Constructed wetlands for landfill leachate treatment: A review

Constructed wetlands (CWs) are engineered systems that are constructed to mimic natural wetlands. These systems simulate the processes that happen in natural wetlands and remove pollutants from wastewater. CWs have been previously used to treat a wide range of waste streams, including landfill leachate, and they have shown relatively good removal efficiencies. Although the literature on using CWs to treat different waste streams has been previously reviewed, there has been no literature review of constructed wetlands for leachate treatment. This critical analysis of available literature on landfill leachate treatment by CWs will help optimize future research in the field. The primary objective of this article is to present a comprehensive overview of the diverse range of practices, applications and research into the use of CW systems for removing contaminants from landfill leachate. This review of 85 papers across 20 countries focusses on the treatment performance of three different types of CWs (free water surface flow; subsurface flow (horizontal and vertical); and hybrid systems), using data from field- and pilot-scale studies, and discusses the impact of design criteria on CW treatment performance. The reported average % removal efficiencies of BOD5, COD, TP, PO4, Ammonia-N, TKN, TN, and TSS, for Horizontal/Vertical/Hybrid/Free water surface CWs were, respectively: 60.1/79.7/72.2/80.6%; 54.5/59.2/56.2/45.4%; 63.5/46.2/-6.4/5.5%; 67.7/62.1/5.2/-1.6%; 67.2/66.7/68.9/70.0%; 45.4/64.2/64.9/10.6%; 72.1/88.2/67.3/81.7%; and 69.3/55.5/51.8/59.5%.