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.

Aplicação de carepa de aço para degradação de 2,4-dinitrofenol por meio de sistema de oxidação avançada do tipo Fenton / Application of steel waste for 2.4-dinitrophenol degradation through Fenton type advanced oxidation system

RESUMO Considerado um poluente prioritário de reconhecida toxicidade e recalcitrância, o 2,4-dinitrofenol (2,4-DNF) presente em águas residuárias dificulta tratamentos convencionais, especialmente os de princípio biológico, como lagoas aeradas e sistema de lodos ativados. Em função de sua potencialidade de transformar a estrutura de poluentes em elementos de capacidade poluidora reduzida, os processos oxidativos avançados (POAs) representam atualmente uma alternativa para o tratamento de efluentes contaminados com compostos dessa natureza. A presente pesquisa teve como objetivo realizar estudos de degradação de 2,4-DNF em solução aquosa por meio de processos de oxidação avançada do tipo Fenton utilizando uma fonte não convencional de ferro na forma de um resíduo siderúrgico (carepa de aço). A condução de um delineamento experimental fundamentado em planejamento fatorial de experimentos revelou que as variáveis quantidade de peróxido de hidrogênio e de carepa influenciaram significativamente a degradação de 2,4-DNF, proporcionando, em condições otimizadas (20 g de carepa, 0,5 mL de H2O2 em pH 3), elevada eficiência na degradação tanto do composto modelo quanto de seus intermediários reacionais, tendo reduzido também a toxicidade aguda medida na forma de inibição de crescimento de E. coli. Ensaios adicionais sugeriram que os mecanismos reacionais pelos quais ocorre a degradação do 2,4-DNF são mediados tanto pela superfície das partículas de carepa quanto pelo ferro lixiviado, caracterizando o processo como uma combinação de oxidação homogênea e heterogênea. Finalmente, ensaios de reusabilidade e operação em reator de fluxo contínuo sugeriram significativa potencialidade do sistema carepa/H2O2.

ABSTRACT Considered a priority pollutant of recognized toxicity and recalcitrance, 2.4-dinitrophenol (2.4-DNP) present in wastewater hinders conventional treatments such as filtration, chemical coagulation, activated sludge system and activated carbon adsorption. Due to the potential of advanced oxidation processes (AOP) to transform the structure of pollutants into elements of reduced pollutant capacity, they presently represent an alternative for the treatment of effluents contaminated with these compounds. The present research aimed to study the degradation of 2.4-DNP in aqueous solution through advanced Fenton-type oxidation processes, using an unconventional source of iron in the form of a steel residue (steel waste). The conduction of an experimental design based on the factorial planning of experiments revealed that the variables hydrogen peroxide quantity and scale significantly influenced 2.4-DNF degradation, providing, under optimized conditions (20 g of steel waste, 0.5 mL of H2O2 at pH 3) high degradation efficiency of both the model compound and its reaction intermediates, as well as reducing acute toxicity, measured as E. coli growth inhibition. Further trials have suggested that the reaction mechanisms by which 2.4-DNF degradation occurs are mediated by both the surface of steel waste particles and the leached iron, characterizing the process as a combination of homogeneous and heterogeneous oxidation. Finally, reusability and continuous flow reactor operation tests suggested the significant potential of the steel waste/ H2O2 system.

Application of zero valent iron (ZVI) immobilized in Ca-Alginate beads for C.I. Reactive Red 195 catalytic degradation in an air lift reactor operated with ozone.

The efficiency of nanoscale zero-valent iron (nZVI) for the recalcitrant organic pollutants degradation has been frequently reported. However, some disadvantages such as low hydraulic conductivity, rapid passivation and consequent loss of reactivity have motivated researchers to study immobilized forms. In this work, calcium alginate beads incorporated with nZVI were prepared, characterized and applied in a catalytic ozonation system of Reactive Red 195 dye (RR195). In order to avoid shearing the calcium alginate beads, an Air lift reactor operated with Air/O3 cycles in an 8 mg L-1 concentration was used. The RR195 treatability tests conducted with a dye concentration of 25 mg L-1, 50 g L-1 of nZVI-Alg beads and an Air/O3 feed flow of 1 L min-1, revealed significant process efficiency, which was not limited only to the dye discoloration. Total discoloration levels were observed in 30 min of treatment and reductions in 97 % of organic matter in 90 min of treatment, measured through the chemical oxygen demand. The typical absorptions of aromatic compounds reduction (λmax =290 nm) and the acute toxicity reduction (Artemia Saline bioassay), contribute to the Alg-nZVI/O3 system potential for the application in the treatment of liquid effluents contaminated with dyes.

Combined fungal and photo-oxidative Fenton processes for the treatment of wood-laminate industrial waste effluent.

The present study reports on the remediation of an effluent from the wood-laminate industry using Pleurotus ostreatus EB 016 in combination with photo-Fenton oxidation. Fermentation of the effluent with P. ostreatus EB-016 was carried out in agitated flasks to evaluate the influence of pH, and concentrations of carbon and nitrogen sources by a multivariate approach. Subsequently, bioassays was conducted in an air-lift bioreactor using the pre-optimized conditions. In addition, photo-Fenton oxidative treatment was employed to degrade recalcitrant compounds, and the ecotoxicity of the effluents were evaluated using Escherichia coli as a biological model. The crude effluent presented high contents of total phenolics (1,220 mg/L), solids (18.45 g/L) and color intensity (8,333 CU), besides high values of chemical (COD 2,477 mg O2./L) and biochemical (BOD5, 8,450 mg O2/L) oxygen demand. Another feature was the high inhibition on Escherichia coli (71%). Reduction of 64% COD was obtained under optimized conditions (pH5.7, 7.5 g/L sucrose, 4.0 g/L ammonium nitrate) in agitated flasks after 10 days treatment. In the air-lift reactor, 50.6% COD and 29.9% total phenols were removed after 10 days. Combination of biotreatment with photo-Fenton oxidation resulted in removal of 99.2% COD and 92.2% phenolics and absence of inhibition on Escherichia coli.

Electro activation of persulfate using iron sheet as low-cost electrode: the role of the operating conditions.

This work assesses the role of the operational conditions upon the electro-activation of persulfate (PS) using sacrificed iron electrode as a continuous low-cost Fe2+ source. An aqueous phenol solution (100 mg L-1) was selected as model effluent. The studied variables include current density (1-10 mA cm-2), persulfate concentration (0.7-2.85 g L-1), temperature (30-90°C) and the solution conductivity (2.7-20.7 mS cm-1) using Na2SO4 and NaCl as supporting electrolyte. A mineralization degree of around 80% with Na2SO4 and 92% in presence of NaCl was achieved at 30°C using 2.15 g L-1 PS at the lowest current density tested (1 mA cm-2). Besides PS concentration, temperature was the main variable affecting the process. In the range of 30-70°C, it showed a positive effect, achieving TOC conversion above 95% (using Na2SO4 under the previous conditions) along with a significant increase in iron sludge, which adversely affects the economy of the process. A lumped and simplified kinetic model based on persulfate consumption and TOC mineralization is suggested. The activation energy obtained for the TOC decay was 29 kJ mol-1. An estimated operating cost of US$ 3.00 per m3 was obtained, demonstrating the economic feasibility of this process.

Nanoscale Fe/Ag particles activated persulfate: optimization using response surface methodology.

This work studied the bimetallic nanoparticles Fe-Ag (nZVI-Ag) activated persulfate (PS) in aqueous solution using response surface methodology. The Box-Behnken design (BBD) was employed to optimize three parameters (nZVI-Ag dose, reaction temperature, and PS concentration) using 4-chlorophenol (4-CP) as the target pollutant. The synthesis of nZVI-Ag particles was carried out through a reduction of FeCl2 with NaBH4 followed by reductive deposition of Ag. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) surface area. The BBD was considered a satisfactory model to optimize the process. Confirmatory tests were carried out using predicted and experimental values under the optimal conditions (50 mg L-1 nZVI-Ag, 21 mM PS at 57 °C) and the complete removal of 4-CP achieved experimentally was successfully predicted by the model, whereas the mineralization degree predicted (90%) was slightly overestimated against the measured data (83%).

Characterization and photocatalytic treatability of red water from Brazilian TNT industry.

The current study aims to characterize and evaluate the photocatalytic treatability of the "red water" effluent from a Brazilian TNT production industry. Analyses were performed using physical, chemical, spectroscopic and chromatographic assays, which demonstrated that the effluent presented a significant pollution potential, mainly due to COD, BOD, solids and to the high concentration of nitroaromatic compounds such as 1,3,5-trinitrobenzene, 1-methyl-2,4-dinitrobenzene, 2-methyl-1,3-dinitrobenzene, 2,4,6-trinitrotoluene-3,5-dinitro-p-toluidine and 2-methyl-3,5-dinitro-benzoamine. By a modified sol-gel and a dip-coating technique, it was possible to obtain a TiO2 film on borosilicate glass substrate which functional composition and microstructure were characterized by infrared spectroscopy and scanning electron microscopy. The evaluation of the photocatalytic treatability using borosilicate-glass-TiO2 demonstrated high degradation efficiency. In this context, a reduction of 32 and 100% for COD and nitroaromatic compounds, respectively, was observed. Although the proposed photocatalytic process has found difficulties in reducing the content of organic matter and effluent color in the red water, its potential for degrading refractory chemical compounds such as the nitroaromatic ones enables it to be used as tertiary treatment.

Optimization of Brazilian TNT industry wastewater treatment using combined zero-valent iron and fenton processes.

This work explores the optimization of combined zero-valent iron and fenton processes for the treatment of TNT industry wastewater, a residue with recognized polluting potential due to its high concentration of 2,4,6-trinitrotoluene and extremely acidic pH due of the nature of the product purification process. The results of the optimization study indicate that the most efficient condition for reducing the concentration of TNT also generates sufficient amounts of iron(II)for the subsequent oxidative treatment through the Fenton reaction. In general, it was observed that the treatment was highly efficient in terms of meeting the main associated environmental parameters, since it reduced acute toxicity, removed 100% of TNT, 100% of the organic nitrogen and 95.4% of the COD.

Use of maize wastewater for the cultivation of the Pleurotus spp. mushroom and optimization of its biological efficiency.

This study evaluated the Pleurotus spp. mushroom production process using an effluent from the maize agroindustrial process as a carbon and nitrogen source and as a wetting agent. A complete experimental design based on factorial planning was used to optimize the biological efficiency and evaluate the effect of the concentration of effluent, pH and species of Pleurotus. The results indicated that the effluent affects the biological efficiency for the production of both species of mushrooms at all pH values studied. The maximum biological efficiency predicted by the model (81.36%) corresponded to the point defined by the effluent contents (X(1)=1), pH (X(2)=-1) and fungus species (X(3)=1), specifically 50%, 5.0 and P. floridae, respectively. The results demonstrated that the effluent is a good alternative for the production of Pleurotus mushrooms.

Biotreatment of an effluent from a wood laminate industry using Lentinula edodes UEC 2019.

The aim of this work was to evaluate the performance of the fungus Lentinula edodes UEC 2019 in the treatment of an effluent derived from a wood laminate manufacturing process. The factorial design methodology was employed to verify the influence of the source of nitrogen, co-substratum and treatment time variables on the color and total phenols reduction. Assays were conducted in Erlenmeyer flasks and bench bioreactor and the obtained results showed that the best conditions for the effluent remediation were observed when using the effluent itself as the nitrogen source (1g/L) and glucose (79 g/L) as co-substratum (glucose) during a treatment period of 30 days. It was possible the remove 92% phenol, 97% color and reduce the COD in the bioreactor by 99% while controlling the temperature, pH and feeding. These results demonstrate that the fungus was able to use the effluent components as substrate and that it has potential for use in wood lamination effluent remediation.

Characterization of wastewater from the Brazilian TNT industry.

The objective of this work was to characterize the effluent originating from a Brazilian TNT production industry. Analyses were performed using physical, chemical, spectroscopic and ecotoxicological assays, which demonstrated that the effluent had a significant pollution potential, mainly due to the low pH and high concentration of TNT (156+/-10mgL(-1)). The results also demonstrated that the effluent presented significant acute toxicity, and could cause countless damages if released into the receiving body without being adequately treated first. The observed pollution potential justifies studies to evaluate treatment technologies or recover the residue generated in the TNT industry.

Combined photocatalytic and fungal processes for the treatment of nitrocellulose industry wastewater.

The objective of this work was to characterize the delignification effluent originating from the delignification industry and evaluate the combination of the fungus and photocatalytic process (TiO(2)/UV system) for the treatment of this effluent. The delignification effluent has proven harmful to the environment because it presents high color (3516 CU), total phenol (876 mg/L) and TOC (1599 mg/L) and is also highly toxic even in a low concentration. The results of photocatalysis were 11%, 25% and 13% higher for reductions in color, total phenol and TOC, respectively. The combined treatments presented benefits when compared to the non-combined treatments. Fungus and photocatalysis in combination proved to be the best treatment, reducing the color, total phenol, toxicity (inhibition of Escherichia coli growth) and TOC by 94.2%, 92.6%, 4.9% and 62%, respectively.

Combined zero-valent iron and fenton processes for the treatment of Brazilian TNT industry wastewater.

The environmental impact caused by the production of explosives made from nitroaromatic compounds such as 2,4,6-trinitrotoluene (TNT) is currently a major concern, mainly due to their toxic nature, a fact that makes these compounds highly harmful. This work evaluated a continual system treatment reactor (CSTR) consisting of column zero-valent iron and a system to promote a fenton reaction in order to create possible definitive routines for treating effluents originating from the TNT production process. The spectrophotometric results demonstrated that this combination of processes was highly efficient in promoting the removal of all the absorbed species at 290 nm and the visible region of the specter. The results also revealed that the combination of treatments was significantly efficient in terms of correcting the effluent's main parameters of relevance, mainly COD (95.5% reduction) and TNT concentration, whose total was converted into nitrous and phenolic compounds and, additionally, the acute toxicity was also significantly reduced (95%). These results indicate that the strategy can serve as an efficient option for effluent treatment, for release into the receiving body, or eventually for use as industrial reuse water.