Enhanced Bioremediation of Heavy Metals from Phosphate Processing Wastewater Using the Indigenous Bacterium Serratia rubidaea NCTC12971

Abstract

Bioremediation using microorganisms have become innovative efficient tools for detoxifying a wide variety of urban and industrial wastewaters. In this study, we investigated for the first time the microbial detoxification of phosphate processing wastewaters (PPWW) by using the indigenous bacterium Serratia rubidaea NCTC12971, having numerous plant growth promoting traits. In fact, the isolated strain exhibited an attractive capacity of phosphate solubilization, siderophore production as well as indole acetic acid (IAA) secretion. Additionally, the strain has significant antifungal effect against Alternaria alternata. The monitoring of the bacterial growth at increasing concentrations of heavy metals showed minimum inhibitory concentrations (MICs) of 8, 6, 3 and 3 mg L⁻¹, respectively for Pb, Cd, Cu and Zn. The 10-days treatment of PPWW by Serratia rubidaea significantly decreases its salinity in terms of electrical conductivity (EC), its chemical oxygen demand (COD), its biochemical oxygen demand (BOD₅) and its total organic carbon (TOC). Regarding heavy metals removal, the detoxification rates were 94.4, 91.5, 85, and 66.5%, for Pb, Cd, Cu, and Zn, respectively. Moreover, the biological treatment of the PPWW declines its phytotoxicity toward lentils (Lens culinaris) and chickpea (Cicer arietinum) seeds germination. Hence, with the PPWW, the germination indices (GI) of chickpea (Cicer arietinum) and lentils (Lens culinaris) were 16.6 and 10%, respectively. While, with the biological treated (BTPPWW), the GI were significantly increased to approximately 76.6% for both seeds mentioned. Such results strengthened the potential use of Serratia rubidaea NCTC12971 for the establishment of biotechnological process aiming to minimize the harmful effects of PPWW as well as its use as plant growth promoting bacteria (PGPB).

Highlights

• This study is the first report investigating the potential use of indigenous bacteria in the bio-treatment of wastewaters discharged from the Tunisian phosphate laundries units.

• Serratia rubidaea NCTC12971 was selected as a potent applicant for heavy metals detoxification.

• Serratia rubidaea NCTC12971 was characterized by its plant growth promoting traits and antifungal activity against Alternaria alternata.

Keywords:

• Phosphate processing wastewaters
• heavy metals
• Serratia rubidaea NCTC12971
• bioremediation
• plant growth promoting bacteria

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was funded by the Ministry of Higher Education and Scientific Research, Tunisia.