Factorial design application in photocatalytic wastewater degradation from TNT industry-red water

Efficient removal of 2,4,6-trinitrotoluene (TNT) from industrial/military wastewater using anodic oxidation on boron-doped diamond electrodes

With growing public concern about water quality particular focus should be placed on organic micropollutants, which are harmful to the environment and people. Hence, the objective of this research is to enhance the security and resilience of water resources by developing an efficient system for reclaiming industrial/military wastewater and protecting recipients from the toxic and cancerogenic explosive compound-2,4,6-trinitrotoluene (TNT), which has been widely distributed in the environment. This research used an anodic oxidation (AO) process on a boron-doped diamond (BDD) electrode for the TNT removal from artificial and real-life matrices: marine water and treated wastewater. During experiments, TNT concentrations were significantly decreased, reaching the anodic degradation efficiency of above 92% within two hours and > 99.9% after six hours of environmental sample treatment. The presented results show the great potential of AO performed on BDD anodes for full-scale application in the industry and military sectors for TNT removal.

Integration of heterogeneous photocatalysis (TiO2/UV) and activated sludge system operated in air lift reactor for the treatment of industrial effluent red water

In the industrial production of the explosive 2,4,6-trinitrotoluene (TNT), purification steps are required to ensure the quality of the product, procedures that generate wastewater of a complex nature and with eco-toxicological potential, called red water, which consists of soluble sulfonates, TNT isomers, and other typical nitro aromatic compounds. The present work aimed to study the effects of integrating heterogeneous photocatalysis based on commercial TiO₂, with a biological process, based on activated sludge, for red water treatment. For the photocatalytic treatment, a 72% reduction in the typical absorption of nitro aromatic compounds (the region between 195 - 275 nm), a 36% reduction in chemical oxygen demand (COD), and a 68% reduction in total phenols were obtained. In the biological treatment, there was a 60% reduction in absorbance in the typical nitro aromatics region (NA), 10% reduction in COD, and 36% reduction in total phenols (FT). The integration of photocatalytic and biological treatments showed promising results compared to the individual processes. Having 94% reduction in NA absorbance, 72% reduction in FT, and 89% reduction in COD with an association of photocatalytic pretreatment followed by biological, and reductions of 88% in NA absorbance, 62% in FT, and 87% in COD for a biological pretreatment followed by the photocatalytic process. In general, when comparing the chemical and biological processes, isolated and integrated, both types of integration showed significantly superior results. They were able to remove the main nitro aromatic constituents of the Red Water effluent.

Investigation of TNT red wastewater treatment technology using the combination of advanced oxidation processes

Different types of advanced oxidation processes and their combinations such as O₃/H₂O₂/UV, O₃/Fenton/UV, O₃/TiO₂/UV, Fenton/H₂O₂/UV, Fenton/TiO₂/UV, TiO₂/H₂O₂/UV, TiO₂/H₂O₂/O₃/UV, TiO₂/O₃/Fenton/UV, TiO₂/H₂O₂/Fenton/UV and O₃/H₂O₂/Fenton/UV were studied for the treatment of undiluted red wastewater from Z113 Factory. The treatment efficiency was evaluated by analyzing chemical oxygen demand (COD) reduction, % degradation of α-TNT, 2,4-DNT, 2,6-DNT, 2,4-DNT-3-SO₃Na and 2,4-DNT-5-SO₃Na. Among studied processes Fenton/TiO₂/O₃/UV was the most effective technology to treat red wastewater. It allows to reduce >99% of COD, α-TNT, 2,4-DNT, 2,6-DNT, 2,4-DNT-3-SO₃Na and 2,4-DNT-5-SO₃Na after 30 h of treatment with optimum operating conditions: rotation speed of 600 rpm, pH of 4 and temperature of 40 °C. According to the chromatograms obtained by gas chromatograph/mass spectrometer (GC/MS), intermediates of the decomposition of pollutants in red wastewater were identified. GC/MS, HPLC, UV-vis and Bacterial Toxicity test were used to assess effluent quality changes before and after treatment. By economic analysis, the studied process had the potential to apply in practice to treat real wastewater at the Z113 Factory.

Optimization of the photocatalytic degradation process of aromatic organic compounds applied to mangrove sediment

Polycyclic aromatic hydrocarbons (PAHs) are part of a class of organic compounds resistant to natural degradation. In this way, heterogeneous photocatalysis becomes useful to degrade persistent organic pollutants, however it can be influenced by environmental variables (i.e.: organic matter) and experimental factors such as: mass of the photocatalyst and irradiation time. The objective of this research was to use a factorial design 2^k as a function of the multiple response (MR) to evaluate simultaneously experimental conditions for the photodegradation of polycyclic aromatic hydrocarbons in contaminated mangrove sediment and its application in oil from Potiguar Basin in Brazil. The sediment samples collected in Belmonte city (Southern Bahia state) were contaminated with 0.25 mg kg⁻¹ of Acenaphthene, Anthracene, Benzo[a]Anthracene, Indene[1,2,3cd]pyrene, Dibenzo[ah]anthracene, Benzo[ghi]pyrene. Factors such as mass of the photocatalyst and irradiation time were evaluated in factorial design 2², with triplicate from the central point, to 1g of the PAH contaminated sediment. After performing the experiments, it was found that the best experimental condition for the degradation of all PAHs indicated by MR was the central point (0.5 g of photocatalyst and 12h of irradiation). For such conditions, the half-life of PAHs varied from 3.51 to 9.37 h and the degradation speed constant between 0.0740 to 0.1973 h⁻¹. The comparison of the optimized methodology between photolysis tests and heterogeneous photocatalysis was performed using the Kruskal-Wallis test, which indicated a difference for the reference solution, where heterogeneous photocatalysis was more efficient in the degradation of PAHs. The optimized methodology was apply in samples contaminated with crude oil from Potiguar Basin, no significant difference was observed in the aromatic fraction, using for the Kruskal-Wallis test. Heterogeneous photocatalysis has shown to be a promising remediation technique to remedy aromatic organic compounds in mangrove sediments.