Biosorption and desorption of chromium using hybrid microalgae-activated sludge treatment system

Abstract

This study utilised a mixed culture of Chlorella vulgaris and bacteria from sludge to treat synthetic tannery wastewater (STWW) in modified stirred-tank photobioreactors (MSTPBRs). The MSTPBRs were fabricated locally and operated at irradiance value of 580 µmol/m2s supplied by red light-emitting diodes at 12:12 light–dark cycles and 100 ± 1 rpm continuous stirring. In each case, 50, 100 and 150 mg/L concentrations of STWW were inoculated with mixed culture of microalgae and bacteria in three MSTPBRs, with the control MSTPBR operating at 50 mg/L of STWW. Chromium concentrations were measured using colorimeter whilst Fourier transform infrared spectroscopy (FTIR) indicated possible Cr biosorption. Maximum Cr (VI) and total Cr removal efficiencies of 93 and 94% were achieved, with more than 78% total Cr recovery. Results from FTIR suggested involvement of Chlorella vulgaris in the Cr biosorption. The hybrid microalgae-bacteria system efficiently treated tannery wastewater with considerable Cr removal efficiencies. The potentials of the system in treating tannery wastewater in larger scale may require further investigation.