16:15 〜 16:30
[AHW24-22] Iron oxides and biochar incorporation into sediment to reduce phosphorus release
キーワード：FeOOH, NBC, Fe-NBC, Iron reduction
Kojima Lake is known as a hypereutrophic lake in western Japan, with extensive sedimentary phosphorus (P) release in summer being the most prominent culprit for severe water quality deterioration. Reducing P loadings in the agricultural drains is effective as it is a major P input to the lake water. The use of biochar or iron oxides as a P adsorbent has been discovered to be an efficient and cost-effective approach. Amorphous ferric oxyhydroxides (FeOOH) are commonly found in aquatic environments and show a strong affinity for P. Because of its greater specific surface area, nanoparticle-sized biochar (NBC) may enhance P adsorption, whereas iron-treated NBC (Fe-NBC) may promote P suppression due to the increased Fe incorporated adsorption sites. During this study, the suppression of P release from FeOOH, NBC, or Fe-NBC added agricultural drainage sediment was investigated under aerobic and anaerobic conditions.
Sediment samples were collected from an agricultural drainage in Miyako Rokku in November 2021. Sediment samples were homogenized and sieved through 0.45 mm to remove large size particles and debris. 0.4 M FeCl3 solution was adjusted to pH 7 by adding 1 M NaOH to prepare FeOOH. Cedar saw wood was impregnated with Fe(NO3)3 aqueous solution and pyrolyzed at 800oC to produce Fe-NBC, while NBC was produced by pyrolizing cedar saw wood at 850oC. Sediment (65 g) without amendment as i) control or amended with FeOOH ii) 25 mmol kg-1 (FeOOH25), iii) 50 mmol kg-1 (FeOOH50),or biochar iv) 1% NBC, v) 2% NBC, vi) 1% Fe-NBC, and vii) 2% Fe-NBC was placed in a 14.6 mm high acrylic column of 4.5 mm internal diameter. Platinum electrode made by connecting to a 10 cm copper wire was installed 1 cm below the sediment interface to monitor sedimentary redox potential. Ultrapure water was filled up to the brim and incubated at 25oC in dark. On the 36th day, the column was closed by placing a silicon plug and continued the incubation for another 36 days under the same experimental atmosphere. Water sampling was conducted on 0, 7, 14, 21, 28 and 36 days during the aerobic and anaerobic incubation and determined PO4-P, NH4-N, NO3-N and Fe the in overlying water. Concentrations of TP and TOC in the overlying water were measured on the 36th day of each incubation condition.
Results showed that FeOOH added treatments had the lowest PO4-P concentrations for the first 36 days of incubation, while other treatments increased until the 7th day and then reduced. The maximum PO4-P released into the overlying water was significantly reduced by the amendments compared to the control. Except for FeOOH added treatments, phosphorus release increased again for the next 7 days after O2 diffusion was inhibited, whereas adding biochar boosted PO4-P release more than the control treatment. However, 2% Fe-NBC addition suppressed PO4-P release more than the 1% Fe-NBC, while PO4-P in NBC treatments did not differ among biochar percentages. At the end of the experiment, FeOOH25 treatment started to release PO4-P from sediment. Although FeOOH50 treatments showed lowest PO4-P concentrations, the strong correlation between Fe and PO4-P concentrations in FeOOH25 (R2=0.826) suggested that the iron reduction would enhance P release from sediment in the future. This study concluded that addition of FeOOH and Fe-NBC effectively suppressed the P release from sediment probably due to the higher Fe3+ availability under aerobic conditions, although those amendments did not show enough potential to suppress P release under anaerobic conditions.
Sediment samples were collected from an agricultural drainage in Miyako Rokku in November 2021. Sediment samples were homogenized and sieved through 0.45 mm to remove large size particles and debris. 0.4 M FeCl3 solution was adjusted to pH 7 by adding 1 M NaOH to prepare FeOOH. Cedar saw wood was impregnated with Fe(NO3)3 aqueous solution and pyrolyzed at 800oC to produce Fe-NBC, while NBC was produced by pyrolizing cedar saw wood at 850oC. Sediment (65 g) without amendment as i) control or amended with FeOOH ii) 25 mmol kg-1 (FeOOH25), iii) 50 mmol kg-1 (FeOOH50),or biochar iv) 1% NBC, v) 2% NBC, vi) 1% Fe-NBC, and vii) 2% Fe-NBC was placed in a 14.6 mm high acrylic column of 4.5 mm internal diameter. Platinum electrode made by connecting to a 10 cm copper wire was installed 1 cm below the sediment interface to monitor sedimentary redox potential. Ultrapure water was filled up to the brim and incubated at 25oC in dark. On the 36th day, the column was closed by placing a silicon plug and continued the incubation for another 36 days under the same experimental atmosphere. Water sampling was conducted on 0, 7, 14, 21, 28 and 36 days during the aerobic and anaerobic incubation and determined PO4-P, NH4-N, NO3-N and Fe the in overlying water. Concentrations of TP and TOC in the overlying water were measured on the 36th day of each incubation condition.
Results showed that FeOOH added treatments had the lowest PO4-P concentrations for the first 36 days of incubation, while other treatments increased until the 7th day and then reduced. The maximum PO4-P released into the overlying water was significantly reduced by the amendments compared to the control. Except for FeOOH added treatments, phosphorus release increased again for the next 7 days after O2 diffusion was inhibited, whereas adding biochar boosted PO4-P release more than the control treatment. However, 2% Fe-NBC addition suppressed PO4-P release more than the 1% Fe-NBC, while PO4-P in NBC treatments did not differ among biochar percentages. At the end of the experiment, FeOOH25 treatment started to release PO4-P from sediment. Although FeOOH50 treatments showed lowest PO4-P concentrations, the strong correlation between Fe and PO4-P concentrations in FeOOH25 (R2=0.826) suggested that the iron reduction would enhance P release from sediment in the future. This study concluded that addition of FeOOH and Fe-NBC effectively suppressed the P release from sediment probably due to the higher Fe3+ availability under aerobic conditions, although those amendments did not show enough potential to suppress P release under anaerobic conditions.