RESUMEN
Computational molecular modelling, mass spectrometry and in-vivo tests with Chlorella vulgaris (C. vulgaris) and Daphnia magna (D. magna) were used to investigate the liposolubility and ecotoxicity of MC-LR degradation by-products generated after oxidation by OH⢠radicals in Fenton process. Exposure of MC-LR (5 µg.L-1) to the most severe oxidation conditions (Fe2+ 20 mM and H2O2 60 mM) resulted in a reduction in the toxin concentration of 96% (0.16 µg.L-1), however, with the formation of many by-products. The by-product of m/z 445 was the most resistant to degradation and retained a toxic structure of diene bonds present in the Adda amino acid. Computational modeling revealed that m/z 445 (tPSA = 132.88 Ų; KOW = 2.02) is more fat-soluble than MC-LR (tPSA = 340.64 Ų; KOW = 0.68), evidencing an easier transport process of this by-product. Given this, toxicity tests using C. vulgaris and D. magna indicated greater toxicity of the by-product m/z 445 compared to MC-LR. When the conversion of MC-LR to by-products was 77%, the growth inhibition of C. vulgaris and the D. magna immobility were, respectively, 6.14 and 0%, with 96% conversion; growth inhibition and the immobility were both 100% for both species.
Asunto(s)
Chlorella vulgaris , Contaminantes Químicos del Agua , Animales , Simulación por Computador , Daphnia/metabolismo , Peróxido de Hidrógeno/metabolismo , Toxinas Marinas/toxicidad , Microcistinas/toxicidad , Contaminantes Químicos del Agua/toxicidadRESUMEN
The influence of acidic and alkaline conditions on the solubilisation process of waste activated sludge (WAS) was investigated using HCl and NaOH at pH 2, 10, 11 and 12. The rise in concentration of solubilised compounds, the influence of reaction time, and the influence of the concentration of total solids (TS) during the solubilisation process were determined. Physical and chemical tests demonstrated that pre-treatment provided a release of compounds from the sludge floc matrix into the soluble fraction, characterising the solubilisation process. The highest degree of WAS solubilisation was observed when a pH of 12 was applied. Although largest effects were already attained after 0.25 h, WAS solubilisation continued reaching an increase in total dissolved solids by a factor 10.4 after 720 hrs. Under these conditions, the dissolved organic carbon (DOC), proteins, and carbohydrates resulted in releases up to 15, 40 and 41 times, respectively; phosphorus increased 5.7 times. Results indicate that by applying alkaline pre-treatment, higher TS concentrations can be treated per reactor volume compared to non-pre-treated WAS. Aerobic and anaerobic biodegradability tests showed increased bioconversion potentials in full-scale treatment plants. The respirometry tests ratify the improvement in solubilisation, with O2 consumption rates increasing 1.4 times, concomitant with an additional 261 mg·L-1 of the COD used, which represents 90% bioconversion of waste activated sludge. Biomethanisation test indicated an increase of 3.6 times relative to the blank.
Asunto(s)
Aguas del Alcantarillado , Eliminación de Residuos Líquidos , Anaerobiosis , CarbonoRESUMEN
The aim of the present study was to evaluate the biological oxidation of sulphide in two different UASB reactors by assessing the occurrence of oxidized forms of sulphur in the effluents and the amount of S0 that could be recovered in the process. The bioreactors employed were an anaerobic hybrid (AH) reactor employing porous polyurethane foam as support media and a micro-aerated UASB reactor equipped with an aeration device above the digestion zone. The AH reactor produced a final effluent containing low concentrations of S2- (3.87% of total sulphur load). It was achieved due to a complete oxidation of 56.1% of total sulphur. The partial biological oxidation that occurred in the AH reactor allowed the recovery of 30% of the sulphur load as S0. The effluent from the micro-aerated UASB reactor contained 5% of the sulphur load in the form of S2-, while 20.9% was present as dissolved SO42- and 46% was precipitated as S0. It is concluded that the AH reactor or micro-aeration carried out above the digestion zone of the UASB reactor favoured the biological oxidation of S2- and the release of odourless effluents. Both technologies represent feasible and low-cost alternatives for the anaerobic treatment of domestic sewage.
Asunto(s)
Reactores Biológicos , Sulfuros/metabolismo , Anaerobiosis , Bacterias/metabolismo , Oxidación-Reducción , Aguas del Alcantarillado , Azufre/metabolismo , Eliminación de Residuos Líquidos , Contaminantes del Agua/metabolismoRESUMEN
The aim of this study was to evaluate the efficiency of two sequencing batch reactors (R1 and R2) at removing nutrient (N and P) and chemical oxygen demand (COD). The two reactors (R1 and R2) were of the same design, operating under identical cycles and had a sludge retention time of 5 d. In R1, the substrate was sewage enriched with cooked and triturated cereals. In R2, the substrate was raw sewage mixed with triturated discarded excess sludge. Respirometry tests were performed to compare the biodegradability of the substrates used during the experimental period. The efficiency of R1 in removing soluble P and N-ammonia was considerably higher (90.4 and 97.2%, respectively) than reactor R2 (60 and 39.2%, respectively). While the effluent generated by R1 contained only minor amounts of N-nitrite and N-nitrate (0.5 +/- 0.4 and 1.7 +/- 0.8 mg L(-1), respectively). The concentrations of nitrite and nitrate in the effluent from R2 were 2 and 7 times higher. The lack of biodegradable COD available for denitrification was responsible for the high concentrations of nitrite and nitrate in the effluent of R2.