Phosphorus Release from Agricultural Drainage Sediments with Iron-Added Sediment Microbial Fuel Cells

This study investigated the long-term performance of iron-added sediment microbial fuel cells (SMFCs) in suppressing phosphorus (P) release from agricultural drainage sediments. Sediment samples were collected from two drainage canals in livestock farming (LS) and pasture-grown (PS) areas in Kasaoka, Japan. Iron-added sediments were prepared by mixing FeCl3·6H2O at 0.05% (wt/wt). A graphite-felt anode and a carbon rod cathode were used in a dual-chamber SMFC (height: 146 mm, diameter: 45 mm), which was operated under open (OC) or closed circuit (CC) conditions at 25°C. The experiments consisted of 8 treatments in triplicate: LS and PS sediments × Fe or no-Fe × OC or CC. Phosphorus release from LS sediment was higher than from PS with a lower total P content. Under the SMFC operation, P release was reduced until day 42. Afterward, P concentrations became similar between OC and CC conditions, and iron addition increased P release from sediment, probably because of P mineralization. Our study suggested that SMFCs effectively reduced P through Fe precipitation until day 42, when the resistor was reduced. However, SMFC operation or iron addition would increase organic matter decomposition in sediment, which in turn enhanced P release from sediment.