Changes in the organic composition of wastewater during biological treatment as studied by NMR and IR spectroscopies

Despite its importance, relatively little is known about the composition an d fate of wastewater organic matter (OM) in treatment plants. Monitoring th e chemical changes in OM during activated sludge treatment can improve our knowledge of the processes involved in the biological elimination of OM. Di rect chemical analyses of treated water OM typically account for about 20% of the OM, and structural information was obtained in this study using Nucl ear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) spectros copic techniques. Distinct changes in the OM during wastewater biological t reatment were underlined. C-13 and H-1 NMR showed that aromatic carbons wer e minor constituents of the samples. Alkyl chains exhibited a more highly b ranched character in treated water, as compared to long chain aliphatic car bons present in wastewater. Carboxyl signals in the 13C NMR spectrum of was tewater could be due to peptide bonds in proteins, whereas in the treated w ater spectrum, this signal could be related to the presence of non-proteina ceous nitrogen. Besides the non-degraded compounds, treated water OM could contain recondensation products of simple molecules. Their refractory chara cter probably derives from their complex structures rather than from partic ular chemical functions, as suggested by the lack of fundamental difference s in the chemical structures of wastewater and treated water OM.