Investigation of protozoa as indicators of wastewater treatment efficiency in constructed wetlands ☆ C.A. Papadimitriou a, ⁎, A. Papatheodoulou b , V. Takavakoglou c , A. Zdragas d , P. Samaras e , G.P. Sakellaropoulos a , M. Lazaridou b , G. Zalidis c a Chemical Process Engineering Research Institute and Department of Chemical Engineering, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece b Department of Zoology, School of Biology, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece c Laboratory of Applied Soil Science, School of Agriculture, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece d National Agricultural Research Foundation, Institute of Veterinary Research, 57001 Thermi, Thessaloniki, Greece e Department of Pollution Control Technologies, Technological Educational Institute of W. Macedonia, 50100, Kozani, Greece abstract article info Article history: Received 24 November 2007 Accepted 9 October 2008 Available online 27 October 2009 Keywords: Protozoa Diversity Constructed wetlands Wastewater treatment efficiency Effluent quality Bioindicators Wetlands represent an efficient wastewater treatment technique, with several benefits over the conventional activated sludge system. Microfaunal community is of outmost importance in treatment processes as the microorganisms are able to achieve substantial decontamination through biodegradation. The objectives of this work were the monitoring of protozoan's abundance and diversity in the matrix of six bench scale Free Water Surface constructed wetlands and the investigation of their applicability as indicator organisms for treatment efficiency in these systems. A correlation between the phosphorous and Total Coliforms removal rates was observed in the presence of increased protozoan taxa, while removal of organic loading and inorganic nitrogen was increased in the case of increased protozoan diversity in the soil/water interface. Results revealed that protozoa may be used as bioindicators of treatment efficiency in constructed wetlands; in addition their presence was related to the effluent quality. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Constructed wetlands represent a natural wastewater treatment process, offering several economic and environmental advantages [1–3]. Constructed wetlands are able to efficiently remove organic sub- stances, suspended solids, pathogens, nutrients and heavy metals [2]. In general, the nature and magnitude of the organic loading determine the balance between the treatment mechanisms and the dominant removal pathways in a constructed wetland [2]. The treatment process is based on the metabolic activities of organisms. Surface flow constructed wetlands are designed to simulate natural wetlands, where the water flows over the soil surface at shallow depths taking advantage of the same processes that occur in natural wetlands, but within a more controlled environment [4,5]. The wastewater treatment systems can be characterized as artificial ecosystems operating under severe conditions in which the key organisms are bacteria and protozoa. Protozoans comprise a large, diverse assortment of microscopic organisms that live as single cells or in colonies. Studies revealed that the most dominant protozoa found in wastewater treatment plants belong to the Ciliophora group [6,7]. They have been identified as disinfection agents, while the predatory activities of protozoa upon dispersed bacteria contribute to the reduction of coliforms [8]. Several authors [8–11] have suggested the use of protozoa as indicator organisms in the assessment of sludge “health and biodegration ability”. The Sludge Biotic Index (SBI), developed by Madoni, demonstrates microfaunal relation between indicator protozoan species and the activated sludge performance [9]. However, reports on protozoan population dynamics in Surface Flow Constructed Wetlands are limited. The aims of this work were the study of the protozoan diversity and abundance in the substrate of surface flow constructed wetlands and the investigation of their potential to be used as bioindicators of treatment and disinfection efficiency. 2. Materials and methods Six bench scale Free Water Surface (FWS) constructed wetlands were used during this study for the treatment of municipal wastewater, obtained from the primary sedimentation tank of a full scale municipal activated sludge plant of Thessaloniki, Northern Greece. The design of the wetlands was based on that suggested by EPA [12]. Wetland outflow was based on a single outlet weir designed to maintain the desired water level in the system and to sustain the functional capacity of the wetland. The FWS wetlands were filled with sandy loam soil, and planted with Typha spp. The design characteristics of the wetlands are presented in Table 1. Desalination 250 (2010) 378–382 ☆ Presented at the 1st Conference on Environmental Management, Engineering, Planning and Economics (CEMEPE), Skiathos, Greece, 24-28 June, 2007. ⁎ Corresponding author. E-mail address: papadim@cperi.certh.gr (C.A. Papadimitriou). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.09.060 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal