Energy-Positive Wastewater Treatment and Nutrient Recovery in a Combined Hydroponics and Microbial Electrochemical System

As the global population grows at a rapid rate, the need for effective wastewater management coupled with resource recovery to preserve natural resources is increasingly critical. Conventional wastewater treatment processes are energy- and chemical- intensive, increasing the demand for fossil fuels that produce greenhouse gases (GHGs). Microbial Electrochemical Systems (MECs) offer promising advantages by simultaneously treating wastewater and producing renewable electricity. In this study, a combined MEC–hydroponic system facilitates lettuce (Lactuca sativa) growth, supported by nutrients recovered from energy-positive wastewater treatment in the MEC anode chamber. The aim is to identify pertinent transmembrane nutrient transport pathways and their potential benefits for lettuce growth and wastewater treatment. This combined setup is a cost-effective 3D-printed reactor wherein the lettuce plants grow in the cathode chamber, immersed in hydroponic wastewater (nutrient solution). This is compared to a standard air cathode cell. Local municipal wastewater was used as the anolyte. Performance was measured through the COD and total nitrogen removal in the anolyte, as well as power generation potential. The combined system had an average COD removal efficiency of 48.98%, an average N removal efficiency of 52.27%, and a peak power density of 4.27 mW/m². The rate of plant growth (measured as wet weight) was found to be 24.88%. In comparison, the standard system had an average COD removal efficiency of 61.59%, an average N removal efficiency of 48.58%, and a peak power density of 0.29 mW/m². These findings demonstrate the potential application of combined MEC–hydroponic systems for both wastewater treatment plants and agricultural systems in a circular economy framework.