Please cite this article in press as: M.-Y. Sultana, et al., Integrated Cr(VI) removal using constructed wetlands and composting, J. Hazard. Mater. (2014), http://dx.doi.org/10.1016/j.jhazmat.2014.06.046 ARTICLE IN PRESS G Model HAZMAT-16055; No. of Pages 8 Journal of Hazardous Materials xxx (2014) xxx–xxx Contents lists available at ScienceDirect Journal of Hazardous Materials j o ur nal ho me pa ge: www.elsevier.com/locate/jhazmat Integrated Cr(VI) removal using constructed wetlands and composting Mar-Yam Sultana a , Abu Khayer Md. Muktadirul Bari Chowdhury a , Michail K. Michailides a , Christos S. Akratos a,∗ , Athanasia G. Tekerlekopoulou a , Dimitrios V. Vayenas a,b a Department of Environmental and Natural Resources Management, University of Patras, G. Seferi 2, GR-30100 Agrinio, Greece b Institute of Chemical Engineering Sciences, Stadiou Str., Platani, GR-26504 Patras, Greece h i g h l i g h t s • An integrated (wastewater and harvested plants) Cr(VI) treatment method is presented. • Wastewater temperature effect on Cr (VI) removal efficiency in CWs was assessed. • For the first time HRT effect on Cr (VI) removal efficiency in CWs was assessed. • CWs were operated under extremely low HRTs of 1 day. • This is the first time that dry biomass of reed plants was treated via composting. a r t i c l e i n f o Article history: Received 25 January 2014 Received in revised form 20 June 2014 Accepted 21 June 2014 Available online xxx Keywords: Chromium HRT HSF constructed wetlands Common reeds Composting a b s t r a c t The present work was conducted to study integrated chromium removal from aqueous solutions in horizontal subsurface (HSF) constructed wetlands. Two pilot-scale HSF constructed wetlands (CWs) units were built and operated. One unit was planted with common reeds (Phragmites australis) and one was kept unplanted. Influent concentrations of Cr(VI) ranged from 0.5 to 10 mg/L. The effect of temperature and hydraulic residence time (8–0.5 days) on Cr(VI) removal were studied. Temperature was proved to affect Cr(VI) removal in both units. In the planted unit maximum Cr(VI) removal efficiencies of 100% were recorded at HRT’s of 1 day with Cr(VI) concentrations of 5, 2.5 and 1 mg/L, while a significantly lower removal rate was recorded in the unplanted unit. Harvested reed biomass from the CWs was co- composted with olive mill wastes. The final product had excellent physicochemical characteristics (C/N: 14.1–14.7, germination index (GI): 145–157%, Cr: 8–10 mg/kg dry mass), fulfills EU requirements and can be used as a fertilizer in organic farming. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Heavy metals cause major environmental pollution through- out the world. Hexavalent chromium, Cr(VI), is one of the most hazardous heavy metals contaminating water resources and has a long resident time in water [1,2]. In contrast, Cr(III) displays a high affinity for organics resulting in the formation of complexes that precipitate as amorphous hydroxide [3]. However, excess quanti- ties of Cr(III) also cause damage to aquatic organisms and disrupt the food chain [4]. Due to the high toxicity of Cr(VI), the European Union regulate Cr(VI) concentrations in surface waters to below ∗ Corresponding author. Tel.: +30 26410 74209; fax: +30 26410 74176. E-mail address: cakratos@upatras.gr (C.S. Akratos). 0.05 mg/L, while total Cr, including Cr(III), Cr(VI) and its other forms, are regulated to below 2 mg/L [5]. Several physicochemical methods are used to remove heavy metals from wastewaters streams including ion exchange [6], acti- vated carbon [7], chemical precipitation [8], adsorption [9], reverse osmosis [10], membrane technologies [11] and activated carbon adsorption [12]. In some cases these physicochemical processes are quite expensive especially when the metal concentrations in the solution range from 1 to 100 mg/L [13]. Furthermore, these meth- ods usually produce large quantities of toxic chemical sludge, which disposal is a major problem [14]. Recent research has focused on constructed wetlands (CWs) for removing heavy metals from different wastewaters [15–21]. Many authors have studied horizontal subsurface flow (HSF) CWs for removing Cr [22–25]. The main processes of Cr uptake by plants are adsorption, chelation and ion exchange [26,27]. Plants also http://dx.doi.org/10.1016/j.jhazmat.2014.06.046 0304-3894/© 2014 Elsevier B.V. All rights reserved.