Removal of Phosphate from Eutrophic Lakes through Adsorption by in Situ Formation of Magnesium Hydroxide from Diatomite

Since in situ formation of Mg­(OH)₂ can efficiently sorb phosphate (PO₄) from low concentrations in the environment, a novel dispersed magnesium oxide nanoflake-modified diatomite adsorbent (MOD) was developed for use in restoration of eutrophic lakes by removal of excess PO₄. Various adsorption conditions, such as pH, temperature and contact time were investigated. Overall, sorption capacities increased with increasing temperature and contact time, and decreased with increasing pH. Adsorption of PO₄ was well described by both the Langmuir isotherm and pseudo second-order models. Theoretical maximum sorption capacity of MOD for PO₄ was 44.44–52.08 mg/g at experimental conditions. Characterization of PO₄ adsorbed to MOD by use of X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and solid state ³¹P nuclear magnetic resonance revealed that electrostatic attraction, surface complexation and chemical conversion in situ were the major forces in adsorption of PO₄. Mg­(OH)₂ formed in situ had a net positive charge on the surface of the MOD that could adsorb PO₄^3‑ and HPO₄^2‑ anion to form surface complex and gradually convert to Mg₃(PO₄)₂ and MgHPO₄. Efficiency of removal of PO₄ was 90% when 300 mg MOD/L was added to eutrophic lake water. Results presented here demonstrated the potential use of the MOD for restoration of eutrophic lakes by removal of excess PO₄

Characterization of Organic Phosphorus in Lake Sediments by Sequential Fractionation and Enzymatic Hydrolysis

The role of sediment-bound organic phosphorus (P_o) on lake eutrophication was studied using sequential extraction and enzymatic hydrolysis by collecting sediments from Dianchi Lake, China. Bioavailable P_o species including labile monoester P, diester P, and phytate-like P were identified in the sequential extractions by H₂O, NaHCO₃, and NaOH. For the H₂O–P_o, 36.7% (average) was labile monoester P, 14.8% was diester P, and 69.9% was phytate-like P. In NaHCO₃–P_o, 19.9% was labile monoester P, 17.5% was diester P, and 58.8% was phytate-like P. For NaOH–P_o, 25.6% was labile monoester P, 7.9% was diester P, and 35.9% was phytate-like P. Labile monoester P was active to support growth of algae to form blooms. Diester P mainly distributed in labile H₂O and NaHCO₃ fractions was readily available to cyanobacteria. Phytate-like P represents a major portion of the P_o in the NaOH fractions, also in the more labile H₂O and NaHCO₃ fractions. Based on results of sequential extraction of P_o and enzymatic hydrolysis, lability and bioavailability was in decreasing order as follows: H₂O–P_o > NaHCO₃–P_o > NaOH–P_o, and bioavailable P_o accounted for only 12.1–27.2% of total P_o in sediments. These results suggest that the biogeochemical cycle of bioavailable P_o might play an important role in maintaining the eutrophic status of lakes

Characterization of Organic Phosphorus in Lake Sediments by Sequential Fractionation and Enzymatic Hydrolysis

The role of sediment-bound organic phosphorus (P_o) on lake eutrophication was studied using sequential extraction and enzymatic hydrolysis by collecting sediments from Dianchi Lake, China. Bioavailable P_o species including labile monoester P, diester P, and phytate-like P were identified in the sequential extractions by H₂O, NaHCO₃, and NaOH. For the H₂O–P_o, 36.7% (average) was labile monoester P, 14.8% was diester P, and 69.9% was phytate-like P. In NaHCO₃–P_o, 19.9% was labile monoester P, 17.5% was diester P, and 58.8% was phytate-like P. For NaOH–P_o, 25.6% was labile monoester P, 7.9% was diester P, and 35.9% was phytate-like P. Labile monoester P was active to support growth of algae to form blooms. Diester P mainly distributed in labile H₂O and NaHCO₃ fractions was readily available to cyanobacteria. Phytate-like P represents a major portion of the P_o in the NaOH fractions, also in the more labile H₂O and NaHCO₃ fractions. Based on results of sequential extraction of P_o and enzymatic hydrolysis, lability and bioavailability was in decreasing order as follows: H₂O–P_o > NaHCO₃–P_o > NaOH–P_o, and bioavailable P_o accounted for only 12.1–27.2% of total P_o in sediments. These results suggest that the biogeochemical cycle of bioavailable P_o might play an important role in maintaining the eutrophic status of lakes