Biological decolorization of reactive anthraquinone and phthalocyanine dyes under various oxidation-reduction conditions.

The decolorization of two anthraquinone dyes (Reactive Blue 4 [RB4] and Reactive Blue 19 [RB19]) and two phthalocyanine dyes (Reactive Blue 7 [RB7] and Reactive Blue 21 [RB21]) was investigated at an initial dye concentration of 300 mg/L using an unacclimated, enrichment culture. The culture was fed a mixture of organic compounds and maintained initially under aerobic conditions, and then progressively developed anoxic/ anaerobic conditions. Biotransformation-related decolorization of the dyes did not take place under aerobic conditions, but use of the feed organic mixture and biomass production by the enrichment culture were not affected. Complete ammonia removal occurred in the control and all dye-amended cultures. The development and extent of nitrification were much lower in the latter cultures, in which ammonia removal via air stripping was the dominant mechanism. Prolonged incubation of the culture under anoxic/anaerobic conditions with multiple carbon source additions resulted in a high decolorization extent of anthraquinone dyes (over 84%) and only partial decolorization of phthalocyanine dyes (49 to 66%). Development of significant methanogenic activity took place in the control and, to a lesser extent, in the two phthalocyanine dye-amended cultures, but the anthraquinone dyes severely inhibited the development of methanogenic activity. The RB4 and RB19 decolorization was attributed to nonreversible, microbially mediated dye transformation(s), demonstrated by the accumulation of decolorization products with absorbance maxima in the 420- to 460-nm region. The decolorization of RB4 and RB19 followed Michaelis-Menten kinetics. At an initial dye concentration of 300 mg/L, the observed maximum decolorization rate per unit biomass was 9.1 and 37.5 mg dye/mg volatile suspended solids x day for the RB4 and RB19, respectively. Thus, partial decolorization of reactive phthalocyanine dyes and extensive biological decolorization of reactive anthraquinone dyes is feasible only under anoxic/anaerobic conditions.

Environmental cadmium levels increase phytochelatin and glutathione in lettuce grown in a chelator-buffered nutrient solution.

Phytochelatins are enzymatically synthesized peptides involved in metal detoxification and have been measured in plants grown at very high Cd concentrations, but few studies have examined the response of plants at lower environmentally relevant Cd concentrations. Using an ethylenediaminetetraacetic acid (EDTA)-buffered nutrient medium, we have varied Cd exposure and measured phytochelatin and glutathione concentrations in romaine lettuce (Lactuca sativa L. var. longifolia Lam. var. Parris Island) grown in a flow-through hydroponic (FTH) system. Very low free ionic Cd (10(-9.6) M) increased average phytochelatin concentrations above those of controls, and increasing Cd resulted in increased phytochelatin production, though increases were tissue dependent. Glutathione concentrations also increased with increasing Cd. In other standard hydroponic experiments, the media were manipulated to vary total Cd concentration while the ionic Cd was fixed. We found that the total amount of Cd (primarily EDTA bound) in the medium altered thiol production in roots, whereas thiols in leaves remained constant. The Cd uptake into roots and translocation to old leaves was also influenced by the total concentration in the medium. Cadmium in all tissues was lower and in some tissues thiol concentrations were higher than in FTH-grown plants grown in identical medium, suggesting that nutrient delivery technique is also an important variable. Though phytochelatin and glutathione production can be sensitive to changes in bioavailable Cd, thiol concentrations will not necessarily reflect the Cd content of the plant tissues.

Reductive decolorization of a textile reactive dyebath under methanogenic conditions.

The objective of the present study was to assess the biological decolorization of an industrial, spent reactive dyebath and its three dye components (Reactive Blue 19 [RB 19], Reactive Blue 21 [RB 21], and Reactive Red 198 [RR 198]) under methanogenic conditions. Using a mixed, methanogenic culture, batch assays were performed to evaluate the rate and extent of color removal as well as any potential toxic effects. Overall, a high rate and extent of color removal (>10 mg/[L.h] and 88%, respectively) were observed in cultures amended with either RB 19 (an anthraquinone dye) or spent dyebath at an initial dye concentration of 300 mg/L (expressed as RB 19 equivalent) and 30 g/L of NaCl. Inhibition of acidogenesis and, to a larger degree, of methanogenesis resulting in accumulation of volatile fatty acids was observed in both RB 19- and spent dyebath-amended cultures. RB 21 (a phthalocyanine dye) and RR 198 (an azo dye) tested at an initial concentration of 300 mg/L did not result in any significant inhibition of the mixed methanogenic culture. Based on results obtained with cultures amended with RB 19 with and without NaCl, as well as a control culture amended with 30 g/L of NaCl, salt was less inhibitory than either RB 19 or the dyebath. Therefore, the toxic effect of the spent dyebath is at least partially attributed to its major dye component RB 19 and NaCl. Further testing of the effect of RB 19 decolorization products on the methanogenic activity in the absence of NaCl demonstrated that these products are much less inhibitory than the parent dye. Although color removal occurred despite the severe culture inhibition, biological decolorization of full-strength reactive spent dyebaths using methanogenic cultures in a repetitive, closed-loop system is not deemed feasible. For this reason, a fermentative and halotolerant culture was developed and successfully used in our laboratory for the decolorization of industrial reactive dyebaths with 100 g/L of NaCl.