Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng Floating treatment wetlands supplemented with aeration and biofilm attachment surfaces for efficient domestic wastewater treatment Jason B.K. Park ⁎ , James P.S. Sukias, Chris C. Tanner National Institute of Water and Atmospheric Research Ltd (NIWA), P.O. Box 11-115, Hamilton, New Zealand ARTICLEINFO Keywords: Floating treatment wetlands Natural wastewater treatment Secondary wastewater treatment Nutrient removal Organic matter removal ABSTRACT Floating Treatment Wetlands (FTWs), comprising a floating matrix or framework vegetated with emergent wetland plants whose roots extend into the water below, have potential for treatment of wastewaters. Low oxygen concentrations beneath FTWs and wash-out of microbial communities can limit decomposition of organic matter and nitrification of ammonium-N in domestic wastewaters. This study aimed to test the utility of two different configurations of FTWs supplemented with mechanically aerated Biofilm Attachment Surfaces (BAS) to provide post-primary treatment of domestic wastewater. Two pilot-scale FTW treatment trains were developed at a domestic wastewater treatment plant in Hamilton, New Zealand using ten 1 m 3 volume tanks, with 1 m 2 square floating mats planted with Carex virgata. These were: (1) a single-pass (direct flow-through) system comprising an aerated FTW tank with subsurface BAS followed by four non-aerated FTW tanks in series, where (endogenous carbon inputs from wetland plants, along with organic carbon from the wastewater would promote denitrification; and (2) a recirculating system incorporating a pre-anoxic phase settling tank with FTW and BAS, followed by an aerated FTW tank with BAS from which 4/5 of the outflow was recirculated back to the initial anoxic stage where the (endogenous) organic matter in the incoming wastewater would provide the primary source of carbon to promote denitrification. The remaining 1/5 flowed into three non-aerated FTWs in series. Performance of each treatment stage was monitored monthly for one year from February 2015 to January 2016 for organic matter (BOD 5 : Biochemical Oxygen Demand; TSS: Total Suspended Solids), nutrients (nitrogen and phosphorus) and E. coli removal. The single-pass system had almost complete removal of both TSS and cBOD 5 with > 93%, maintaining the final effluent TSS and cBOD 5 concentrations at below 5 and 4 mg L -1 respectively. The single-pass system had a lower NH 4 -N reduction (4.9 g m -2 d -1 ) compared with that in the recirculating system(6.9gm -2 d -1 ), but achieved higher denitrification (1.7 g m -2 d -1 ) than that in the recirculating system (1.4gm -2 d -1 ) as more organic carbon from the inflow wastewater was available in the single-pass system for denitrification. The recirculating FTW system achieved slightly higher removal of Total-P (TP: 44.9%) and Dissolved Reactive Phosphorus (DRP: 29.7%) than those in the single pass FTW system (TP: 36.7%; DRP: 24.3%), and both systems had a similar ~3-log E. coli reduction (from 10 6 to 10 3 MPN100ml -1 ) during the one-year experimental period. This one-year pilot-scale FTW study showed that FTWs supplemented with mechanically aerated BAS could be a practically option to retrofit existing waste stabilisation ponds to enhance organic matter, nitrogen and E. coli reduction. Furthermore, they may have some potential advantages over other types of intensified constructed wetlands, since they don’t need costly graded gravel (or other solid media), provide ready access to aeration diffusers for maintenance purposes, have low susceptibility to clogging, and can be more readily de-sludged if required. 1. Introduction Floating Treatment Wetlands (FTWs), one of many diverse appli- cations of constructed wetland technologies, involve emergent wetland plants growing hydroponically on mats or structures floating on the surface of a pond or tank (Headley and Tanner, 2012; Pavlineri et al., 2017). Emergent wetland plants are supported on a floating frame, raft or mat, with their shoots and leaves remaining above the water level, while their roots grow down into the water column. Due to the un- availability of soil nutrients, the FTW plants take their nutrition directly from the water column (Zhou and Wang, 2010; Headley and Tanner, 2012; Pavlineri et al., 2017). The hanging network of roots, as well as https://doi.org/10.1016/j.ecoleng.2019.105582 Received 31 May 2019; Received in revised form 19 August 2019; Accepted 24 August 2019 ⁎ Corresponding author. E-mail address: jason.park@niwa.co.nz (J.B.K. Park). Ecological Engineering 139 (2019) 105582 Available online 30 August 2019 0925-8574/ © 2019 Elsevier B.V. All rights reserved. T