Abstract:
This article reports the phytoremediation efficiencies of water hyacinth (Eichhornia crassipes (Mart.) Solms) grown under different
nutritional conditions for Al rich wastewaters in batch type constructed wetlands (floating aquatic macrophyte-based plant treatment
systems). This study was conducted for 15 weeks after 1 week acclimatization by culturing young water hyacinth (average height of
20 ± 2 cm) in 590 L capacity fiberglass tanks under different nutrient concentrations of 2-fold [56 and 15.4 mg/L of total nitrogen
(TN) and total phosphorous (TP), respectively], 1-fold, 1/2-fold, 1/4-fold and 1/8-fold with synthetic wastewaters containing 5.62 Al
mg/L. A control set-up of hyacinths comprising only Al with no nutrients was also studied. A mass balance was carried out to
investigate the phytoremediation efficiencies and to identify the different Al removal mechanisms from the wastewaters. Chemical
precipitation of Al(OH)3 was a dominant contribution to Al removal at the beginning of the study, whereas adsorption of Al3+
to sediments was observed to be a predominant Al removal mechanism as the study progressed. Phytoremediation mainly due to
rhizofiltration was also an important mechanism of Al removal especially during the first 4 weeks of the study in almost all the set-ups.
However, chemical precipitation and sediment adsorption of Al3+ was a dominant contribution to Al removal in comparison with
phytoremediation. Plants cultured in the control set-up showed the highest phytoremediation efficiency of 63% during the period
of the 4th week. A similar scenario was evident in the 1/8-fold set-up. Hence we conclude that water hyacinth grown under lower
nutritional conditions are more ideal to commence a batch type constructed wetland treating Al rich wastewaters with a hydraulic
retention time of approximately 4 weeks, after which a complete harvesting is recommended.
