Bioremediation of Non-Essential Toxic Elements Using Indigenous Microbes in Soil Following Irrigation with Treated Wastewater

Treated wastewater (TWW) is recognised as an alternative irrigation source to mitigate global water scarcity for irrigation purposes. However, one of the challenges of using TWW as an irrigation source is the accumulation of non-essential toxic elements in soil post-irrigation. Thus, this study determined whether indigenous microbes that are tolerant to toxic elements would remediate non-essential toxic elements in contaminated soil following irrigation with TWW. Soil from a fallowed field at the University of Limpopo Experimental Farm was irrigated with TWW in pots for 12 weeks. After that, an incubation study was established to assess the abilities of Escherichia coli, Staphylococcus aureus, Aspergillus flavus, and Pseudomonas aeruginosa to remediate the contaminated soil over 12 weeks. Both water and soil samples (non-contaminated, contaminated, and remediated) were analysed for toxic elements: Aluminium (Al), Arsenic (As), Chromium (Cr), Cadmium (Cd), and Lead (Pb). Data were analysed using GenStat 20th edition. The results revealed that irrigation with TWW increased the concentration of non-essential toxic elements in soil by 110%, 31%, 31%, 31%, and 54% for Al, As, Cr, Cd, and Pb, respectively. The inoculation of soil with indigenous microbes led to the decline in the concentration of non-essential toxic elements in soil. Furthermore, soils inoculated with S. aureus led to a reduction in Cr to levels below those observed prior to irrigation with TWW. Overall, the findings of the study effectively convey that these indigenous microbes can be used for bioremediation.