Synthesis of novel algal extracellular polymeric substances (EPS)-based hydrogels for the efficient removal and recovery of phosphorus from contaminated waters: Development, characterisation, and performance

Adsorption is an effective and reliable method to recover phosphorus (P) from sewages. Extracellular polymeric substances (EPS) and agarose are common polysaccharides bioresources, and their carboxylic and phenolic hydroxyl groups can directly adsorb P via ion exchange and hydrogen bonding mechanisms. Here, we designed EPS-based and Fe-modified hydrogels (agarose (AG)- and agarose-humic (AH)- based hydrogels) for P recovery. The results showed that AG and AH hydrogels could adsorb 33.9 and 67.7 mg P g � 1, respectively. Both asdeveloped hydrogels showed > 75% of the maximal adsorption capacity in the tested pH conditions (3-10). Coexisting anions (i.e., SO42-, NO3 -, and CO32-) did not significantly affect the adsorption performance, except for CO32- which inhibited the process. Intraparticle diffusion controlled the adsorption process. After adsorption, large amounts of FePO4 and Fe2(HPO4)3 were generated in the hydrogels, confirming that ligand exchange was the major driving force.

Automated summary

Adsorption is an effective method for phosphorus recovery from sewages, and EPS-based and Fe-modified hydrogels showed high adsorptive capacity. The hydrogels could adsorb P via ion exchange and hydrogen bonding mechanisms, and had good performance under a wide range of pH conditions. Coexisting anions did not significantly affect the adsorption process, with the exception of CO32-. Ligand exchange was the major driving force for phosphorus adsorption.