9:45 AM - 10:00 AM
[AHW22-04] Suppression of phosphorus release from sediment in an agricultural drainage by placing Iron(III) amended sediment microbial fuel cell
Keywords:Sediment microbial fuel cell (SMFC), Ferric oxyhydroxide , Ferric oxide, Phosphorus adsorption
Excessive discharge of phosphorus (P) fertilizer from agricultural lands increases a P level in eutrophic lakes. Fe3+ is a key P fixing agent in riverine sediment and iron reducing reactions take place during anaerobic organic matter decomposition, resulting in high rates of P release from sediment. Sediment microbial fuel cells (SMFCs) are a modern technology that can prevent iron reduction in anaerobic sediment by operating as an external electron acceptor. Besides, iron oxide can play a role as an electron conduit between bacterial cells and anode, enhancing the electron transferring capacity. This study examined influence of different forms of iron addition into sediment on SMFCs performances and P release from sediment.
Surface sediment (0-5 cm) were collected from an agricultural drainage canal in Miyakorokku (N=34.56, E=133.90), Okayama, Japan. 0.4 M FeCl3 solution was pH neutralized by adding 1 M NaOH to prepare amorphous bulk ferric oxyhydroxide (FeOOH). Ferric oxide (Fe2O3) was used as a crystalline form of iron. Each iron type was mixed with sediment at 50 mmol kg-1. A dual chamber SMFC prototype was prepared by connecting the anode compartment made of an acrylic pipe (D = 45 mm, H = 146 mm) with the 0.2 M KCl filled cathode chamber through a 15% KCl salt bridge. 130 g of sediment samples were placed in the anode chamber, in which 3 x 3 cm carbon felt connected carbon rod was embedded in sediment. A Pt electrode was placed 4 cm below the sediment-water interface to measure sedimentary Eh. A carbon rod 10 cm long was used as the cathode. The impact of different amendments was examined under both open (OC) and closed (CC) circuit conditions. All treatments were triplicated and pre-incubated as OCs at 25oC for 48 h. Then, the chambers were kept for another 400 h at 25oC in the dark.
FeOOH addition significantly reduced P concentration in the overlying water in both OC and CC treatments. The larger specific surface area and the higher positive charge of FeOOH would have increased P adsorption on the sediment. P concentrations peaked at 120 h in all treatments. This is attributed to the release of PO43--P from decomposition of organic matter. On the other hand, SMFCs reduced P release from sediment because organic matter decomposition in CC treatments would produce Fe3+ near the anode, leading to the suppression of P release from sediment. However, CCs with FeOOH did not reduce P release compared to OCs probably because both reduced P release from sediment largely and the effect of SMFC was negligible. Electricity generation was not increased by iron amendments because the internal resistivity was not improved by Fe3+ amendment. More NH4+-N was released from sediment by iron addition presumably because of the increased decomposing rates of organic matter. In contrast, SMFCs could reduce N release in Fe added SMFCs probably by the microbial assimilation. Thus, this study suggested that P release from sediment can be suppressed by SMFCs, and Fe addition into sediment would fix more P in sediment. Further experiments should be conducted to assess the long-term effects of SMFCs.
Surface sediment (0-5 cm) were collected from an agricultural drainage canal in Miyakorokku (N=34.56, E=133.90), Okayama, Japan. 0.4 M FeCl3 solution was pH neutralized by adding 1 M NaOH to prepare amorphous bulk ferric oxyhydroxide (FeOOH). Ferric oxide (Fe2O3) was used as a crystalline form of iron. Each iron type was mixed with sediment at 50 mmol kg-1. A dual chamber SMFC prototype was prepared by connecting the anode compartment made of an acrylic pipe (D = 45 mm, H = 146 mm) with the 0.2 M KCl filled cathode chamber through a 15% KCl salt bridge. 130 g of sediment samples were placed in the anode chamber, in which 3 x 3 cm carbon felt connected carbon rod was embedded in sediment. A Pt electrode was placed 4 cm below the sediment-water interface to measure sedimentary Eh. A carbon rod 10 cm long was used as the cathode. The impact of different amendments was examined under both open (OC) and closed (CC) circuit conditions. All treatments were triplicated and pre-incubated as OCs at 25oC for 48 h. Then, the chambers were kept for another 400 h at 25oC in the dark.
FeOOH addition significantly reduced P concentration in the overlying water in both OC and CC treatments. The larger specific surface area and the higher positive charge of FeOOH would have increased P adsorption on the sediment. P concentrations peaked at 120 h in all treatments. This is attributed to the release of PO43--P from decomposition of organic matter. On the other hand, SMFCs reduced P release from sediment because organic matter decomposition in CC treatments would produce Fe3+ near the anode, leading to the suppression of P release from sediment. However, CCs with FeOOH did not reduce P release compared to OCs probably because both reduced P release from sediment largely and the effect of SMFC was negligible. Electricity generation was not increased by iron amendments because the internal resistivity was not improved by Fe3+ amendment. More NH4+-N was released from sediment by iron addition presumably because of the increased decomposing rates of organic matter. In contrast, SMFCs could reduce N release in Fe added SMFCs probably by the microbial assimilation. Thus, this study suggested that P release from sediment can be suppressed by SMFCs, and Fe addition into sediment would fix more P in sediment. Further experiments should be conducted to assess the long-term effects of SMFCs.