RESUMO
OBJECTIVES: This study evaluated the effect of particle size and dosage of granular activated carbon (GAC) on methane production from the anaerobic digestion of raw effluent (RE) of swine wastewater, and the solid (SF) and liquid (LF) fractions. The effect of temperature using the selected size and dosage of GAC was also evaluated. METHODS: 60 mL of swine wastewater were inoculated with anaerobic granular sludge and GAC at different dosages and particle size. The cultures were incubated at different temperatures at 130 rpm. The kinetic parameters from experimental data were obtained using the Gompertz model. RESULTS: The cultures with the LF and GAC (75-150 µm, 15 g/L) increased 1.87-fold the methane production compared to the control without GAC. The GAC at 75-150 µm showed lower lag phases and higher Rmax than the cultures with GAC at 590-600 µm. The cumulative methane production at 45 °C with the RE + GAC was 7.4-fold higher than the control. Moreover, methane production at 45 °C significantly increased with the cultures LF + GAC (6.0-fold) and SF + GAC (2.0-fold). The highest production of volatile fatty acids and ammonium was obtained at 45 °C regardless of the substrate and the addition of GAC contributed to a higher extent than the cultures lacking GAC. In most cases, the kinetic parameters at 30 °C and 37 °C were also higher with GAC. CONCLUSIONS: GAC contributed to improving the fermentative and methanogenesis stages during the anaerobic digestion of fractions, evidenced by an improvement in the kinetic parameters.
Assuntos
Carvão Vegetal , Águas Residuárias , Animais , Suínos , Anaerobiose , Temperatura , Reatores Biológicos , MetanoRESUMO
In this work, anthraquinone-2-sulfonate (AQS) was covalently immobilized onto activated carbon cloth (ACC), to be used as redox mediator for the reductive decolorization of reactive red 2 (RR2) by an anaerobic consortium. The immobilization of AQS improved the capacity of ACC to transfer electrons, evidenced by an increment of 3.29-fold in the extent of RR2 decolorization in absence of inhibitors, compared to incubations lacking AQS. Experiments conducted in the presence of vancomycin, an inhibitor of acidogenic bacteria, and with 2-bromoethane sulfonic acid (BES), an inhibitor of methanogenic archaea, revealed that acidogenic bacteria are the main responsible for RR2 biotransformation mediated by immobilized AQS. Nonetheless, the results also suggest that some methanogens are able to maintain their capacity to use immobilized AQS as an electron acceptor to sustain the decolorization process, even in the presence of BES.
Assuntos
Compostos Azo/metabolismo , Biotransformação , Carvão Vegetal/química , Antraquinonas , Compostos Azo/química , Bactérias/metabolismo , Carvão Vegetal/metabolismo , Cor , Corantes/metabolismo , Naftalenossulfonatos , Oxirredução , TriazinasRESUMO
Geobacter sulfurreducens and anthraquinone-2-sulfonate (AQS) were used suspended and immobilized in barium alginate during the biotransformation of 4-nitrophenol (4-NP). The assays were conducted at different concentrations of 4-NP (50-400â¯mg/L) and AQS, either in suspended (0-400⯵M) or immobilized form (0 or 760⯵M), and under different pH values (5-9). G. sulfurreducens showed low capacity to reduce 4-NP in absence of AQS, especially at the highest concentrations of the contaminant. AQS improved the reduction rates from 0.0086 h-1, without AQS, to 0.149â¯h-1â¯at 400⯵M AQS, which represent an increment of 17.3-fold. The co-immobilization of AQS and G. sulfurreducens in barium alginate beads (AQSi-Gi) increased the reduction rates up to 4.8- and 7.2-fold, compared to incubations with G. sulfurreducens in suspended and immobilized form, but in absence of AQS. AQSi-Gi provides to G. sulfurreducens a barrier against the possibly inhibiting effects of 4-NP.
Assuntos
Alginatos/química , Antraquinonas/química , Biotransformação , Geobacter/metabolismo , Nitrofenóis/química , Concentração de Íons de Hidrogênio , OxirreduçãoRESUMO
The simultaneous removal of sulfide and p-cresol was carried out by using a marine-denitrifying consortium collected in the coastal zone of Sonora, Mexico. Different experimental conditions were used to evaluate the capacity of the consortium to simultaneously eliminate nitrate, sulfide, and p-cresol. For instance, the first set of assays was conducted at different sulfide concentrations (20, 50, and 100 mg S(2À) L(À1) ), with a fixed concentration of p-cresol (45 mg C L(À1) ). The second set of assays was developed at different concentrations of p-cresol (45, 75, and 100 mg C L(-1) ), in the presence of 20 mg S(2À) L(À1) . In all cases, the concentration of nitrate was stoichiometrically added for the complete oxidization of the substrates. The results showed removal efficiencies up to 92% for p-cresol and nitrate at 20 and 50 mg S(2À) L(À1) ; whereas at 100 mg S(2À) L(À1) removal efficiencies were 77% and 59% for p-cresol and nitrate, respectively. On the other hand, sulfide (20 mg L(À1) ) was completely removed under different concentrations of p-cresol tested, with a partial accumulation of nitrite according to the increment of p-cresol concentration. The results obtained indicate that the marine consortium was able to simultaneously remove the pollutants studied.
Assuntos
Cresóis/metabolismo , Desnitrificação , Sedimentos Geológicos/microbiologia , Consórcios Microbianos/fisiologia , Nitratos/metabolismo , Sulfetos/metabolismo , Poluentes Químicos da Água/metabolismo , Biodegradação Ambiental , México , Nitrato Redutase/metabolismo , Nitritos/metabolismo , Nitrogênio/metabolismo , OxirreduçãoRESUMO
Humus constitutes a very abundant class of organic compounds that are chemically heterogeneous and widely distributed in terrestrial and aquatic environments. Evidence accumulated during the last decades indicating that humic substances play relevant roles on the transport, fate, and redox conversion of organic and inorganic compounds both in chemically and microbially driven reactions. The present review underlines the contribution of humus-reducing microorganisms in relevant environmental processes such as biodegradation of recalcitrant pollutants and mitigation of greenhouse gases emission in anoxic ecosystems, redox conversion of industrial contaminants in anaerobic wastewater treatment systems, and on the microbial production of nanocatalysts and alternative energy sources.
Assuntos
Substâncias Húmicas , Microbiologia do Solo , Biodegradação Ambiental , Biotransformação , Poluentes Ambientais/metabolismoRESUMO
The capacity of an anaerobic sediment to achieve the simultaneous biodegradation of phenol and carbon tetrachloride (CT) was evaluated, using humic acids (HA) as redox mediator. The presence of HA in sediment incubations increased the rate of biodegradation of phenol and the rate of dehalogenation (2.5-fold) of CT compared to controls lacking HA. Further experiments revealed that the electron-accepting capacity of HA derived from different organic-rich environments was not associated with their reducing capacity to achieve CT dechlorination. The collected kinetic data suggest that the reduction of CT by reduced HA was the rate-limiting step during the simultaneous biodegradation of phenol and CT. To our knowledge, the present study constitutes the first demonstration of the simultaneous biodegradation of two priority pollutants mediated by HA.
Assuntos
Tetracloreto de Carbono/metabolismo , Substâncias Húmicas/análise , Fenol/metabolismo , Anaerobiose , Biodegradação Ambiental , Tetracloreto de Carbono/química , Elétrons , Halogenação , Cinética , Fenol/química , Poluentes do Solo/isolamento & purificação , Fatores de TempoRESUMO
A novel technique to immobilize humic substances (HS) on an anion exchange resin is presented. Immobilized HS were demonstrated as an effective solid-phase redox mediator (RM) during the reductive biotransformation of carbon tetrachloride (CT) and the azo model compound, Reactive Red 2 (RR2). Immobilized HS increased â¼4-fold the extent of CT reduction to chloroform by a humus-reducing consortium in comparison to incubations lacking HS. Immobilized HS also increased 2-fold the second-order rate constant of decolorization of RR2 as compared with sludge incubations lacking HS. To our knowledge, the present study constitutes the first demonstration of immobilized HS serving as an effective solid-phase RM during the reductive biotransformation of priority contaminants. The immobilizing technique developed could be appropriate for enhancing the redox biotransformation of recalcitrant pollutants in anaerobic wastewater treatment systems.