ODOURS EMITTED FROM DISSOLVED AIR FLOTATION UNITS

Abstract

The dissolved air flotation (DAF) units at Bedok Wastewater Treatment Plant was considered as a source of malodour nuisance. This study was carried out to identify the malodorous air at the unit by gas chromatography-mass spectrometric (GC-MS) technique. On-site preconcentration of the air samples was carried out using Tenax-GC packed cartridge tube as the sampling trap. The trapped compounds were then desorbed on the GC-MS to obtain the chromatographic profile. Compounds which were present in the air at the DAF were found to consist mainly the aliphatic hydrocarbons from C9 to C14. The odorous compounds detected was toluene, meta-, para- and orthoxylene, phenol, dimethyl disulphide and dimethyl disulphides, ethylbenzene, propylbenzene, chloroethylene, chlorobenzene and the higher alkyl benzene. Phenol was found to be the most dominant compound detected. Pilot test was carried out to evaluate the performance of granular activated carbon and a chemisorbent, viz. Purafil, in removing the malodorous air emitted from the dissolved air flotation unit. The granular activated carbon columns were found to be very effective in adsorbing almost all the compounds present in the untreated air. The Purafil was not effective in removing the bulk of the hydrocarbon compounds. However, sensory analysis of the filtered air showed that Purafil was most effective for the treatment of the malodours.