Comparison of ciprofloxacin degradation in reclaimed water by UV/chlorine and UV/persulfate advanced oxidation processes

Effective reduction and recovery of As(III) and As(V) from alkaline wastewater by thiourea dioxide: Efficiency and mechanism

For alkaline wastewater with high arsenic concentration, the traditional lime precipitation inevitably produces large amounts of hazardous waste. Herein, a heat-activated reduction method employing thiourea dioxide (TDO) as the reductant was proposed to efficiently remove and recover As(III)/As(V) from alkaline wastewater in the form of valuable As(0). More than 99.9% of As(III)/As(V) (2-400 mM) were reduced to As(0) with a high purity of more than 99.5 wt% by TDO within 30 min. The highly reductive eaq- and SO2- radical generated during TDO decomposition contribute to the arsenic reduction, and the contribution ratios of eaq- and SO2- radical were estimated to be approximately 57.6% and 42.4% for As(III) removal and 62.2% and 37.8% for As(V) removal, respectively. The arsenic reduction was greatly improved by increasing pH and temperature, which could accelerate the cleavage of C-S bond in TDO for the eaq- and SO2- formation. The presence of dissolved oxygen, which can not only scavenge eaq-/SO2- but also directly oxidize SO22-, had a negative effect on the arsenic removal. The presence of CO32- slightly suppressed the arsenic removal due to the eaq- scavenging effect while SiO32-, PO43-, Cl-, SO42- and NH4+ had negligible effects. The proposed method was a potential technology for the efficient removal and reduction of arsenic in alkaline wastewater.

Synergistic degradation of trimethoprim and its phytotoxicity via the UV/chlorine process: Influencing factors on removal and kinetic

Occurrence of trimethoprim (TMP), recalcitrant antibiotic, and its adverse effect on ecosystem have been reported in several countries. The study aims to remove the TMP and its phytotoxicity via a UV/chlorine process, compared with chlorination and UV irradiation alone. Various treatment conditions including chlorine doses, pHs, and TMP concentrations was conducted with synthetic waters and effluent waters. The UV/chlorine process exhibited a synergistic effect on the TMP removal, compared with chlorination and UV irradiation alone. The UV/chlorine process was the most effective in removing TMP, followed by chlorination. The UV irradiation slightly affected the TMP removal (less than 5%). The UV/chlorine process completely removed TMP by 15 min contact time, while chlorination for 60 min could achieve 71% of TMP removal. The TMP removal fitted well with the pseudo first-order kinetics, and the rate constant (k') increased with higher chlorine doses, lower TMP concentrations and low pH. HO• was the major oxidant affecting the TMP removal and its degradation rate, compared with other reactive chlorine species (e.g., Cl•, OCl•). The TMP exposure increased the phytotoxicity by decreasing a germination rate of Lactuca sativa and Vigna radiata seeds. The use of UV/chlorine process could effectively detoxify the TMP, resulting in the phytotoxicity level of treated waters equivalent or lower than those of TMP-free effluent water. The detoxification level depended on the TMP removal, and it was about 0.43-0.56 times of TMP removal. The findings indicated the potential use of UV/chlorine process in removing TMP residual and its phytotoxicity.

Kinetic study on methylene blue removal from aqueous solution using UV/chlorine process and its combination with other advanced oxidation processes

This study investigated the kinetic degradation of methylene blue (MB) by a UV/chlorine process and its combination with other advanced oxidation processes. The ∙OH and reactive chlorine species (RCS: Cl∙, ClO∙, etc.) were the primary reactive species, which accounted for 56.7% and 37.6% of MB degradation at pH 7, respectively. The second-order rate constant of Cl∙ towards MB was calculated to be 2.8 × 10⁹ M^-1 s^-1. When the pH increased from 3 to 7, k_MB by ∙OH increased from 0.15 to 0.21 min^-1 before being reduced to 0.11 min^-1 at pH 11. k_MB by RCS continuously reduced from 0.16 to 0.13 min^-1 when the pH was increased to 11. Humic acid (HA), Br^-, and Cl^- inhibited the degradation with k_MB in the order: k_MB (in HA) < k_MB (in Br^-) < k_MB (in Cl^-). HCO₃^- increased k_MB from 0.37 to 0.48 min^-1. The experimental and modeling methods fit well, indicating the effectiveness of using Kintecus® in predicting concentrations of free radicals in complex water matrices. TOC removal was achieved at 60% after 30 min in a control process and it was strongly inhibited by the presence of HA, with 22% removal achieved at 5 mg_c L^-1 HA. UV/chlorine/electrochemical oxidation (UV/chlorine/EO) significantly improves k_MB from 0.37 to 0.94 min^-1 at a high current (240 mA), while UV/chlorine/H₂O₂ decreased k_MB at a low concentration of 0.01 mM H₂O₂ (k_MB decreased by 6.1%). The results indicate that the energy cost for UV irradiation was the main cost in MB treatment in both UV/chlorine and UV/persulfate (UV/PS) processes, accounting for 91% and 84%, respectively.

Degradation of Antibiotics via UV-Activated Peroxodisulfate or Peroxymonosulfate: A Review

The ultraviolet (UV)/H2O2, UV/O3, UV/peroxodisulfate (PDS) and UV/peroxymonosulfate (PMS) methods are called UV-based advanced oxidation processes. In the UV/H2O2 and UV/O3 processes, the free radicals generated are hydroxyl radicals (•OH), while in the UV/PDS and UV/PMS processes, sulfate radicals (SO4•−) predominate, accompanied by •OH. SO4•− are considered to be more advantageous than •OH in degrading organic substances, so the researches on activation of PDS and PMS have become a hot spot in recent years. Especially the utilization of UV-activated PDS and PMS in removing antibiotics in water has received much attention. Some influencing factors and mechanisms are constantly investigated and discussed in the UV/PDS and UV/PMS systems toward antibiotics degradation. However, a systematic review about UV/PDS and UV/PMS in eliminating antibiotics is lacking up to now. Therefore, this review is intended to present the properties of UV sources, antibiotics, and PDS (PMS), to discuss the application of UV/PDS (PMS) in degrading antibiotics from the aspects of effect, influencing factors and mechanism, and to analyze and propose future research directions.

Antibiotics degradation by UV/chlor(am)ine advanced oxidation processes: A comprehensive review

Antibiotics are emerging contaminants in aquatic environments which pose serious risks to the ecological environment and human health. Advanced oxidation processes (AOPs) based on ultraviolet (UV) light have good application prospects for antibiotic degradation. As new and developing UV-AOPs, UV/chlorine and derived UV/chloramine processes have attracted increasing attention due to the production of highly reactive radicals (e.g., hydroxyl radical, reactive chlorine species, and reactive nitrogen species) and also because they can provide long-lasting disinfection. In this review, the main reaction pathways of radicals formed during the UV/chlor (am)ine process are proposed. The degradation efficiency, influencing factors, generation of disinfection by-products (DBPs), and changes in toxicity that occur during antibiotic degradation by UV/chlor (am)ine are reviewed. Based on the statistics and analysis of published results, the effects caused by energy consumption, defined as electrical energy per order (EE/O), increase in the following order: UV/chlorine < UV/peroxydisulfate (PDS)< UV/H₂O₂ < UV/persulfate (PS) < 265 nm and 285 nm UV-LED/chlorine (EE/O). Some inherent problems that affect the UV/chlor (am)ine processes and prospects for future research are proposed. The use of UV/chlor (am)ine AOPs is a rich field of research and has promising future applications, and this review provides a theoretical basis for that.

Insight into the degradation of ciprofloxacin by medium-pressure UV-activated monochloramine process

The degradation efficiency and mechanisms of ciprofloxacin (CIP), a typical antibiotic, by a medium-pressure ultraviolet/chloramine (MPUV/NH₂Cl) treatment were investigated. The results showed that CIP degradation by MPUV/NH₂Cl was significantly higher than that by NH₂Cl oxidation and MPUV photolysis, and that this degradation processes were consistent with pseudo-first-order kinetics. The initial CIP concentration (7.5-30.2 μM) and the presence of HCO₃^- (0.5-10 mM) significantly inhibited CIP degradation with k_obs,CIP 0.0090-0.0069 and 0.0078-0.0048 cm²/mJ. In contrast, NO₃^- (50-500 μM) and Br^- (0.5-10 mM) significantly promoted the degradation with k_obs,CIP 0.0078-0.0102 and 0.0078-0.0124 cm²/mJ. The effect of Cl^- (0.5-10 mM) and natural organic matter (1-5 mg/L) were negligible. The NH₂Cl dosage (30-60 μM) presented a dual effect, in which its increase within the optimal concentration range (30-40 μM) accelerated CIP degradation due to the formation of reactive radicals, whereas an excessive increase (40-60 μM) quenched the free radicals, ultimately quenching the free radicals and inhibiting the degradation. The optimum pH for CIP degradation under MPUV/NH₂Cl treatment was 7.0. The contribution of reactive halogen species (i.e., reactive chlorine species and reactive nitrogen species) to CIP degradation was substantially greater than that of hydroxyl radicals under acidic or neutral conditions. We identified the degradation products of CIP and proposed degradation pathways, which included defluorination and cracking of the piperazine ring, with the latter being dominant. Compared to haloacetic acid (HAA) and nitrogenous disinfection byproducts (N-DBPs), MPUV/NH₂Cl significantly reduced trihalomethane (THM) production and theoretical cytotoxicity by 80.1% and 78.4% respectively, compared to the background experiment in natural water at a UV dose of 300 mJ/cm².

Degradation of the typical herbicide atrazine by UV/persulfate: kinetics and mechanisms

Atrazine (ATZ), a widely used herbicide, had received a significant amount of attention due to its widespread detection in aquatic environments as well as its potential risks to human health. UV/persulfate (PS) process is an emerging technology for degrading organic pollutants in water. Thus, the degradation of ATZ by a UV/PS process was investigated in this study. The results showed that the removal rate of ATZ was 98.4% with a PS dosage of 2 mg/L and an initial ATZ concentration of 0.1 mg/L. In addition, a relatively high degradation efficiency was obtained under pH = 7. However, the addition of humic acid (HA) reduced the removal rate of ATZ. Hydroxyl radicals (•OH) and sulfate radicals (•SO₄^-) respectively contributed to 21.7% and 29% of the ATZ degradation. The ATZ degradation pathway was proposed, and the main reactions of ATZ in this UV/PS process included dechlorination, demethylation, and deethylation. Moreover, the toxicity of ATZ and its degradation products was assessed using the Toxicity Estimation Software Tool (TEST), and the results showed that the toxicity of the ATZ solution was reduced after the UV/PS process. These results indicate that UV/PS shows good promise as a remediation technique for the treatment of persistent herbicides such as ATZ in contaminated water.

Solar Light-Assisted Oxidative Degradation of Ciprofloxacin in Aqueous Solution by Iron(III) Chelated Cross-Linked Chitosan Immobilized on a Glass Plate

The massive worldwide use of antibiotics leads to water pollution and increasing microbial resistance. Hence, the removal of antibiotic residues is a key issue in water remediation. Here, we report the solar light-assisted oxidative degradation of ciprofloxacin (CPF), using H2O2 in aqueous solution, catalyzed by iron(III) chelated cross-linked chitosan (FeIII-CS-GLA) immobilized on a glass plate. The FeIII-CS-GLA catalyst was characterized by FTIR and 57Fe-Mössbauer spectroscopies as well as X-ray diffraction, revealing key structural motifs and a high-spin ferric character of the metal. Catalytic degradation of CPF was investigated as a function of solar light irradiation time, solution pH, concentration of H2O2 and CPF, as well as cross-linker dosage and iron(III) content in FeIII-CS-GLA. The system was found to serve as an efficient catalyst with maximum CPF degradation at pH 3. The specific ·OH scavenger mannitol significantly reduces the degradation rate, indicating that hydroxyl radicals play a key role. The mechanism of catalytic CPF degradation was evaluated in terms of pseudo-first-order and Langmuir-Hinshelwood kinetic models; adsorption of CPF onto the FeIII-CS-GLA surface was evidenced by field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. FeIII-CS-GLA can be reused multiple times with only minor loss of catalytic efficiency. Antimicrobial activity tests performed against both Gram-negative (Escherichia coli DH5α, Salmonella typhi AF4500) and Gram-positive bacteria (Bacillus subtilis RBW) before and after treatment confirmed complete degradation of CPF. These results establish the immobilized FeIII-CS-GLA as a rugged catalyst system for efficient photo-Fenton type degradation of antibiotics in aqueous solutions.

Degradation of ciprofloxacin using UV-based advanced removal processes: Comparison of persulfate-based advanced oxidation and sulfite-based advanced reduction processes

In this study, the degradation of ciprofloxacin (CIP) in wastewater was investigated using UV-based sulfate radical advanced oxidation processes (SR-AOP) and UV-based advanced reduction processes (ARP). More specifically, a comparison of the UV-based persulfate advanced oxidation process (the UV/PS process) and the UV-based sulfite advanced reduction process (the UV/sulfite process) was made. Considering the UV-based SR-AOPs, the UV/PS process was much more efficient than the UV-based peroxymonosulfate advanced oxidation process (the UV/PMS process), with pseudo first order reaction rate constants (k_obs) of 0.752 and 0.145 min^-1, respectively. For the UV-based ARPs, the UV/sulfite process was the most efficient, compared to the UV/sulfide and the UV/dithionite process (k_obs of 0.269, 0.0157 and 0.0329 min^-1, respectively). The optimal process parameters for both the UV/PS and the UV/sulfite process were determined and the contribution of the produced reactive species were identified. For the UV/PS process, maximal CIP degradation was found at pH 8, and both OH and SO₄^- were responsible for CIP degradation. For the UV/sulfite process, H and e_aq^- were responsible for CIP degradation, with e_aq^- being the predominant radical at pH 8.5. Although CIP degradation was much faster for the UV/PS process, the UV/sulfite process was determined to be much more efficient in the defluorination of CIP.