Investigation of natural organic matter (NOM) character and its removal in a chlorinated and chloraminated system at Rand Water, South Africa

Abstract

In its natural environment, natural organic matter (NOM) is not problematic. However, during water treatment NOM does affect water quality specifically during the disinfection step, where if NOM is present it reacts with disinfectants resulting in the formation of disinfection by-products. To emphasize the importance of NOM monitoring during potable water treatment this study aimed to characterize NOM and evaluate NOM removal by a conventional water treatment plant considering seasonal trends. NOM was characterized by making use of NOM polarity and specific ultraviolet absorbance. NOM removal was monitored with high-performance size exclusion chromatography, dissolved organic carbon (DOC) and UV254 analyses. The polarity rapid assessment method indicated that the hydrophobic and hydrophilic NOM fractions within the surface water increased during a period of heavy rain when floods occurred, but conversely decreased during an average rain season. Although NOM character showed variability during the 5-year study period, seasonal relationship during high and low flow seasons between aromatic NOM and total trihalomethane (TTHM) formation was not evident. Aromatic NOM was not the only precursor to TTHM formation, which stresses the need to implement advanced NOM characterization techniques during NOM monitoring to study reactivity of the individual NOM fraction with the disinfectant used at the water treatment plant.

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

“…The HPI has high THM and HAA formation potential for waters with low humic content characterized by low SUVA compared to the HPO fraction (Karapinar et al, 2014). Additionally, the HPI fraction is characterized by a low C/O ratio and SUVA < 2 is indicative of less aromatic carbon content (Marais et al, 2017). Therefore, it can be conjectured that the drop in the HPI fraction was due to the formation of DBPs.…”

“…The hydrophobic character as measured by SUVA decreased down the treatment train, with a significant reduction (p < 0.05) observed during the disinfection (18%) treatment step. SUVA < 2 L•mg -1 •m -1 indicates a hydrophilic character of NOM; this fraction is often recalcitrant to treatment (Marais et al, 2017). Because of this, it was expected that coagulation should not cause a substantial reduction in NOM (11.6%).…”

Natural Organic Matter Character in Drinking Water Distribution Systems: A Review of Impacts on Water Quality and Characterization Techniques

“…Figure 1 below provides an overview of the various effects of NOM fractions, highlighting their impact on the formation of DBPs and other influences within the system. As such, the use of various characterization techniques to interpret both its functional and structural aspects are needed [102]. There are several existing methods commonly used for high-frequency NOM quantification, including TOC/DOC and UV-light adsorption at specific wavelengths such as 254 nm (UV254) [103].…”

“…There are several existing methods commonly used for high-frequency NOM quantification, including TOC/DOC and UV-light adsorption at specific wavelengths such as 254 nm (UV254) [103]. Despite their quick results, As such, the use of various characterization techniques to interpret both its functional and structural aspects are needed [102]. There are several existing methods commonly used for high-frequency NOM quantification, including TOC/DOC and UV-light adsorption at specific wavelengths such as 254 nm (UV254) [103].…”

Characterization of natural organic matter in South African drinking water treatment plants: Towards integrating ceramic membrane filtration

“…This is because of the passage of the assimilable organic carbon fraction (AOC) through the pores of the membrane even in the NF range (1-10 nm). The AOC represents the low molecular DOC fraction assimilated by specific strains of bacteria for growth, whereas BDOC is a measure of the gross amount of DOC that is biodegraded over a fixed time frame by a microflora of bacteria suspended or fixed on media such as glass beads (Marais et al, 2017). It is vital to measure BDOC because it gives an indication of the potential of bacterial proliferation in the distribution.…”