Algae organic matters (AOM), including intracellular organic matters (IOM) and extracellular organic matters (EOM), are causing numerous water quality issues, among which formation of disinfection ...byproducts (DBPs) and odor & taste (O&T) compounds are of particular concern. In this study, physiochemical properties of IOM and EOM of
Microcystic aeruginosa under an exponential growth phase (2.01 × 10
11/L) were comprehensively characterized. Moreover, the yields of DBPs during AOM disinfection and O&T-causing compounds were quantified. Hydrophilic organic matters accounted for 86% and 63% of DOC in IOM and EOM, respectively. Molecular weight (MW) fractions of IOM in <1 kDa, 40–800 kDa, and >800 kDa were 27%, 42%, and 31% of DOC, respectively, while EOM primarily contained 1–100 kDa molecules. Besides, a low SUVA (0.84 L/mg m) and the specific fluorescence spectra suggested that AOM (especially IOM) was principally comprised of protein-like substances, instead of humic-like matters. The formation potentials of chloroform, chloroacetic acid, and nitrosodimethylamine were 21.46, 68.29 and 0.0096 μg/mg C for IOM, and 32.44, 54.58 and 0.0189 μg/mg C for EOM, respectively. Furthermore, the dominant O&T compound produced from EOM and IOM were 2-MIB (68.75 ng/mg C) and β-cyclocitral (367.59 ng/mg C), respectively. Of note, dimethyltrisulfide became the prevailing O & T compound following anaerobic cultivation.
Display omitted
► Characterized AOM (EOM & IOM). E.g. Hydrophilicity, Molecular distribution, and EEM. ► Evaluate EOM and IOM-derived DBPs (e.g. NDMA) for different organic sub fractions. ► Evaluated EOM and IOM-derived O&T compounds before and after anaerobic incubation.
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.
Display omitted
•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.
•The APAP degradation exhibited a pseudo-first-order kinetics pattern well.•The Fe3O4 was stable without significant leaching of iron to water during reaction.•XPS and EPR results show that Fe2+Fe3+ ...cycle was answerable for radical generation.•The removal of APAP is a result of oxidation due to both OH• and SO4−•.
Magnetic nano-scaled particles Fe3O4 were studied for the activation of peroxymonosulfate (PMS) to generate active radicals for degradation of acetaminophen (APAP) in water. The Fe3O4 MNPs were found to effectively catalyze PMS for removal of APAP, and the reactions well followed a pseudo-first-order kinetics pattern (R2>0.95). Within 120min, approximately 75% of 10ppm APAP was accomplished by 0.2mM PMS in the presence of 0.8g/L Fe3O4 MNPs with little Fe3+ leaching (<4μg/L). Higher Fe3O4 MNP dose, lower initial APAP concentration, neutral pH, and higher reaction temperature favored the APAP degradation. The production of sulfate radicals and hydroxyl radicals was validated through two ways: (1) indirectly from the scavenging tests with scavenging agents, tert-butyl alcohol (TBA) and ethanol (EtOH); (2) directly from the electron paramagnetic resonance (ESR) tests with 0.1M 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO). Plausible mechanisms on the radical generation from Fe3O4 MNP activation of PMS are proposed based on the results of radical identification tests and XPS analysis. It appeared that Fe2+Fe3+ on the catalyst surface was responsible for the radical generation. The results demonstrated that Fe3O4 MNPs activated PMS is a promising technology for water pollution caused by contaminants such as pharmaceuticals.
•The antipyrine decomposition exhibited a pseudo-first-order kinetics pattern well.•The kobs with irradiance or oxidant dosage presented a linear relationship well.•The kobs exhibit an exponential ...trend as a function of AP0 for three systems.•UV/H2O2 behaved best at pH 2.5–10, while UV/PS behaved best at pH 10.0–11.5.•Cost for chemicals was firstly taken into account in calculation of the EE/O values.
Degradation of antipyrine (AP) in water by three UV-based photolysis processes (i.e., direct UV, UV/H2O2, UV/persulfate (UV/PS)) was studied. For all the oxidation processes, the AP decomposition exhibited a pseudo-first-order kinetics pattern. Generally, UV/H2O2 and UV/PS significantly improved the degradation rate relevant to UV treatment alone. The pseudo-first-order degradation rate constants (kobs) were, to different degrees, affected by initial AP concentration, oxidant dose, pH, UV irradiation intensity, and co-existing chemicals such as humic acid, chloride, bicarbonate, carbonate and nitrate. The three oxidation processes followed the order in terms of treatment costs: UV/PS>UV>UV/H2O2 if the energy and chemical costs are considered. Finally, the AP degradation pathways in the UV/H2O2 and UV/PS processes are proposed. Results demonstrated that UV/H2O2 and UV/PS are potential alternatives to control water pollution caused by emerging contaminants such as AP.
•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 ▪.
Display omitted
•Combination of UV and chlorine improved PNT degradation than UV or chlorine alone.•Chlorination, OH and reactive chlorine species contributed to PNT degradation.•NOM and alkalinity ...showed significant scavenging effects on PNT degradation.•Intermediates and disinfection byproducts were identified during UV/chlorine process.•The acute toxicity was decreased in UV/chlorine AOP compared with chlorination.
The degradation of phenacetin (PNT) by the combination of low-pressure mercury lamp and chlorine (UV/chlorine), an advanced oxidation process (AOP) of recent interest, was systematically investigated in terms of degradation kinetics, effects of chlorine dosage and water parameters, oxidation products as well as toxicity evaluation. The degradation of PNT followed pseudo first-order kinetics. The first-order rate constant (kobs) in the UV/chlorine AOP was 4.3, 8.4, and 11.1 times that of dark chlorination, UV/H2O2, and UV/PS, respectively, with the same molar dosage of oxidant at pH 7.2. Radical quenching tests suggested that chlorination, OH and reactive chlorine species were responsible for the UV/chlorine oxidation of PNT with contributions of 26.33%, 14.6% and 59.07%, at pH 7.2. As chlorine dosage gradually increased from 100 to 500 μM, the corresponding kobs monotonically increased from 0.0229 to 0.216 min−1. kobs was not apparently affected by the pH and coexisting chloride, but decreased by 56.5% and 75.4% in the presence of 10 mM HCO3− and 10 mg/L NOM. Slight decreases (around 15%) of kobs occurred in the raw water and tap water tests, while little effect was observed in filtered water samples compared with ultrapure water tests. Six typical disinfection byproducts including trichloromethane (TCM), chloral hydrate, dichloropropanone, trichloropropanone, trichloronitromethane, and dichloroacetonitrile were detected. The TCM yields increased to 159.95 μg/L within 20 min reaction of UV/chlorine, comprising 13.3% of the degraded PNT (per mole of carbon). The acute toxicity to luminescent bacterium Q67 by UV/chlorine was lower than chlorination under similar reaction conditions.
The photocatalysis of bromate (BrO3(-)) attracts much attention as BrO3(-) is a carcinogenic and genotoxic contaminant in drinking water. In this work, TiO2-graphene composite (P25-GR) photocatalyst ...for BrO3(-) reduction were prepared by a facile one-step hydrothermal method, which exhibited a higher capacity of BrO3(-) removal than P25 or GR did. The maximum removal of BrO3(-) was observed in the optimal conductions of 1% GR doping and at pH 6.8. Compared with that without UV, the higher decreasing of BrO3(-) on the composite indicates that BrO3(-) decomposition was predominantly contributed to photo-reduction with UV rather than adsorption. This hypothesis was supported by the decreasing of BrO3(-) with the synchronous increasing of Br(-) at nearly constant amount of total Bromine (BrO3(-) + Br(-)). Furthermore, the improvement of BrO3(-) reduction on P25-GR was observed in the treatment of a tap water. However, the efficiency of BrO3(-) removal was less than that in deionized water, probably due to the consumption of photo-generated electrons and the adsorption of natural organic matters (NOM) on graphene.
Heat-activated persulfate oxidation of diuron, was evaluated in this study. Sulfate radicals SO4- was the principal oxidizing agent responsible for the diuron degradation. The diuron decomposition ...exhibited a pseudo-first-order kinetics pattern at all the conditions tested and the observed rate constants well fit the Arrhenius equation. Typically, high temperature, high persulfate dose, and low initial diuron concentration increased the decomposition rate of diuron. At the tested pH range of 5.5–8.1, the highest degradation rate occurred at pH 6.3. The three groundwater anions inhibited the diuron decomposition with the following order: CO32->HCO3->Cl-. The major oxidation products in this study were C15H15ON3Cl4 (P3, m/z=376.2), C16H16O4N3Cl4 (P4, m/z=420.3), and C17H17O7N3Cl4 (P5, m/z=465.4), different from those produced during hydroxyl radical-induced advanced oxidation. Display omitted
► The diuron decomposition exhibited a pseudo-first-order kinetics pattern in tests. ► High temperature, high oxidant dose, and low initial diuron dose favored reaction. ► At the tested pH range of 5.5–8.1, the highest degradation rate occurred at pH 6.3. ► Anions inhibited diuron decomposition with order: CO32->HCO3->Cl-. ► Oxidation products of diuron differs with OH·or SO4-· induced advanced oxidation.
Heat-activated persulfate oxidation of diuron, a commonly found herbicide in groundwater, was evaluated in this study. Sulfate radicals SO4- was the principal oxidizing agent responsible for the diuron degradation. The diuron decomposition exhibited a pseudo-first-order kinetics pattern at all the conditions tested. The observed rate constants determined at 50–70°C well fit the Arrhenius equation, yielding an activation energy of 166.7±0.8kJmol−1. Temperature, persulfate dose, initial diuron concentration, pH, and three common groundwater solutes (CO32-,HCO3-, and Cl−), to different degrees, influenced the degradation. Typically, high temperature, high persulfate dose, and low initial diuron concentration increased the decomposition rate of diuron. At the tested pH range of 5.5–8.1, the highest degradation rate (kobs=0.18min−1) occurred at pH 6.3. The three groundwater anions inhibited the diuron decomposition with the following order: CO32->HCO3->Cl-. The major oxidation products in this study were C15H15ON3Cl4 (P3, m/z=376.2), C16H16O4N3Cl4 (P4, m/z=420.3), and C17H17O7N3Cl4 (P5, m/z=465.4), different from those produced during hydroxyl radical-induced advanced oxidation. The in situ chemical oxidation (ISCO) technology can be achieved in practice through combination with in situ thermal remediation.
