Life cycle assessment and costing of wastewater treatment systems coupled to constructed wetlands

Abstract

This study evaluates the environmental and economic performance (ecoefficiency) of two decentralized, small-scale, wastewater treatment systems coupled to constructed wetlands. System One comprises a vertical and a horizontal flow wetland. System Two comprises a vertical subsurface flow wetland with artificial aeration. A life cycle assessment based on data from two actual pilot structures was carried out. The functional unit was 1 m3 of treated water over a 20-year long lifetime. The systems were modeled in open LCA software, with the aid of Ecoinvent 3.3 data, and the impact assessment was based on the ReCIPe method. Results have demonstrated that foreground emissions such as direct greenhouse gas released from the septic tank and nutrients released in the effluent have driven potential impacts related to Climate Change, Photochemical Oxidants, and Freshwater Eutrophication. Artificial aeration reduces the area required for the installation of the system and electricity consumption was responsible for only 7% of total Climate Change related potential impact. Technologies that reduce direct (foreground) liquid and airborne emissions will improve the environmental performance of the systems. The analysis of the aerated wetland has shown that the operation stage had the greatest environmental impact potential for all analyzed impact categories, with results varying between 64% for Human Toxicity and 100% for Freshwater Eutrophication. The life cycle cost per cubic meter of treated sewage for the aerated system was 1.8 times smaller than that of the system without aeration. Thus, aeration is cost-effective for small-scale wastewater treatment systems coupled to constructed wetlands.