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

Welldone Moyo Welldone Moyo,Bhekie B Mamba Bhekie B Mamba,Nhamo Chaukura Nhamo Chaukura,Machawe M Motsa Machawe M Motsa,Titus Am Msagati Titus Am Msagati,Sebastiaan Gj Heijman Sebastiaan Gj Heijman,Thabo Ti Nkambule Thabo Ti Nkambule

doi:10.17159/wsa/2020.v46.i1.7893

Welldone Moyo Welldone Moyo, Bhekie B Mamba Bhekie B Mamba + Show 5 more

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https://doi.org/10.17159/wsa/2020.v46.i1.7893

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Journal: Water SA	Publication Date: Jan 30, 2020
Citations: 3	License type: CC BY-NC 4.0

Affiliation: University of South Africa

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.

Highlights

The fate of natural organic matter (NOM) in drinking water treatment processes remains contentious due to the heterogeneous nature and structural complexity of NOM
This indicates the water treatment plant (WTP) has the capacity to significantly reduce the aromatic content of NOM throughout the treatment stages
Coagulation is usually the major NOM removal process, research has shown that SUVA < 2 L·mg-1·m-1 implies that the major portion of NOM in the water is of non-humic substances and that less than 25% should be removed when SUVA < 2 (Lavonen, 2015)

Summary

Introduction

The fate of natural organic matter (NOM) in drinking water treatment processes remains contentious due to the heterogeneous nature and structural complexity of NOM. Compounding this is its temporal and spatial variability, making efforts to remove it uncertain (Nkambule et al, 2012). Detrimental to water treatment and distribution, NOM is the major contributor to the fouling of membranes and activated carbon, is a precursor to the formation of disinfection by-products (DBPs), impacts on the organoleptic properties of water, and certain fractions of NOM promote biological growth in distribution networks (Lobanga et al, 2013; Lyon et al, 2014; Hua et al, 2015; Park et al, 2016). Current research characterizes NOM with emphasis on properties such as biodegradable dissolved organic carbon (BDOC), polarity, UV absorption, fluorescence intensity, and molecular weight fractions (He et al, 2013; Chen et al, 2017; Li et al, 2017a)

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