Electrically enhanced microalgae-bacteria systems for wastewater treatment under low-temperature conditions

Low temperatures severely limit biological activity and pollutant removal in municipal wastewater treatment systems. This study comparatively evaluated micro electric fields (MEF) and pulsed electric fields (PEF) for enhancing a microalgae-bacteria system (MBS) treating real municipal wastewater at 5 - 15 degrees Celsius. Both electric field modes significantly improved biomass accumulation, photosynthetic pigment synthesis, Extracellular polymeric substances (EPS) production, and nutrient and chemical oxygen demand (COD) removal compared with non-electrified controls. PEF provided stronger short-term stimulation of biomass growth and pollutant removal, particularly at 10 - 15 degrees Celsius, whereas MEF showed more stable enhancement at 5 degrees Celsius. Phosphorus removal exhibited a pronounced electrochemical-biological synergy, electrocoagulation created favorable flocculation conditions, while biological assimilation and EPS-mediated aggregation contributed over 60% of total TP removal across all temperatures. Energy analysis further showed that PEF reduced volumetric energy consumption by 20 - 50% relative to MEF at equivalent voltages. Overall, electro-assisted microalgal-bacterial treatment offers an energy-efficient strategy for wastewater management under low temperature conditions.