ORGANIC-COMPOUNDS AT DIFFERENT STAGES OF A REFINERY WASTE-WATER TREATMENT-PLANT

In this study organic compounds in dichloromethane extracts of wastewa ter samples taken at different stages of a mineral oil refinery wastew ater treatment plant were analysed by gas chromatography using a mass selective detector. Main constituents of the raw wastewater were n-alk anes, iso-alkanes, cyclic alkanes, aromatic hydrocarbons, and phenols. Also small concentrations of some heterocycles were detected. The dat a suggest that flotation is a suitable pre-treatment step for removing the major part of alkanes, aromatics and phenols. The flotation prote cts biological stages against inhibitory effects of e.g. phenols. The activated sludge process removes most of the remaining gas chromatogra phically detectable organics and only three iso-alkanes, traces of car boxylic acids and - exhibiting the highest concentration - acetic acid 2-(2-butoxyethoxy)-ethyl ester were found in the clarified effluent o f the activated sludge process. These detected substances cannot expla in the relatively high COD of the sedimentation effluent and it is ass umed that the main part of the COD of the biologically treated mineral oil refinery wastewater is represented by humic material formed in th e activated sludge process. As in the raw wastewater also volatile aro matics (e.g. toluene, xylenes, ethylbenzene) were detected it is recom mended to collect and treat the off-gas of notation units applied for petrochemical wastewater purification.