Nitrate Adsorption onto Unmodified Calcium–AlginateBeads: Equilibrium Behaviour and Adsorption Constraints

MieowKee Chan; Daria Kudritskaya; Nii Chien Ng; Yan Zu Ng; Tengku Faris Imran bin Tengku Amirruzaini

doi:10.70922/x1cwty85

Authors

MieowKee Chan SEGi University Author https://orcid.org/0000-0002-0805-9395
Daria Kudritskaya Author
Nii Chien Ng Author
Yan Zu Ng Author
Tengku Faris Imran bin Tengku Amirruzaini Author

DOI:

https://doi.org/10.70922/x1cwty85

Keywords:

adsorption, nitrate removal, langmuir , optimisation , alginate beads

Abstract

Excessive nitrate contamination in water bodies due to agricultural runoff and aquaculture effluents poses a serious threat to aquatic ecosystems and drinking water safety. Thus, a sustainable and cost-effective treatment technology is required. This study investigated the effectiveness and the adsorption mechanism of neat alginate beads for nitrate removal from aqueous solution. Alginate beads were synthesized via crosslinking a 2 wt% alginate solution in a 5 wt% CaCl2 solution and subsequently tested in batch experiments using nitrate solutions ranging from 10 to 100 ppm. The objectives of this study were to identify the most effective adsorbent dosage, ranging from 1 to 20 g, and determine the best-fitting equilibrium isotherm model. The results showed that the nitrate removal efficiency peaked at ~35% at the most effective dosage of 5 g. No significant improvement was observed at higher dosages due to bead aggregation. Isotherm analysis indicated the Langmuir model provided the best fit of R2 = 0.9701. This confirmed that adsorption was dominated by a monolayer mechanism on uniform sites. The calculated maximum adsorption capacity for the neat alginate was 0.414 mg/g. This was lower than the capacities achieved by modified alginate composites reported in literature. This indicated that the inherent functional groups of pure alginate beads were inadequate for practical, high-efficiency nitrate remediation. This highlighted the critical need for chemical modification or utilization of alginate in immobilized biological systems to enhance affinity and achieve competitive performance for nitrate removal.

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