Constructed wetlands with recycled concrete for wastewater treatment in cold climate: Performance and life cycle assessment

Abstract

This study investigated the technical, environmental, and economic feasibility of using recycled construction material (concrete) as substrate in constructed wetlands for cold climate decentralized domestic wastewater treatment. The wastewater treatment efficiency was examined, and life cycle assessment (LCA) and cost benefit analysis were performed. The technical feasibility was assessed in lab-scale two-stage wetland systems with recycled concrete or lava stone as substrates, which were operated at 22 °C and 5 °C with local wild plants and vegetables. The wetlands removed ∼85 % and ∼51 % of organics and ∼67 % and ∼34 % TN at 22 °C and 5 °C, respectively; no significant difference was found between concrete and lava stone. The heavy metal contents in the cultivated vegetables met WHO standards for human consumption, showing the feasibility of nutrient recovery from the treated wastewater. A comparative LCA of septic tank standalone, septic tank + constructed wetland (with recycled concrete), and gravity-driven ceramic membrane (GDCM) system was performed. This aims to illustrate the benefits of intensifying the existing treatment process (i.e., septic tank) with the constructed wetland, with an alternative membrane-based treatment technique as benchmark. The LCA results revealed that using waste materials as the substrate in constructed wetlands could reduce the environmental impact of wetlands. Installation of the wetland as posttreatment of the septic tank (1) could reduce ∼50 % of eutrophication potential without increasing global warming impact compared to the septic tank alone; (2) had ∼90 % higher global warming impact and ∼40 % lower eutrophication impact compared to GDCM. Economic analysis revealed that the total cost of septic tank + constructed wetland (0.143 €/m3) was comparable to the septic tank alone (merely 3.5 % difference), and 49 % lower than that of GDCM (with recycled membranes). Therefore, the septic tank + constructed wetland scenario could be favorable for sensitive areas with eutrophication potential regarding its technical, economical, and environmental feasibility.