Investigating the fate of natural organic matter at a drinking water treatment plant in South Africa using optical spectroscopy and chemometric analysis

Abstract

The removal dynamics of biodegradable dissolved organic carbon (BDOC) and natural organic matter (NOM) polarity fractions at a water treatment plant (WTP) in South Africa was studied using UV-Vis absorbance, fluorescence excitation-emission matrix, and two-dimensional synchronous fluorescence spectroscopy (SFS). This study gave insights into the transformation of NOM due to treatment processes. The objectives of the study were: (i) to use chemometric analysis and two-dimensional SFS correlations to investigate the evolution of NOM arising from treatment processes, and (ii) to access the chemical profile dynamics of polarity and BDOC fractions throughout the treatment train. The UV254 absorbance, which indicates aromaticity, reduced by 45% along the WTP. Gaussian fitting of UV-Vis data showed a decreasing trend in intensity and number of bands along the treatment process. The removal efficiency of NOM components followed the order: humic-like (HL) > tyrosine-like (TYL) > fulvic-like (FL) > tryptophan-like (TPL) > microbial-like (MBL). At the source, the relative distribution of the hydrophobic (HPO), hydrophilic (HPI), and transphilic (TPI) fractions was 45%, 31%, and 24%, respectively. The HPI was recalcitrant to treatment, and the TYL component of the HPI fraction was conjectured to be a disinfection byproduct limiting reagent. The HL and FL components of the BDOC fraction were the major substrates for bacterial growth. According to two-dimensional-SFS correlation, TYL, TPL, and MBL varied concurrently across the treatment stages. Used for the first time in South Africa, the robustness of a multi-dimensional approach of optical methods coupled with chemometric tools for the assessment of the fate of NOM along the treatment processes was revealed by this study.

Monitoring the characteristics and removal of natural organic matter fractions in selected South African water treatment plants

“…These results suggest that tyrosine-, tryptophan-and fulvic-like matter were transformed or degraded concurrently throughout the treatment process. Our previous study found tyrosine to be more susceptible to treatment than the other fractions (Moyo et al 2020). This suggests NOM characteristics, treatment regimen and chemicals used play a role in the ease of removal of NOM fractions.…”

Comparative removal efficiencies of natural organic matter by conventional drinking water treatment plants in Zimbabwe and South Africa

“…Dissolved organic carbon was determined in the filtered samples using a total organic carbon analyzer (Teledyne Tekmar, TOC fusion). The method for the determination of BDOC is reported elsewhere (Moyo et al, 2020). Briefly, washed sand (100 g) was placed in 500-ml Erlenmeyer flasks covered with aluminium foil, and the water sample (300 ml) was added.…”

“…and attributed it to the accumulation of dead microbes in the sand of the DAFF filters (Moyo et al, 2020). However, further research is needed to conclusively explain this phenomenon.…”

Fast Tracking and Detection of Organic Matter in an Urban Sewage Treatment Plant Using Fluorescence Spectroscopy and UV-Vis Absorption Spectroscopy

“…Optical methods provide advantages such as rapid detection, simple operation, and non-destructive sample analysis [7]. In recent years, with the advancement of new technologies such as optical and spectroscopic techniques, notably the emergence of three-dimensional fluorescence spectroscopy and UV-Vis absorption spectroscopy, rapid real-time monitoring of wastewater treatment plants has been rendered feasible [8][9].…”