Comparison of the formation of N-nitrosodimethylamine (NDMA) from algae organic matter by chlor(am)ination and UV irradiation

The role of biochar in algal source water treatment: Algal cells integrity and N-Nitrosodimethylamine (NDMA) formation potential

The effects of unmodified and modified biochars (BC) made by tea (TBC), coconut shell (NBC), corn straw (SBC), and orange peel (OBC) on algae removal efficiency and NDMA formation potential (NDMA-FP) in algae-containing water were investigated. The algae removals (12 %-45 %) and NDMA-FP reductions (1 %-20 %) were enhanced by unmodified BC, indicating that the potential application of BC in algae removal and NDMA formation risk control. Cu(Ⅰ/Ⅱ)-modified BC (Cu(Ⅰ/Ⅱ)-BC) significantly promoted algae removal efficiency (up to 80 %) with the most significant physical membrane damage to Microcystis aeruginosa (85-99 %), leading to an increase in NDMA-FP (21 %-31 %). In contrast, Fe(Ⅲ)-modified BC (Fe(Ⅲ)-BC) not only exhibited superior algae removal performance (5 %) with minimal physical damage (membrane damage rate < 15 %), but also provided better control over NDMA-FP (2 %-23 %). Fe(Ⅲ)-BC performed strong adsorption capacity for AOM, with an adsorption efficiency of up to 86 %. NDMA-FP control in algae-containing water by BC depended on its physical damage to cells and AOM adsorption. A positive correlation was observed between membrane damage and AOM adsorption. These findings support optimizing algal removal and NDMA-FP control in drinking water treatment.

Responses of Microcystis aeruginosa to polystyrene microplastics: Growth dynamics and implications for water treatment

The understanding of microplastics (MPs) has advanced significantly with their accumulation in aquatic environments, but their potential impact on cyanobacterial blooms remains inadequately understood. Herein, the dynamic fluctuating effects of polystyrene (PS) on Microcystis aeruginosa were investigated throughout its growth cycle, as well as the action of algal organic matter in the disinfection by-products formation. The maximum inhibition of algal cell growth and phycobiliprotein content by PS during the adaptation phase reached 56.3 % and 76.3 %, respectively. With the extension of exposure time, the inhibitory effect gradually transitions into promotive effect. PS exposure increased the content of extracellular organic matter and enhanced the THMs formation during chlorination, with trihalomethanes concentrations of 62.8 and 101.9 μg/L in the control and PS treatment groups, respectively. Moreover, the reactive oxygen species levels in PS-exposed algal cells were only 71.5 % of those in the control group, and total antioxidant capacity levels, superoxide dismutase and catalase activities were also lower. However, the microcystin content exposed PS was increased to 1.2 times that of the control group. The presence of PS in aquatic environments increases the levels of algal organic matter and microcystin, potentially threatening water quality. This study provides new insights into the combined effects of microplastics on freshwater algae and valuable data on potential risk associated with MPs.

Formation mechanisms of carcinogenic N-nitrosamines from dissolved organic matter derived from nitrogen-containing microplastics during chloramine disinfection

The high occurrence of microplastics (MPs) in water treatment facilities may complicate the source-control of disinfection by-products. Herein, we reported that the carcinogenic N-nitrosamines, such as N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA), were generated during monochloramine disinfection of water in which nitrogen-containing microplastics (N-MPs, such as polyamide and polyacrylonitrile) were present. The precursors of NDMA and NDEA were mainly derived from the dissolved organic matter released from N-MPs (N-MP-DOM), which were characteristic of a significantly higher proportion of polar and non-cationic fractions, favouring the N-nitrosamine formation. The results of excitation-emission-matrix spectra and orbitrap-mass spectrometry indicated that the polar components were mainly CHON and highly hydrogen-saturated molecules (H/C ≥ 1.5) (such as protein-like substrates), which are potential precursors of N-nitrosamines. Further mass difference network analysis revealed that the reactions of amine and nitro/nitroso groups in the precursors made predominant contribution to the generation of N-nitrosamines. Two potent NDMA precursors bearing a (CH3)2N-R structure were identified based on the diagnostic fragments (e.g., 45.0578 Da and m/z 58.0651) and in silico fragmentation tool (MetFrag 2.2) in MS2 spectra. Our findings provide valuable insights into understanding the potential risks of N-MPs due to monochloramine disinfection in water treatment systems.

Research progress on the generation of NDMA by typical PPCPs in disinfection treatment of water environment in China: A review

The drugs and personal care products in water sources are potential threats to the ecological environment and drinking water quality. In recent years, the presence of PPCPs has been detected in multiple drinking water sources in China. PPCPs are usually stable and resistant to degradation in aquatic environments. During chlorination, chloramination, and ozonation disinfection processes, PPCPs can act as precursor substances to generate N-nitrosodimethylamine (NDMA) which is the most widely detected nitrosamine byproduct in drinking water. This review provides a comprehensive overview of the impact of PPCPs in China's water environment on the generation of NDMA during disinfection processes to better understand the correlation between PPCPs and NDMA generation. Chloramine is the most likely to form NDMA with different disinfection methods, so chloramine disinfection may be the main pathway for NDMA generation. Activated carbon adsorption and UV photolysis are widely used in the removal of NDMA and its precursor PPCPs, and biological treatment is found to be a low-cost and high removal rate method for controlling the generation of NDMA. However, there are still certain regional limitations in the investigation and research on PPCPs, and other nitrosamine by-products such as NMEA, NDEA and NDBA should also be studied to investigate the formation mechanism and removal methods.

Impact of changes in biofilm composition response following chlorine and chloramine disinfection on nitrogenous disinfection byproduct formation and toxicity risk in drinking water distribution systems

In practical drinking water treatment, chlorine and chloramine disinfection exhibit different mechanisms that affect biofilm growth. This study focused on the influence of biofilm composition changes, especially extracellular polymeric substance (EPS) fractions, on the potential formation and toxicity of nitrogenous disinfection by-products (N-DBP). Significant differences in microbial diversity and community structure were observed between the chlorine and chloramine treatments. Notably, the biofilms from the chloramine-treated group had higher microbial dominance and greater accumulation of organic precursors, as evidenced by the semi-quantitative confocal laser-scanning microscopy assay of more concentrated microbial aggregates and polysaccharide proteins in the samples. Additionally, the chloramine-treated group compared with chlorine had a higher EPS matrix content, with a 13.5 % increase in protein. Furthermore, the protein distribution within the biofilm differed; in the chlorine group, proteins were concentrated in the central region, whereas in the chloramine group, proteins were primarily located at the water-biofilm interface. Notably, functional prediction analyses of protein fractions in biofilms revealed specific functional regulation patterns and increased metabolism-related abundance of proteins in the chlorine-treated group. This increase was particularly pronounced for proteins such as dehydrogenases, reductases, transcription factors, and acyl-CoA dehydrogenases. By combining the Fukui function and density functional calculations to further analyse the effect of biofilm component changes on N-DBP production under chlorine/chloramine and by assessing the toxicity risk potential of N-DBP, it was determined that chloramine disinfection is detrimental to biofilm control and the accumulation of protein precursors has a higher formation potential of N-DBPs and toxicity risk, increasing the health risk of drinking water.

Formation of disinfection by-products from microplastics, tire wear particles, and other polymer-based materials

Disinfection by-products (DBPs) are formed through the disinfection of water containing precursors such as natural organic matter or anthropogenic compounds (e.g., pharmaceuticals and pesticides). Due to the ever increasing use of plastics, elastomers, and other polymers in our daily lives, polymer-based materials (PBMs) are detected more frequently and at higher concentrations in water and wastewater. The present review provides a comprehensive and systematic analysis of the contribution of PBMs - including elastomers, tire waste, polyelectrolytes, and microplastics - as precursors of DBPs in water and wastewater. Literature shows that the presence of PBMs can lead to the leaching of dissolved organic matter (DOM) and subsequent formation of DBPs upon disinfection in aqueous media. The quantity and type of DBPs formed strongly depends on the type of polymer, its concentration, its age, water salinity, and disinfection conditions such as oxidant dosage, pH, temperature, and contact time. DOM leaching from elastomers and tire waste was shown to form N-nitrosodimethylamine up to concerning levels of 930 ng/L and 466,715 ng/L, respectively upon chemical disinfection under laboratory conditions. Polyelectrolytes can also react with chemical disinfectants to form toxic DBPs. Recent findings indicate trihalomethanes formation potential of plastics can be as high as 15,990 µg/L based on the maximum formation potential under extreme conditions. Our analysis highlights an overlooked contribution of DOM leaching from PBMs as DBP precursors during disinfection of water and wastewater. Further studies need to be conducted to ascertain the extent of this contribution in real water and wastewater treatment plants.