Abstract:
The current study focused on the impact of heavy metals Zn(II) and Cu(II), regularly found in conjunction with
lead in industrially polluted areas, on the Pb(II) bioprecipitation capabilities and metabolic activity of an
industrially isolated microbial consortium. The experiments were performed with Pb(II) concentrations of 80
ppm and varying concentrations of Zn(II) (40 ppm and 80 ppm) and Cu(II) (40 ppm, 100 ppm, and 150 ppm).
Different conditions were tested namely; Pb(II)&Zn(II), Pb(II)&Cu(II), Zn(II) only, and Cu(II) only. The
experiments were run for a period of 7 days, where the residual aqueous Pb(II), Zn(II), and Cu(II) measured
the degree of removal of each metal. The growth activities for each combination of metals were quantified
using CFU plate count analysis by plating the final sample of the 40 ppm Zn(II) and Cu(II) runs (including and
excluding Pb(II)) on agar plates spiked with a constant 80 ppm Pb(II). The results were compared to previous
experiments conducted with samples containing only 80ppm Pb(II).
Pb(II) concentrations decreased by 69% and 25% in the presence of 40 ppm and 80 ppm Zn(II), respectively.
A grey precipitate was only observed in the presence of 40 ppm Zn, with no precipitate observed with 80 ppm
Zn(II). Additionally, a limited attenuation in the Zn(II) concentrations of 12 % and 7% were measured for the 40
ppm Zn(II)&Pb(II) and 80 ppm Zn(II)&Pb(II) runs respectively. The results suggest different removal
mechanisms present in the 40 ppm and 80 ppm Zn(II) runs, with a precipitation mechanism at 40 ppm Zn and
a biosorption mechanism at 80 ppm of Zn(II).
Pb(II) concentrations decreased by 0%, 32%, and 26% for the 40 ppm, 100 ppm, and 150 ppm Cu(II)&Pb(II)
runs respectively. The corresponding Cu(II) concentrations decreased by 50%, 63%, and 71% respectively,
indicating a competitive removal mechanism with no observed production of coloured precipitate, such as
biosorption. The Cu(II) only runs exhibited removal percentages of 64%, 63%, and 53% for the 40 ppm, 100
ppm, and 150 ppm runs. During growth activity analysis it was observed that the samples containing
Pb(II)&Zn(II) and Pb(II)&Cu(II) showed significantly less growth than that of the Pb(II) only plates previously
tested at 5.47±0.83 × 108 CFU/mL, compared to 1.131±0.065 × 107 CFU/mL and 5.98±1.86 × 106 CFU/mL
respectively. It can be concluded that the bioprecipitation mechanism of Pb(II) as previously observed are
severely inhibited by elevated concentrations of Zn(II) and Cu(II), resulting in an adsorption mechanism
dominating. Additionally, it was found that Pb(II) promotes metabolic activity while Zn(II) and Cu(II) inhibits
metabolic activity. This is possibly as a result of inhibition of the Pb(II) precipitation mechanism. These results
indicate that Zn(II) and Cu(II) ions need to be removed prior to bioprecipitation and recovery of Pb(II) using the
specific industrial consortium.
