NOM characterization and removal at six Southern African water treatment plants

Abstract

Abstract. Organic pollution is a major concern during drinking water treatment. Major challenges attributed to organic pollution include the proliferation of pathogenic micro-organisms, prevalence of toxic and physiologically disruptive organic micropollutants, and quality deterioration in water distribution systems. A major component of organic pollution is natural organic matter (NOM). The operational mechanisms of most unit processes are well understood. However, their interaction with NOM is still the subject of scientific research. This paper takes the form of a metastudy to capture some of the experiences with NOM monitoring and analysis at a number of Southern African Water Treatment Plants. It is written from the perspective of practical process selection, to try and coax some pointers from the available data for the design of more detailed pilot work. NOM was tracked at six water treatment plants using dissolved organic carbon (DOC) measurements. Fractionation of the DOC based on biodegradability and molecular weight distribution was done at a water treatment plant in Namibia. A third fractionation technique using ion exchange resins was used to assess the impact of ozonation on DOC. DOC measurements alone did not give much insight into NOM evolution through the treatment train. The more detailed characterization techniques showed that different unit processes preferentially remove different NOM fractions. Therefore these techniques provide better information for process design and optimisation than the DOC measurement which is routinely done during full scale operation at these water treatment plants. Further work will focus on streamlining and improving the reproducibility of selected fractionation techniques, characterization of NOM from different water sources, and synthesis of the results into a systematic, practical guideline for process design and optimisation.

Molecular Characteristics and Differences of Effluent Organic Matter from Parallel Activated Sludge and Integrated Fixed-Film Activated Sludge (IFAS) Processes

“…Molecular formula assignments were based on the following elements: 1 H, 12 C, 16 O, 14 N, 32 S. The isotopes 13 C and 34 S were also included to cross-validate assigned molecular formulas. The same calibration procedure used in a previous study of EfOM were used 1 and a mass accuracy of 0.2 ppm was achieved.…”

“…A detailed chemical analysis of wastewater effluent is intrinsic to the understanding of chemical dynamics and treatment efficiency . Since the late 1990s, the electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) technique, though cost-prohibitive for many environmental applications, has made great strides in identifying thousands of molecular formulas in aquatic natural organic matter (NOM). − However, most chemical characterization of complex organic matrices to date has focused on NOM in natural environments − and chemical characterization studies related to engineered water systems also focused mainly on NOM and its effect during water treatment process and on the resulting drinking water quality. − Recently a study demonstrated the versatility of FT-ICR MS as a technique that can provide a detailed chemical characterization of wastewater treatment effluent organic matter (EfOM) …”

Biological stability of water in water distribution systems. The effect of water treatment trials

“…This results from the lower organic contamination levels in infiltration water (Table 1). High content of dissolved organic carbon, especially NBDOC in TOC prove the predominance of hydrophobic substances in all types of raw water [19]. Therefore, processes used in the discussed trial systems guaranteed an effective elimination of TOC.…”

“…Such high efficiency of the above processes guaranteed a significant percentage increase in biologically stable samples with regards to phosphate concentration even after the first treatment steps (Table 3). Additionally, phosphate ions in WTT1 and WTT2 were assimilated by microorganisms inhabiting the surface of GAC deposits [8,19]. The effectiveness of removal of phosphate ions averaged at 83.7% (WTT1), 88.8% (WTT2) and 92.1% (WTT3).…”

Micropollutant Degradation Mechanism

“…NOM is a major membrane foulant and may inhibit the removal of organic micro-pollutants by activated carbon. NOM should be carefully considered when choosing the optimal process and design for organic removal (Haarhoff, 2010).…”