Heavy Metal Removal Capability of Bacterial Isolates from Awash Tannery Effluents and Wastewater Sources of Selected Rivers in Addis Ababa
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Date
2024-08
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Addis Ababa University
Abstract
Heavy metals from various industrial processes for different purposes pollute soil and groundwater worldwide. They have toxic, mutagenic, and carcinogenic effects, which pose health risks to the natural biota. Microbe-based biological treatment methods are an environmentally benign and more efficient
heavy metal removal technology than conventional ones. The objective of this study was to evaluate the heavy metal removal capability of naturally occurring heavy metal-resistant bacteria both in NAM-SHM and in the actual wastewater, which was collected from ATE and selected tributaries of AARW. The
result showed that four of the 130 heavy metal-resistance isolates were identified based on their morphological and molecular characteristics. Isolates S. xylosusT14Cd and B. cereusT4Zn were obtained from the Cd and Zn metal-supplemented NAM of the ATE, while S. xylosysW1Cr and S.
xylosusW12Pb were obtained from the Cr and Pb of the selected tributaries of AARW. For all those isolates, 30°C and pH 8 were the optimum growth conditions. Isolates S. xylosusW1Cr, S. xylosusT14Cd, S. xylosusW12Pb, and B. cereusT4Zn were shown to have MICs of 3500, 4000, 5000, and 7000 ppm
against Cr6+, Cd2+, Pb2+, and Zn2+, respectively. Isolates’ resistance order to a mixture of heavy metals Pb2+, Zn2+, Cr2+, and Cd2+ in 3:3:1:1 (50-800 ppm), respectively, was MCC>S. xylosusT14Cd>S. xylosusW1Cr>S. xylosusW12Pb>B. cereusT4Zn. On the NAM-SHM inoculation, isolates S. xylosusT14Cd, S. xylosusW12Pb, and B. cereusT4Zn gave the maximum removal efficiency for Cd2+ (82.19%), Pb2+ (84.24%), and Zn2+ (80.94%) metals in 8 days, respectively, and Cr6+ (69.9%) was recorded for S. xylosusW1Cr in 6 days of incubation. Whereas, for MCC Cr6+ (79.36%), Cd2+ (88.66%), and Zn2+ (90.22%) in 8 days, and Pb2+ (93.44%) in 6 days, removal efficiency was recorded.
The maximum removal efficiency of S. xylosusW1Cr and S. xylosusW12Pb was 83.00 and 79.60% in 6 days, while S. xylosusT14Cd, B. cereusT4Zn, and MCC was 84.88, 76.05, and 87.98% of Cr6+ in 8 days of incubation on the ATE. Moreover, the maximum removal efficiency of S. xylosusW1Cr was 89.75, 98.33, 97.57, and 99.46% of Cr6+, Cd2+, Pb2+, and Zn2+, respectively, on the selected tributaries of AARW in 6 days of incubation. After 6 days of incubation, S. xylosusT14Cd was able to remove the maximum concentration of metals from AARW, with values of 89.76, 99.89, and 99.08% of Cr6+, Cd2+, and Pb2+, respectively, and 99.12% of Zn2+ after 8 days. S. xylosusW12Pb was able to remove up to 99.03% of
Zn2+ on same medium in 8 days of incubation and also 88.70, 98.93, and 97.77% of Cr6+, Cd2+, and Pb2+, respectively, in 6 days. Similarly, the maximum removal efficiency of B. cereusT4Zn was also 80.48 and 97.25% of Cr6+ and Zn2+, respectively, in 8 days of incubation, while 98.35 and 83.28% of Cd2+ and
Pb2+, respectively, in 6 days. Whereas, for MCC Cr6+ (90.29%) and Zn2+ (99.99%), in 8 days, while Cd2+ (99.97%) and Pb2+ (99.37%), in 6 days of incubation, removal efficiency was recorded. In conclusion, the four tested isolates are highly efficient for the removal of heavy metals from the NAMSHM and actual wastewater samples. Hence, using these identified and tested bacteria for heavy metal bioremediation is recommended for tannery factory effluents and other industries.
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Keywords
Biological Treatment, Heavy Metals, Heavy Metal-Resistant Bacteria, Wastewater