Characterization of a Biologically Treated Wastewater from Oil Reclaiming: Recording of Low Molecular Weight Organics and Estimation of Humic Substances

Wastewater originating from oil reclaiming (COD about 300 mg/l, TOC about 70 mg/l) which was pretreated by equalization, neutralization, adsorption to activated sludge from a publicly owned treatment work, flocculation, and flotation and finally oxidized in an activated sludge process was analyzed for humic acids and gas chromatographically detectable organic compounds. The humic acid concentration was estimated to represent about 15% of the COD. Hydrocarbons were detected in activated sludge, but no hydrocarbons were identified gas chromatographically. In the two analyzed wastewater samples ethers (mainly containing polyethoxy structures), carboxylic acids and carboxylic acid esters were found. In one sample several nitrogen compounds (amines and amides) were detected. Except for 1,1'-oxybis-(2-methoxy)-ethane, which was a constituent of both samples, the organic gas chromatographically detectable compounds differed completely from sample to sample. This is obviously due to changing composition of the processed spent oils.