Application of photoelectrochemical chemical oxygen demand to drinking water

Abstract

MATERIALS AND METHODSModel compound preparation. Three amino acids (tyrosine, tryptophan, phenylalanine), three carboxylic acids (sodium acetate, sodium oxalate, and sodium formate), and two reference standards (potassium hydrogen phthalate [KHP] and caffeine) were used as model organic compounds. These model organic compounds are summarized in Table 1.Carboxylic acids and amino acids are found in natural waters and can make up 8% and 2-3% of COD in natural waters, respectively (Langlais et al, 1991). Relative proportions of amino acids to organic matter surrogates such as DOC can vary considerably from source to source. In a survey of 16 utilities across the United States, Dotson and Westerhoff (2009) found that raw water total amino acid concentration accounted for between 0.19 and 11.6%, or 3.5%, on average, of raw water DOC. As summarized by Dotson and Westerhoff (2009), amino acids are precursors to regulated and unregulated DBPs, and amino acids with aromatic side chains, such as tryptophan and tyrosine, can have the highest DBP yields on a carbon basis. KHP was chosen because it is commonly used as a reference standard for TOC determination. Finally, caffeine was chosen as it is commonly used as a marker for human contamination.Model compound stock solutions (100 mg C/L) were prepared by diluting chemical in deionized (DI) water (Millipore). Stock solutions were then further diluted with DI water to 0.25, 0.5, 1, 3, and 5 mg C/L as TOC in the range of 1.5-5 mg/L represents common raw and treated water TOC content in surface water in Nova Scotia. Model compounds were prepared for TOC and COD.Surface water collection. Samples were collected from four surface water treatment plants in Nova Scotia. Treatment trains included one biofiltration plant (Pockwock Lake), one ultrafiltration/nanofiltration membrane plant (Fletcher Lake), and two conventional filtration plants (Lake Major and Bennery Lake). Details of the treatment process for each plant are described in Table 2.Samples included raw water, prefiltered water, filtered water, and finished water from each location, with the exception of prefiltered water and finished water from Fletcher Lake. Raw water samples were taken from the plant's raw water intake at all locations. Prefiltered water was taken from the final flocculation tank for the Pockwock and Bennery Lake samples, and from the top of the clarifier, prior to prechlorine addition, for the Lake Major sample. A prefiltered sample was not taken at Fletcher Lake because no

Biomass Evolution in Full‐Scale Anthracite‐Sand Drinking Water Filters Following Conversion to Biofiltration

“…As anthracite media is not recognized for its adsorptive capacity, substrate could be available to the biomass as hydrophilic organic material that was not adsorbed to alum floc during coagulation. Stoddart and Gagnon (2014) demonstrated that TOC and DOC had the same concentration following biofiltration at this plant, which indicates that organic material enmeshed in floc material was physically removed. However, the photoelectrochemical chemical oxygen demand concentration was decreased following coagulation/flocculation (adsorption) and then further decreased through biofiltation (biodegradation) (Stoddart & Gagnon 2014).…”

“…Stoddart and Gagnon (2014) demonstrated that TOC and DOC had the same concentration following biofiltration at this plant, which indicates that organic material enmeshed in floc material was physically removed. However, the photoelectrochemical chemical oxygen demand concentration was decreased following coagulation/flocculation (adsorption) and then further decreased through biofiltation (biodegradation) (Stoddart & Gagnon 2014). For Atlantic Canada surface water, hydrophilic acids are significant contributors to haloacetic acid (HAA) formation (Kent et al 2014) and during biofilter operation at this facility, the degradation of HAA precursors was evident (Stoddart & Gagnon 2015).…”

Full‐Scale Prechlorine Removal: Impact on Filter Performance and Water Quality

“…This is consistent with a recent finding in which, using data from several pilot-and full-scale studies, no correlation between ATP concentrations and DOC removal was identified (Pharand et al 2014). However, as described in Stoddart and Gagnon (2014), additional data from this facility indicate that a 0.26 mg/L DOC reduction across the biofilter can correspond to a 1.5 mg/L removal of oxidizable organic matter (as measured through photoelectrochemical chemical oxygen demand) across the filter. As a result, it is hypothesized that more biological transformation of NOM may occur than is detectable by DOC.…”

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

“…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 have allowed researchers to rapidly quantify COD during drinking water treatment using photoelectrochemical chemical oxygen demand (peCOD) (Stoddart & Gagnon, 2014).…”

“…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 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.…”