Comparative kinetic study on biodecolorization of synthetic dyes by Bjerkandera adusta SM46 in alginate beads-packed bioreactor system and shaking culture under saline-alkaline stress

Industrial dye wastewater contains a high saline concentration and is of an alkaline condition that may inhibit biological treatment. Finding suitable methods for the application of biological decolorisation is important. This research aimed to compare dye biodecolorization by Bjerkandera adusta SM46 using three different methods: (1) alginate-packed bioreactor (APB), (2) submerged-immobilised beads (SIB), and (3) submerged-free cell (SFC) under saline-alkaline and non-saline conditions. Five synthetic dyes with different molecular properties were used: Remazol brilliant blue R (RBBR), Azure B (AB), Brilliant red (BR), Brilliant green (BG), and Reactive green (RG). The results show that B. adusta SM46 was able to decolourise 10.8–97.3% of the dye samples in all methods and conditions, and even up to concentration 500 mg/L under the saline-alkaline condition. Evaluation of kinetic studies revealed the effectivity of the dye removal in SFC over SIB and APB. The highest degradation rate constant (k₁) was achieved for RBBR and the lowest k₁ was for RG. The values of k₁ for SFC, SIB and APB were 0.034, 0.024, and 0.015 respectively for RBBR and 0.013, 0.003, and 0.004 respectively for RG. Treatment using submerged-free cell (SFC) resulted in the greatest and most rapid decolorisation, compared with all other treatments except BR. However, immobilisation on alginate beads increased the reusability of the fungus for sequential batches under saline-alkaline stress. Therefore, selection of a suitable method for dye decolorisation could be proposed, allowing enhancement of the removal process under high saline-alkaline stress, which is usually found in industrial dye wastewater.