ecological engineering 32 ( 2 0 0 8 ) 238–243 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ecoleng A comparison of bacterial removal efficiencies in constructed wetlands and algae-based systems Mercedes Garc´ ıa a,* , F´ elix Soto b , Juan M. Gonz ´ alez b , Eloy B´ ecares c a Pyrenean Institute of Ecology-CSIC, Apdo. 202, 50080 Zaragoza, Spain b AmbiNor, Mois´ es de Le ´ on 7-2, 24006 Le´ on, Spain c Department of Ecology, Faculty of Biology, University of Le´ on, 24071 Le ´ on, Spain article info Article history: Received 25 June 2007 Received in revised form 5 November 2007 Accepted 24 November 2007 Keywords: Constructed wetlands Macrophytes Algae pond Faecal indicators Removal rates abstract Constructed wetlands and algae-based systems have been compared regarding their effi- ciencies on faecal bacteria removal. Two types of constructed wetlands, sub-surface (SSF) and free water surface (FWS) flow systems, and two more types of algae-based systems, high rate algae ponds (HRAP) and maturation pond (MP) have been studied for two years. All systems treated the same wastewater from a rural locality in Le´ on (northwest of Spain). Hydraulic retention time was 3 days for both wetland systems, 20 days for the maturation pond and 10 days for the high rate algae pond. Total coliforms, faecal coliforms, faecal Strep- tococci, Clostridium perfringens, and Staphylococci were analyzed in the influent and effluents of each system. A comparison among the wetland systems showed that SSF were more efficient than FWS system when considering surface removal rates (cfu removed/m 2 /d). Nevertheless, differences were not statistically significant. Considering mean removal effi- ciencies (in log unit), results showed that higher reductions were observed in FWS for most of the groups except for clostridia and Staphylococci. Concerning algae-based systems, MP showed higher removal efficiencies than HRAP, getting higher surface removal rates in the HRAP. Generally constructed wetlands were more efficient than algae-based systems when considering both, efficiencies in % and surface removal rates. © 2007 Elsevier B.V. All rights reserved. 1. Introduction It exists a significant number of reseraches in the use of wetlands for treating wastewater and its reuse (Hammer and Bastian, 1989; Mitsch and Jorgensen, 1989; Moshiri, 1993; Kadlec and Knight, 1996). Some of the existing bacterial removal mechanisms, such as physical retention, predation, oxygen release into the rhizosphere, the activity of attached bacteria in the macrophyte roots, or the ability of some helo- phytes to produce root exudates that inhibit bacterial growth, have been studied before (Seidel, 1976; Gopal and Goel, 1993; Vincent et al., 1994; Ottov´ a et al., 1997; Brix, 1997; Garc´ ıa et ∗ Corresponding author. Tel.: +34 976716118; fax: +34 976716019. E-mail addresses: mercedes@ipe.csic.es (M. Garc´ ıa), ebecm@unileon.es (E. B ´ ecares). al., 2004). Wetland hydraulic regime has a direct influence in bacterial removal mechanisms. In free-water systems with surface flow, the hydraulic conductivity, of both the gravel bed and the rhizosphere zone, is negligible (Kadlec and Knight, 1996), and the main role of macrophytes is to provide an extra surface for the development of the biofilm on the plant sub- merged parts (Kadlec and Knight, 1996). In those systems with sub-surface water flow, the hydraulic conductivity of the sub- strate is an important design parameter to take into account. Moreover, wastewater interacts directly with the rhizosphere, and roots, besides acting as support for biofilms, have addi- tional functions (Brix, 1997). 0925-8574/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2007.11.012