Microbial Pb(II)-precipitation: the influence of oxygen on Pb(II)-removal from aqueous environment and the resulting precipitate identity

Abstract

The study aimed to quantify the lead(II) bio-precipitation effectiveness, and the produced precipitate identities, of industrial consortia under aerobic and anaerobic batch conditions. The consortia were obtained from an automotive battery recycling plant and an operational lead mine in South Africa. The experiments were performed in the complex growth medium Luria-Bertani broth containing 80 ppm lead(II). The precipitation and corresponding removal of lead(II) were successfully achieved for both aerobic (yellow/brown precipitate) and anaerobic (dark grey/black precipitate) conditions. The removal of lead(II) followed similar trends for both aeration conditions, with the majority of lead(II) removed within the initial 48 h, followed by a marked decline in removal rate for the remainder of the experiments. The final lead(II) removal ranged between 78.11 ± 4.02% and 88.76 ± 3.98% recorded after 144 h. The precipitates were analysed using XPS which indicated the presence of exclusively PbO and elemental lead in the aerobic precipitates, while PbO, PbS, and elemental lead were present in the anaerobic precipitates. The results indicated an oxidationreduction mechanism with lead(II) as an electron acceptor in both aerobic and anaerobic conditions, while a sulphide-liberation catabolism of sulphur-containing amino acids was evident exclusively in the anaerobic runs. This study provides the first report of bacterial bio-reduction in aqueous lead(II) to elemental lead through a dissimilatory lead reduction mechanism. It further provides support for the application of bioremediation for the removal and recovery of lead from industrial waste streams through the application of bacterial biocatalysts for direct elemental lead recovery.

Microbial Removal of Pb(II) Using an Upflow Anaerobic Sludge Blanket (UASB) Reactor

“…The results for the XPS analysis for runs 2 and 3b are presented in Figure 7 The presence of Pb 0 was not detected in these samples, just like in the results fo XRD. It was reported in a previous study by this team that the oxidation of elemen to PbO is highly likely in a system containing any oxygen [30]. The ORP measu throughout the experimentation suggested an anoxic system, as well as the possi oxygen ingress in the sample during sample preparation, which were both likely utors to the oxidation of Pb 0 to PbO.…”

Insight into the Metabolic Profiles of Pb(II) Removing Microorganisms

“…XPS results were acquired with to aim to shed light on the precipitate identity and give more insight into the microbial metabolism. The XPS results for the 80 LB samples as reported in a previous project [ 21 ] are compared to new data for the 500 Sim samples after 6 days of experimentation in Table 3 below.…”

“…The pH was unchanged before and after anaerobic experimentation, ranging between 5.5 and 6.5, indicating that this reaction would not be the likely culprit for the formation of PbO. It can, thus, be concluded that the precipitate initially only consisted of PbS and Pb 0 [ 21 ].…”

“…The results from XPS analysis are further described in the following with relation to the amount of Pb(II) removed from the samples as described in 2019 [ 21 ] and 2020 [ 9 ] by this team. This section aims to determine whether there are sufficient nutrients present to interact with the amount of Pb found in the pellet (precipitate) as well as the amount needed for anaerobic denitrification.…”

“…From a combination of these results, it was found that 67.9 ppm Pb(II) was present in the pellets of the 80 ppm (80 LB) samples and 254.7 ppm in the 500 ppm (500 Sim) samples after 6 days [ 21 ] with an XPS ratio of 0.46:0.54 and 0.41:0.59 to (PbO and Pb 0 ):(PbS), respectively.…”