Performance Comparison of Eichhornia crassipes and Salvinia natans on Azo-Dye (Eriochrome Black T) Phytoremediation

Organic pollutants, such as dyes, have a negative effect on the aqueous environment, therefore, their elimination from water bodies is a high priority. In this work, Eichhornia crassipes and Salvinia natans, both model plants with high phytoremediation efficiency, were exposed to various concentrations (Ci = 50–500 mg/L) of Eriochrome Black T (EBT). Their capacity to assimilate EBT was studied for 16 days of exposure, similar to natural conditions and by spectrophotometric monitoring of the dye concentration (EE. crassipes; 150 mg/L = 33%; ES. natans; 150 mg/L = 71.5%). The changes of the experimental parameters (pH—equalised by day 5, temperature, humidity, light intensity) were followed, and plant growth and biochemical responses to toxic stress effects (photosynthetic pigments, Energy-dispersive X-ray spectroscopy (EDX)—decreased effect of P, Mg, Ca, S and K, Scanning electron microscopy (SEM), defense enzyme) were examined. Furthermore, changes in oxidative- and photo-degradation of EBT in time and the solid-state properties (SEM, EDX, Fourier-transform infrared spectroscopy-FTIR) of the dye were investigated. Our results demonstrate that, despite the toxic stress, both species succeeded in reducing the dye-concentration of the water and S. natans proved to be more efficient in binding and removing organic dyes. With our findings, we proved that both plants alleviated the abiotic stress of dye contamination.

Heavy-metal extraction from sewage sludge using phosphorous-based salts: optimization process with Na2H2P2O7

Land application is one of the important disposal alternatives for sewage sludge, but availability of potential toxic metals often restricts its uses. Three phosphorous-based salts (Na₂H₂P₂O₇, K₄P₂O₇, KH₂PO₄) were studied as potential metal extractants. The conclusions of the research were that greater extractive efficiency is achieved through a 30-min process of vertical shaking with disodium diacid pyrophosphate - Na₂H₂P₂O₇ - at a concentration of 0.2 M at pH 2. Alternatively, the optimized process with oscillating shaking equipment would require 60 min. In both cases the average of set of extracted metals is around 50%. A second extraction process with potassium pyrophosphate - K₄P₂O₇ at pH 6 achieved the reduction of further total amounts of metal, upper 65% with respect to the initial content. In this way the sludge could be used in land applications, with restrictions on each soil, according to the limit values specified in the future regulations.