Mean oxidation state of organic carbon: A novel application to evaluate the extent of oxidation of natural organic matter in drinking water biological treatment

Abstract

s and new works from the Work, to alter and revise the Work, and to make commercial use of the Work, provided the user gives appropriate credit (with a link to the formal publication through the relevant DOI), provides a link to the licence, and that the licensor is not represented as endorsing the use made of the work. The full details of the licence are available at http://creativecommons.org/licenses/by/4.0/. The chapter is from the book Microbiological Sensors for the Drinking Water Industry, Torben Lund Skovhus and Bo Højris (Eds.). doi: 10.2166/9781780408699_0197 198 Microbiological Sensors for the Drinking Water Industry et al., 1983). The intermediates of incomplete oxidation would be quantified as TOC/ DOC. This disadvantage limits further understanding about the transformation of NOM, especially during biological treatment of drinking water (e.g., biofiltration). In both complete oxidation and incomplete oxidation, the formation of bonds between oxygen and carbon and the deformation of bonds between hydrogen and carbon increase the oxidation state of organic carbon (Kroll et al., 2011). Combining chemical oxygen demand (COD) with TOC/DOC measurement can provide valuable information on the oxidation state of organic carbon during drinking water treatment. However, the conventional dichromate COD method is not sensitive enough to measure COD in surface water (Rittman & Huck, 1989; Stoddart & Gagnon, 2014). Advancements in sensor development for the determination of COD in water (Zhang et al., 2004) have allowed researchers to rapidly quantify COD during drinking water treatment using photoelectrochemical chemical oxygen demand (peCOD) (Stoddart & Gagnon, 2014). When applied in a full-scale biofiltration drinking water treatment plant, peCOD removal was greater than TOC/DOC removal (Stoddart & Gagnon, 2014), which indicated peCOD might be more sensitive than TOC/DOC analysis for understanding biological treatment performance. Even though peCOD indicated a promising application in drinking water treatment performance monitoring, the lack of understanding of the relationship between peCOD and TOC/DOC in drinking water limits its application. This is due in part to many years of TOC/DOC data which supports our understanding of NOM in drinking water. There is a need to construct a “bridge” to connect the conventional TOC/DOC evaluation system and novel approaches such as the peCOD evaluation system. Therefore, a concept of mean oxidation state (MOS) of organic carbon (Cos), combining TOC/DOC and peCOD, is introduced in this study. The major advantages of this method are: (i) Cos could provide more information about the transformation of NOM than TOC/DOC, especially when incomplete oxidation dominates the biochemical reactions of treatment; (ii) theoretically, Cos only responds to oxidationreduction reactions, which means that physical removal (e.g., filtration, precipitation and adsorption) does not change the value of Cos; (iii) Cos is a dimensionless number that is not affected by the concentration fluctuation of NOM and only represents the oxidation potentials of organic carbon. In addition, it may be possible to correlate Cos with biomass concentration, as determined by measurements such as adenosine triphosphate (ATP), to further understand NOM removal mechanisms during biological drinking water treatment processes, such as biofiltration.