Utilizing fluorescence excitation-emission matrix to profile natural organic matter removal performance by the Kingdom of Eswatini conventional drinking water treatment plants

Natural Organic Matter (NOM) in water arises from decomposed plant and animal matter and is ubiquitous in drinking water sources. Conventional water treatment systems in many emerging economies are incapacitated to remove NOM to acceptable levels thus posing potential public health hazards. Fluorescence spectroscopy has emerged as a useful tool in detecting and tracking the transformation and behavior of NOM as it traverses the treatment trains. Four water treatment plants coded: MBA; MAT; NHL and SIM formed part of the study sites, supplying water to urban areas spread across the four physiographic regions of Eswatini. Sample points were after each successive treatment stage. For all source water samples, the humic fraction was predominant (48, 67, 75 and 76 % for SIM, MAT, NHL and MBA, respectively) followed by the fulvic-like fraction (48, 24, 16 and 15 % for SIM, MAT, NHL and MBA, respectively). The overall removal efficiency of fluorescent NOM fractions by the respective plants was in the order: MAT (83 %) > MBA > (78 %) > SIM (68 %) > NHL (50 %). Intriguingly, the tyrosine-like fraction was removed up to 60 % overall for all plants although it contributed only about 2 % of the total fluorescent fractions. Such a finding reinforces the utility of FEEM as a powerful analytical tool capable of analyzing minute quantities. Thus, this work extends our understanding of NOM character and transformation in water treatment processes for the purpose of improving NOM removal through process optimization.