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•UV/chlorine process was applied to inactivate M. aeruginosa.•A kinetic model was developed to describe the mechanism for chlorine decay.•Flow cytometry and confocal laser scanning ...microscopy were used.•UV/chlorine pretreatment can improve coagulation of algae.
Inactivation of Microcystis aeruginosa by UV/chlorine process was investigated in this study. Chlorine decay with or without the presence of algal cells was modeled based on a kinetic model, and the second-order rate constant between chlorine and algal cells was determined to be 3.3 × 10−4 (mgC/L)−1 s−1. Flow cytometry as well as confocal laser scanning microscopy were used to characterize the cell integrity of M. aeruginosa. Results demonstrated that UV/chlorine pre-oxidation was responsible for the inactivation of M. aeruginosa, and the inactivation efficiency increased with the increasing dosage of chlorine. UV/chlorine process can significantly change the surface characteristics of M. aeruginosa and enhance the coagulation efficiency. Moreover, due to the destruction of algal cells, microcystin-LR would be released and then degraded during pre-oxidation, and the releasing endotoxin could be removed during subsequent coagulation-sedimentation process. This study suggests that UV/chlorine process might be a potential alternative for the pretreatment of cyanobacterial cells in treating cyanobacteria-laden water.
Advanced oxidation processes (AOPs) are ideal alternative to remove contaminants of emerging concern (CECs). Nitrate and nitrite commonly co-exist with CECs in surface water, groundwater, and ...agricultural runoffs, which impact the performance of AOPs. Interests in investigation on the impacts of nitrate/nitrite on CEC degradation in AOPs have grown exponentially, due to the participation of reactive nitrogen species (RNS). RNS as a daughter radical in AOPs, are generally formed from photolysis of nitrate/nitrite or reactions of nitrate/nitrite with hydroxyl radical. It was documented that nitrate/nitrite in photochemical AOPs could accelerate CEC degradation, while that in non-photochemical AOPs usually play an inhibitory role. Except the performance of AOPs, nitrate/nitrite present in AOPs also have significant impact on the degradation pathway of CECs, of which the typical one is the nitration/nitrosation of CECs. Formation of nitrated/nitrosated CEC products in AOPs is almost inevitable when nitrite is present in water, because RNS are typical nitrating/nitrosating agents. The nitrated/nitrosated products not only show higher toxicity, but have higher formation potential of nitro/nitroso disinfection byproducts. Therefore, nitrate/nitrite can be used as a source of hydroxyl radical and RNS in photochemical AOPs (especially at λ > 280 nm), and should be avoided in non-photochemical AOPs. Besides, using pretreatment to turn nitrite to nitrate is a useful method to reduce the formation of nitrated/nitrosated CECs. Overall, this critical review aims to summarize the all-round impacts of nitrate/nitrite on AOPs, and provide practical implications to better utilize the naturally present nitrate/nitrite.
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•NO3−/NO2− enhances CEC degradation in photochemical AOPs (λ > 280 nm).•Photo induced decomposition of NO3−/NO2− leads to the nitr(os)ation of CECs.•NO2− play an important role in nitr(os)ation of CECs in non-photochemical AOPs.•Typical N-DBPs are generated from NO3−/NO2− when AOPs are set before disinfection.
A novel advanced oxidation process using boron-doped diamond (BDD) anode to activate persulfate (PS) with low concentration of electrolyte was systematically investigated in this study. Compared to ...direct electrochemical oxidation of atrazine (ATZ) using BDD anode, the addition and activation of PS significantly declined the demand for electrolytes. It was confirmed by scavenger experiments that both radical and non-radical oxidation occurred in this system. Degradation of ATZ was enhanced with the increase of current density and dosage of PS, and decrease of initial pH. However, the increase of current density can also lead to the decrease of current efficiency, then increase of energy consumption. Besides, the inhibitory effect of anions on the degradation of ATZ followed the order of HCO3−>H2PO4−>NO3−, while the presence of Cl− accelerated the degradation of ATZ. Furthermore, the degradation products mainly resulting from de-alkylation, de-chlorination, and hydroxylation were detected. Due to the distinctive preference to ethyl group in BDD/PS system, the formation of deethyl-atrazine was quicker than that of deisopropyl-atrazine. The study aims to provide a comprehensive understanding on the potential application of BDD/PS system in water treatment.
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•Demand for electrolyte decreased significantly in BDD/PS system.•Both radical and non-radical oxidation occurred in BDD/PS system.•Dealkylation and dechlorination are two main reactions in degradation of ATZ.
Bisphenol (BP) analogues in wastewater effluent and groundwater pose a potential threat to human health due to their ability to disrupt steroidogenesis. A new solar-assisted electrochemical process ...(SECP) was developed and evaluated for the degradation of BP analogues. The effects of quenchers, current density, initial pH, supporting electrolyte, and aqueous matrix on the removal kinetics of bisphenol AF (BPAF) and bisphenol A (BPA) were investigated. The kinetic constants of BPAF, BPA, and bisphenol S (BPS) in the SECP with irradiation intensity of 500 mW cm−2 were 0.017 ± 0.002 min−1, 0.022 ± 0.002 min−1, and 0.012 ± 0.001 min−1, respectively. The changes in the degradation rates of BPAF, BPA, and BPS in the presence of quenchers indicated the relative contribution of hydroxyl radical (●OH) oxidation, anodic electrolysis, and singlet (1O2) oxygenation in the degradation of BPs in the SECP. The enhanced rate of generation of ●OH and 1O2 was observed in the SECP compared with those in the conventional electrochemical system. The identification of the transformation products (TPs) of BPAF demonstrated that hydroxylation, ring cleavage, β-scission, and defluorination were the major processes during the oxidation in the SECP. The conversion to fluoride ions (76%) and mineralization of total organic carbon (72%) in the SECP indicated further degradation of TPs. The results from this study improved our understanding of the degradation of BP analogues in the electrooxidation irradiated by solar light and help to establish the application potential of the SECP for the effective degradation of emerging contaminants in wastewater.
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•The enhanced performance of SECP was investigated for removal of bisphenol analogues.•SECP showed a synergistic effect on generation of.●OH and 1O2 for BPAF and BPA removal.•Transformation products and degradation pathways of BPAF in SECP were identified.•SECP exhibited hydroxylation, ring cleavage, β-scission, and defluorination process of BPAF removal.
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•A kinetic model is built from reactions and parameters in literature.•An optimum molar ratio of Fe2+ and PS at 1:1 was favorable for ATZ degradation.•SO4− is the predominant radical ...species in Fe2+/PS system.
In this paper, a mathematical model on Fe(II)-activated persulfate oxidation of atrazine (ATZ) was tested using the rate constants from literature, and the degradation kinetics and mechanism of ATZ degradation in Fe(II)/persulfate (Fe2+/PS) system were investigated to verify the model. Some influence factors were taken into consideration in this model, including molar ratio of Fe2+ and PS, initial ATZ concentration, natural organic matter (NOM) concentration, tertiary butanol (TBA) and methanol (MeOH) concentrations. Corresponding experimental data could be predicted accurately according to this model. Both experimental data and predicted results implied that a molar ratio of Fe2+ and PS at 1:1, low initial ATZ and NOM concentrations were favorable for ATZ degradation. Besides, the radical species were determined via evaluating the effect of TBA and MeOH, and results confirmed that both sulfate radical (SO4−) and hydroxyl radical (OH) existed in this system. To investigate the predominant radical in Fe2+/PS system, nitrobenzene (NB) was used as a probe compound which only react with OH. According to the degradation efficiency of NB and ATZ in Fe2+/PS system, it could be concluded that only small amount of OH were produced and SO4− made a major contribution to ATZ degradation in Fe2+/PS system. Experimental data, as well as the mathematical model in this study, improved our understanding on the effect of operating parameters for ATZ degradation in Fe(II)-based advanced oxidation processes.
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•UV/chlor(am)ine can effectively degrade DTA compared with chlor(am)ine alone.•RCS and HO are main species in UV/chlorine and UV/chloramine processes.•UV/chlorine is effective in ...degrading DTA in natural waters.•Cytotoxicity in UV/chloramine increased after 24 h due to iodoform formation.
This study compared the degradation efficiency of diatrizoate (DTA) by UV/chlorine and UV/chloramine processes. DTA could be effectively degraded by the UV/chlorine and UV/chloramine processes compared with chlorination and chloramination solely. Although the UV/chlorine process was more sensitive to the variations of oxidant dosages, solution pH, the concentration of bicarbonate and chloride, UV/chlorine degraded DTA more efficiently than UV/chloramine process. The reactive chlorine species (RCS) and hydroxyl radical (HO) are predominant contributors to DTA degradation in the UV/chlorine and UV/chloramine processes respectively, and the specific contribution of each reactive specie changed with solution pH. The performance of UV/chlorine and UV/chloramine processes on DTA degradation was obviously inhibited in natural waters (e.g., wastewater, rainwater, river water and tap water), however, degradation of DTA in the UV/chlorine are still satisfactory compared with UV/chloramine process. Formation of chloroform, dichloroacetonitrile, and iodoform (IF) from DTA was observed in both UV/chlorine and UV/chloramine processes. It is notable that formation potential of IF from DTA was significantly enhanced in UV/chloramine process, and thus the overall cytotoxicity of generated DBPs in UV/chloramine process is far greater than that in UV/chlorine process.
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•Cu(I) showed better performance than Fe(II) to activate peroxymonosulfate.•EGCG can accelerate copper conversion from Cu(II) to Cu(I).•O2 play an important role during BPA ...degradation in Cu(II)/EGCG/PMS process.•SO4−, HO, and Cu(III) are main contributor to BPA degradation in this process.
Transition metals to activate peroxymonosulfate (PMS) has promising prospect to remove emerging organic contaminants, among which copper is an alternative because of its relatively high regulated concentration in drinking water and wide use of organic copper pesticide. Cu(I) shows good performance on the activation of PMS, while Cu(II) is reported to have no ability to activate PMS, which is the most stable valent in natural environment. In this study, degradation of bisphenol A (BPA) by Cu(II)/PMS process was significantly enhanced with involvement EGCG, because Cu(II) was transformed to Cu(I) and chelated by EGCG. Batch experiments were conducted to investigate the impacts of Cu(II), EGCG and PMS concentration and co-existing components including natural organic matters, alkalinity, and chloride ion. The impacts of solution pH and dissolved oxygen on BPA degradation were also evaluated to interpret the roles of Cu(I) and superoxide radical in Cu(II)/EGCG/PMS process, and the generated concentration of Cu(I) was determined. Possible generation pathway of Cu(III) were also proposed. By quenching experiment and electron paramagnetic resonance analysis, hydroxyl radical and sulfate radical in Cu(II)/EGCG/PMS process were confirmed to be main contributors for BPA degradation. Furthermore, transformation products of BPA were identified and their respective eco-toxicities were calculated. This work aims to unravel the interaction of EGCG and Cu(II), and provide a deep insight to the copper conversion in the presence of EGCG and PMS.
In this study, the degradation of 2-methylisoborneol (2-MIB) and geosmin (GSM) was evaluated by electrochemical oxidation (EO) using boron-doped diamond (BDD) electrode. Both 2-MIB and GSM could be ...degraded efficiently in sulfate electrolyte compared to inert nitrate or perchlorate electrolytes, implying that in-situ generated persulfate may be responsible for contaminants degradation. The observed linear relationship between 2-MIB (GSM) degradation rates and persulfate generation rates further proved that the in-situ generated persulfate enhanced 2-MIB (GSM) degradation. Moreover, a divided electrolytic cell was employed to investigate the effect of cathodic reactions on contaminants degradation and persulfate generation, and results confirmed that both anodic and cathodic reactions participated in 2-MIB (GSM) degradation. High current density and low solution pH were found to be favorable for 2-MIB and GSM degradation. The degradation intermediates were identified and the possible pathways of 2-MIB and GSM degradation were proposed. This study indicated that the EO process with BDD anode could be considered as a potential alternative for the removal of 2-MIB and GSM.
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•In-situ formed and activated persulfate is responsible for 2-MIB and GSM removal.•Both anodic and cathodic reactions participate in the generation of persulfate.•High current density and low pH were favorable for 2-MIB and GSM removal.•Possible pathways of 2-MIB and GSM degradation were proposed.
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•A kinetic model was developed to simulate the degradation of carbamazepine.•The second-order rate constant between CBZ and HO radicals was determined.•The electrical energy per order ...during the VUV process was calculated.•A possible degradation pathway of CBZ in VUV process was proposed.
Vaccum-ultraviolet (VUV) is effective for elimination of organic contaminants in aqueous environment and degradation of carbamazepine (CBZ) by VUV irradiation was systematically investigated in this study. A dynamic kinetic model was developed to simulate the destruction of CBZ that is mainly initiated by hydroxyl radicals (HO). The second-order rate constant of the reaction between CBZ and HO was determined to be 1.4 × 109 M−1 s-1. Effect of initial CBZ concentration, VUV irradiation intensity and natural organic matter (NOM) were further investigated in several batch experiments. The predicted CBZ removal rates increased with the increasing VUV intensity, while decreased with the increasing initial CBZ and NOM concentrations. Based on the electrical energy per order (EE/O) calculation, the optimal VUV intensity was determined to be 7.5 × 10-8 Einstein s−1. Meanwhile, several intermediates/products were identified and their time-dependent evolution profiles were determined, and finally a plausible degradation pathway of CBZ was proposed. Ecotoxicity assessment indicated that the potential toxicity of CBZ and its oxidation products should be paid more attention in the VUV process.
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•A novel EGCG/Fe2+/PDS process was proposed to oxidize organic contaminant.•EGCG accelerates the cycle of Fe(II)/Fe(III) and chelates with iron ions.•Generation of sulfate and ...hydroxyl radicals was verified in the system.•The addition of EGCG performs better than hydroxylamine and ascorbic acid.
A kind of green tea extract, epigallocatechin-3-gallate (EGCG) was introduced into Fe2+ activated persulfate (Fe2+/PS) system to enhance the degradation efficiency of atrazine. The involvement of EGCG improved atrazine degradation significantly in the pH range of 2.0–7.0, which could be interpreted by the strong reducing and chelating ability of EGCG. EGCG showed a better performance than hydroxylamine and ascorbic acid in modified Fe2+/PS systems, as the presence of EGCG could not only accelerate the transformation of Fe3+ to Fe2+, but prevent the formation of iron precipitation. Batch experiments were conducted and atrazine degradation depended upon the dosage of EGCG, persulfate, Fe2+, and other water quality parameters including initial pH, co-existing anions and natural organic matters. Radical quenching test and electron paramagnetic resonance (EPR) analysis were also performed and results showed that two kinds of radicals (sulfate radicals and hydroxyl radical) were verified to exist and play a significant role on atrazine degradation in the Fe2+/EGCG/PS system. Moreover, possible intermediates of atrazine were identified by HPLC/MS/MS and degradation pathways of atrazine and EGCG were proposed. This study aims to provide a comprehensive understanding on the potential application of EGCG to enhance degradation of refractory organics in water.
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