Control of internal phosphorus loading in eutrophic lakes using lanthanum-modified zeolite

- Lanthanum modified zeolite (LMZ) was prepared from coal fly ash.
- LMZ greatly reduced P levels in water overlying sediment within 212 day period.
- Release of P from sediment under high pH or anoxic conditions was impeded by LMZ.
- Releasable P species in sediment was converted to stable species by adding LMZ.
- LMZ was shown to be a promising material to control internal P loading in lakes.

Tackling the release of phosphorus (P) from sediments remains a challenge to mitigating the eutrophication of lakes. The current study investigated the efficacy of lanthanum-modified zeolite (LMZ), which was developed from coal fly ash via a one-pot process, to reduce P levels in a simulated water-sediment system. LMZ was dosed to bind releasable P fractions (i.e., labile P, reductant-soluble P, NaOH-P, and organic P fractions) in sediment of shallow lakes. LMZ treatment was found to be effective at decreasing the P concentration in water overlying sediment. On average, total P and soluble-reactive P were reduced by 81.1% and 86.9% in a 28-day sediment core incubation experiment and by 57.1% and 72.8% in a 212-day mesocosm experiment, respectively. LMZ decreased P release from sediment under high pH value (∼10.0) and anoxic conditions by 45.8% and 87.4% for total P and by 52.9% and 94.0% for soluble-reactive P, respectively. Adding LMZ induced a change of P in sediment from releasable P fractions to refractory P forms. Although aquatic parameters interfered with P binding, increasing the LMZ dosage enhanced the effect of LMZ. The control of internal phosphorus loading by LMZ was explained as follows: (i) capture of P from water; (ii) inhibition of P release from sediment; (iii) enhancement of P retention capacity of sediment; and (iv) inactivation of sediment P via the formation of stable P forms.

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