Skip to main content

Assessment of nitrogen containing disinfection by-products and their precursors in drinking waters of the Mediterranean Basin

Final Report Summary - N-DBPS (Assessment of nitrogen containing disinfection by-products and their precursors in drinking waters of the Mediterranean Basin)

Disinfection of drinking water is a successful measure to reduce water-borne diseases and protect health. However, epidemiological evidence links bladder cancer to disinfection by-products (DBPs) formed during drinking water treatment. Disinfection with chlorine is relevant in many European countries and previous research has highlighted the need to improve water quality and decrease concentration of DBPs in countries of the Mediterranean Basin such as Spain. In particular, of the many DBPs currently investigated in drinking water, unregulated nitrogen containing DBPs (N-DBPs) are considered among the most toxic ones. Dissolved organic nitrogen, which acts as precursor for these DBPs, is increasing in many drinking water sources due to usage of impaired waters or climate change. Therefore, there is a need for research to prepare water utilities for these changes, evaluate treatment strategies, and consider the need for adaptation to more stringent regulations. By improving our knowledge on N-DBP precursors, engineered strategies can be better tailored to mitigate its formation and reduce their presence in our water networks. The first objective of this project was to generate knowledge on the occurrence of N-DBPs and its precursors during the production of both drinking and recycled water. The second objective was to develop analytical methodologies to provide early detection methods for smart decision taking to avoid the presence of N-DBPs in final waters.

The first step of the project was to establish the DBP analytical capabilities at the host institution. To this aim, we developed and implemented a gas chromatograph coupled to a mass spectrometer (GC/MS) method to measure volatile DBPs. A solid phase microextraction (SPME) methodology was also optimized for extraction of the following DBPs: 4 trihalomethanes (THMs), 4 haloacetonitriles (HANs), 2 halopropanones, 1 halonitromethane. The limit of quantification of this methodology was 0.1 µg/L. Additionally, we development and implemented a GC/MS method with SPME to measure N-nitrosodimethylamine (NDMA). This methodology had a limit of quantification of 50 ng/L. Finally, an adaptation of a solid phase extraction (SPE) methodology to enable measurement of NDMA by GC/MS at concentrations below 50 ng/L was also implemented. The limit of quantification of this methodology was 1 ng/L and it was used during research of NDMA concentration of final drinking waters.

Once the analytical capabilities were established at the host institution, we monitored different drinking water treatment plants from Spain. In all cases, regulated DBPs were found below guideline levels and non-regulated ones were found below the limits (if available) proposed by the World Health Organization. Different treatment trains were studied to evaluate the removal of the precursors. Among them, conventional treatment based on coagulation-filtration, granular activated carbon (GAC), ozonation and reversed electrodyalisis used for production of drinking water studied. All of them proved efficiency to remove N-DBP precursor. Moreover, a pilot plant including a nanofiltration (NF) membrane followed by a membrane bioreactor (MBR) used for water recycling was investigated. We observed that N-DBP formation potential removal by the NF membrane was above very high and that N-DBP formation potential removal by the MBR was superior during aerobic operation. Finally, we also compared the performance of the MBR with conventional activated sludge (CAS), and observed that MBR removes better N-DBP precursors than CAS during aerobic operation while CAS performs better than the MBR during anoxic operation.

Finally, an analytical method based on extraction followed by online SPE-liquid chromatography coupled to mass spectrometry was developed during this study to detect specific N-DBP precursors. This method can detect 15 precursors of N-DBPs in less than 10 minutes with minimal handling of the samples (only requires filtration). The main advantages of the developed method are high sensitivity (limits of detection in the sub ng/L range), selectivity due to the use of tandem mass spectrometry, precision and minimum sample manipulation as well as fast analytical response. We used this method to evaluate the presence of N-DBP precursors in different drinking waters from Spain.

Additionaly, as part of the validation procedure, the method was applied in a sampling campaign for the analysis of influent and secondary effluent of a wastewater treatment plant (WWTP) in Girona, Spain. Finally, the effluent from a nanofiltration (NF) membrane system used for water recycling was also monitored. The percentage of NDMA formation explained by the measured precursors was also quantified.The compounds selected could explain around 10% of the NDMA formation potential found in the three different matrices.