RESUMO
In this study, chitosan-modified bentonite was synthesized using the coprecipitation method. When the Na2CO3 content was 4% (weight of soil) and the mass ratio of chitosan to bentonite was 1:5, the adsorption performance of the chitosan/bentonite composite was best. The adsorbent was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller measurement. Various characterization results demonstrate that chitosan successfully entered the bentonite interlayer and increased layer spacing but did not modify bentonite's laminar mesoporous structure, and the -CH3 and -CH2 groups of chitosan appeared on chitosan-modified bentonite. Tetracycline was used as the target pollutant in the static adsorption experiment. The adsorption capacity was 19.32 mg/g under optimal conditions. The adsorption process was more consistent with the Freundlich model and the pseudo-second-order kinetic model, indicating that it was a nonmonolayer chemisorption process. The adsorption process is a spontaneous, endothermic, entropy-increasing process, according to thermodynamic characteristics.
RESUMO
In northwest China, the limited amount of water resources are classified mostly as brackish water. Nanofiltration is a widely applied desalination technology used for brackish water treatment; however, membrane fouling restricts its application. Herein, we modified the membrane with triethanolamine (TEOA) and optimized the operating conditions (transmembrane pressure, temperature, and crossflow velocity) to control the nanofiltration membrane fouling by brackish water. Based on the physiochemical characteristics and desalination performance of the prepared membranes, the membrane modified with 2% TEOA (MPCM2) was identified as the optimal membrane, and 0.5 MPa, 25 °C, and 7 cm/s were identified as the optimal operating conditions through a series of nanofiltration experiments. Moreover, the membrane cleaning procedure for fouled MPCM2 was further determined, and a two-step cleaning procedure using ethylene diamine tetraacetic acid disodium followed by HCl with a permeance recovery rate of 98.77% was identified as the optimal cleaning procedure. Furthermore, the characterizations of the fouled and cleaned MPCM2 showed that the optimized cleaning procedure could recover the properties of MPCM2 to near virgin. This study is of great significance for the long-term stable operation of nanofiltration processes in brackish water treatment to ensure the supply of healthy water in the water-deficient areas of northwest China.
