This work presents the first comprehensive investigation of natural organic matter (NOM) fraction removal using ceramic membranes in South Africa. The rate of removal of bulk NOM (measured as UV₂₅₄ and DOC % removal), the biodegradable dissolved organic carbon (BDOC) fraction, polarity-based fractions, and fluorescent dissolved organic carbon (FDOM) fractions was investigated from water abstracted from drinking water treatment plants (WTPs) in South Africa. Further, mechanisms of ceramic membrane fouling by waters of South Africa were studied. Ceramic membranes removed more than 80% DOC from samples from coastal WTPs, whereas for inland plants, the removal was between 60% and 75% of DOC. FDOM was removed to at least 80% regardless of the site of the plant. The BDOC removal by the ceramic membranes was above 85%. The hydrophobic fraction was the most amenable to removal by ceramic membranes regardless of the site of sample abstraction (above 60% for all sites). The freshness index (β:α) correlated strongly to UV₂₅₄ removal (R² = 0.96), thus UV₂₅₄ removal can serve as a proxy for the susceptibility to removal of such class of NOM by ceramic membranes. This investigation demonstrated that ceramic membranes could be a valuable technology if integrated into the existing WTPs. Practitioner Points: The removal of bulk parameters by ceramic membrane was greater than unit conventional processes used in all the sampled water treatment plants. The hydrophobic polarity-based fraction of NOM was the most amenable to removal by ceramic membranes regardless of the site of the WTP. Polarity-based fractions, aromaticity, and initial DOC had a combined influence on the removal of organic matter by ceramic membranes as explained by principal component three.

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This study demonstrates the fundamental differences in fouling development and mechanisms of unfiltered and 0.45 µm pre-filtered water samples on ceramic membranes. Robust characterization of the feed waters was conducted using gravimetric analysis, optical methods and modeling techniques. UV₂₅₄ removal and suspended solids (SS) for the unfiltered samples presented a strong correlation (R² = 0.87). Further, SS exhibited strong correlations with fluorescent fractions (R² = 0.82; 0.81 and 0.74 for C1; C2 and C3, respectively). This observation confirmed the significance of inorganic particles in the development of a combined fouling layer with fluorescent organic components. The fouling development rate for water sampled from Plattenburg Bay (PL) was higher than the rest of the 0.45 µm pre-filtered samples. This was attributed to the low conductivity (175 µS.m^-1) of the water sample, translating to a low ionic strength environment. Samples collected from Hermanus River (HL) and Lepelle River (OL) had similar SS quantity (87.6 mg/L and 88.4 mg/L, respectively), and modified fouling index (MFI) values for raw samples were 6625 and 8060 s/L², respectively, despite a very large difference in the content of organic matter (22.67 mg/L.C and 9.81 mg/L.C). This could be due to organic matter attaching onto the surface of particles and reducing the adsorption of NOM within membrane pores and/or onto the membrane active layer. This study demonstrated the extent of in situ background electrolytes, foulant concentration, foulant-foulant interactions, foulant-membrane interaction and physicochemical properties of feed stream on fouling development and mechanisms.

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This study used spectroscopic methods to investigate the fate and dynamics of natural organic matter (NOM) as it traverses the treatment train at three water treatment plants (WTPs) in South Africa. The character, quantity, and removability of NOM at specific treatment stages was investigated by measuring changes in dissolved organic carbon (DOC) concentration, specific ultra-violet absorbance, UV absorbance, various spectroscopic indices, and maximum fluorescence intensity levels. A novel method of identifying and quantifying fluorescent fractions by combining synchronous fluorescence spectroscopy (SFS) and Gaussian peak fitting is presented. The dynamics of NOM removal were modeled using 2D-SFS correlation spectroscopy. Humic and fulvic substances dominated coastal plants and were the most amenable for removal by coagulation as shown by Hermanus WTP (plant H), which had a 42% DOC removal at the coagulation stage. Tyrosine-like, tryptophan-like and microbial humic-like substances were degraded or transformed concurrently at plant Flag Bushiole (FB) whereas, at plant H, fulvic-like matter was transformed first followed by tyrosine-like then humic-like matter. Through 2D-SFS, this study revealed that NOM transformation was varied as a consequence of NOM character, the type and dosage of treatment chemicals used, and WTPs operational parameters.

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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.

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This work reports on the fundamental factors influencing inter-foulant and foulant-membrane interactions during simulated dissolved organic matter removal using ceramic nanofiltration. Fouling tests were performed using sodium alginate (SAL), humic acid (HA) and bovine serum albumin (BSA) as model foulants. Fouling potentials of each foulant and their mixtures were investigated using feed solutions containing fixed concentrations of K+, Na+, Mg2+ and Ca2+ with a total ionic strength of 10 mM. The impact of modification by atomic layer deposition on fouling mitigation was also assessed. The flux decline in the first 100 min for single foulants was 4.16 × 10-2, 2.69 × 10-2 and 1.60 × 10-2 Lm-2 for SAL, HA and BSA, respectively. These results demonstrated that for the single foulants, deposition on the membrane surface in the early stages of filtration was primarily governed by membrane-foulant interactions. Interestingly, cake filtration was the least fouling mechanism in feed solutions composed of BSA and SAL (R2 = 0.519, 0.374 for BSA + SAL and BSA + SAL + HA, respectively) and the most favorable fouling mechanism of feed solution which included HA and SAL (R2 = 0.972). The water contact angle dropped from 58o to 35° after coating, thus improving its anti-fouling properties.@en

This study presents an investigation on the fate of natural organic matter (NOM) and its dynamics throughout the treatment train at various drinking water treatment plants (WTP) in South Africa. The characteristics, concentration and removal efficiencies of NOM at various treatment stages on the basis of dissolved organic carbon, UV absorbance, specific ultra-violet absorbance, spectroscopic indices, maximum fluorescence intensity (Fmax), and polysaccharides removal, were studied. The highest polysaccharide concentration was in coastal plants compared to inland plants for the raw water samples. A Parafac model fitting four components was established for the raw waters, and validated based on the split half criteria. The Fmax values of the components was higher for terrestrial humic-like component (C1) and fulvic-like component (C2) than for humic-like components (C3), and for protein-like component (C4). Strikingly, the mean Fmax values for C2 and C3 were higher for plants located on the south west coast of South Africa than the plants located inland. While the humification index and UV ₂₅₄ removal correlated (R ² = 0.797), the correlation between the freshness index (β:α) and UV ₂₅₄ removal was also mild (R ² = 0.787). The removal efficiencies of bulk NOM were higher than for FNOM in the rapid sand filtration (RSF) stage, regardless of the location of the plants, suggesting that the RSF process is more efficient in removing non-fluorescent NOM than FNOM fractions. This study demonstrated the capability of optical methods in characterizing the fate, occurrence and removal of NOM in surface waters.

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