Search

In this study, mild temperature was applied to enhance norfloxacin (NOR) degradation in nanoscale zero-valent copper (nZVC) activated persulfate (PS) process and the underlying activation mechanism was detailedly elaborated. Results showed that the activation performance of nZVC was far superior than that of micro zero-valent copper (mZVC), and almost complete elimination of 31.32 μM NOR was achieved within only 5 min in the condition of 0.05 g/L nZVC and 1.0 mM PS at 40 °C. The in-situ generated Cu+ was found to be the pivotal active copper species for PS activation and the presence of dissolved oxygen was favorable for its release. Mild temperature not only accelerated the Cu+ release from the nZVC corrision, but provided more opportunity for intermolecular collision to quickly form reactive oxygen species. SO4−∙ and ∙OH played the primary role for NOR destruction, while O2−· and H2O2 served as the mediators for copper cycling. The higher PS concentration favored NOR removal, whereas overdosing nZVC exerted the negative impact. Further increasing reaction temperature significantly accelerated the elimination of NOR in nZVC/PS process. The satisfactory removal of NOR was achieved under the acidic and neutral conditions. The NOR oxidation in the tested process was found to follow four routes and the cleavage of piperazine ring was determined to be the primary one. These encouraging results demonstrated that mild temperature enhanced nZVC/PS process was a promising strategy for the treatment of refractory and non-biodegradable industrial wastewater.

The presence of serotonin-norepinephrine reuptake inhibitors (SNRIs) such as venlafaxine (VEN) in surface waters has caused some concerns due to their harmful impacts on the human health and environment security. In the study, ultraviolet (UV) coupled with chlorine was developed for degrading VEN. Among the experiments, the UV/chlorine process demonstrated the highest performance in eliminating VEN. UV irradiation alone played a negligible role in VEN degradation. 39.56% of VEN was degraded by dark chlorination in 30 min, while 76.02% of VEN was decayed by UV/chlorine treatment within 30 min. Adding chlorine dosage and raising solution pH both facilitated the VEN removal. HCO3−, Cl− and HA inhibited VEN degradation during UV/chlorine treatment in accordance with predicted data. Furthermore, Kintecus software was applied to simulate the process of VEN degradation. Under UV/chlorine co-exposure, hydroxyl radical (HO·), chlorine and reactive chlorine species (RCS) were all proved to provide significant contribution to VEN oxidation. Note that both experimental and predicted contributions of HO· decreased as solution pH increased from 5.0 to 8.0. Four transformation pathways of VEN during UV/chlorine process were elucidated on basis of the DFT calculation and LC/MS analysis. Moreover, ECOSAR model program showed that UV/chlorine process reduced ecological toxicity of VEN obviously. Considering the influence of various factors, the most economical experimental conditions consist of chlorine (2.0–4.0 mg L−1) and pH (7.0–8.0).

As a typical iron-based oxide semiconductor with abundant reserves, α-Fe2O3 has been widely used in the domain of photocatalysis and environmental remediation. Here, sulfur doped α-Fe2O3 (S-α-Fe2O3) has been successfully fabricated through coprecipitation, hydrothermal and calcination processes and applied to activate persulfate (PS) for carbamazepine (CBZ) degradation under UV irradiation. Systematic characterizations were conducted to analyze the morphology, structure and chemical composite of S-α-Fe2O3. UV/PS/S-α-Fe2O3 process showed remarkably enhanced photocatalytic performance for CBZ degradation. The degradation rate constant (7.78 × 10−2 min−1) was about 2.2 and 14.1 times as high as that of UV/PS/α-Fe2O3 (3.60 × 10−2 min−1) and UV/PS (5.53 × 10−3 min−1) processes, respectively. With increasing PS concentration and photocatalyst dosage, the removal efficiency of CBZ both increased. UV/PS/S-α-Fe2O3 process can efficiently and steadily operate in a wide pH range of 3.0–8.0. The introduction of water matrix species (i.e. chloride, bicarbonate, nitrate and humic acid) exerted different effects on CBZ degradation. S-dopant was doped via forming ≡FeIII-SO42- bond on S-α-Fe2O3 surface, and doped sulfur functioned as surface electrons trapping centers derived from DFT study. The band gap value of S-α-Fe2O3 was reduced and the separation efficiency of photogenerated electrons and holes was improved. Hydroxyl radicals, sulfate radicals, superoxide radicals and holes all contributed to CBZ destruction. Furthermore, two major routes of CBZ degradation were proposed as hydroxylation and deamination, then followed by decarbonxylation, ketonization and ring cleavage based on the results of HPLC-MS and DFT calculation.

The environmental impact and health risk of carbamazepine (CBZ) in water environment has been continuously reported. Ultraviolet C (UVC)/persulfate (PS) and UVC/chlorine (NaClO) processes were confirmed to be able to efficiently eliminate CBZ through the oxidation by reactive radicals (52.82% SO4−· and 44.21% ·OH in UVC/PS system, 53.47% RCS and 43.84% ·OH in UVC/chlorine process, pH 7.0). The second-order rate constants of CBZ reacted with ·OH, SO4−· and RCS were determined to be 8.2 × 109, 9.1 × 108 and 4.2 × 1010 M−1 s−1, respectively. In both processes, increasing oxidants dosage and rising temperature was favorable for elimination, while increasing CBZ concentration retarded its degradation rate. The coexisting of NOM, SO42− and CO32–/HCO3– presented the inhibitory effect, while NO3– promoted the removal. NH4+ exerted an inhibitory effect in UVC/chlorine process, while exerted no obvious influence in UVC/PS system. Cl− posed a promoting role in UVC/PS treatment and a dual effect in UVC/chlorine process. pH affected the quantum yield of chlorine photolysis and the formation of RCS and ·OH. The degradation of CBZ oxidation via UVC/chlorine process was more pH dependent. 12 and 14 CBZ oxidation products were identified in UVC/PS and UVC/chlorine systems, respectively. SO4−·, RCS and ·OH were readily to attack C = C in CBZ molecule, mainly yielding hydroxylated CBZ, epoxy CBZ, pyridine aldehydes and ketones. Of the disinfection by-products (DBPs) assessed, both processes controlled the formation of haloacetic acids, while increased the generation of trichloromethane, especially via UVC/chlorine process. UVC/chlorine process was more economical and effective (EEO UVC/chlorine = 0.2213 kWh L−1), whereas UVC/PS process was safer in terms of DBPs and toxicity control.

Pre-magnetized Fe0/persulfate (pre-Fe0/PS) process was innovatively employed for controlling the pollution of p-arsanilic acid (p-ASA). This process showed favorable removal performance, achieving almost complete elimination of 10 mg/L p-ASA within 30 min at the reaction conditions of 0.2 g/L pre-Fe0 and 1 mM PS. The increase of PS concentration and pre-Fe0 dosage was conducive to the degradation. The coexistence of Cl−, NO3− and SO42− accelerated the removal, however the presence of HCO3− and HA presented the opposite trend. The p-ASA degradation decelerated gradually with increasing pH from 5 to 9. Its removal was caused by the attack of reactive oxygen species (i.e., SO4− , OH, O2− ), which could be continuously formed via the Fe2+/Fe3+ cycle in solution and on pre-Fe0 surface. In pre-Fe0/PS system, SO4− in solution, surface-bound SO4− , OH, OH in solution, O2− in solution and Fe(IV) contributed to the p-ASA degradation. A plausible transformation route related to the break of C-N and As-C bonds, the substitution of OH group was put forward. More importantly, the released inorganic arsenic during p-ASA decomposition could be effectively controlled through multiple functions including the precipitation, co-precipitation and sorption, which was well confirmed by XPS, FTIR and XRD analysis. Pre-Fe0/PS and Fe0/PS pretreatments both reduced the generation of C-DBPs except for chloral hydrate, while increased the formation of N-DBPs except for trichloroacetamide.

As an emerging semiconductor different from regular white TiO2, black TiO2 has attracted intensive attention on visible light driven photocatalysis for degrading dyes, but rarely for degradation of antibiotics. In this study, black anatase-TiO2 was demonstrated to be an effective catalyst for tetracycline (TC) visible light photodegradation. 66.2% removal efficiency of TC was achieved over black TiO2 under visible light illumination, while white TiO2 and N-doped TiO2 exhibited 43.4% and 59.6% removal efficiencies, respectively. Furthermore, only ⋅O2− radicals played an important role in TC photodegradation over white TiO2, whereas both ⋅O2− and h+ were responsible for the degradation over black TiO2 and N-doped TiO2. Different from white TiO2 for visible light photocatalytic TC degradation that follows photosensitization, the visible light photodegrataion over black TiO2 is due to photoexcitation.

In this study, the degradation of carbamazepine (CBZ) was comparatively investigated by UV-LED/persulfate (PS) and UV-LED/H2O2 processes in the presence of trace Cu2+ at neutral pH. Results showed that the introduction of trace Cu2+ accelerated CBZ degradation and more favorable performance was achieved in UV-LED/PS process. As oxidants dosage raised from 0.2 to 1.0 mM, the pseudo-first-order rate constant (kobs) value of CBZ both linearly increased in UV-LED/PS/Cu2+ and UV-LED/H2O2/Cu2+ processes. The promotion effect of Cu2+ at low level was more significant than that at high level in both processes at neutral pH. With reducing solution pH from 7.2 to 3.1, the kobs value dramatically increased from 0.136 to 0.399 min−1 in UV-LED/PS/Cu2+ process, while its value exhibited the imperceptible change in UV-LED/H2O2/Cu2+ process. OH functioned as the major contributor to CBZ degradation in two processes in pH range of 3.1–7.2. The addition of humic acid (HA), HCO3− and Cl− impeded CBZ degradation in UV-LED/H2O2/Cu2+ process. As for UV-LED/PS/Cu2+ process, the kobs value significantly increased in the presence of Cl−, while the introduction of HA and HCO3− restrained the removal. Total eleven degradation intermediates of CBZ were identified and a reasonable degradation pathway was proposed based on HPLC-MS/MS analysis and the calculation of Gaussian program. The acute toxicities of reacted solution enhanced in both processes within 15 min, especially in UV-LED/PS/Cu2+ process. In terms of electrical energy per order value, UV-LED/PS/Cu2+ process was found to be more cost-effective than UV-LED/H2O2/Cu2+ process. It was also noticed that UV-LED/PS process was more effective for CBZ removal in natural water in the presence of trace Cu2+.

The combination of UV and monochloramine (UV/NH2Cl) was investigated to eliminate tetracycline (TC) in water. The results indicated that TC degradation by UV/NH2Cl oxidation far exceeded that by UV photolysis and dark chloramination and these processes well fitted pseudo-first-order kinetics. With the increase of NH2Cl dosage, the pseudo-first-order rate constant (kobs) value increased linearly during TC chloramination, while the growth rate of kobs presented a gradual downward trend in UV/NH2Cl process. TC degradation by UV photolysis, dark chloramination and UV/NH2Cl oxidation displayed highly pH-dependent. As solution pH increased from 5.0 to 9.0, the TC removal increased during UV photolysis, while decreased during dark chloramination. For UV/NH2Cl process, the TC degradation showed a decreasing trend with increasing pH from 5.0 to 7.0, but further increasing pH to 9.0 presented an increasing trend. Reactive chlorine species acted as the major contributors to TC degradation in pH range of 6.0–8.0. TC degradation was not apparently affected after the introduction of HA and chloride, but was substantially accelerated in the presence of HCO3−. The proposed degradation pathways involved the hydroxylation, demethylation, dehydration and chlorine substitution processes. Compared with dark chloramination, the N-Nitrosodimethylamine (NDMA) generation was enhanced during TC oxidation by UV/NH2Cl process. The NDMA concentration increased with increasing solution pH from 6.0 to 8.0 and also elevated in the presences of humic acid (HA), nitrite, nitrate and ammonium during TC oxidation by chloramination and UV/NH2Cl. The results of acute toxicity test demonstrated that the toxicity of the reacted solution exhibited similar trends during dark chloramination and UV/NH2Cl treatment and was found to be obviously higher than UV photolysis.

The comparative study on the elimination of tetracycline (TC) utilizing UVC and UVC/PS processes was systematically conducted. The TC degradation via UVC irradiation and UVC/PS treatment well fitted pseudo first-order kinetics. Hydroxyl radicals ( OH) and sulfate radicals (SO4− ) were identified as the primary reactive species in UVC/PS process. Based on competition kinetic method, the second-order reaction rate constants of TC reacting with OH and SO4− were calculated as 4.6 × 109 and 2.2 × 109 M−1 s−1, respectively. The contributions of UVC photolysis, OH and SO4− to TC degradation were calculated as 5.91%, 61.97% and 28.11% at pH 7.0, respectively. The TC degradation in UVC and UVC/PS process was highly pH-dependent and enhanced with the increase of solution pH. Water matrix constituents played the multiple roles in TC degradation, including radical sensitizer, radical quencher and light absorber. Natural organic matters, CO32– and HCO3– enhanced the degradation during UVC photolysis, whereas the opposite phenomenon occurred in UVC/PS process. Cl− presented the inhibitory effect, while TC degradation can be accelerated by NO3– both in UVC and UVC/PS processes. The TC degradation in UVC/PS process can be classified into the hydroxylation, demethylation, decarbonylation, photocyclinzation, dehydration and cleavage of C N bond. After UVC and UVC/PS pretreatment, the decreased formation of dichloroacetic acid and trichloroacetic acid and the increased production of trichloromethane have been found. The TC removal was evaluated in terms of electrical energy per order, and its value can be considerably reduced via the combination of UVC and PS. Except for ultrapure water, the removal of TC from real waters by UVC/PS treatment could also be desirable.

A heterogeneous Fenton-like process was studied using synthesised goethite (α-FeOOH) and hydrogen peroxide (H 2 O 2 ) to degrade p -chloronitrobenzene ( p CNB) in water. The effect on the treatment efficiency of the initial pH, the dosage of hydrogen peroxide and goethite and the presence of humic acid and bicarbonate were quantified. At the optimal conditions (pH = 6.0, H 2 O 2 = 6.6 mg/L, and goethite = 333 mg/L), over 80% of p CNB was removed within 30 min. Humic acid and bicarbonate were found to inhibit the p CNB degradation, probably because they compete with p CNB for the OH produced. Intermediate oxidation products were identified, and a p CNB oxidation pathway is proposed. The findings demonstrate that α-FeOOH combined with H 2 O 2 has potential as an advanced oxidation process for water pollution control.