Accelerated mineralization of textile wastewater under 222 nm irradiation from Kr/Cl2 excilamp: an environmentally friendly and energy efficient approach.

The textile dyeing and manufacturing industry is the major producer of significant amounts of wastewater that contain persistent substances such as azo dyes that require adequate remediation measures. Far ultraviolet at 222 nm light may provide an advantage for contaminants degradation as compared to conventional UV sources (254 nm). In this paper, the degradation of reactive black 5 (RB5) in artificial wastewater has been performed using a 222 nm Kr/Cl2 excimer source under direct photolysis and an advanced oxidation process using TiO2/H2O2. The solution pH, catalyst concentration, 222 nm intensity, initial concentration of dye, and addition of H2O2 influence the degradation rate constant. The molar absorption coefficient, quantum yield of RB5 at 222 nm and the electrical energy per order (EEO) from different treatment methods have been reported. RB5 shows 1.26 times higher molar absorption at 222 nm than at 254 nm. The EEO for excimer-222/H2O2 ( ∼ 13 kWh/m3) is five times lower than that of the excimer-222/TiO2 process, which makes the process energy efficient. The degradation of wastewater has been carried out at three distinct pH values (2, 6, and 10), and the pH level of 10 exhibited the highest degree of degradation. The degradation rate in the alkaline medium is 8.27 and 2.05 times higher than in the acidic or ambient medium. Since textile effluent is highly alkaline, this result is significant, as no neutralization of the wastewater is required, and direct treatment is possible. A possible degradation pathway has been established based on Fourier transform infrared spectroscopy (FTIR) and high resolution mass spectroscopy (HRMS) analysis. The phytotoxicity of the treated wastewater has also been evaluated for its suitability for reuse in agriculture. The study reveals that the excimer-222/H2O2 treated wastewater significantly enhanced the germination percentage of Raphanus sativus seed (97%) compared to dye wastewater-grown seeds (75%). This work offers crucial information for future studies on the direct and indirect photolysis of azo dyes, as well as insight into the process of RB5 degradation under Kr/Cl2 excimer radiation.

Environmentally Friendly UV-C Excimer Light Source with Advanced Oxidation Process for Rapid Mineralization of Azo Dye in Wastewater.

Wastewater discharged from the textile industry contains approximately 15% unfixed dyes, predominantly 60-70% azo dyes. These unfixed dyes are a major environmental concern due to their persistence and potential toxicity. In this paper, an environmentally friendly mercury-free XeI* excilamp emitting 253 nm UV light is reported, and the same has been utilized for the degradation of azo dyes using the advanced oxidation process (AOP) with TiO2/H2O2. A new process is developed in which one electrode of excilamp is coated with TiO2 nanoparticles that improves the efficiency of the dye degradation. Additionally, the effects of varying TiO2 loading concentrations, XeI*-excimer light intensity, starting dye concentration, suspension pH, and H2O2 addition are examined. The outcomes of this study confirm 13 times faster degradation in XeI*-excimer/H2O2 than in XeI*-excimer/TiO2, attributed to an abundance of hydroxyl radicals generated by the modified XeI*-excimer/H2O2. Also, the degradation of RB5 in the modified XeI*-excimer/H2O2 is 2.3 times faster as compared to that of the bare electrode XeI*-excimer/H2O2. A more than 95% reduction in chemical oxygen demand has been achieved in 40 min in the case of XeI*-excimer/H2O2. In this study, a maximum energy yield of 5712 mg/kWh is reported. Furthermore, a high degree of degradation is found in the alkaline medium (pH 10). Because textile effluent is highly alkaline, this result is significant, and direct treatment of azo dyes is possible. The use of the developed source in industrial applications appears to be highly promising based on testing on a real wastewater matrix. The treated effluent has been utilized to study its reusability for agricultural purposes on the germination of radish seeds in soil, and ∼26% enhanced germination has been observed compared to dye wastewater.

Analysis of a UV photocatalytic oxidation-based disinfection system for hydroxyl radicals, negative air ions generation and their impact on inactivation of pathogenic micro-organisms.

This work presents a large-scale surface disinfection system, which has a unique lantern arrangement of ultraviolet-C (UV-C) light (254 nm) in conjunction with nanotechnology in a protective biosafety environment. Shadow regions are best dealt in this system by the generation of hydroxyl radicals (•OH) and negative air ions at sites where UV light cannot penetrate. More than 35 000 negative air ions/cm3 along with •OH were produced continuously in the disinfection chamber through the advanced photocatalytic oxidation process [UV-C + titanium dioxide (TiO2)]. The arrangement has been made to provide an optimized UV irradiation (∼2 mW/cm2) throughout the disinfection system. In order to distinguish between effects arising from (i) the action of UV dose alone and (ii) the action of UV dose along with •OH and negative air ions, E. coli and P. aeruginosa were chosen for bacterial testing and two interventions were made. The first intervention involved placing only UV lamps in the disinfection chamber to see the effect of only UV dose on bacterial inactivation efficiency. The second intervention involved placing the TiO2 nanoparticle coated aluminum plates along with UV lamps; this allows for the generation of negative air ions and •OH inside the disinfection chamber and enhanced bacterial inactivation efficiency. More than 95% bacterial inactivation efficiency has been reported in the case of UV-C + TiO2 compared to only 77% in UV only at the same time interval (90 s).

Efficient deactivation of aerosolized pathogens using a dielectric barrier discharge based cold-plasma detergent in environment device for good indoor air quality.

Air pollution is one of the top 5 risks causing chronic diseases according to WHO and airborne transmitted pathogens infection is a huge challenge in the current era. Long living pathogens and small size aerosols are not effectively dealt with by the available indoor air purifiers. In this work, a dielectric barrier discharge (DBD) based portable cold-plasma detergent in environment device is reported and its disinfection efficiency has been analyzed in the indoor environment of sizes up to 3 × 2.4 × 2.4 m3. The deactivation efficiency of total microbial counts (TMCs) and total fungal counts (TFCs) is found to be more than 99% in 90 min of continuous operation of the device at the optimized parameters. The complete inactivation of MS2 phage and Escherichia coli bacteria with more than 5 log reduction (99.999%) has also been achieved in 30 min and 90 min of operation of the device in an enclosed environment. The device is able to produce negative ions predominantly dominated by natural plasma detergent along with positive ions in the environment similar to mother nature. The device comprises a coaxial DBD geometry plasma source with a specially designed wire mesh electrode of mild steel with a thickness of 1 mm. The need for feed gas, pellets and/or differential pressure has been eliminated from the DBD discharge source for efficient air purification. The existence of negative ions for more than 25 s on average is the key advantage, which can also deactivate long living pathogens and small size aerosols.

Photocatalytic oxidation conveyor "PCOC" system for large scale surface disinfection.

In this paper, we present a surface decontamination system that substitutes traditional chemicals and scrubbing agents, which will be useful for the general public during a pandemic. The technique is based on a hybrid process in which UV-C light and its photons interact with metal oxide nano-catalysts to generate hydroxyl radicals, which can enhance the deactivation process, and the system can work even in the shadow regions via a dry process. The optimum number of UV light sources in combination with TiO2 nanoparticles catalysts on aluminum plates have been used synergistically in the system. The UV dose in the disinfection chamber has been optimized, which is between 60 and 500 mJ/cm2 throughout the disinfection chamber. The concentration of hydroxyl radicals is reported more than 25 000 ions/cm3 within the disinfection chamber. These ions are circulated throughout the disinfection volume. The disinfection efficiency has been tested on bacteria and spores, and the obtained results are correlated. Around 8 log reductions in the counts of the test bacteria of Escherichia coli and Klebsiella pneumoniae have been achieved in just 2 min of exposure in the continuous operation of the system. Tests have also been performed on Geobacillus stearothermophilus spores, and the method described here is the result of multiple tests, a review of the scientific literature, and the incorporation of current laboratory practice. The deactivation tested in the system is larger than that of known bacteria and viruses in terms of UV-doses, signifying its utility during the pandemic.