Fate of N-nitrosodimethylamine and its precursors during a wastewater reuse trial in the Llobregat River (Spain)

In summer 2019, a full-scale trial was carried out to investigate the effects in drinking water quality when
tertiary treated wastewater was discharged into the Llobregat River upstream of the intake of one of the major
drinking water treatment plants of Barcelona and its metropolitan area. Two scenarios were investigated, i.e.
discharging the reclaimed water with and without chemical disinfection with chlorine. This study investigates
the concentration of N-nitrosodimethylamine (NDMA) as the specific disinfection conditions employed in this
trial may favor its formation. To this aim, both NDMA and NDMA formation potential, were measured. The river
contained NDMA at very low concentrations, but the concentration of NDMA precursors was already high. The
NDMA concentration was reduced from discharge to the river to drinking water intake probably due to a
combined effect of dilution and photolysis. The formation potential was also reduced probably due to dilution
and biodegradation. The concentration of NDMA in the drinking water was always low (<7.3 ng/L), although the
formation potential was above 10 ng/L in one sample. Dissolved organic matter characterization by high resolution
mass spectrometry revealed differences between the nature of the organic matter in the river before and
after reclaimed water discharge.