PARAFAC model as an innovative tool for monitoring natural organic matter removal in water treatment plants Sikelelwa N. Ndiweni, Michael Chys, Nhamo Chaukura, Stijn W. H. Van Hulle and Thabo T. I. Nkambule ABSTRACT The increase of fluorescent natural organic matter ( fNOM) fractions during drinking water treatment might lead to an increased coagulant dose and filter clogging, and can be a precursor for disinfection by-products. Consequently, efficient fNOM removal is essential, for which characterisation of fNOM fractions is crucial. This study aims to develop a robust monitoring tool for assessing fNOM fractions across water treatment processes. To achieve this, water samples were collected from six South African water treatment plants (WTPs) during winter and summer, and two plants in Belgium during spring. The removal of fNOM was monitored by assessing fluorescence excitation–emission matrices datasets using parallel factor analysis. The removal of fNOM during summer for South African WTPs was in the range 69–85%, and decreased to 42–64% in winter. In Belgian WTPs, fNOM removal was in the range 74–78%. Principal component analysis revealed a positive correlation between total fluorescence and total organic carbon (TOC). However, TOC had an insignificant contribution to the factors affecting fNOM removal. Overall, the study demonstrated the appearance of fNOM in the final chlorinated water, indicating that fNOM requires a customised monitoring technique. Sikelelwa N. Ndiweni Nhamo Chaukura Thabo T. I. Nkambule (corresponding author) Nanotechnology and Water Sustainability Research Unit, College of Science, Engineering and Technology, University of South Africa, Florida Campus, 1709, Johannesburg, South Africa E-mail: nkambtt@unisa.ac.za Michael Chys † Stijn W. H. Van Hulle LIWET, Department of Green Chemistry and Technology, Ghent University, Campus Kortrijk, Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium † Present address: VEG-i-TEC, Ghent University, Campus Kortrijk, Graaf Karel De Goedelaan 5, B-8500 Kortrijk, Belgium Key words | excitation–emission matrices, fluorescent natural organic matter, parallel factor analysis, protein to humic ratio, water treatment processes INTRODUCTION Natural organic matter (NOM) in water sources reduces the performance of water treatment plants (WTPs), downgrades water quality, and increases operational costs (Sillanpaa et al. ). Fluorescent natural organic matter ( fNOM) is lar- gely made up of humic-like, fulvic-like, and protein-like components (Shao et al. ). Currently, parameters used for tracking recalcitrant fNOM are turbidity, total organic carbon (TOC), UV 254 , pH, and conductivity (Ndiweni et al. ). However, these monitoring tools do not have capabili- ties to reveal enough information to fast track the removal of problematic fNOM fractions. For instance, online turbidity measurements for raw water were proven to be unreliable compared to tryptophan-like (tryp-like) and humic-like fluorescence (FL) measurements (Sorensen et al. ). A conventional WTP commonly uses different water treat- ment stages such as coagulation, sedimentation, sand filtration (SF), and chlorination. The effects of fNOM on water treat- ment include fouling of filtration media such as membranes and activated carbon (AC) (Shao et al. ). Moreover, during coagulation, flocculation, filtration, ozonation and chlorination, fNOM fractions can transform to form secondary products, which are more toxic and complex compared to the parent compounds (Brumer et al. ). Secondary product refers to compounds formed when ozone breaks down large molecules to small molecules that exhibit varying character- istics. Secondary product can also be used to refer to product formed when fNOM fractions react with chlorine disinfection by-products (DBPs), which are potentially formed (Chaukura et al. ). When traces of biodegradable fNOM are present in the chlorination stage, there is a possibility of bacterial regrowth and corrosion in the water distribution system (Baghoth & Amy ). These DBPs such as trihalomethanes and haloacetic acids stimulate cancer cells in humans; hence when optimising WTPs it is important to ensure that water is safe for consumption (Haarhoff et al. ). Analysing unknown heterogeneous fNOM, some of which can occur at low relative concentrations or below detection limit, is a challenge (Liu et al. ). In order to identify 1786 © IWA Publishing 2020 Water Science & Technology | 81.8 | 2020 doi: 10.2166/wst.2020.136 Downloaded from http://iwaponline.com/wst/article-pdf/81/8/1786/710307/wst081081786.pdf by guest on 05 November 2021