Comparison of liquid-liquid extraction system and extraction-evaporation system for high concentrations of phenolic wastewater

Liquid-liquid extraction system (LLES), including extraction section and reverse extraction section, had been applied successfully in the treatment of phenolic wastewater. In this paper, a novel pilot scale system, the extraction-evaporation system (EES) without reverse extraction section was introduced. The treatment capacity of both LLES and EES reached 4.0 m(3)/h. According to experimental results and econornical analysis, EES had higher removal efficiency and lower treatment cost than those of LLES in the treatment of the phenolic wastewater containing 3,200-6,300 mg/L phenol, the concentrations of most resin and dye industrial effluents. The highest extractive efficiency of EES could reach 99.0% within the concentration range of 4,000-5,000 mg/L phenol, and remnant phenol in wastewater varied from 43.6 to 51.2 mg/L. The highest extracted efficiency in LLES arrived at 98.2% and the remaining phenol concentration reached 95.0 mg/L. The average removal efficiency of EES increased 1%, and the treatment cost of EES decreased 4.6%. The pretreated wastewater by EES was able to meet the demands of biological or adsorptive process. Despite that the total investment cost of EES was higher than that of LLES, treatment cost of wastewater per ton by EES was lower than that of LLES.