Pollutant removals employing unsaturated and partially saturated vertical flow wetlands: A comparative study Tanveer Saeed a,⇑ , Guangzhi Sun b a Department of Civil Engineering, University of Asia Pacific, Dhaka 1215, Bangladesh b School of Engineering, Edith Cowan University, Joondalup, WA 6027, Australia highlights  Unsaturated wetland system showed higher nitrification and organics removals.  Denitrification was achieved through internal organic carbon generation.  Unsaturated vertical flow system was efficient at lower input hydraulic loadings.  Saturated systems illustrated higher nitrogen removals at greater input loadings.  Sulfate and coliform removals were influenced by environmental parameters. article info Article history: Received 12 April 2017 Received in revised form 11 May 2017 Accepted 12 May 2017 Available online 13 May 2017 Keywords: Hydraulic loading variation Nitrogen Organics Saturated media Vertical flow wetlands abstract This paper provides a comparative evaluation between unsaturated and partially saturated vertical flow (VF) wetlands, that were employed to investigate nitrogen, organics, sulfate and coliform removals from municipal wastewater. The wetlands included organic straw materials as the main media and were planted with Canna indica species. Media saturation proportion in partially saturated systems ranged between 15.0 and 45.0% (with respect to media volume). Performance analyses indicated simultaneous nitrogen (52.7%) and biodegradable organics (47.0%) removals in unsaturated VF wetland. Mean ammo- niacal nitrogen (NH 4 -N) and total nitrogen (TN) removal rates were recorded as 1.30 and 1.26 g/m 2 d, respectively. Organic carbon (C) leaching from the straw media supported denitrification of the nitrified products in unsaturated system. In contrast, nitrification was the limiting step in partially saturated VF wetlands due to the development of anoxic/anaerobic conditions inside the media. Nitrogen removal per- centages ranged between 29.0 and 42.0% between these wetlands. Decrease of aerobic zones also reduced aerobic organic removals in these systems. Nitrogen and organics removals improved across unsaturated VF wetland, when input hydraulic loadings were 50.0% reduced. In contrast, saturated VF wetlands showed lower nitrogen removal rates when subjected to reduced hydraulic loadings, probably due to uneven distribution of wastewater flow (inside the media). Partially saturated VF system (with 45.0% sat- uration ratio) showed higher sulfate removals (41.6%); mean sulfate removal rate was 0.75 g/m 2 d. Anaerobic conditions of such wetland coupled with C availability from the straw media allowed observed removals. Coliform mortality was higher in VF wetlands that were operated under more aerobic conditions. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction Vertical flow (VF) wetlands are often employed either as sole treatment technologies or combined with horizontal flow (HF) wetlands, to provide treatment of different wastewaters [1–5]. These wetlands are often operated under intermittent hydraulic loadings [6]. Such operational feeding allows higher atmospheric oxygen penetration inside the employed bed matrix, which often controls aerobic nitrification and organics removals from wastew- aters [7,8]. A major disadvantage of VF wetlands could be attributed to lack of organic C and presence of aerobic conditions, which do not favor classical denitrification process [9]. To overcome such drawback, alternative operational strategies for example: continuous aera- tion, intermittent aeration, tidal flow, multiple tides and effluent http://dx.doi.org/10.1016/j.cej.2017.05.072 1385-8947/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail addresses: dr.tanveer@uap-bd.edu, tanveer@alumni.ait.asia (T. Saeed). Chemical Engineering Journal 325 (2017) 332–341 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej