In a recent study by the UPWATER project partner IDAEA-CSIC, researchers tested a novel hybrid constructed wetland system to tackle contaminants of emerging concern (CECs) in wastewater. The system combines floating root mats (FRM) and bioelectrochemical wetlands (BW), both enhanced with biochar, to target a broad spectrum of trace organic pollutants.
At laboratory scale, the setup achieved over 99% removal of most targeted CECs across different hydraulic loading rates. The complementary mechanisms of FRM and BW contributed to the strong performance, with compound-specific analysis confirming that the hybrid approach was especially effective for diverse pollutant profiles.
Encouraged by these results, the team scaled up the design to a pilot plant at a municipal wastewater treatment facility in the Barcelona metropolitan area. The pilot plant consisted of three reactors containing different percentages of each type of wetland in the hybrid system: 25/75, 50/50 and 75/25% of FRM/BW and one reactor containing 100% bioelectrochemical wetland filled with biochar. Over the course of a year, the pilot treated secondary effluent under varying loads (200, 400 and 800 mm/day) and seasonal conditions (summer and winter).
- The hybrid configurations achieved good removals, with decreasing efficiency found with increasing proportion of FRM, but scale-up introduced challenges such as reduced hydraulic retention time and preferential flow paths, which lowered overall efficiency compared to lab conditions.
- The 100% bioelectrochemical wetland reactor achieved the highest average removal efficiency (78%) for CECs at pilot scale, outperforming hybrid combinations.
- Seasonal effects were evident, with reduced removal during colder months.
- The system tolerated well an increase in the HRL (hydraulic loading rate) of up to 400 mm/day, with decreasing efficiencies at 800 mm/day.
Despite upscaling challenges, these results highlight the potential of biochar-based bioelectrochemical wetlands as a low-energy, nature-based solution for removing persistent trace contaminants from polluted water.