Thriving in salty environments: Aspergillus niger's halotolerance and BTEX biodegradation potential

Benzene, toluene, ethylbenzene, and xylene (BTEX) can be found in marine and estuarine waters due to accidental spills of oil and derivatives, as well as in production water and effluents discharged from petrochemical plants. Addressing the bioremediation of these compounds in saline environments and effluents with elevated salinity levels is imperative. In this study, the halotolerance of Aspergillus niger was assessed by subjecting it to a stepwise increase in salinity, achieved through progressive addition of NaCl from 2 to 30‰ (v/v). The fungal strain exhibited optimal growth support up to a salinity concentration of 25‰, accompanied by a biomass production rate of (0.93 ± 0.11) g.d^-1. The adapted biomass was employed in batch reactors to evaluate the biodegradation of BTEX (1,500 mg.L^-1). In the absence of sucrose, the reactors inoculated with fungi demonstrated almost complete BTEX removal within 7 days, with rates ranked as follows: benzene (1.12 d^-1) > toluene (0.78 d^-1) > ethylbenzene (0.65 d^-1) > xylene (0.63 d^-1). Enhanced BTEX removal rates were obtained in the presence of sucrose, notably with 2 g.L^-1: benzene (3.63 d^-1) > toluene (2.10 d^-1) > ethylbenzene (1.56 d^-1) > xylene (1.50 d^-1). Notably, benzene was found to be the sole compound adsorbed onto the fungal mycelium (1.50 ± 0.19) to (13.35 ± 4.72) mg.g^-1 of biomass.