Determination of structure and origin of refractory organic matter in bio-epurated wastewater via spectroscopic methods. Comparison of conventional and ozonation treatments

With the widely used activated sludge treatment most of the organic matter (OM) of wastewater can be removed, but the composition and origin of the refractory OM in treated water are poorly known. The structures occurring in treated water are more difficult to elucidate than those of the OM originally present in wastewater, since the classical hydrolysis-chromatography methods are not suitable for the analysis of such samples. C-13 and N-15 solid-state Nuclear Magnetic Resonance (NMR), liquid-state H-1 NMR and infrared (IR) were used in the present study. A treatment procedure including a stage of ozonation of the sludge, used to reduce the sludge production, was studied along with a conventional treatment line. The OM in the water treated through the ozonated line was mainly composed of proteins and sugars moieties, while the aliphatic compounds dominant in the wastewater were efficiently removed. The conventional treatment was more efficient in terms of OM removal hut led to the formation and/or enrichment of unknown products with high oxidation and branching levels. These products contained C=O groups, while the nitrogen was found in amide groups, refractory to the treatment.