Effect of different bypass rates and unit area ratio in hybrid constructed wetlands
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RESEARCH ARTICLE
Effect of different bypass rates and unit area ratio in hybrid constructed wetlands Omar Gael Gonzalo 1 & Isabel Ruiz 1 & Manuel Soto 1 Received: 19 March 2020 / Accepted: 1 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This study presents the performance of a hybrid constructed wetland (Bp(VF + HF)2:1) system which consists of an unsaturated vertical flow (VF) unit followed by a saturated down-flow unit simulating horizontal flow (HF) with HF/VF area ratio of 0.5 and influent bypass to the HF unit. Treating synthetic wastewater simulating municipal wastewater, optimum total nitrogen (TN) removal (57%) was reached at 39% bypass and surface loading rate (SLR) of 33 g BOD5/m2 day and 9.7 g TN/m2 day (overall system). On the other hand, treating actual municipal wastewater, the system reached 63% TN removal at 30% bypass and SLR of 18 g BOD5/m2 day and 4.7 g TN/m2 day. Surface removal rates reached 5.5 and 3.0 g TN/m2 day for synthetic and municipal wastewater. Surface nitrification rate in the VF unit was in the range of 5.0–7.4 and 3.6–3.8 g N/m2 day for synthetic and municipal wastewater, respectively, indicating a large effect of wastewater characteristics on the nitrification process. Infiltration rate in the VF unit remained high and far from clogging risk. Overall greenhouse gas emissions were 0.11 (N2O) and 0.41 (CH4) g/m2 day which corresponded to emissions factors (relative to total organic carbon and TN influent) of 0.7% (N2O) and 3.6% (CH4). Compared with a similar system with a different HF/VF area ratio of 2.0, organic matter and nitrogen removal efficiency was similar, but surface removal rates were about 3 times higher. Keywords Hybrid constructed wetlands . Vertical flow . Horizontal flow . Nitrogen removal . Influent bypass
Introduction Constructed wetlands (CWs) represent an alternative to conventional wastewater treatment systems, particularly for the sanitation of small communities (Kumar and Dutta 2019). However, single-stage CWs cannot always reach the strictest nitrogen discharge limits to surface water bodies. N removal efficiency reported for constructed wetlands is variable, ranging from high removals of over 90% to removals as low as 11%, and even the consideration that N removal efficiency could not exceed 50% existed, even with optimal design (Xu et al. 2013). In fact, none of the conventional CWs such as the unsaturated vertical flow (VF), the saturated horizontal flow
Responsible Editor: Alexandros Stefanakis * Manuel Soto [email protected] 1
Department of Chemistry, University of A Coruña, Rúa da Fraga 10, 15008 A Coruña, Galiza, Spain
(HF) and free water systems alone can achieve effective total nitrogen (TN) removal due to their inability to provide alternant aerobic and anoxic conditions for the subsequent nitrification/denitrification processes (Canga et al. 2011; Hu et al. 2014). The only exception to this general rule is the use of hydraulic saturated, horizontal or vertical flow systems when operated at very low surface loadin
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