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

Abstract

A direct comparison between parallel activated sludge and integrated fixed-film activated sludge (IFAS) processes was performed in this study because both treatments received the same primary effluent, although differences may still remain due to different return flow rates. Modern ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was applied to characterize the complexity of effluent organic matter (EfOM) and to evaluate both processes in their abilities to change the EfOM molecular composition. At different stages during the two processes a direct comparison of the performance and changes in molecular composition of the IFAS with those of the activated sludge was undertaken. Large differences in the molecular composition between both processes were only apparent in the early stage of the aeration cells and the first cell of the IFAS possibly due to the higher flow rate and a delay in aerobic bacterial degradation. Despite the double flow rate (0.263 m(3) s(-1)) in the IFAS reactors compared to the activated sludge, by the end of the treatment the EfOM composition of both processes were undistinguishable from each other. However, a much more complex EfOM was generated in both processes, suggesting that bacteria are responsible for an increase in molecular diversity in the effluent.

The effect of advanced secondary municipal wastewater treatment on the molecular composition of dissolved organic matter

“…The dominance of CHO formulas agrees with one previous study of secondary and secondary clarifier effluents using negative ESI FT-ICR MS, which found that 52.7–61.1% of the formulas contained only C, H, and O when CHOS were considered for formula assignments (Tseng et al, 2013). In contrast, two previous FT-ICR MS studies that were limited to CHOS formula assignments found that primary effluent and secondary effluent were dominated by CHOS formulas, with 27–34% of formulas containing only C, H, and O (Gonsior et al, 2011; Tseng et al, 2013). The other sample types included here (e.g., UV disinfection and struvite precipitation) have not been previously analyzed by high-resolution mass spectrometry.…”

“…DOM was eluted from the cartridges with methanol and eluents were stored in the dark at 4°C until aliquots were poured off for analysis. The extraction procedure retained approximately 60% of DOC, which is similar to previous studies that concentrated wastewater-derived samples via SPE (Gonsior et al, 2011; Phungsai et al, 2016; Tseng et al, 2013; Urai et al, 2014). …”

“…In total, 2,106–3,013 unique molecular formulas were identified in each sample using negative mode (Table 2), and 815–1,949 formulas were identified in positive mode (Table S4). The number of assigned negative mode formulas is similar to past studies of wastewater effluent by FT-ICR MS (Gonsior et al, 2011; Tseng et al, 2013). …”

“…Past FT-ICR MS studies of wastewater have focused on CHOS formulas because they are highly abundant and ionize well in negative mode, as observed here. These studies report that 73% of primary effluent, 40.6–42.2% of secondary effluent, and 8–18% of advanced effluent formulas contain S, all of which are higher than the abundance of S-containing formulas in natural DOM samples (Gonsior et al, 2011; Mesfioui et al, 2012; Tseng et al, 2013). All of the Nine Springs samples have CHOS formulas within the protein and lignin-like regions, while the primary effluent also contains lipid- and carbohydrate-like CHOS formulas (Fig.…”

“…Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) is widely applied to determine molecular formulas in DOM from natural aquatic systems (Hertkorn et al, 2008; Koch et al, 2007), but has received little attention for the characterization of DOM in waste-water treatment systems. Previous studies of wastewater DOM by FT-ICR MS focused on formulas containing only C, H, O, and S and are limited to either single samples or samples collected during one treatment process (e.g., secondary treatment; Gonsior et al, 2011; Mesfioui et al, 2012; Shakeri Yekta et al, 2012, Tseng et al, 2013). Despite these limitations, the past studies indicate that DOM in wastewater treatment systems is highly complex, rich in S-containing formulas, and distinctive from DOM present in natural systems.…”