Extracellular organic matter (EOM) and intracellular organic matter (IOM) of Microcystis aeruginosa have been reported to contribute to the formation of carbonaceous disinfection by-products (C-DBPs) ...and nitrogenous disinfection by-products (N-DBPs). Little is known about DBPs formation from different molecular weight (MW) fractions, especially for N-nitrosodimethylamine (NDMA). This study fractionated EOM and IOM into several MW fractions using a series of ultrafiltration membranes and is the first to report on the C-DBPs and N-DBPs formation from chlorination and chloramination of different MW fractions. Results showed that EOM and IOM were mainly distributed in low-MW (<1 KDa) and high-MW (>100 KDa) fractions. Additionally, the low-MW and high-MW fractions of EOM and IOM generally took an important part in forming C-DBPs and N-DBPs, either in chlorination or in chloramination. Furthermore, the effects of pre-ozonation on the formation of DBPs in subsequent chlorination and chloramination were also investigated. It was found that ozone shifted the high-MW fractions of EOM and IOM into lower MW fractions and increased the C-DBPs and N-DBPs yields to different degrees. As low-MW fractions are more difficult to remove than high-MW fractions by conventional treatment processes, therefore, activated carbon adsorption, nanofiltration (NF) and biological treatment processes can be ideal to remove the low-MW fractions and minimize the formation potential of C-DBPs and N-DBPs. Moreover, the use of ozone should be carefully considered in the treatment of algal-rich water.
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•Algal organic matters were fractionated into six molecular weight (MW) fractions.•Low-MW and high-MW fractions contributed to most disinfection by-products (DBPs).•Pre-ozonation shifted the high-MW to low-MW fractions and increased DBPs yields.
•CoFe2O4 MNPs tested as heterogeneous catalyst for the activation of oxone.•The catalytic performance was typically affected by several key operating parameters.•The catalyst exhibited good stability ...and easily recovered with excellent reusability.•Degradation pathway was proposed according to the results of LC-MS/MS analysis.
A magnetic nanoscaled catalyst cobalt ferrite (CoFe2O4) was successfully prepared and used for the activation of oxone to generate sulfate radicals for the degradation of diclofenac. The catalyst was characterized by transmission electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The effects of calcination temperature, initial pH, catalyst and oxone dosage on the degradation efficiency were investigated. Results demonstrated that CoFe2O4-300 exhibited the best catalytic performance and almost complete removal of diclofenac was obtained in 15min. The degradation efficiency increased with initial pH decreasing in the pH range of 5–9. The increase of catalyst and oxone dosage both had the positive effect on the degradation of diclofenac. Moreover, CoFe2O4 could retain high degradation efficiency even after being reused for five cycles. Finally, the major diclofenac degradation intermediates were identified and the primary degradation pathways were proposed.
•Thermally activated persulfate (TAP) technology can decompose CBZ efficiently.•Sulfate radicals play the primary role in TAP oxidation.•The best CBZ degradation can be achieved at acidic ...conditions.•Coexisting anions and cations exhibit opposite effect on the CBZ degradation.•Six intermediate products are identified using LC–MS/MS.
Sulfate radicals-based advanced oxidation processes have been applied in water treatment and in situ chemical oxidation. Batch experiments were conducted to investigate the influencing factors including persulfate dosage, initial carbamazepine (CBZ) concentrations, solution pH, coexisting inorganic anions and cations on the decomposition of CBZ using thermally activated persulfate (TAP) technology. The results showed that TAP oxidation was efficient process for the CBZ degradation in water. The generation of sulfate radicals was accounted for the CBZ degradation in TAP system. The CBZ degradation rate constant increased as persulfate dosage increased and decreased as the initial CBZ concentrations increased. The CBZ decomposition rate decreased with the increasing pH and the best degradation occurred at pH 3. The exception was the strong alkaline condition under which a higher CBZ degradation performance was achieved. Coexisting inorganic anions slowed down the CBZ degradation to different degrees and the inhibiting effect abided by the following order: CO32->HCO3->Cl->SO42->NO3-. In contrast, coexisting cations could significantly enhance the CBZ degradation, and the promoting effect was in the order of Fe2+>Cu2+>Fe3+. In this study, six major intermediate products were generated during the TAP oxidation.
Degradation of diethyl phthalate (DEP) by ultraviolet/persulfate (UV/PS) process at different reaction conditions was evaluated. DEP can be degraded effectively via this process. Both tert-butyl ...(TBA) and methanol (MeOH) inhibited the degradation of DEP with MeOH having a stronger impact than TBA, suggesting sulfate radical (▪) and hydroxyl radical (HO) both existed in the reaction systems studied. The second-order rate constants of DEP reacting with ▪ and HO were calculated to be (6.4±0.3)×107 M−1s−1 and (3.7±0.1)×109 M−1s−1, respectively. To further access the potential degradation mechanism in this system, the pseudo-first-order rate constants (ko) and the radical contributions were modeled using a simple steady-state kinetic model involving ▪ and HO. Generally, HO had a greater contribution to DEP degradation than ▪. The ko of DEP increased as PS dosages increased when PS dosages were below 1.9 mM. However, it decreased with increasing initial DEP concentrations, which might be due to the radical scavenging effect of DEP. The ko values in acidic conditions were higher than those in alkaline solutions, which was probably caused by the increasing concentration of hydrogen phosphate (with higher scavenging effects than dihydrogen phosphate) from the phosphate buffer as pH values rose. Natural organic matter and bicarbonate dramatically suppressed the degradation of DEP by scavenging ▪ and HO. Additionally, the presence of chloride ion (Cl−) promoted the degradation of DEP at low Cl− concentrations (0.25–1 mM). Finally, the proposed degradation pathways were illustrated.
•Removal of DEP by UV/PS process at various reaction conditions was investigated.•DEP can be degraded effectively via UV/PS process.•A simple steady-state kinetic model was used to study the degradation mechanism.•The contribution of HO to DEP degradation was higher than that of ▪.
•Degradation of clofibric acid (CA) was studied by UV/PS and UV/chlorine.•The second-order rate constants of CA with SO4−, OH and Cl were determined.•Impacts of different conditions including oxidant ...dosage, pH, Cl− and HCO3− were discussed.•UV/chlorine was found to be more cost-effective.•The disinfection by-products (DBPs) formation was evaluated during followed chlor(am)ination.
This study investigated the UV/persulfate (UV/PS) and UV/chlorine processes as alternative method for the removal of clofibric acid (CA). The formation of disinfection byproducts (DBPs) during subsequent chlor(am)ination was also evaluated. The degradation of CA followed the pseudo-first order kinetics. The second-order rate constants of CA with SO4−, OH and Cl were respectively determined as kSO4-,CA=(1.73±0.01)×109M−1s−1, kOH,CA=(2.72±0.08)×109M−1s−1 and kCl,CA=(9.76±0.15)×1010M−1s−1. The degradation rate constant increased with increasing oxidant dosage in UV/PS and UV/chlorine processes. The degradation rate constant was found to be the highest at pH 9 and decreased dramatically at pH 11 in UV/PS process. For UV/chlorine, the rate constant continuously decreased with increasing pH from 3 to 11. Presence of HCO3− and Cl− had different effects (promotion and/or inhibition) on CA degradation in both processes. An inhibition effect was observed in the presence of NOM for the two UV-based processes. The higher CA removal in real water suggested the two processes were suitable for treating water containing CA, and the UV/chlorine was more cost-effective than UV/PS based on the total cost of electrical energy. Compared with the chlor(am)ination of CA, the UV/PS and UV/chlorine pre-oxidation significantly impacted the DBP formation during subsequent chlor(am)ination, which indicated the application of the two UV-based processes needs to be carefully balanced against the downstream effect on DBP formation.
•Comparison between the degradation of diuron by chlorination and UV/chlorine process.•The relative contribution of active species in UV/chlorine process.•Impacts of different conditions including ...oxidant dosage, pH, etc. were discussed.•The degradation pathway of diuron during UV/chlorine was proposed using LC-ESI/MS.•The DBPs formation was evaluated during followed chlor(am)ination after pre-chlorination and UV/chlorine process.
The degradation of diuron by chlorination and UV/chlorine process and the formation of disinfection by-products (DBPs) was investigated in this study. The degradation of diuron followed the pseudo first-order kinetics model. In UV/chlorine process, hydroxyl radical were proved to provide more contribution in the oxidation. The degradation kinetics increased with the increasing of chlorine dosage and the decreasing of natural organic matter (NOM) dosage. However, the degradation pathways were defined using high performance liquid chromatography coupled with a TSQ Quantum quadrupole mass spectrometer (HPLC-ESI/MS). The formation of DBPs after chlorination and chloramination was defined using gas chromatography with elect ion capture detector (GC-ECD) and gas chromatography–mass spectrometer (GC–MS). Several kinds of DBPs including chloroform (TCM), 1,1-dichloroacetone (1,1-DCP), 1,1,1-trichloroacetone (1,1,1-TCP), trichloronitromethane (TCNM), dichloroacetamide (DCAcAm) and trichloroacetamide (TCAcAm) was identified in this study.
► The pseudo-second-order model can well describe the adsorption performance of diuron onto MWCNTs. ► The Polanyi–Manes isotherm showed the best fitting with the equilibrium data. ► The thermodynamic ...parameters indicated that the adsorption of diuron onto MWCNTs was spontaneous and exothermic. ► The adsorption of diuron onto MWCNTs was found to be pH dependent and favorable under neutral and basic conditions. ► The presence of Cu2+ had different effect on the adsorption of diuron onto as-prepared and oxidized MWCNTs.
The adsorption of diuron onto as-prepared and oxidized multiwalled carbon nanotubes (MWCNTs) from aqueous solution has been studied through batch experiments, in which the effect of contact time, temperature, pH and coexisting Cu2+ were investigated. The adsorption performance of diuron onto MWCNTs fitted the pseudo-second-order model and apparent equilibrium was reached within 1h. The experimental data showed good correlation with Freundlich, Langmuir and Polanyi–Manes models in the range of experimental concentrations, but followed Polanyi–Manes model most appropriate. The calculated thermodynamic parameters showed adsorption of diuron onto MWCNTs was exothermic and spontaneous. Except for the introduction of oxygen-containing functional groups onto the surfaces of MWCNTs, the oxidized treatment of as-prepared MWCNTs can also increase the surface area and the pore volume, which resulted in the increase adsorption of diuron in this study. The adsorption of diuron was found to be pH dependent, and more adsorption was observed under neutral and basic conditions. The presence of Cu2+ has no significant effect on the adsorption of diuron onto as-prepared MWCNTs, on the contrary, the presence of Cu2+ can greatly decrease the adsorption of diuron onto oxidized MWCNTs. In addition, competitive adsorption was greater at higher than at lower diuron concentrations.
Bench scale tests were conducted to study the effect of chlorine dioxide (ClO2) oxidation on cell integrity, toxin degradation and disinfection by-product formation of Microcystis aeruginosa. The ...simulated cyanobacterial suspension was prepared at a concentration of 1.0×106cells/mL and the cell integrity was measured with flow cytometry. Results indicated that ClO2 can inhibit the photosynthetic capacity of M. aeruginosa cells and almost no integral cells were left after oxidation at a ClO2 dose of 1.0mg/L. The total toxin was degraded more rapidly with the ClO2 dosage increasing from 0.1mg/L to 1.0mg/L. Moreover, the damage on cell structure after oxidation resulted in released intracellular organic matter, which contributed to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) as disinfection by-products. Therefore, the use of ClO2 as an oxidant for treating algal-rich water should be carefully considered.
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•ClO2 can inhibit photosynthetic capacity of Microcystis aeruginosa.•Cell lysis and toxin degradation were observed after ClO2 oxidation.•DOC release contributed to the formation of THM and HAA.
● Urban water systems are challenged by climate change. ● Proactive adaptation and positive mitigation were proposed as the coping strategies. ● Proactive adaptation is to enhance the resilience of ...urban water systems. ● Positive mitigation is to strengthen the energy conservation and carbon reduction.
Urban water systems are facing various challenges against climate change, impacting cities' security and their sustainable development. Specifically, there are three major challenges: submersion risk of coastal cities as glaciers melt and sea level rises, more and severe urban flooding caused by extreme weather like intensified storm surge and heavy precipitation, and regional water resource patterns challenged by alteration of spatial distribution of precipitation. Regarding this, two strategies including proactive adaptation and positive mitigation were proposed in this article to realize the reconstruction and optimization of urban water systems, to enhance their resilience, and eventually increase their adaptability and coping ability to climate change. The proactive adaptation strategy consists of 1) construction of sponge cities to accommodate the increased regular rainfall and to balance the alterations of spatial redistribution of precipitation; 2) reconstruction of excess stormwater discharge and detention system to increase capability for extreme precipitation events based on flood risk assessment under future climate change; 3) deployment of forward-looking, ecological, and integrated measures to improve coastal protection capability against inundation risks caused by climate change and sea level rise. The positive mitigation strategy is to employ the systematic concept in planning and design and to adopt advanced applicable energy-saving technologies, processes, and management practices, aiming at reduction in flux of urban water systems, reinforcement in energy conservation and carbon reduction in both water supply systems and wastewater treatment systems, and thus a reduction of greenhouse gas emission from urban water systems.
