Abstract
Henry’s law constant is an important equilibrium factor in the mass transfer process of volatile organic compounds (VOCs). A single equilibration technique (SET) was adopted to measure the air-water dimensionless (KH) and the dimensionless apparent (K’H) of Henry’s law constant in an air-wastewater system and air-activated sludge for VOCs at 298 K. Hydrophilic VOCs (methanol, isopropanol and acetone) and hydrophobic VOCs (toluene and p-xylene) were used as target compounds. Deionized (DI) water, (DI-water diluted and a pasteurized wastewater (abbreviated as wastewater) with a maximum dissolved total organic carbon (TOC) content of 700 mg/L) and DI-water diluted and pasteurized activated sludge (abbreviated as mixed liquor) with a maximum suspended solid concentration of 40,000 mg/L were used as liquids. K’H of the target hydrophilic compounds in the mixed liquor with a maximum-suspended solid concentration were 8.9 to 19.9% higher than those in DI water. Those for toluene and p-xylene decreased up to 70.8 and 88.3% in the mixed liquor, respectively. K’H of all the test compounds in the wastewater was only 1 to 11% smaller than those in DI water. A model was proposed for correlating K’H with wastewater TOC and activated sludge concentration using an organic carbon-water partition coefficient (KOC) and activated sludge-water partition coefficient (KP) as model parameters.
Highlights
Emissions of volatile organic compounds (VOCs) from wastewaters and exhaust gases are often overlooked as sources of exposure to hazardous substances
This study provides phase equilibrium information for hydrophilic and hydrophobic VOC treatment by bioscrubbers or bubble column
K’H Variation in Mixed Liquor and Wastewater Using the single equilibration technique (SET) method, experimental K’H data for methanol, isopropanol, acetone, toluene and p-xylene in mixed liquor at 298 K are shown in Fig. 1 K’H corresponding to MLSS = 0 was for compounds partitioning between air and DI water, i.e., K’H = KH
Summary
Emissions of volatile organic compounds (VOCs) from wastewaters and exhaust gases are often overlooked as sources of exposure to hazardous substances. A suspended-growth system includes a sorption unit which utilizes an activated sludge liquid as a scrubbing liquor followed by an aerated activated sludge reactor for further oxidation of the scrubbed contaminants (Overcamp et al, 1993; Burgess et al, 2001). For effective removal of the gaseous contaminants, equilibrium of VOCs between air, wastewater and activated sludge has become an important topic. The appearance of dissolved organic compounds (e.g., humic and fulvic acids) in water will affect the water solubility. The existence of suspended organic solids in liquid can enhance the solubility of VOCs of low water solubility. By the sorption of the biomass, the total VOC contents in the liquor will be raised; that is, the existence of biomass will increase the apparent solubility of VOCs in the liquor
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