Application of recyclable nano zero-valent iron encapsulated L-cysteine catalytic cylinder product for degradation of BTEX in groundwater by persulfate oxidation

Abstract

Abstract Benzene, toluene, ethylbenzene and xylene (BTEX) possess a negative impact on the environment and human beings due to their highly toxic and carcinogenic properties. In this study, persulfate (PS) activated by nano zero-valent iron (nZVI) coupled with chelated L-cysteine (L-cys) process was investigated for BTEX degradation in contaminated groundwater. BTEX degradation had a significant acceleration and improvement with the removal from 62.7 to 100% along with the increasing dosage of L-cys from 0.12 to 0.27 M in 24 h. Further, the compact nZVI catalytic cylinder and nZVI encapsulated L-cys catalytic cylinder were successfully manufactured by encapsulating nZVI, and nZVI and L-cys together with additives of cement, river sand, stearic acid (SA) and zeolite. The SEM image, XRD patterns and FTIR spectra showed that the manufactured catalytic cylinder had a porous structure and encapsulated nZVI and L-cys successfully. Six successive cycles of BTEX degradation were completed and the degradation rate decreased gradually in each cycle. The catalytic activity of nZVI encapsulated L-cys catalytic cylinder was superior to nZVI catalytic cylinder in each cycle. The electron paramagnetic resonance (EPR) results indicated that HO• was the dominant active species in the BTEX degradation process. Benzoic acid (BA) scavenge experiments showed that L-cys could increase the yield of HO• in the PS/nZVI system. The HO• yields of PS/nZVI encapsulated L-cys catalytic cylinder system were 3.2 to 4.8 fold higher than those of the PS/nZVI catalytic cylinder system. The possible mechanisms of PS activation by nZVI encapsulated L-cys catalytic cylinder were supposed. Homogeneous Fenton reaction and heterogeneous catalysis on the nZVI surface are two co-existence mechanisms in the PS/nZVI encapsulated L-cys catalytic cylinder system. The findings of this study provide new insights into the mechanism of nZVI encapsulated L-cys catalytic cylinder activating PS, showing its potential applications for the remediation of groundwater.