Solid-state 13C NMR to assess organic matter transformation in a subsurface wetland under cheese-dairy farm effluents

Solid-state 13C NMR were used to follow organic matter transformation in a subsurface wetland under the effluent of a small cheese-dairy farm under a Mediterranean climate. The results showed that the ratios commonly used to quantify humification, (aromaticity and Alkyl-C/O-Alkyl-C ratios) can be considered as relevant chemical indicators of organic matter transformation. Polysaccharides were transformed throughout the subsurface wetland whereas aromatic, phenolic and alkyl compounds accumulated. Furthermore, Phenolic-C signal and O-Alkyl-C signal were negatively correlated to proteases and β-galactosidase activities showing that recalcitrant molecules actually accumulated. These results were correlated with high purification yields: the average decrease in chemical demand in oxygen was 90.75% and that in Total Kjeldahl Nitrogen was 75.65%. Thus subsurface wetlands can be considered as an efficient technology to purify effluents with high organic matter contents, such as cheese-dairy effluent, under drastic climate conditions. Furthermore this study highlights the fact that solid-state 13C NMR is a suitable tool to follow organic matter transformation.