Efficient removal of phosphate ions on activated algae biomass: Biosorption characteristics and practical implications

Removal of pollutants and the more efficient use of the natural materials are two key elements in achieving sustainable development. That is why the use of algae biomass (which are a renewable resource) in biosorption processes has received special attention over time. In this study, algae biomass ( Ulva intestinalis ) was activated with 1 N HNO 3 solution (H1-AB) and 1–3 N Ca(NO 3 ) 2 solution (Ca1-AB, Ca2-AB and Ca3-AB), and the obtained biosorbents were used for the removal of phosphate ions from aqueous media, compared to raw algae biomass (AB). The experiments were performed as a function of initial concentration of phosphate ions and contact time, at pH of 6.5 and room temperature (20 ± 1 °C), previously established as optimal conditions. The experimental data were analyzed using different isotherm and kinetic models. The equilibrium data were best described by the Langmuir model, and the obtained values of the maximum biosorption capacity follow the order: Ca1-AB (158.73 mg g −1 ) > Ca2-AB (92.59 mg g −1 ) > Ca3-AB (89.29 mg g −1 ) > H1-AB (53.47 mg g −1 ) > AB (39.21 mg g −1 ). The kinetic data were well fitted by the pseudo-second order kinetic model, which suggests that all biosorption processes occur through physico-chemical interactions on the surface of the biosorbents. Based on the experimental results, Ca1-AB was selected for further desorption studies and tests on river water samples. Desorption of phosphate ions on Ca1-AB requires moderate conditions (1 N NaCl solution and short contact time), which suggests the possibility of gradual release of phosphate ions from the loaded-biosorbent. Tests for the removal of phosphate ions by biosorption from the river water samples showed that Ca1-AB has a much higher technological efficiency (12 times higher) and a lower treatment cost (over 50 %) compared to AB. All these results demonstrate the usefulness of this adsorbent in practical applications. • Ulva intestinalis -based biosorbents are used for the removal of phosphate ions. • Activation of algae biomass with 1 N Ca(NO 3 ) 2 allows obtaining the most efficient biosorbent. • Maximum biosorption capacity was 158.73 mg phosphate ions per g of biosorbent. • Desorption of phosphate ions occurs through a ligand exchange process. • Technological and economic performances recommend this biosorbent for large-scale applications.