# Optimizing Modified Activated Carbon Fiber for Organic Pollutant Removal from Reverse Osmosis Concentrate: Response Surface Modeling and Optimization

## TL;DR

This study explores using iron-modified activated carbon fiber to efficiently remove organic pollutants from reverse osmosis concentrate, optimizing conditions for maximum effectiveness.

## Contribution

The novel contribution is the development and optimization of Fe-ACF for ROC treatment using response surface methodology and detailed adsorption mechanism analysis.

## Key findings

- Fe-ACF adsorption is primarily governed by chemisorption and intraparticle diffusion.
- The Langmuir–Freundlich model best fits the adsorption isotherm with a maximum capacity of 12.21 ± 0.80 mg/g.
- Optimal adsorption occurs at pH 4.18, 34.63 °C, 547.91 rpm stirring, and 1.55 g/L adsorbent dosage.

## Abstract

The adsorption of organics in ROC by Fe-ACF is mainly dominated by chemisorption.

The Langmuir–Freundlich isotherm model provided the best fit to the experimental data.

RSM analysis confirmed that pH is the dominant factor affecting Fe-ACF’s adsorption.

The adsorption mechanism involves hydrogen bonding, π–π interactions, surface complexation, among others.

Reverse osmosis concentrate (ROC) contains relatively high levels of refractory organic pollutants, posing significant challenges due to its difficult treatment and high environmental risks. Therefore, efficient and convenient removal strategies are essential. In this study, a self-developed iron-modified activated carbon fiber (Fe-ACF) was employed as an adsorbent to remove organic pollutants from ROC. Additionally, response surface methodology (RSM) was applied to model the adsorption process, identify and evaluate key influencing parameters, and optimize operational conditions. The adsorption mechanisms and regeneration stability of Fe-ACF were also investigated. Kinetic analysis revealed that the adsorption process is predominantly governed by chemisorption, with intraparticle diffusion identified as the primary rate-limiting step. Isothermal adsorption studies demonstrated that the Langmuir–Freundlich model best describes the adsorption behavior, yielding a theoretical maximum adsorption capacity of 12.21 ± 0.80 mg/g. Thermodynamic analysis confirmed that the adsorption process is spontaneous, endothermic, and driven by an increase in entropy. The RSM optimization identified pH as the dominant factor. The optimal adsorption conditions were a pH of 4.18, a temperature of 34.63 °C, a stirring speed of 547.91 rpm, and an adsorbent dosage of 1.55 g/L. The adsorption mechanism involves hydrogen bonding, π–π interactions, surface complexation, and electrostatic forces. Fe-ACF exhibits competitive regeneration stability and structural integrity. In summary, Fe-ACF demonstrates significant potential as a treatment material for ROC.