Contrasting mediation actions on interactions of phosphorus with lanthanum modified zeolite by terrestrial- and algal-derived dissolved organic matter.

La-based phosphorus-inactivating agents (PIAs) have increasingly been applied and extensively investigated to control internal phosphorus loading in lakes. Dissolved organic matter (DOM) exists ubiquitously in eutrophic lakes, and can interfere with phosphate binding to PIAs. However, the current studies have mostly focused on the humic substances (HA), but the role of algal-derived organic matter (ADOM), which is the main source in eutrophic lakes, is still not adequately understood. In this study, the interactions of HA and ADOM with lanthanum-modified zeolite (LMZ), and the roles of individual fluorescent DOM components were investigated and compared. HA was mainly composed of humic-like components (microbial humic-like C1-HA and terrestrially-derived humic-like C2-HA), while ADOM was dominated by protein-like components (tryptophan-like C1-ADOM and tyrosine-like C2-ADOM), and contains biodegradable humic-like component (C3-ADOM) that different from HA components. C1-HA and C2-HA had strong affinity for LMZ, and can compete with P for active sites. For ADOM, C1-ADOM and C3-ADOM were the important components to interact with LMZ, and under neutral condition, some C1-ADOM can act as a bridge to provide more binding sites for P and promote the P immobilization. In contrast, in alkaline environment, the interaction between the zwitterion protein-like molecules and phosphate generated a more significant suppression effect on P immobilization by LMZ, compared with HA. Therefore, the application of PIAs should be avoided in the period with a high loading of protein-like substances, but due to the biodegradability of ADOM, its long-term effects need to be further studied.