Environmental and economic assessment of a floating constructed wetland to rehabilitate eutrophicated waterways

While the reduced carbon footprint of conventional constructed wetlands (CW) for wastewater treatment has been de-scribed in the literature, far less information is available on the economic performance of floating filters and their ap-plication for the treatment of other pressing environmental problems such as freshwater eutrophication. This investigation describes the technical characteristics and the environmental life cycle assessment (E-LCA) and a life cycle cost (LCC) analysis of a Typha domingensis floating constructed wetland (FCW) designed and constructed to reha-bilitate eutrophicated waterways and which also produces biomass for animal feed. The analysis is based on a precise material, energy and economic inventory from a demonstration project built in the Alagon river basin (central Spain). The E-LCA followed a cradle-to-grave approach, used the EF3.0 impact assessment methodology and was referred to two complementary functional units related to the water treatment capacity of the floating filter: 1 m3 of treated water and 1 kg of N fixed, both over a 10-year operating cycle. Climate change emissions were estimated at 0.012 kg CO2 eq./m3, which included 0.082 kg CO2 eq./m3 caused by the construction, operation and decommissioning of the infrastructure, minus 0.070 kg CO2 eq./m3 credits from the production of fodder for animal feed. Considering its nitrogen uptake capacity, this may be represented as 0.845 kg CO2 eq./kg N. Most of this carbon footprint comes from the construction (63.2 %) and the operation (31.1 %) stages, with the former being dominated by auxiliary materials (mainly plastics and cereal straw) needed to build the infrastructure and the energy system (mainly PV panels). This same pattern is replicated in most other environmental categories and the aggregated single score. Further research is needed to quantify with precision direct CH4 and N2O emissions produced during the operation stage, whose contribution can be significant (up to 64.8 % over indirect LCA emissions). The LCC analysis resulted in discounted expenses over the 10-year cycle of 44,083 euro and revenues derived from the sale of fodder for animal feed of 11,429 euro, resulting in a net present value of 32,654 euro. These expenses may be represented as 0.302 euro/m3 of treated water (or 21.1 euro/kg of N fixed). The monetary cost and environmental footprint per functional unit of floating CW are lower than those reported for other conventional small-scale wastewater treatment technologies.

Automated summary

This study presents a method for designing and constructing a floating wetland that can rehabilitate eutrophicated waterways and produce biomass for animal feed. The environmental life cycle assessment and life cycle cost analysis show that the carbon footprint and economic performance of this wetland are lower than those of other conventional small-scale wastewater treatment technologies.