Assessment of the pollutant elimination efficiency by gas chromatography/mass spectrometry, liquid chromatography–mass spectrometry and –tandem mass spectrometry: Comparison of conventional and membrane-assisted biological wastewater treatment processes

Abstract

The elimination efficiency of advanced conventional biological wastewater treatment was compared to membrane-assisted biological wastewater treatment. The sum parameter analyses dissolved organic carbon (DOC) and chemical oxygen demand (COD) or substance-specific analyses such as gas chromatography combined with mass spectrometry, flow injection analysis (FIA–MS) and liquid chromatography (LC–MS) in combination with mass or tandem mass spectrometry (MS–MS) were applied to assess elimination of hardly eliminable compounds in both types of wastewater treatment plants (WWTP). Reduction of DOC and COD in wastewater treatment processes confirmed a favourable elimination efficiency. Substance-specific methods which were applied in addition permitted a qualitative and semi-quantitative assessment of elimination with a visual pattern recognition approach. In order to identify pollutants either the NIST library of electron impact mass spectra for unpolar compounds or the laboratory-made collision-induced dissociation spectra library for polar pollutants was used. To assess elimination efficiency FIA–MS in the selected ion monitoring mode (SIM) besides high selective substance-specific mass spectrometric techniques such as parent ion scans and neutral loss scans were used for quantification. Results proved that membrane-assisted treatment was more effective than advanced biological treatment. In both types of WWTPs predominantly unpolar pollutants were eliminated, while all effluents were dominated by polar compounds of anthropogenic and biogenic origin. These unpolar and polar compounds which had been identified as hardly eliminable are reported about. Quantitative results obtained by FIA–MS, LC–MS and MS–MS for the elimination of alkyl polyglycol ethers, nonylphenol ethoxylates and linear alkylbenzenesulfonic acids from wastewater are presented.