Odors from Dissolved Air Flotation Process

The complex mixture of gaseous compounds directly above the dissolved air flotation (DAF) unit of a wastewater treatment plant is simultaneously scrubbed through four filter columns, each filled with a commercial grade of activated carbon, until odor breakthrough as determined by an odor panel, had occurred. Air samples are collected at the influent and effluent ports of the activated carbon columns for analysis on a gas chromatograph-mass spectrometer (GCMS) system and for determination of odor levels by dynamic olfactometry. The capacity of each activated carbon grade for removing the odor emitted at the DAF unit is then evaluated. Compounds which may cause the odor in the DAF air are identified to be toluene, meta-, and orthoxylenes, phenol, dimethyl sulphides, alkyl benzenes, and chlorinated hydrocarbons such as chlorobenzenes. These compounds are effectively removed by activated carbon. Organoleptic tests reveal that the odor concentration of the odorous DAF air averaged about 35 standard odor units (SOU)/m3. The capacity of the activated carbons tested ranges from about 2,650 SOU kg to 13,960 SOU kg. The alkali-impregnated carbons are found to be less effective than the nonalkali-impregnated carbons in the treatment of the odorous gases from the DAF unit, even though previous research has shown them to be most effective when hydrogen sulphide and other sulphides are present in the off-gas stream.