Enhancing ethanol fermentability of an artificial acid hydrolyzate with anion exchange resin treatment.

To assess the effectiveness of anion exchange resins (Dowex M43 and Dowex monosphere 66) in neutralization and detoxification of an acid hydrolyzate solution, a fermentation medium containing inhibitors was inoculated with Saccharomyces cerevisiae. When treated with resins at a 1:1 ratio (vol:wt) for up to 20 min, 55-67% of furan and more than 95% of phenolic compounds were removed. Ethanol fermentation activity in resin-treated fermentation medium was the same as the control. There was 21-43% of the total sugar loss after one resin treatment, depending on the sugar concentration. Additional treatments increased sugar retention rate to 95%.

Assessment of the efficacy of chelate-assisted phytoextraction of lead by coffeeweed (Sesbania exaltata Raf.).

Lead (Pb), depending upon the reactant surface, pH, redox potential and other factors can bind tightly to the soil with a retention time of many centuries. Soil-metal interactions by sorption, precipitation and complexation processes, and differences between plant species in metal uptake efficiency, transport, and susceptibility make a general prediction of soil metal bioavailability and risks of plant metal toxicity difficult. Moreover, the tight binding characteristic of Pb to soils and plant materials make a significant portion of Pb unavailable for uptake by plants. This experiment was conducted to determine whether the addition of ethylenediaminetetraacetic acid (EDTA), ethylene glycol tetraacetic acid (EGTA), or acetic acid (HAc) can enhance the phytoextraction of Pb by making the Pb soluble and more bioavailable for uptake by coffeeweed (Sesbania exaltata Raf.). Also we wanted to assess the efficacy of chelates in facilitating translocation of the metal into the above-ground biomass of this plant. To test the effect of chelates on Pb solubility, 2 g of Pb-spiked soil (1000 mg Pb/kg dry soil) were added to each 15 mL centrifuge tube. Chelates (EDTA, EGTA, HAc) in a 1:1 ratio with the metal, or distilled deionized water were then added. Samples were shaken on a platform shaker then centrifuged at the end of several time periods. Supernatants were filtered with a 0.45 mum filter and quantified by inductively coupled plasma-optical emission spectrometry (ICP-OES) to determine soluble Pb concentrations. Results revealed that EDTA was the most effective in bringing Pb into solution, and that maximum solubility was reached 6 days after chelate amendment. Additionally, a greenhouse experiment was conducted by planting Sesbania seeds in plastic tubes containing top soil and peat (2:1, v:v) spiked with various levels (0, 1000, 2000 mg Pb/kg dry soil) of lead nitrate. At six weeks after emergence, aqueous solutions of EDTA and/or HAc (in a 1:1 ratio with the metal) or distilled deionized water were applied to the root zones. Plants were harvested at 6 days after chelate addition to coincide with the duration of maximum metal solubility previously determined in this study. Results of the greenhouse experiment showed that coffeeweed was relatively tolerant to moderate levels of Pb and chelates as shown by very slight reductions in root and no discernable effects on shoot biomass. Root Pb concentrations increased with increasing levels of soil-applied Pb. Further increases in root Pb concentrations were attributed to chelate amendments. In the absence of chelates, translocation of Pb from roots to shoots was minimal. However, translocation dramatically increased in treatments with EDTA alone or in combination with HAc. Overall, the results of this study indicated that depending on the nature and type of Pb-contaminated soil being remediated, the bioavailability and uptake of Pb by coffeeweed can be enhanced by amending the soil with chelates especially after the plants have reached maximum biomass.

Bioavailability and uptake of lead by coffeeweed (Sesbania exaltata Raf.).

Lead (Pb) is recognized as one of the most pervasive environmental health concerns in the industrialized world. While there has been a substantial reduction in the use of Pb in gasoline, water pipes, and Pb-based residential paint, residual Pb from their use is still in the environment and constitutes an important source of Pb in the atmosphere, water, and soil. Soil acts as a sink for these anthropogenic sources of Pb, accumulating the deposits over time in the upper 2 - 5 cm of undisturbed soil. Generally, Pb binds strongly to soil particles and renders a significant soil-metal fraction insoluble and largely unavailable for phytoremediation or plant uptake. A major objective of current phytoremediation research, therefore, is to induce desorption of Pb from the soil matrix into solution and increase the propensity for plant uptake. We hypothesized that the bioavailability of Pb for plant uptake can be increased through chelate amendments. To test this hypothesis, we mixed delta top soil and peat (2:1) and added lead nitrate [Pb (NO3)2[ to generate a Pb-contaminated soil concentration of 2000 mg Pb/kg dry soil. After incubating the Pb-spiked soil in a greenhouse for 6 weeks, Sesbania plants were grown in the soil and harvested at 6, 8, and 10 weeks after emergence. Six days before each harvest, a chelating agent, ethylenediaminetetraacetic acid (EDTA) was applied to the root zone as an aqueous solution in a 1:1 ratio with the Pb concentration in the soil. Sequential extraction procedures were used to assess selective chemical fractions of Pb in the soil. Our results showed that a higher exchangeable fraction of Pb was available for plant uptake after chelate amendment compared to pre-chelate amendment. We also saw higher root and shoot Pb uptake after chelate amendment compared to pre-chelate amendment, especially at 10 weeks after emergence. Together, these results suggest that chelate amendments can promote the bioavailability of Pb in the soil and increased the propensity for uptake by plants into roots and shoots. Further, these results indicate that Sesbania exaltata can be grown under elevated Pb conditions and may be suitable as a potential crop rotation species for phytoextraction.