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From lab to field: Testing nature-based solutions (NBS)

The UPWATER project explores nature-based strategies to mitigate groundwater pollution assessing the effectiveness of novel designs of constructed wetlands: floating root mats and bioelectrochemical wetlands.

The project aims to specifically evaluate the effect of the type of filling material, vegetation presence and applied hydraulic loading rate on pollutant removal (nutrients and emerging pollutants), exploring the most effective configurations.

To do so, two lab-scale experiments were set and fed with real secondary treated wastewater from the Besòs case study area. First, floating root mats (Figure 1) were tested in pools made of unreactive material, where the effect of vegetation mats (Cyperus papyrus) and the addition of biochar to the vegetation mats were evaluated. Parallelly, bioelectrochemical wetlands (Figure 2) were tested using columns, each filled with one of the three materials (biochar, coke or sand) and planted with Phragmites australis, a common plant used in constructed wetlands.

Figure 2. Experimental set-up showing bioelectrochemical wetlands with coke, biochar and sand columns fed with wastewater treatment plant effluent spiked with relevant emergent pollutants.  

The experiments revealed that the most successful configurations were root mats with biochar addition and bioelectrochemical wetlands filled with biochar. For instance, root mats combined with biochar achieved up to 90% removal efficiency for certain pollutants at specific hydraulic loading rates, while bioelectrochemical wetlands with biochar removed over 95% of emerging pollutants under their tested conditions.

The addition of zero valent iron (ZVI) to the columns was further evaluated, but did not lead to the expected improvements. Instead, the average removal efficiencies of pollutants either decreased or showed no significant improvement across all studied treatments when ZVI was introduced, probably due to a negative impact on the biofilm.

The research results of these two lab studies led to the development of a combined prototype, integrating the most effective configurations of root mats and bioelectrochemical wetlands. This prototype showed a high removal efficiency of emerging pollutants and nutrients (> 90%), suggesting potential for upscaling to pilot-scale. The study concluded with recommendations for constructing a pilot plant.

In addition, the use of Compound Specific Isotope Analysis (CSIA) is currently being evaluated  for additional characterization of the treatment efficiency and for distinguishing transformation processes of selected emerging contaminants.

The innovative character of the UPWATER laboratory experiments highlights the project’s contribution to sustainable water management practices, aiming to enhance water quality by addressing pollution at its source. The findings are significant for environmental scientists, engineers, and policymakers interested in innovative solutions for water pollution and resource management.

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