Enhancement in Ni–Cd Phytoremediation Efficiency of Helianthus annuus L. from Battery Waste Contaminated Soil by Bacterial Augmentation, Isolated from E-Waste Contaminated Sites

The study investigates enhancement of Ni–Cd phytoremediation efficiency of Helianthus annuus grown on Ni–Cd battery’s electrolyte (eW) contaminated soil augmented with two e-waste tolerant and metal solubilizing bacteria. H. annuus was grown outdoor on simulated eW contaminated soil (eW1%, eW2% and eW4%), augmented with Brucella intermedium (E1) and Bacillus velezensis (EW8) , separately. The bioavailability of Ni (61–65%) and Cd (30–57%) within the soil was enhanced, with bacterial augmentation. Between both the bacteria, EW8 augmentation resulted higher Ni accumulation (µg g −1 ) viz. root (236.6), stem (66.5), leaves (18.5), and flower (10.8), respectively in H. annuus and also for Cd, i.e., 389.1, 100.5, 26.5 and 4.9, respectively against eW4%. Although the translocation factor was < 1 however, the bioaccumulation factor enhanced with bacterial augmentations viz. Ni (0.27–0.33) and Cd (0.19–0.34). EW8 enhanced metal bioavailability resulting in higher metal uptake in the plant, in contrast E1 having greater plant growth promotion activities, enhanced the plant growth. The antioxidant enzyme activities (SOD, APX, GST, GR, GPX and POD) were higher in plants with EW8 than E1. With rise in eW contamination, translocation of Cd increased over Ni. The improvement in the soil quality indices of the contaminated soil through phytoremediation was greater with bacterial augmentation than without. The rate of uptake of Ni ( V max ) was greatly enhanced by bacterial augmentation, however, it was effective within narrow range of metal concentration ( K m ), whereas, the maximum rate of Cd uptake was attained for a higher concentration, which was further enhanced by bacterial augmentation. Hence, phytoremediation of eW contaminated soil can improve the soil quality and is enhanced by tolerant bacterial augmentation, which has plant growth promotion activities. Highlights Bacillus velezensis EW8 enhances Ni–Cd bioavailability from eW contaminated soil. Brucella intermedia E1 exhibiting PGPA enhances Helianthus annuus growth. Ni uptake is higher at lower contamination and Cd uptake at higher contamination. The soil quality enhances with phytoremediation and greater with bacterial augmentation.