Abstract
Effective regeneration of powdered activated carbon (PAC) is the key to reduce the operating cost of the PAC in wastewater treatment processes. In this study, volatile acetone and semi-volatile aniline were selected to investigate the regeneration characteristics of ultrasonically enhanced low-temperature thermal process. The results showed that the regeneration efficiency of the PAC that had adsorbed aniline or acetone increased with the increase in ultrasonic power, and optimal value of frequency and regeneration times were determined. The concentration and properties of organic solvents had a significant influence on the ultrasonic regeneration process. With the increase in heating temperature and regeneration time, the regeneration efficiency increased, but the loss of mass of the saturated PAC increased noticeably. With the combination of ultrasonic treatment in a solvent with low temperature heating, the PAC regeneration efficiency was successfully improved, and the PAC mass loss rate was noticeably reduced. The microjet, shock wave, and cavitation effects produced by ultrasonic treatment restored the specific surface area of the PAC, expanded its mesopore volume, and increased the pore diameter. A reasonable selection of the regeneration solution and optimization of the ultrasonic treatment conditions could create favorable conditions for subsequent low temperature thermal regeneration.
Highlights
As a broad-spectrum adsorbent, powdered activated carbon (PAC) can adsorb various pollutants in water, such as refractory organic compounds [1], humic acid [2], microbial metabolites [3], and heavy metals [4]
When the ultrasonic power was increased from 60 to 180 W, the regeneration efficiency of the PAC adsorbed aniline increased from 45.60% to 62.29%, and that of acetone increased from 30.89% to 45.30%, respectively (Figure 1a)
The results showed that the regeneration efficiency of the PAC could be improved by prolonging the ultrasonic treatment time properly, but after a certain regeneration time was reached, the regeneration efficiency of the PAC remained basically unchanged, and even decreased in some instances
Summary
As a broad-spectrum adsorbent, powdered activated carbon (PAC) can adsorb various pollutants in water, such as refractory organic compounds [1], humic acid [2], microbial metabolites [3], and heavy metals [4]. It is widely used for the purification of source water [5], emergency water treatment [6], and advanced treatment of printing–dyeing wastewater [7]. Due to the fact that PAC is a costly material [8], it is usually regenerated and recycled when it is used in a water or wastewater treatment process. The thermal regeneration method is subdivided into low-temperature (105 ◦ C–200 ◦ C) and high-temperature (450 ◦ C–900 ◦ C)
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