The dewatered sludge from the production process of cassava alcohol plant was used as raw material. Response surface methodology was applied to optimize the preparation of cassava alcohol sludge activated carbon. At the same time, a series of characterization analysis was carried out for the optimal product, which was applied to the treatment of gallic acid wastewater. The results showed that the optimal preparation conditions were: activation temperature of 489℃, impregnation time of 14 h, activation time of 51 min, zinc chloride concentration of 21.53%, the adsorption iodine value under this condition was 521.64 mg/g. The results of characterization to CASAC suggested that the BET surface was found as 441.86 m2/g and the average pore diameter as 2.50 nm. It was full of different sizes of small pores on the carbon surface. The activated carbon owned a low metal content but more oxygen-containing functional group after activation process. The effects of carbon dosage, pH, contact time and solution temperature on the removal of gallic acid from water were investigated. It is suggested that the sample carbon could remove gallic acid efficiently, and the removal rate of gallic acid increased with the increase of carbon dosage and the decrease of pH value. The adsorption of gallic acid by cassava alcohol sludgy-based activated carbon was in line with pseudo second-order kinetics model as well as Freundlich isothermal model. The maximum adsorption capacity was 126.72 mg/g. The diffusion mechanism showed that the adsorption process was influenced by the diffusion of liquid film in addition to the diffusion within particles. Thermodynamic analysis indicated that the adsorption of gallic acid was a spontaneous process of heat absorption and entropy increase. This study provided a theoretical basis for the preparation of high-performance activated sludge and the application of high concentration of natural organic wastewater treatment.
The effect of different hydrophilic/hydrophobic humic acid on the removal of bromide adsorbed on magnetic ion exchange resin was studied. When the pH value of the solution was 7.0, the presence of four humic acid components (very hydrophobicity, slightly hydrophobicity, polar hydrophilicity, neutral hydrophilicity) reduced the removal efficiency of bromide. In contrast, the hydrophobic components of humic acid had the most significant adverse effect on the removal efficiency of bromide. Humic acid weakened the pH dependence of the adsorption process of bromide on resin. The fractions of humic acid can accelerate the adsorption rate of bromide. The adsorption equilibrium was attained quickly. With or without the fractions of humic acid, the kinetic processes of bromide adsorbed on resin agreed with the pseudo-second-order model. Because of the competitive adsorption, the humic acid fractions reduced significantly the equilibrium adsorption capacity of resin for bromide. The adsorption equilibrium can be simulated by Langmuir and Freundlich isotherm model. The existence of HA components can reduce the spontaneity of adsorption system, and the very hydrophobicity component had more significant effect. The results of this investigation were of great significance for the effective control of bromide in water sources.
