ABSTRACT
Investigou-se o efeito de diferentes mediadores redox (MR) na remoção de cor de corantes azo e antraquinônico pelo uso de lodo granular anaeróbio sob condições mesofílicas (30ºC) e termofílicas (55ºC). Comprovou-se em experimento em batelada que a adição de concentrações catalíticas de MR pode ter um efeito marcante nas taxas de descoloração do corante azo Reactive Red 2 (RR2), mas o mesmo comportamento não pode ser obtido com o corante antraquinônico Reactive Blue 5 (RB5). Entretanto, com ambos os corantes, o simples aumento da temperatura de incubação para condições termofílicas fez acelerar consideravelmente os processos de descoloração, comparados com condições mesofílicas. Por exemplo, a constante de primeira ordem "k" da redução dos corantes RR2 e RB5, foi aumentada em 6,2 e 11 vezes, respectivamente, à 55ºC quando comparado com 30ºC. Por fim, comprovou-se em experimentos de fluxo contínuo, a boa performance do tratamento termofílico na descoloração redutiva de corantes azo.
The effect of different redox mediators (RM) on colour removal of azo and anthraquinone dyes was investigated with anaerobic granular sludge under mesophilic (30ºC) and thermophilic (55ºC) conditions. Batch experiments revealed that an addition of catalytic concentrations of RM provided a remarkable effect on the decolourisation rates of the azo dye Reactive Red 2 (RR2), but the same effect could not be obtained with the anthraquinone dye Reactive Blue 5 (RB5). Nevertheless, for both dyes, the temperature increase to thermophilic conditions was an effective strategy to considerably accelerate the decolourisation process compared to mesophilic conditions. For instance, the first-order rate constant "k" of RR2 and RB5 reduction, was increased in 6.2 and 11-fold, respectively, at 55ºC in comparison with 30ºC. Such an effect of the temperature on the reductive decolourisation of azo dye was also verified in continuous flow experiments.
Subject(s)
Coloring Agents , Contaminant Removal , Industrial Effluent Treatment , Industrial Sludges , Oxidation-Reduction , Textile IndustryABSTRACT
The thermophilic (55 degrees C) anaerobic conversion of methanol was studied in an unbuffered medium (pH 4+/-0.2) and in a phosphate buffered medium (pH 6.4+/-0.1), in both cases without bicarbonate addition. Our cultivated sludge consortium was unable to degrade methanol under acidic conditions. During the 160 d of continuous operation of an up-flow anaerobic sludge blanket (UASB) reactor (R1), at an organic loading rate (ORL) of 6 gCOD/(l.d) and pH around 4, only 5% of the applied methanol load was consumed and no methane (CH4) was detected. However, hydrogenotrophic methanogens were found to be resistant to exposure to such conditions. At the end of the trial, the hydrogenotrophic methanogenic activity of the sludge was 1.23+/-0.16 gCOD/(gVSS.d) at neutral pH. With methanol as the test substrate, the addition of bicarbonate led to acetate accumulation. A second reactor (R2) was operated for 303 d at OLRs ranging from 5.5 to 25.4 gCOD/(l.d) in order to assess the conversion of methanol at neutral pH (phosphate buffered) in a bicarbonate deprived medium. The reactor performance was poor with a methanol-COD removal capacity limited to about 9.5 gCOD/(l.d). The system appeared to be quite susceptible to any type of disturbance, even at low OLR. The fraction of methanol-COD converted to CH4 and acetate was found to be unaffected by the OLR applied. At the end of the trial, the outcome of the competition was about 50% methanogenesis and 50% homoacetogenesis.
