Cyclic solubilization and release of polycyclic aromatic hydrocarbons (PAHs) using gemini photosensitive surfactant combined with micro-nano bubbles: a promising enhancement technology for groundwater remediation

Abstract

Polycyclic aromatic hydrocarbons (PAHs) have posed serious risks to the groundwater environment. Surfactant-enhanced remediation (SER) is a promising strategy, as it can increase the solubilization efficiency of PAHs contaminants. However, this technology is still hampered due to low efficiency and high cost for the separation of pollutants after solubilization. Through the combination of micro-nano bubbles (MNBs) with a gemini photosensitive surfactant (N1, N2-bis[4-[4-[(4-butylphenyl) azo] phenoxy] butyl]-N1, N2-tetramethylethane-1,2-diammonium bromide, AzoPBT), herein we present a significantly enhanced efficiency of phenanthrene (Phe) solubilization and surfactant cycling. Notably, the presence of MNBs was conducive to the dissolution and release of Phe by reducing the CMC and γ of trans-AzoPBT (from 0.52 mmol/L and 28.94 mN·m−1 to 0.39 mmol/L and 27.88 mN·m−1) and increasing the difference of interfacial properties between trans and cis-AzoPBT, which was owing to the electrostatic interaction. Groundwater chemical parameters, i.e., ions, pH and organic matter would affect the solubilization ability of trans-AzoPBT. Mg2+ and Ca2+ inhibited the solubilization while SO42− promoted the solubilization, depending on their radius, electronic quantity and solution pH. A change in the HA level up to 8 mg/L had a negatively effect on the solubilization ability. High release rate (69.39 %) of cis-AzoPBT for Phe and high recovery rate (89.37 %) for tans-AzoPBT were obtained in the AzoPBT/MNBs mixed aqueous solution. Compared to MNBs combined with conventional cationic surfactants, AzoPBT/MNBs mixed aqueous solution exhibited better synergistic solubilization performance, and the apparent solubility of Phe increased from 26.74 % to 31.61 %. Overall, this study demonstrates the enhanced solubilization of PAHs by photosensitive surfactants combined with MNBs, which provides valuable insights of the effective utilization of surfactants in the remediation of PAHs-contaminated groundwater with SER technology.