Multistage fluidized bed bioreactor for dye decolorization using immobilized polyurethane foam: A novel approach

[Display omitted] •Multistage fluidized bed reactor was developed for CR decolorization.•Porous stainless steel box (PSSB) was designed for PUF localization.•Dye decolorization was enhanced with PSSB based M-FBBR. A multistage fluidized bed bioreactor (M-FBBR) was developed for Congo Red (CR) dye removal using Polyurethane foam (PUF)-immobilized Bacillus subtilis. The active surface area for microbial growth and biological interaction are important factors to be considered for immobilization mediated decolorization. In the present study, the active surface area can be improved in the reactor in two ways, (i) by avoiding the accumulation of PUF on the top surface of reaction volume and (ii) by providing free moving foams in larger number. To achieve this, existing FBBR was modified by introducing a porous stainless steel box (PSSB), which is autoclavable, custom made, and cost-effective. To elucidate this, dye decolorization studies were conducted in both FBBR and M-FBBR. The enhanced CR dye removal was observed in M-FBBR. Further, optimization study for M-FBBR approach showing the maximum CR dye removal (92%), was obtained at a dye concentration of 100 mg/L, PUF weight- 5 g, pH-8, and glucose concentration- 4 g/L respectively. Extensive mineralization has been performed for synthetic and real textile wastewater (RTW), and the significant COD reduction (86.6%, 90.15%) and TOC reduction (57.54%, 69.13%) were observed for synthetic wastewater and RTW respectively.