Recently, increasing attention has been paid to antibiotic resistance in stormwater runoff. However, there is no available literature about the control of antibiotic resistant bacteria (ARB) through 365 nm ultraviolet light-emitting diode (UVA/LED). In this study, batch experiments were conducted to investigate ARB inactivation kinetics, effects of light intensity and water matrix (including suspended solid (SS) concentration, initial pH and bacteria concentration), and potential transmission risks after UVA/LED irradiation. Results showed that ARB inactivation efficiencies reached 6.31 log reduction at 8 mW/cm 2 (86 J/cm 2 ) of UVA/LED for 180 min. ARB inactivation efficiencies increased with the increase of light intensity, and showed a linear relationship. ARB inactivation decreased with increasing SS levels, and the largest inactivation efficiencies was 3.56 log reduction at 50 mg/L of SS. Initial pH had slight effect on ARB inactivation through UVA/LED irradiation. A low initial bacteria concentration (10 5 CFU/mL) was not necessarily associated with good ARB inactivation (3.59 log reduction). After UVA/LED irradiation, ARB was hardly detected during 12 hr of dark repair, and the transfer frequency of kanamycin resistance gene was increased to 5.43 × 10 −4 . These suggested that the application of UVA/LED to inactivate ARB in stormwater runoff was feasible and desirable in this study. ARB inactivation reached 6.31 log reduction at 8 mW/cm 2 of UVA/LED for 180 min. UVA/LED inactivation kinetics could be well described by the first-order model. Initial pH and bacteria levels had weak effects for ARB inactivation. Potential risks of ARB could be blocked after 60 min of UVA/LED disinfection.
The degradation of ofloxacin (OFX) at low concentration in aqueous solution by UVA-LED/TiO 2 nanotube arrays photocatalytic fuel cells (UVA-LED/TiO 2 NTs PFCs) was investigated. TiO 2 nanotube arrays (TiO 2 NTs) photoanode prepared by anodization-constituted anatase–rutile bicrystalline framework. The results indicated that the degradation efficiency of OFX by UVA-LED/TiO 2 NTs PFC was significantly enhanced by 14.3% compared with UVA-LED/TiO 2 NTs photocatalysis. The pH affected the degradation efficiency markedly; the highest degradation efficiency (95.0%) and the pseudo-first-order reaction rate constant k value (0.049 min −1 ) were achieved in neutral condition (pH 7.0). The degradation efficiency increased with the increasing concentration of dissolved oxygen (DO) in the UVA-LED/TiO 2 NTs PFC. The main reactive species of OFX degradation are positive holes (h + ) and superoxide ion radicals (O
·− 2
) in a DO sufficient condition. Furthermore, the possible pathways of OFX degradation were proposed.
Wanhe Qi,Songming Zhu,Abubakar Shitu,Zhangying Ye,Dezhao Liu
Under Minamata Convention restrictions, mercury-free UV source was in need for ultraviolet disinfection in recirculating aquaculture systems (RAS). Ultraviolet emitting diodes (UV-LEDs) seemed a potential mercury-free UV source and had gained increasing attention in water disinfection. In this study, a mercury-free UVA-LED and low concentration peroxymonosulfate (PMS) combination was proposed for E. coli (CGMCC 1.3373) inactivation and real RAS wastewater disinfection. Results showed that UVA-LED and low concentration PMS combination enhanced E. coli inactivation over UVA-LED alone. A synergistic effect on E. coli inactivation with synergy factor of 58.7 % was found when combining UVA-LED irradiation with 1 mg/L PMS. Kinetic rate constant increased by up to 139 % by UVA-LED and 1 mg/L PMS combination, which implied the required UV fluence to 2-log E. coli inactivation was saved up to 42 %. Also, UVA-LED and 1 mg/L PMS combination showed disinfection potential for real RAS wastewater treatment. Mechanism study revealed that the Cl − , · OH and SO 4 ·- played important roles and · OH was dominant radical in saline solution by UVA-LED/PMS process compared to that in phosphate buffered solution(PBS). The E. coli inactivation was caused by UVA-LED irradiation and reactive species generated in UVA-LED/PMS system. Our study provided a potential strategy to introduce the mercury-free UV-LED into RAS and a better understanding of UVA-LED/PMS disinfection process.
The influence of pH and dissolved oxygen (DO) on the degradation of ofloxacin (OFX) in water by UVA-LED/TiO 2 nanotube arrays photocatalytic fuel cell (UVA-LED/TNA PFC) was investigated. The degradation pathway depended on the location of OFX frontier orbital with different ionization states and the role of reactive oxidative species (ROSs) played with varied pH and DO values. In presence of DO, the quencher tests revealed that O 2 − played a key role at pH 3.0, 7.0 and 11.0, while OH made its greatest contribution at pH 3.0 and the effect of h + was largely inhibited at pH 11.0. Hydroxylation for cationic OFX was more significant, while demethylation and piperazinyl ring oxidation for anionic OFX occurred more quickly compared to other forms. Besides, zwitterionic OFX underwent decarboxylation and combination of demethylation & hydroxylation more easily. Much higher power generation was observed in presence of DO at pH 7.0, probably due to the enhanced adsorption of OFX on the TNA, and DO could amplify the electric potential between the two electrodes. The degradation efficiencies were almost the same in presence or absence of DO, but the pathways were different and e- aq may replace O 2 - as the leading ROSs in absence of DO.
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