Simultaneous Degradation, Dehalogenation, and Detoxification of Halogenated Antibiotics by Carbon Dioxide Radical Anions

Despite the extensive application of advanced oxidation processes(AOPs)in water treatment,the efficiency of AOPs in eliminating various emerging contaminants such as halogenated antibiotics is constrained by a number of factors.Halogen moieties exhibit strong resistance to oxidative radicals,affecting the dehalogenation and detoxification efficiencies.To address these limitations of AOPs,advanced reduction processes(ARPs)have been proposed.Herein,a novel nucleophilic reductant—namely,the carbon dioxide radical anion(CO_(2)^(·-))—is introduced for the simultaneous degradation,dehalogenation,and detoxification of florfenicol(FF),a typical halogenated antibiotic.The results demonstrate that FF is completely eliminated by CO_(2)^(·-),with approximately 100%of Cland 46%of Freleased after 120 min of treatment.Simultaneous detoxification is observed,which exhibits a linear response to the release of free inorganic halogen ions(R^(2)=0.97,p<0.01).The formation of halogen-free products is the primary reason for the superior detoxification performance of this method,in comparison with conventional hydroxyl-radical-based AOPs.Products identification and density functional theory(DFT)calculations reveal the underlying dehalogenation mechanism,in which the chlorine moiety of FF is more susceptible than other moieties to nucleophilic attack by CO_(2)^(·-).Moreover,CO_(2)^(·-)-based ARPs exhibit superior dehalogenation efficiencies(>75%)in degrading a series of halogenated antibiotics,including chloramphenicol(CAP),thiamphenicol(THA),diclofenac(DLF),triclosan(TCS),and ciprofloxacin(CIP).The system shows high tolerance to the pH of the solution and the presence of natural water constituents,and demonstrates an excellent degradation performance in actual groundwater,indicating the strong application potential of CO_(2)^(·-)-based ARPs in real life.Overall,this study elucidates the feasibility of CO_(2)^(·-)for the simultaneous degradation,dehalogenation,and detoxification of halogenated antibiotics and provides a promising method for their regulation during water or wastewater treatment.

Nitrate reduction by·CO_(2)^(-) from UV-activated HCOOH

To address the environmental and health hazards of nitrate(NO_(3)^(-))in water,a denitrification advanced reduction process(ARP)using only formic acid(HCOOH)activated by ultraviolet(UV)light was proposed.The efficiency,influencing factors,mechanism,and kinetics of the reduction were investigated through component analysis and radical detection.Results show that,after 90 min of UV illumination,the reduction and gas conversion ratios of 50 mg/L NO_(3)^(-)-N reach 99.9%and 99.8%,respectively,under 9 mM of C_(0)(HCOOH),pH=3.0,and N_(2) aeration.Meanwhile,96.7%of HCOOH is consumed and converted into gas.The NO_(3)^(-)-N conversion process includes the transformation to NO_(2)^(-)-N,followed by a further reduction to gas and a direct conversion into gas,introducing small amounts of nitrite and ammonia.The carbon dioxide anion radical(·CO_(2)^(-))from HCOOH/HCOO^(-)is the principal cause of NO_(3)^(-)-N reduction by UV/HCOOH/N 2 ARP.In contrast,·CO_(2)^(-)production is caused by the hydroxyl radical(·OH).The NO_(3)^(-)-N reduction efficiency is enhanced by the increase in the light intensity,considerably affected by the initial pH,and less affected by inorganic anions,including Cl^(-),H_(2)PO_(4)^(-),and HCO_(3)^(-)/CO_(3)^(2-).The initial HCOOH concentration and light intensity are the main factors that influence the NO_(3)^(-)-N reduction rate.

Degradation of metoprolol by UV/sulfite as an advanced oxidation or reduction process:The significant role of oxygen

The degradation of metoprolol(MTP)by the UV/sulfite with oxygen as an advanced reduction process(ARP)and that without oxygen as an advanced oxidation process(AOP)was comparatively studied herein.The degradation of MTP by both processes followed the first-order rate law with comparable reaction rate constants of 1.50×10^(-3)sec^(−1)and 1.20×10^(-3)sec^(−1),respectively.Scavenging experiments demonstrated that both e^(−)_(aq)and H·played a crucial role in MTP degradation by the UV/sulfite as an ARP,while SO_(4)^(·−)was the dominant oxidant in the UV/sulfite AOP.The degradation kinetics of MTP by the UV/sulfite as an ARP and AOP shared a similar pH dependence with a minimum rate obtained around pH 8.The results could be well explained by the pH impacts on the MTP speciation and sulfite species.Totally six transformation products(TPs)were identified from MTP degradation by the UV/sulfite ARP,and two additional ones were detected in the UV/sulfite AOP.The benzene ring and ether groups of MTP were proposed as the major reactive sites for both processes based on molecular orbital calculations by density functional theory(DFT).The similar degradation products of MTP by the UV/sulfite process as an ARP and AOP indicated that e^(−)_(aq)/H·and SO_(4)^(·−)might share similar reaction mechanisms,primarily including hydroxylation,dealkylation,and H abstraction.The toxicity of MTP solution treated by the UV/sulfite AOP was calculated to be higher than that in the ARP by the Ecological Struc-ture Activity Relationships(ECOSAR)software,due to the accumulation of TPs with higher toxicity.

Photo enhanced degradation of contaminants of emerging concern in waste water

Emerging contaminants are posing serious global threats to the environment due to their diversity,recalcitrant nature and bioaccumulation.More disturbing is the fact that current wastewater treatment systems do not have the capacity to deal with these class of compounds.The quest to develop new technologies to mitigate the adverse effects of these contaminants has engendered new research interest on photo-enhanced processes.Photo-enhanced processes,with the potential of mineralizing environmental pollutants,currently appears to be the main viable technology for dealing with emerging contaminants.The process of contaminant degradation could either proceed via oxidation or reduction routes,referred to as advanced oxidation processes(AOPs)and advanced reduction processes(ARPs)respectively.Recently,different processes have been incorporated into a single system in order to explore the synergy that ensue from the combination of these processes.These processes that are currently at the front line in dealing with various classes of emerging contaminants,whose presence in the environment continues to grow on a daily basis,are the focus of this review.