Distinct microbial communities enriched in water-saturated and unsaturated reactors influence performance of integrated hydroponics-microbial electrochemical technology

[Display omitted] •Distinct microbes develop in water-saturated and unsaturated iHydroMET reactors.•Aerobes (e.g. Pirellula) enabled high COD removal in water-unsaturated reactors.•Anammox bacteria and denitrifiers favored N removal in water-saturated reactors.•Electroactive microbes contributed to high voltage in water-saturated reactors.•Partial water-saturation reactor condition is key to improve iHydroMET performance. This study aimed to understand the wastewater treatment and electricity generation performance besides the microbial communities of the integrated Hydroponics-Microbial Electrochemical Technology (iHydroMET) systems operated with water-saturated and water-unsaturated reactors. The organics removal was slightly higher in the water-unsaturated system (93 ± 4 %) than in the water-saturated system (87 ± 2 %). The total nitrogen removal and electric voltage were considerably higher in the water-saturated system (42 ± 5 %; 111 ± 8 V per reactor) than in the water-unsaturated system (18 ± 3 %; 95 ± 9 V per reactor). The enhanced organics and nitrogen removal and high voltage output in respective conditions were due to the dominance of polysaccharide-degrading aerobes (e.g., Pirellula), anammox bacteria (e.g., Anammoximicrobium), denitrifiers (e.g., Thauera and Rheinheimera), and electroactive microorganisms (e.g., Geobacter). The differential performance governed by distinct microbial communities under the tested conditions indicates that an appropriate balancing of water saturation and unsaturation in reactors is crucial to achieving optimum iHydroMET performance.