Adsorption Characteristics of Modified Magnetic Coffee Waste for Removal of Tetracycline from Water

Abstract

Tetracycline (TC) is applied in many areas as a broad-spectrum antibiotic. However, TC is hardly absorbed by organisms. Most of them released and can increase the resistance of bacteria. In this point of view, plenty of TC usage will make much burden to the water environment. Therefore, it requires removal from water.

In this work, the coffee waste (CW) was used as an adsorbent to remove TC from water. The CW was modified by depositing a layer of magnetic iron oxide to synthesize magnetic coffee waste (M-CW). The characterization of CW and M-CW was performed using a scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), x-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier Transform Infrared Spectroscopy (FT-IR). The batch adsorption experiments were conducted to investigate the effect of pH, adsorbent dosage, TC concentration, and time on adsorption. Furthermore, the mechanism of adsorption was studied by kinetics (zero-order, pseudo-first order, pseudo-second order, Elovich, and intra-particle diffusion) and isotherms (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich). Also, the response surface methodology (RSM) was employed to model and optimize the combined effect of factors on TC removal using M-CW. The empirical model was developed, statistically established through analysis of variance (ANOVA), and experimentally verified to represent adsorption of TC on M-CW. The model was adopted to identify optimum removal conditions to remove TC from water.

The characterization work shows that iron oxide (35 w/w %) was successfully deposited on M-CW. The batch experiments showed that the TC is removed best at weak acidic to neutral conditions (pH: 5-7). M-CW dosage at 0.25g/L, the TC adsorption capacity up to 127mg/g. After 56hours, the adsorption process reaches equilibrium. The experiment data fitted Pseudo-second order, Elovich, and the Langmuir model well. The theoretical maximum TC uptake capacity can be up to 102 mg/g, as calculated using the Langmuir model. It was observed that over 95% TC can be removed by M-CW at optimized conditions using RSM. This study may facilitate further investigations into the application of using waste material to remove micropollutants from water.