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In this study, N-doped TiO2 (TiON) coated coal fly ash cenospheres (CFACs) was synthesized for photocatalytic disinfection against Escherichia coli (E. coli). Based on the physi-chemical evaluation of the TiON coated CFACs (TiON-CFACs), the disinfection efficiencies of E. coli under three different light sources, namely, ultraviolet A (UVA), visible light (VL), and the light emitting diodes with a wavelength of 420 nm (LED-420), were investigated. Then, a three-factor, four-level orthogonal experiment was designed to evaluate the influences of dosage, pH, and light intensity on its disinfection efficiency. The TiON-CFACs were effective under UVA, LED-420, and VL irradiation, with disinfection efficiencies of 5.78 log (45 min UVA), 5.84 log (180 min LED-420) and 5.97 log (300 min VL), respectively. The optimal disinfection efficiency was achieved at an initial pH of 6 under LED-420 irradiation at 40 mW/cm2 with a dosage of 4 g/L TiON-CFACs. The mechanism of disinfection was further investigated using a range of free radical scavengers. Findings indicated that H2O2 appeared to play an indispensable role in E. coli disinfection. Moreover, the TiON-CFACs showed a stable disinfection efficiency of 5 log, even when the substance was recycled for four times, indicating the reliability and stability of the material. The results showed that the TiON-CFACs are promising in water treatment for photocatalytic disinfection of E. coli.

An ultrasound/ultraviolet (US/UV) baffled reactor was developed to fill the gap in ultraviolet (UV) disinfection associated with disinfection efficiency. According to the previously selected operational condition, a continuous-flow US/UV baffled reactor was continuously operated in a wastewater treatment plant at a pilot scale for nearly three months, and the disinfection influent and effluent were analyzed, including fecal coliforms, Escherichia coli , and fecal streptococci . The US/UV baffled reactor could guarantee a high effluent disinfection performance in terms of fecal coliforms removal even with the fluctuation of the secondary effluent. All the disinfected effluents satisfied the requirement of the “Pollutants Discharge Standard of Municipal Wastewater Treatment Plant in China” (fecal coliforms below 1000 CFU/L for class 1A), and 87% of the tested fecal coliforms concentration in the disinfected effluent was below 100 CFU/L, nearly eliminating all fecal coliforms. Further analysis of the E. coli and fecal streptococci showed the broad disinfection ability and high disinfection efficiency of the US/UV baffled reactor. The flexibility of the specific energy consumption for the disinfection system depends on the water quality.

Ultraviolet (UV) disinfection is highly recommended owing to its high disinfection efficiency and disinfection by-products free, and UV Light-Emitting Diodes (UV LEDs) is increasingly becoming an alternative of mercury UV lamps for water disinfection owing to its long lifetime, low input power, and absence of problems on disposal. However, renovation of existing UV lamps faces the challenges for UV disinfection associated with disinfection efficiency and photoreactivation, and modified UV disinfection process is required for practical application. In this study, mathematical rule of disinfection and photoreactivation in a US enhanced UV disinfection system was investigated. UV LED with peak emission at 254nm (UV-C LED) was selected as representative for UV lamps, and a low frequency US was used as pretreatment followed by UV disinfection. The disinfection efficiency of Escherichia coli in deionized water (DI), DI water with kaoline suspension (DIK), and secondary effluent (SE) of municipal wastewater treatment plant were analyzed. Moreover, photoreactivation of E. coli in DIK water within 6h after disinfection was conducted. The experimental results showed that the disinfection efficiencies had good fit with Chick-Watson first-order linear model, and US pretreatment increased the inactivation rate constant for E. coli, which increased from 0.1605 to 0.1887 in the DIK water. Therefore, US pretreatment with UV disinfection have potential to shorten the retention time and reduce the reactor volume. Moreover, the number of photoreactivated E. coli in effluent was reduced under UV-C LED disinfection with US pretreatment compared with that under UV-C LED disinfection alone. The order of maximum percentage of photo-reactivated E. coli was as follows: UV-C LED disinfection alone at 30mJ/cm2>UV-C LED disinfection at 25mJ/cm2 with US pretreatment>UV-C LED disinfection at 30mJ/cm2 with US pretreatment. The survival ratio versus photoreactivation time showed a good fit to second-order logistic model. US pretreatment in UV-C LED disinfection could improve disinfection efficiency, reducing photoreactivation in the effluent as well, which offers a promising practical application technology.

In this study, a series of Ag/AgBr/g-C3N4 nanosheet (CNNS) photocatalysts were prepared by a more environmental-friendly method. The prepared material was characterized and then applied in photocatalytic disinfection of Escherichia coli (E. coli) under mild visible light for the first time. Results showed that all E. coli (108 CFU/mL) could be eliminated under irradiation at 20 mW·cm−2 within 120 min. Based on the energy band determination and electron spin resonance analysis, the Z-scheme in the photocatalyst was responsible for the enhanced disinfection effects where Ag nanoparticles acting as the electron mediator. Scavenger experiments demonstrated that photogenerated holes and superoxide radicals were the main reactive species. The variations in cell membrane permeability, cell membrane structure, enzyme activities and ATP concentration were monitored, and results indicated that the reactive species overwhelmed the bacterial defense mechanism, leading to the penetration of bacterial membranes, release of ions, protein fragmentation, and eventually, inactivation.