Thermally treated oyster shells elevate biofilm viability and nutrient removal in sediment microbial fuel cells

Sediment microbial fuel cells (SMFC) effectively treat benthic pollutants and simultaneously generate bioelectricity. This study evaluates novel application of thermally treated oyster shell (COS) at 600°C to promote biofilm viability and benthic nutrient removal for 375 days. Sustaining microbial biomass adhesion and viability on anode surface is essential for long-term SMFC operation, which relies on sediment microbial metabolism. In CLSM imaging, green fluorescence in COS-10g and COS-20g reflect high biovolumes of viable microbial biomass, correlated with increased COS dosing. FESEM shows that COS-10g and COS-20g produce the thickest and most densely packed biofilms on anode surfaces. Maximum viable biofilm thickness is 40 μm, with biovolumes of 242,698 and 140,610 pixels and viabilities of 91.2% and 85.8% for COS-10g and COS-20g, linked to Ca 2+ elution from COS. High biofilm viability improves mass electron transport by reducing charge transfer resistance to 193 Ω (COS-10g) and 84 Ω (COS-20g), coinciding with higher biofilm viability at higher COS dosing. SMFC enhances PO 4 -P removal across all COS cases, reducing PO 4 -P from 1.92 to 0.30 mg/L in COS-10g, while control cases remain up to 1.8 mg/L, highlighting the synergistic effect of SMFC and COS addition. COS addition with SMFC operation does not result in pH elevation that would deteriorate sediment microbial activity, maintaining sediment pH between 6.392 and 6.503 throughout operation. COS-10g shows the highest sediment ORP of −94.2 mV, reflecting notable biofilm viability for microbial oxidation in sediment. Valorizing thermally treated COS waste improves SMFC by boosting microbial biomass and nutrient removal for bioelectricity generation.