Biotransformation of chromium by means of phytoremediation with vetiver (vetiveria zizanioides), and later earthworm composting with red Californian earthworm (eisenia foetida)

This research studies biotransformation of chromium (Cr) in the tanneries sewage, combining phytoremediation (with zizanioides) ad later Earthworm composting (with Eisenia foetida) from Vetiver roots with Cr content. The study started by the implementation of phytoremediation in subsurface flow wetland where tanneries sewage flows and it was possible to absorb an initial concentration of 3818mg. kg-1 of CR in the sewage to 3735 mg. kg-1of Cr in the Vetiver roots. After that, an Earthworm composting was implemented in six beds, with three replicas in each one, in which different quantities of Vetiver roots were added with Cr to the Earthworm composting and the half of them were also added nourishment. Measurements were carried out on days 7, 14, 21 and 28 of dependent variables such as mortality, length, weight, diameter, presence of juveniles and cocoons. In this part of the essay, it was found that Eisenia foetida tolerates Cr concentrations and its bioconcentration factor was between 0.143 and 0.274. Furthermore, the acute toxicity was determined CL50, and the chronic toxicity NOEC, NOEC, confidence limits upper and lower to 95% for the concentration values and Cr. As for the decreasing of Cr in the Earthworm composting, 70.9% was found for the best trial. Finally, a model of mortality behavior was determined according to the Cr concentration with correlation of 0.999 and R-squared that explains 99.8% of the mortality variations.