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Low molecular weight (MW) charged organic matter is poorly removed by conventional coagulants but contributes to disinfection byproduct formation during chlorination of drinking waters. We hypothesized that CIEX, a new Al-based hybrid coagulant with ion-exchange functional groups, would be new mechanistic approach to remove low MW organic matter during coagulation and would perform better than polyaluminum chloride (PACl) or metal-salt based coagulants. We measured coagulation performance using dissolved organic carbon (DOC) in a high hardness surface water. CIEX achieved excellent turbidity removal and removed 20% to 46% more DOC than FeCl3, Al2(SO4)3, or PACl, depending on dose. The improved DOC removal was attributable to better removal of low MW organic matter (<2 kDa). We further studied removal mechanisms in a model water containing a low MW organic acid (salicylic acid (SA)). CIEX achieved high removal of organic acids (>90% of SA) independent of pH, whereas removal by metal salts was lower (<15%) and was strongly pH dependent. CIEX ion-exchange capability is facilitated by its covalently bound quaternary ammonium group, which conventional coagulants lack. Plus, unlike other cationic polymers that react with chloramines to form N-nitrosodimethylamine (NDMA), CIEX has a low molar yield (9.3 x 10-7 mol NDMA per mol CIEX-N). [ABSTRACT FROM AUTHOR]

Electrochemical reduction of carbon dioxide (CO2) to useful chemical materials is of great significance to the virtuous cycle of CO2. However, some problems such as high overpotential, high applied voltage, and high energy consumption exist in the course of the conventional electrochemical reduction process. This study presents a new CO2 reduction technique for targeted production of formic acid in a microbial electrolysis cell (MEC) driven by a microbial fuel cell (MFC). The multiwalled carbon nanotubes (MWCNT) and cobalt tetra-amino phthalocyanine (CoTAPc) composite modified electrode was fabricated by the layer-by-layer (LBL) self-assembly technique. The new electrodes significantly decreased the overpotential of CO2 reduction, and as cathode successfully reduced CO2 to formic acid (production rate of up to 21.0 ± 0.2 mg·L-1-h-1) in an MEC driven by a single MFC. Compared with the electrode modified by CoTAPc alone, the MWCNT/CoTAPc composite modified electrode could increase the current and formic acid production rate by approximately 20% and 100%, respectively. The Faraday efficiency for formic acid production depended on the cathode potential. The MWCNT/CoTAPc composite electrode reached the maximum Faraday efficiency at the cathode potential of ca. -0.5 V vs Ag/AgCl. Increasing the number of electrode modification layers favored the current and formic acid production rate. The production of formic acid was stable in the MFC-MEC system after multiple batches of CO2 electrolysis, and no significant change was observed on the performances of the modified electrode. The coupling of the catalytic electrode and the bioelectrochemical system realized the targeted reduction of CO2 in the absence of external energy input, providing a new way for CO2 capture and conversion. [ABSTRACT FROM AUTHOR]

Because aqueous ions can influence the defluoridation of the electrocoagulation (EC) process, the effects of Ca2+ and Mg2+ were investigated. The behaviors and mechanisms of EC defluoridation in Ca2+-containing systems were different from those in Mg2+-containing systems. An increase in Ca2+ concentration improved the defluoridation efficiency (eF), but it could not change the optimal molar ratio of OH- and F- to Al3+ (rOH+F). The highest eF can usually be obtained at rOH+F = 3 for defluoridation. Only a small portion of Ca2+ entered into the flocs, and Ca2+ could not influence the mechanism of EC defluoridation. For the Mg2+-containing system, the optimal rOH+F increased with increasing Mg2+ concentration. The optimal rOH+F was maintained at 3 after the Mg2+ concentration was corrected using the obtained correction coefficient of 0.3435. About 50% to 70% of the total Mg2+ entered into the flocs. From the XRD analysis, it was found that some Mg—Al—F layered double hydroxides (LDHs) were formed by Mg2+, F-, and Al3+ during electrolysis. It is proposed for the first time that the formation of Mg—Al—F LDH is one of the mechanisms for EC defluoridation in systems containing both F- and Mg2+. [ABSTRACT FROM AUTHOR]

Covalently bound organic silicate aluminum hybrid coagulants were synthesized by employing two silane coupling agents [diethoxydimethylsilane (DEDMS), γ-aminopropylmethyldiethoxysilane (APDES)] as silicon sources. An additional coagulant was synthesized using another silane-tetraethylorthosilicate (TEOS) for comparison. Both the coagulant with DEDMS and that with APDES as the silicon source were shown to be covalently bound by infrared (IR) analysis. All three hybrid coagulants were characterized by pH, zeta potential, Al species distribution, and transmission electron microscopy (TEM) analysis. The results indicated that the silicon source played a significant role in aspects of the chemical and physical structure, Al species distribution, and electrochemistry characteristics. Specifically, the coagulant with APDES as the silicon source featured the highest zeta potential value, the highest content of Al13, and reticulated aggregate. The coagulation behaviors of the three hybrid coagulants were also investigated by treating synthetic water containing humic acid (HA). The hybrid coagulant with APDES as the silicon source exhibited the best coagulation behavior in terms of HA removal and turbidity removal, due to the combination of the zeta potential, Al species distribution, and organic functional groups. [ABSTRACT FROM AUTHOR]