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

  • Welldone Moyo Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa (UNISA), Johannesburg, South Africa
  • Nhamo Chaukura Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa (UNISA), Johannesburg, South Africa
  • Machawe M Motsa Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa (UNISA), Johannesburg, South Africa
  • Titus AM Msagati Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa (UNISA), Johannesburg, South Africa
  • Bhekie B Mamba Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa (UNISA), Johannesburg, South Africa
  • Sebastiaan GJ Heijman Department of Civil Engineering and GeoSciences, Technical University of Delft, Delft, The Netherlands
  • Thabo TI Nkambule Nanotechnology and Water Sustainability (NanoWS) Research Unit, University of South Africa (UNISA), Johannesburg, South Africa
Keywords: biodegradable dissolved organic carbon, natural organic matter, optical spectroscopy, two-dimensional correlations, water treatment

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.

Views
  • Abstract 101
  • PDF 69
Views and downloads are with effect from 11 January 2018
Published
2020-01-30
Section
Research paper