Microbial Pb(II) precipitation : the effects of aeration conditions and glucose presence on a lead-mine consortium

Abstract

Increasing non-localised outputs of lead to the environment, in conjunction with limited raw lead supplies, have generated interest in the recovery of lead from polluted sources and areas. This study aimed to quantify the effects of aerobic and anaerobic conditions, as well as the presence and absence of glucose, on the effectiveness of an industrially obtained consortium at precipitating aqueous lead(II) under batch conditions. The consortium was obtained from an operational lead mine in the Northern Cape, South Africa. The experiments were performed aerobically and anaerobically, using 80 ppm lead(II) in a rich growth media in the presence and absence of 33 g/L glucose. The residual aqueous lead(II) was used as a measure of the lead(II) precipitation, and the metabolic activity were used as a measure of the active biomass (biocatalyst) present in the system. Without glucose, it was observed that 61.74±1.91 % and 80.74±2.53 % of lead(II) was removed within 2 d under aerobic and anaerobic conditions respectively. Whereas with 33 g/L glucose, the lead(II) removal was 42.91±0.35 % and 39.38±0.90 % within 9 d under aerobic and anaerobic conditions respectively. Biological activity was promoted under aerobic conditions in the presence of glucose with an almost tenfold difference in metabolic activity, however this activity did not translate into a significant improvement in lead(II) removal. The results indicate a dissimilatory lead(II) reduction mechanism in which lead(II) is used as an electron acceptor and consequently led to anaerobic respiration. The presence of glucose introduced a fermentation mechanism which led to a marginal decrease in pH of the system, under anaerobic conditions. The fermentation mechanism provided an alternative energy producing metabolism preventing dissimilatory reduction as an energy generating process leading to an absence in lead-precipitation.