Investigating an electro-bio-chemical phytoremediation of multi-metal polluted soil by maize and sunflower using RSM-based optimization methodology

Abstract

Accumulation of heavy metals (HMs) in soil has become a serious environmental problem due to various anthropogenic activities. Phytoremediation is one of the most cost-effective and environmentally friendly techniques for removing HMs from contaminated soil. However, it is remarked as a slow way of remediation, and it may need some amendments. Thus, in this study, a phytoremediation-based method of zinc (Zn) cadmium (Cd) lead (Pb) and nickel (Ni), comprised of sunflower and maize, was amended by the electro-bio-chemical treatments, comprised of ethylene glycol tetraacetic acid (EGTA), Bacillus subtilis and electrical current. Moreover, the performance of the system was optimized by the response surface methodology (RSM), to optimize the performance of both reactors. A high R2 value of non-linear second-order model showed satisfactory function of RSM in optimizing the performance of the remediation system. The electrical current and EGTA were the main significant factors in increasing growth parameters and translocation factor (TF) of some HMs, respectively. The highest values of shoot dry weight and TF were 15.62 g pot−1 (run 2) and 2.11 (run 4) which belonged to maize and Zn in sunflower, respectively. To achieve the highest possible response, the following optimal values were predicted: electrical current of 2 V cm−1, EGTA concentration of 0.04 mmol kg−1, and Bacillus subtilis level of 1.4 × 109 CFU pot−1 for maximized shoot dry weight efficiencies of 16.14 g pot−1. Also electrical current of 1.97 V cm−1, EGTA concentration of 1.68 mmol kg−1, and Bacillus subtilis level of 0.21 × 109 CFU pot−1 for maximized TF of Zn efficiencies of 1.6. The use of a combination of treatments was more successful than each treatment alone in the removal of HMs by maize and sunflower.