Advances in the Analysis of Odorous Substances in Drinking Water Disinfection

In recent years, the issue of odor in drinking water has gained global attention, with disinfection being a significant source of water odor. Residual disinfectants and the generation of odorous disinfection byproducts (DBPs) contribute to the unpleasant taste and smell of drinking water. Accurate quantitative analysis is crucial for addressing and mitigating these odorous substances in drinking water, despite their low concentration levels. A recent article published in the journal TrAC Trends in Analytical Chemistry reviews the key techniques involved in the analysis of odorous substances, emphasizing recent advancements in the detection and quantification of residual disinfectants and various odorous DBPs.

Ensuring the quality of drinking water is essential for safeguarding public health, and the presence of odors plays a vital role in assessing water quality. Odors in drinking water are primarily caused by odorants exceeding their odor threshold concentrations (OTCs). Studies conducted in China revealed widespread odor issues in both source water and finished water in numerous drinking water treatment plants. While previous research predominantly focused on naturally occurring odorous substances from bacterial and algal metabolites, anthropogenically produced odorous substances stemming from disinfection have often been overlooked.

Disinfection is a crucial step in water treatment, effectively eliminating pathogens and reducing waterborne diseases. However, it can also give rise to various odorous DBPs, some of which pose health risks to humans. Chlorine disinfection, for instance, produces odorous compounds such as halophenols (HPs) and haloanisoles (HAs), while ozone disinfection generates different odorous aldehydes. Studies have confirmed that over 40% of drinking water odor issues are related to disinfection. The extremely low OTCs of these odorous DBPs make their identification and quantification imperative.

Chemical analysis provides a reliable means of identifying and quantifying odorous substances, offering insights into their presence and impact on water quality. Determining residual disinfectants and odorous DBPs involves three key steps: sampling, sample preparation, and instrumental analysis. Collecting representative samples while minimizing the loss of volatile odorous DBPs during collection and storage is vital. Sample pretreatment is crucial for achieving highly selective and sensitive analysis of odorous DBPs.

Traditional pretreatment methods, such as liquid-liquid extraction (LLE) and solid-phase extraction (SPE), are labor-intensive and require large volumes of organic solvents. More recent techniques like dispersed liquid-liquid microextraction (DLLME) and solid-phase microextraction (SPME) offer advantages such as efficiency, cost-effectiveness, and environmental friendliness. Additionally, automated techniques like purge and capture (P&T) and closed-loop stripping analysis (CLSA) have been employed for the fully automated analysis of odorous DBPs.

Advancements in instrumental analysis techniques have significantly improved the detection of odorous substances. Residual disinfectants are commonly detected using N-N-diethyl p-phenylenediamine (DPD) colorimetry, leading to the development of commercial test strips and various colorimetric sensors. Sensors based on electrochemical or optical detection mechanisms have also been developed. Gas chromatography (GC) separation is commonly employed for odorous DBPs, with two-dimensional chromatography (GC × GC) enhancing separation capabilities. Liquid chromatography (LC) techniques are used for odorous DBPs with high polarity or poor thermal stability. Various detectors, including flame ionization detectors (FIDs), electron capture detectors (ECDs), ultraviolet (UV) detectors, and mass spectrometry (MS) detectors, are used in conjunction with chromatographic separation.

This review article provides an overview of recent advancements in the analysis of odorous substances in drinking water, with a focus on the quantitative analysis of characteristic odorous DBPs and residual disinfectants. It underscores the importance of accurate and sensitive detection methods to assess and mitigate water odor issues. In the pursuit of safer drinking water, ongoing research aims to enhance sampling techniques, improve sensor sensitivity, optimize sample pretreatment efficiency, and explore advanced detection techniques. Accurately detecting and quantifying odor-causing substances in drinking water is essential for maintaining water quality and public health.

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Reference

(1) Qiu, J.; Ouyang, G. et al. Advances in the Analysis of Odorous Substances Derived from Drinking Water Disinfection. TrAC, Trends Anal. Chem. 2023, 167, 117224. DOI: https://doi.org/10.1016/j.trac.2023.117224.