Experimental study of the removal NOx and SO2 from flue gas using the O3/H2O2, and O3/UV processes

The study investigates the effect of different parameters for the removal of SO2 and NOx through a wet process concurrently. Two separate processes have been compared for the removal of flue gases, that is, Ozone/UV and H2O2/UV. The research aims to develop a comparative study for the removal of SO2 and NOx simultaneously using Ozone/H2O2 and UV light and find the energy consumption (also known as EEO) for each process. Combining UV with O3 and H2O2 play a crucial role in generating hydroxyl radicals. Different combinations of Ozone/H2O2, flue gas, and UV intensity were studied at different pH and temperatures of the solution to achieve maximum removal of the flue gases. For, the ozonation process it was observed that the removal% of flue gases increases with increasing UV intensity, and at higher UV intensity (250 W), the removal% for NOx is 92% and SO2 is 95% simultaneously at optimum temperature 308 K. For H2O2/UV process (250 W UV intensity), removal% for NOx is 95% and SO2 is 100% at 313 K, 0.3 LPM flow rate of flue gases. The EEO values obtained for both processes were less than 1 for 95% NOx/SO2 removal efficiency.

Current status of hypochlorite technology on the wastewater treatment and sludge disposal: Performance, principals and prospects

As cost-effective and high-efficient oxidants, the hypochlorite chemicals have been widely utilized for bleaching and disinfection. However, its potential applications in wastewater treatment and sludge disposal were less concerned. This paper mainly summarized the state-of-the-art applications of hypochlorite technology in wastewater and sludge treatment based on the main influencing factors and potential mechanisms of hypochlorite treatment. The results indicated that the hypochlorite approaches were not only effective in pollutants removal and membrane fouling mitigation for wastewater treatment, but also contributed to sludge dewatering and resource recovery for sludge disposal. The ClO^- and large generated free active radicals (i.e., reactive chlorine species and reactive oxygen species), which possessed strong oxidative ability, were the primary contributors to the pollutants decomposition, and colloids/microbes flocs disintegration during the hypochlorite treatment process. The performance of hypochlorite treatment was highly associated with various factors (i.e., pH, temperature, hypochlorite types and dosage). In combination with the reasonable activators (i.e., Fe²⁺ and ultraviolet), auxiliary agents, and innovative processes (i.e., hydrothermal and electro-oxidation), the operational performance of hypochlorite technology could be further enhanced. Finally, the feasibility and benefits of hypochlorite application for wastewater and sludge treatment were analyzed, and the existing challenges and future research efforts that need to be made have also prospected. The review can hopefully provide a theoretical basis and technical guidance to extend the application of hypochlorite technology for wastewater treatment and sludge disposal on large scale.

Enhanced oxidative removal of NO by UV/in situ Fenton: Factors, kinetics and simulation

A series of experiments on the oxidative removal of NO from flue gas using a novel in situ Fenton (IF) system was performed in the presence of ultraviolet light (UV). The comparison tests revealed that the in situ Fenton system facilitated by UV (UV/IF) has a better oxidation ability of NO than that of the IF system due to the photochemical effect on the generation of oxidative species like (OH). Both of the aforementioned oxidation efficiencies were higher than that of the conventional Fenton system (CF) depending on the premix of Fe²⁺ and H₂O₂ solutions, which attribute to the improvement of (OH) yield and valid utilization with continuous addition of fresh reagents and UV radiation. In follow-up experiments, the effects of UV power, gas flow rate, reagent temperature, Fe²⁺/H₂O₂ molar ratio, initial pH, initial concentration of NO and SO₂ and volume fraction O₂ and CO₂ on the oxidative removal of NO by UV/IF method were investigated respectively. Moreover, the results of kinetic analysis indicated that NO oxidation was confirmed to have a pseudo-first-order kinetics pattern. The rate constants decreased slightly with increasing liquid temperature, and then the apparent activation energy of NO oxidation reactions in the UV/IF system was calculated as -5.62 kJ/mol by the Arrhenius equation. Furthermore, the reaction mechanism and application prospects concerning NO oxidative removal by using the UV/IF system was speculated in brief. Finally, the computational fluid dynamics (CFD) simulations revealed that the improvement of axial and radial gas hold-up would enhance the gas-liquid contact and accelerate the oxidation reactions on the interface. In addition to reasonable control of process parameters, the optimization of reactor interior structure needs to be carried out via CFD simulation and experimental validation in future research, both are favourable to promote the NO oxidation efficiency and large-scale development of this technology.

Effects of system parameters and residual ions on the oxidation removal of NO by Fenton method

In the present work, the effects of relevant system parameters on the oxidation removal of NO using the Fenton method were discussed in detail. Moreover, the impacts of ions remaining in the coal-fired process on the NO oxidation efficiency were investigated specifically. The experimental results showed that the oxidation efficiency of NO decreased with the increase of gas flow rate, reagent temperature, and CO₂ volume fraction in the evaluated range, while it increased first and then decreased with the increase of gas temperature, NO initial concentration, O₂ volume fraction, initial pH of reagent, and Fe²⁺/H₂O₂ molar ratio. In addition, the corresponding impact mechanism of the system parameters was discussed respectively. Although the SO₂ showed a competitive effect on the utilization of oxidative radicals, the Fenton system also showed an ability for simultaneous removal of NO and SO₂. Furthermore, the results indicated that the NO oxidation efficiency would be influenced by the residual ions, such as Ca²⁺, Mg²⁺, Na⁺, SO₄^2-, and Cl^-. The presence of the mentioned ions showed an inhibiting effect on the oxidation removal of NO in the first few minutes, while the NO oxidation efficiency would be enhanced in the bulk stage of the tests. The positive effect trended to be more obvious with the decline of the ion dosage. Subsequently, the influence mechanism of the aforesaid residual cations and anions was supposed and proposed preliminarily.