Enhanced electron transfer and methane production from low-strength wastewater using a new granular activated carbon modified with nano-Fe3O4

Granular activated carbon (GAC) was modified by the addition of conductive nano-Fe3O4 for use in the anaerobic digestion of low-strength wastewater. This new material, called magnetic granular activated carbon (MGAC), was fabricated by the facile co-precipitation method. The MGAC exhibited superior electro-conductivity, electron transfer rate, and methane production. The observed conductivity of the MGAC (17.5 ± 0.6 mS cm−1) was 2.03 times that of the GAC (8.6 ± 0.3 mS cm−1). With the MGAC, the effluent total chemical oxygen demand concentration (44.5 ± 1.5 mg L−1) was 33% lower than that obtained with the GAC and 43% lower than that obtained in the control experiment (with no conductive additive). The methane production obtained with the MGAC (4.7 ± 0.2 mL per cycle) was 3.6 times that of the control and 1.57 times that of the GAC. The anaerobic system with the MGAC exhibited stronger electrochemical response to riboflavin and cytochrome C. The peak current at 0 V (reduction peak, cytochrome C) of the MGAC was 45.1 μA, which was 54.0% higher than that of the GAC and 54.8% higher than that of the control. The electron accepting capability [56.71 ± 0.70 μmol e− (g char)−1] was 2.75 times that of the GAC. The MGAC also exhibited a higher abundance of functional microorganisms. These results demonstrated that the MGAC enhanced the electron transfer between bacteria and archaea, improved methane production, and produced high-quality effluent.