Adsorption of Congo red and tetracycline onto water treatment sludge biochar: characterisation, kinetic, equilibrium and thermodynamic study

Abstract

In this study, readily available inexpensive water treatment sludge (WTS) was used to prepare adsorbent for the removal of Congo red (CR) and tetracycline (TC) from aqueous solutions. The structural characteristics and adsorption properties of WTS biochar were characterised via scanning electron microscope, energy dispersive X − ray spectroscopy, Brunauer − Emmett − Teller and Fourier Transform infrared spectroscopy. In batch experiments, the adsorption factors, kinetics, isothermal curves and thermodynamics of the adsorption properties were investigated. The optimum preparation condition of WTS biochar was 400 °C for 4 h under O2 − limited pyrolysis, which exhibited increased specific surface area and pore structures. The best adsorption was observed when the pH of the CR and TC solutions was 7 and 4, respectively. The adsorption process followed the pseudo − second − order model, indicating that the main control step was the chemical adsorption process. Isotherm data were best described by the Langmuir model, and the maximum adsorption capacities for CR and TC were 116.4 and 58.5 mg·g−1, respectively. Thermodynamic parameters revealed that the adsorption process was spontaneous and endothermic. According to the analysis, the adsorption mechanism of CR could be attributed to electrostatic attraction, π–π conjugation and hydrogen bonding, whereas that of TC was potentially associated with cation exchange, complex precipitation, π–π conjugation and hydrogen bonding.

Application of modified water treatment residuals in water and wastewater treatment: A review

“…A number of studies found that the optimal temperature range for thermal activation is up to 600 °C, after which crystalline transformation of amorphous Al/Fe WTRs into mineral crystals starts taking place [ 20 ]. Some of the researchers attempted to reuse WTRs by modifying it to a more reliable porous material, such as biochar via pyrolysis, an oxygen-limited thermal treatment, and hydrochar via hydrothermal carbonization [ 50 , 51 ]. This enhances its adsorption potential for various organic and inorganic pollutants by increasing adsorption sites related to Al and Fe [ 52 ].…”

“…It is the pH at which net surface charge on the surface become neutral and the numbers of positive and negative charges of the adsorbent are equal [ 6 ]. The pH pzc value aids in interpretation of the adsorption potential of modified WTRs under different pH values [ 1 , 51 ]. When the solution pH exceeds pH pzc , the surface of adsorbents is negatively charged showing strong potential to attract positively charged pollutants such as methylene blue, Pb 2+ and Cu +2 .…”

“…They suggested that both physio-sorption and chemical sorption including surface precipitation, electrostatic attraction, ion exchange and pore diffusion mechanisms are responsible for adsorption of MB on modified WTRs. In another study, He et al [ 51 ] reported that electrostatic attraction, π–π conjugation and hydrogen bonding governs the adsorption mechanism of Congo red dye on the surface of thermally treated WTR biochar. According to Chantaramanee et al [ 6 ], adsorption of MB molecules to surface of thermal and acid activated WTRs hold for both physio and chemisorption mechanisms.…”

Characteristics of Tetracycline Adsorption on Commercial Biochar from Synthetic and Real Wastewater in Batch and Continuous Operations: Study of Removal Mechanisms, Isotherms, Kinetics, Thermodynamics, and Desorption

“…To study the adsorption of TC onto biochar, the following kinetic models were used in their linear forms [23,28]:…”

“…The biochar produced at 700 • C achieved a maximum removal efficiency of approximately 47% at pH = 3 and a biochar dose of 1.25 g/L [22]. With biochar prepared from a water treatment plant's sludge and used for TC adsorption, the removal efficiency achieved was 96.72% at a biochar dose of 4 g/L and an initial TC concentration of 60 mg/L [23]. ZVI@biochar has been used to remove tetracycline, oxytetracycline (OTC), and chlortetracycline (CTC) from aqueous solutions and wastewater.…”