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The monochloroacetic, dichloroacetic and trichloroacetic acid (MCAA, DCAA and TCAA) removed by metallic iron under controlled dissolved oxygen conditions (0, 0.75, 1.52, 2.59, 3.47 or 7.09 mg/L DO) was investigated in well-mixed batch systems. The removal of CAAs increased first and then decreased with increasing DO concentration. Compared with anoxic condition, the reduction of MCAA and DCAA was substantially enhanced in the presence of O2, while TCAA reduction was significantly inhibited above 2.59 mg/L. The 1.52 mg/L DO was optimum for the formation of final product, acetic acid. Chlorine mass balances were 69-102%, and carbon mass balances were 92-105%. With sufficient mass transfer from bulk to the particle surface, the degradation of CAAs was limited by their reduction or migration rate within iron particles, which were dependent on the change of reducing agents and corrosion coatings. Under anoxic conditions, the reduction of CAAs was mainly inhibited by the available reducing agents in the conductive layer. Under low oxic conditions, the increasing reducing agents and thin lepidocrocite layer were favorable for CAA dechlorination. Under high oxic conditions, the redundant oxygen competing for reducing agents and significant lepidocrocite growth became the major restricting factors. Various CAA removal mechanisms could be potentially applied to explaining the effect of DO concentration on iron efficiency for contaminant reduction in water and wastewater treatment., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The direct incorporation of chloramines and dissolved organic nitrogen (DON) may provide the nitrogen for nitrogenous disinfection byproducts (N-DBPs). This study explores the contributions of natural DON and chloramine incorporation to the formation of N-DBPs during chloramination. This study also evaluates the relationship between N-DBPs and carbonaceous DBPs by investigating four sources of dissolved organic matter with different DON-to-dissolved organic carbon (DOC) ratios. During chloramination, dihaloacetonitrile (DXAN) formation is correlated with the summation of trihalomethanes (THMs) and dichloroacetic acids (DXAAs) yield in molar basis at pH > 6. This study tests the formation kinetics of THMs, DXAAs, and DXANs during chloramination, explores the changes in DBP formation potential before and after a sequence of ozonation and chloramination, and tracks the nitrogen source of dichloroacetonitrile. The results support the hypothesis that THMs, DXAAs, and DXANs mainly derive from similar precursors upon chloramination. In addition, the precursor of HANs was approximately 10% (on a molar basis) of that of THMs and HAAs combined. The N-nitrosodimethylamine (NDMA) formation potential is correlated with DON/DOC in hydrophilic and transphilic fractions. Isotope (15)N-labeled monochloramine coupled with LC-electrospray ionization-tandem mass spectrometry was used to explore the nitrogen source of NDMA formed in chloraminated organic fractions. The results indicate that the nitroso group of the formed NDMA originates mainly from chloramines., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

A kinetic model was developed to predict dichloroacetic acid (DCAA) formation in chloraminated systems. Equations describing DCAA formation were incorporated into an established comprehensive monochloramine-natural organic matter (NOM) reaction model. DCAA formation was theorized to be proportional to the amount of NOM oxidized by monochloramine and described by a single dimensionless DCAA formation coefficient, theta(DCAA) (M(DCAA)/M(DOC(ox)). The applicability of the model to describe DCAA formation in the presence of six different NOM sources was evaluated. DCAA formation could be described by considering a single NOM source-specific value for theta(DCAA) over a wide range of experimental conditions (i.e., pH, NOM, free ammonia, and monochloramine concentrations). DCAA formation appears to be directly proportional to the amount of active chlorine (monochloramine and free chlorine) that reacted with the NOM under these experimental conditions. Values of theta(DCAA) for all six NOM sources, determined by nonlinear regression analysis, varied from 6.51 x 10(-3) to 1.15 x 10(-2) and were linearly correlated with specific ultraviolet absorbance at 280 nm (SUVA(280)). The ability to model monochloramine loss and DCAA formation in the presence of NOM provides insight into disinfection by-product (DBP) formation pathways under chloramination conditions. The subsequent model and correlations to SUVA has the potential to aid the water treatment industry as a tool in developing strategies that minimize DBP formation while maintaining the microbial integrity of the water distribution system.