Temperature effects on Henry's law constants for four VOCs in air-activated sludge systems

A single equilibration technique (SET) was adopted to measure the air–water dimensionless Henry's law constants (KH) and the air-activated sludge mixed liquor ones (K′H) for volatile organic compounds (VOCs). Hydrophilic VOCs (methanol and isopropanol) and hydrophobic ones (toluene and p-xylene) were used as target compounds. Deionized water (DI water) and DI water suspended with a pasteurized activated sludge (the mixed liquor) were used as testing liquids. Mixed liquor suspended solid (MLSS) concentrations were from zero to approximately 40,000 mg L−1 and the equilibrium temperatures from 288 to 303 K. Results indicate that for the hydrophilic compounds K′H/KH raised slightly with increasing MLSS in the mixed liquor. K′H/KH for the hydrophobic compounds raised with the increasing MLSS, and the maximum decreases of K′H from KH were 86–88% (288 K) and 68–73% (303 K) for MLSS=40,000 mg L−1. Temperature variations of K′H could reasonably be regressed by the van’t Hoff's equation and the phase change enthalpy ΔH′ increase approximately linearly with increasing MLSS for hydrophobic toluene and p-xylene. K′H variation can be controlled by MLSS concentration and temperature in activated sludge system. Lower temperatures and higher MLSS concentrations should result in a lower K′H for hydrophobic VOCs, while higher MLSS concentrations in a higher K′H for hydrophilic VOCs.