Ecotoxicological evaluation of effluent from bovine slaughterhouses disinfected by peracetic acid (PAA) using the bioindicator Girardia tigrina.

The evaluation of the ecotoxicological effects of the effluent after treatment with peracetic acid is relevant to help establish reference concentrations for the disinfection process and waste recovery. Therefore, the objective of this work was to evaluate the ecotoxicity of effluent from a bovine slaughterhouse treated with peracetic acid on Girardia tigrina. The toxicity bioassays for planaria were the acute test (LC50) and chronic assays: locomotion, regeneration, reproduction and fertility. The results showed that the effluent treated with peracetic acid showed less toxicity than the effluent without application of peracetic acid. The effluent after peracetic acid application showed a chronic toxic effect in the reduction of locomotor speed in all studied disinfectant concentrations (0.8, 1.6, 3.3 and 6.6 µg L-1 of peracetic acid) and a delay in the formation of G. tigrina photoreceptors at the concentration of 6.6 µg L-1 of peracetic acid. Peracetic acid concentrations of 0.8, 1.6 and 3.3 µg L-1 were not toxic for blastema regeneration, photoreceptor and auricle formation, fecundity and fertility. In addition, this study assists in defining doses of peracetic acid to be recommended in order to ensure the wastewater disinfection process without causing harm to aquatic organisms.

When treatment increases the contaminant's ecotoxicity: A study of the Fenton process in the degradation of methylene blue.

The degradation of dyes can generate harmful by-products, thereby requiring the need to evaluate the toxicity to aquatic organisms. This study aims to evaluate the chronic ecotoxicity of methylene blue dye degraded by the Fenton process using the non-target planarian Girardia tigrina as a sensitive bioindicator of environmental contamination. The bioassays evaluated the lethality of several concentrations of the untreated and degraded dye methylene blue (MB), as well as, their sub-lethal effects on locomotion, feeding, regeneration, and reproduction. In both acute and chronic tests, the degraded dye had a stronger toxic effect when compared to the untreated dye. This negative effect after treatment was mainly associated with the presence of residual hydrogen peroxide and iron (and consequently the hydroxyl radical formed). We conclude that the utilization of the Fenton process using less oxidizing agents should be considered as important alternatives for the protection of aquatic ecosystems, without compromising the efficient removal of MB.

Fenton-type process using peracetic acid: Efficiency, reaction elucidations and ecotoxicity.

Recent studies on Fenton-type processes involving peracetic acid (PAA) stimulated further development of advanced oxidative processes (AOPs). The objective of this work was to provide new information about such processes, elucidate their reaction mechanisms both experimentally and theoretically, and verify their possible uses. The Fenton-type reaction of PAA with Fe3+ exhibited a greater dye degradation efficiency than the Fenton process, while the efficiency of the PAA reaction with Fe2+ was very close of Fenton process. Moreover, the processes photocatalyzed by solar radiation demonstrated comparable efficiencies due to the photoreduction of Fe3+ to Fe2+. By conducting theoretical calculations, it was found that the formation of oxidizing radicals during the reaction of PAA with Fe2+ was not thermodynamically favorable and, therefore, unsuitable for practical use. In contrast, the processes occurred in the PAA/Fe3+ system included thermodynamically spontaneous reactions that generated peroxyl (CH3C(O)OO•), alkoxyl (CH3C(O)•), and hydroperoxyl (HO2•) radicals. The ecotoxicological tests demonstrated that the toxicity of the PAA to the organism Dugesia tigrina can be attributed to the presence of H2O2.

Peracetic acid: Structural elucidation for applications in wastewater treatment.

Peracetic acid (PAA) is an oxidizer widely used for the sterilization of equipment in hospitals, pharmaceutical, cosmetic and food industries and also for water and wastewater disinfection. Even with its increasing applications, there have been no previous theoretical studies that explain the experimental results based on its molecular behavior. In this context, this work used calculations based on the density functional theory (DFT) combined with experimental results to elucidate the decomposition mechanisms of PAA for predicting its stability and the possible products generated from its decomposition. The results obtained showed that the protonation of PAA promoted its spontaneous decomposition in acetic acid and molecular oxygen. The hydrolysis mechanism of PAA in acidic medium indicated that the low energy difference involved in the mechanism's stages is responsible for the equilibrium between PAA and H2O2. The structural and electronic comparison of PAA with H2O2 showed that the O-O bond length of PAA is longer than that of H2O2 and is also weaker, therefore may demonstrate greater efficiency in advanced oxidative processes by photocatalysis.