Treatment Of Gallic Acid Production Wastewater By Extraction And Biological Process

Alkali hydrolysis is the major production process of gallic acid in China. Wastewater produced from the alkali hydrolysis process contains a high level of salt, organic compounds and gallic acid which is economically valuable. On account of the bacteriostasis of gallic acid, the treatment of the wastewater is difficult. There wasn’t an effective gallic acid recovery technology and biosafe disposal treatment technology. Consequently, recycling gallic acid from gallic acid production wastewater and biosafe disposal treatment were investigated in this paper.Compared with other gallic acid recovery process, extraction process has the advantage of high efficiency, simple operation, the recoverable extractant and low cost. The extractants that have been reported in literatures are stripping inefficient. To recover high-purity gallic acid, it is needed to find an extratant with high efficiency in extraction and stripping process. In the paper, MIBK and30%TBP-kerosene was screened out from four extractants, MIBK,30%TBP-kerosene, butanol and EA. A series of extraction and stripping experiments were carried out using these two extractants, the main conclusions are as follows:The pH value of extraction raffinate should be controlled to be under2.5in the extraction process, and be controlled from7to8in stripping process while using MIBK as extractant. And the pH value of extraction raffinate should be controlled to be under3in the extraction process, and be controlled from6to10in stripping process while using30%TBP-kerosene as extractant. The multistage extraction rate using these two extractants could reach90%by choosing the phase ratio at1, with the initial pH value of wastewater lower than2.5. The extraction rate could be improved by increasing the phase ratio. The third phase produced in extraction process using30%TBP-kerosene as extractant could be eliminated by cationic polycrul amide pretreatment of gallic acid wastewater. The third phase produced in stripping process using30%TBP-kerosene as extractant could be eliminated by adjusting pH.The raffinate was diluted and treated by expanded granular sludge bed and biological contact oxidation tank. The results showed that the COD removal rate of the anaerobic process kept above60%, and the maximum organic load of the anaerobic process reached17.27kg-(m3·d)-1The COD removal rate of biological contact oxidation tank was not stable, but basically kept above60%. The COD concentration of effluent from one-stage biological contact oxidation tank ranged from300to400mg-L"1stably. The COD concentration of effluent from two-stage biological contact oxidation tank could be lower than200mg-L"1.Advanced treatment of the effluent from biological treatment process was investigated by different methods. The results showed that color and COD concentration of the effluent by PFC flocculation, Fenton treatment and activated carbon adsorption could meet the national emission standards.