Impacts of chloride-form anion exchange seawater regeneration performance

ABSTRACT

Seawater was investigated as an alternative regenerant source to conventional salt-imported brine solutions in an anion exchange process treating surficial Florida coastal groundwater for the removal of sulfate and organics. Bench-scale column testing revealed that filtered Sarasota Bay seawater efficiently regenerated the anion resin media; however, sulfate exchange capacity decreased by 8.42% compared with conventional 10% salt regeneration methods. Addition of 3% sodium chloride increased regeneration efficiency, reduced exchange capacity losses to 2.4% as compared to conventional 10% salt regeneration methods. Regeneration resulted in 2.13 mg/L of bromide leakage; however, addition of 3% sodium chloride to seawater reduced bromide leakage to 1.25 mg/L. A correlation between bromide exchange and the regenerant chloride-to-bromide molar ratio (CBMR) was observed, yielding less bromide exchange at higher CBMRs. Bromide adsorption followed pseudo 2nd order kinetics and chemisorption was the rate controlling step. Increasing the CBMR of the regenerant was found to shift adsorption behaviour, allowing intra-particle diffusion to occur sooner. Bromide equilibrium appeared to follow a logarithmic decay as the CBMR of the regenerant increased. Intra-particle and film diffusion mechanisms were evaluated that indicated the presence of diffusion-based processes and more than one rate controlling step. An empirical function was derived to approximate bromide equilibrium adsorption in relation to a regenerant’s CBMR. Seawater as a regenerant when enhanced with sodium chloride shows promise as an anion exchange regenerant; additionally, classification of a seawater regenerant’s CBMR can provide insight into the kinetic and equilibrium relationships of bromide exchange.

GRAPHICAL ABSTRACT

KEYWORDS:

• Anion exchange
• bromide
• chloride-to-bromide molar ratio
• equilibrium and kinetics
• seawater regeneration

Acknowledgments

The research reported herein was funded, in part, on behalf of the City of Sarasota Utilities Department via UCF agreement 16208213. Additional funding was provided by UCF’s Research Foundation’s Jones Edmunds Fund 1620-8A22. The opinions and findings expressed in this research are those of the authors and do not necessarily reflect the view of UCF (Orlando, FL) or its Research Foundation. The contributions of students in the UCF Water Quality Engineering Research Group who assisted in field and laboratory work are greatly appreciated. The data that support the findings of this study are available from the corresponding author upon reasonable request.

Data availability statement

Please be advised that the data that support the findings of this study are available from the corresponding author, S.J Duranceau, upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by City of Sarasota Florida: [grant number 1620-8213]; Jones Edmunds Research Fund: [grant number 1620-8A22].