et al., 1998; Caselles-Osorio et al., 2007), to biological growth within the CWs (Kadlec and Watson, 1993; Suliman et al., 2006), and to plant litter deposition (Tanner et al., 1998; Nguyen, 2000). The presence of sulphide accumulation is linked to overloading conditions or a lack of aerobic conditions (Wiessner et al., 2005; Stein et al., 2007). 0925-8574/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2008.07.008