Hydrophobic deep eutectic solvents for the sono-degradation of organic pollutants in wastewater

Phenol and 4-nitrophenol (4-NP) are hazardous, recalcitrant, and biorefractory contaminants found in wastewater generated from process industries. Even in low concentrations, they are highly poisonous. The degradation of these pollutants in wastewater is imperative due to their solubility in water and their toxicity to the biosphere. In this study, two long-chain, organic acid based hydrophobic deep eutectic solvents (HDESs) were prepared, characterized, and used in synergy with hydrogen peroxide for the ultrasonic degradation of these pollutants in wastewater. These HDESs are menthol–decanoic acid (MC 10 ) and menthol–dodecanoic acid (MC 12 ). The HDESs were used in synergy with hydrogen peroxide for the degradation of phenol and 4-NP. The effects of different process variables such as pH, oxidant dose, temperature, and time on phenol and 4-NP degradation efficiency in simulated wastewater were studied. For phenol degradation, pH 4 provided the best result while for 4-NP, pH 5 provided the best result. For the MC 10 -HDES/H 2 O 2 system, an oxidant dose of 15% v/v and temperature 60 °C yielded the best degradation efficiency of 76% for phenol and 94.46% for 4-NP while for the MC 12 -HDES/H 2 O 2 system, an oxidant dose of 17% v/v and temperature 60 °C yielded the best degradation efficiency of 58.98% for phenol and 61.08% for 4-NP. The process parameters with the best results were then used to treat refinery wastewater. The percentage reductions in total organic compounds (TOC) were 88.75 and 67.08% for MC 10 - and MC 12 -HDES/H 2 O 2 systems respectively. The recyclability of the HDESs was also investigated for three runs. The percentage of TOC reduced from 88.75 to 33.33% for MC 10 and from 67.08 to 11.25% for MC 12 . These results prove this process to be effective for the treatment of wastewater contaminated with phenol and 4-NP.