Characterization of molecular dissolved organic matter removed by modified eucalyptus-based biochar and disinfection by-product formation potential using Orbitrap mass spectrometric analysis.

Biochar is an alternative adsorbent, with similar characteristics to activated carbon, that can be applied to water treatment to remove dissolved organic matter (DOM) as disinfection by-product (DBP) precursors with comparable efficiency and better cost-effectiveness and sustainability relative to commercial alternatives. We applied non-targeted analysis with Orbitrap mass spectrometry to investigate changes in molecular DOM and DBP formation after treating DOM-containing water with biochar. Two surface water sources, Phong River (PR) in Khon Kaen, Thailand and Suwannee river (SR), USA, were tested using three types of eucalyptus-derived biochar (i.e., KOH-modified, calcined, and both) were selected as adsorbents and compared to commercial coconut-based activated carbon (ccAC). The results showed that calcination increased the surface area, pore volume, and functional groups of biochar responsible for adsorption. The calcined biochar achieved higher DOC removal efficiencies for both rivers than other adsorbents. PR contains more adsorbable DOM as over 800 molecules with carbon, hydrogen, and oxygen (CHO) features that were decreased or totally removed by all adsorbents. In contrast, for SR treatment, KOH-modified and calcined biochar was found to decrease over 800 CHO features, compared to around 500 and 400 CHO features for calcined biochar and ccAC, respectively. However, numerous background CHO features with reduced character (i.e., low degree of oxidation) were found after water treatment by calcined biochar, resulting in higher DBP formation after chlorination compared to the other adsorbents. The results of this study have important implications for future preparation of biochar for water treatment.

Changes in molecular dissolved organic matter and disinfection by-product formation during granular activated carbon filtration by unknown screening analysis with Orbitrap mass spectrometry.

The minimization of disinfection by-product (DBP) formation by the removal of its precursors before water disinfection is a highly effective approach. Granular activated carbon (GAC) filtration is widely used for water treatment, but our understanding of molecular dissolved organic matter (DOM) remains insufficient. This research investigates the removal of DOM and the minimization of DBP formation by pilot-scale coal- and coconut-based granular activated carbon filtrations (coAC and ccAC, respectively) using unknown screening analysis with Orbitrap mass spectrometry. DOM adsorption rates by both GACs were fitted with pseudo-second order models with initial adsorption rates of 0.005 mg g-1 min-1 and 0.022 mg g-1 min-1 for ccAC and coAC, respectively. Based on observations, ccAC was more effective in the removal of dissolved organic carbon and prolonged adsorption longer than coAC, as the breakthrough of coAC was found on Day 10. ccAC removed compounds with carbon, hydrogen, and oxygen (CHO features) with a wide range of oxidation states, as indicated by the carbon oxidation state (Cos), and a wide range of unsaturation, as indicated by oxygen subtracted double bond equivalent per carbon ([DBE-O]/C), while coAC selectively removed only those CHO features with less oxidized characters. Less oxidized compounds (low Cos) were preferentially removed with less contact time, while more oxidized compounds needed more contact time to adsorb on the GACs. A biofilm was developed on Day 60, and many CHO features were found to have increased after GAC treatment on Day 60, indicating the formation of microbial products. Chlorination resulted in a decrease in many CHO and CHO with Cl atom (CHOCl) features and the formation of CHOCl DBPs more than CHO DBP features. ccAC was effective in the minimization of trihalomethane (THM) and CHOCl DBP feature formations on Day 10 and Day 60, while coAC was found to be much less effective.

Characterization of lower Phong river dissolved organic matters and formations of unknown chlorine dioxide and chlorine disinfection by-products by Orbitrap mass spectrometry.

Dissolved organic matter (DOM) have been reported as precursors of disinfection byproducts (DBPs) and its molecular characteristics are rarely investigated due to its complexity. In this study, changes in the characteristics of DOM were investigated in the lower Phong River in Thailand in dry season and after the first rain in rainy season, using a non-targeted analysis with Orbitrap mass spectrometry. The river was rich with CHO features dominated by lignin-like molecules, while lipid-like molecules increase after domestic wastewater discharges. Wastewater discharge released DOM with higher molecular weight (MW) that was less oxygenated (low O/C) and less oxidized (low carbon oxidation state [Cos]). A lake affected by anthropogenic activities contributed more oxidized DOM into the river, while surface runoff carried DOM that is more oxygenated (high O/C), less hydrogenated (low H/C), and more oxidized (high Cos) to the stream. Water treatment further modified DOM to be lower MW. Approximately three hundred Cl-containing features (CHOCl) detected upstream were also found downstream. Disinfection by chlorine (Cl2) or chlorine dioxide (ClO2) formed both CHO and CHOCl DBPs. Low chlorine dosage applied to upstream and downstream samples resulted in many common unknown DBPs while increasing chlorine dosage resulted in more unique DBPs. At the same dosage, Cl2 reacted with DOM more than ClO2, including more oxidized molecules that are refractory to ClO2. Both Cl2 and ClO2 produced chlorinated and non-chlorinated DBPs, and some DBPs were commonly found by both disinfections. Cl2-produced DBPs were more unsaturated (higher [DBE-O]/C) and oxidized (higher Cos) than ClO2-DBPs.