1 Introduction
Azo dyes are widely used in various industries, and the discharge of azo
dye-containing wastewater poses a significant threat to human health and
the environment. Microbial decolorization has been recognized as one of
the most effective and environmentally friendly methods for treating azo
dye wastewater (Pandey et al., 2007; Yin et al., 2016). Immobilization
of microorganisms on the surface of a biofilm carrier has become an
increasingly popular technology in this field. Microbial immobilization
technology employs physical or chemical methods to restrict cell
migration, and the carrier provides optimal conditions for microbial
reproduction and a protective surface for the biofilm (Mjla et al.,
2021; Shao et al., 2017). Embedded or attached microorganisms can create
aggregates on the carrier’s surface, enhancing the efficiency and
stability of microbial dye treatment (Sarti et al., 2016).
The choice of carrier material is critical to the effectiveness of
wastewater biological treatment. Various types of carrier fillers,
including thermoplastic plastics, minerals, fiber materials, and waste
materials, can be used in the production of carrier fillers (Jagaba et
al., 2021). For example, the removal rate of Congo red dye by the
low-density polyethylene-polypropylene (LDPE-PP) carrier-based moving
bed biofilm reactor (MBBR) using microorganisms isolated from
dye-polluted soil as inoculum was as high as 99.2% (Sonwani et al.,
2021). The decolorization rate of Anthraquinone Blue RS by a continuous
up-flow packed bed reactor using Bacillus flexus TS8, Proteus
mirabilis PMS, and Pseudomonas aeruginosa NCH isolated from
textile wastewater as inoculum and corn cob biochar as carrier material
was up to 90% (Mohanty and Kumar, 2021). Studies have shown that the
carrier is a medium for biofilm proliferation, and its surface and
material characteristics determine the properties of the biofilm, which
may affect the diversity of the biofilm community (Chu and Wang, 2011;
Abu Bakar et al., 2020). The type of polymer used in the biofilm carrier
has a significant impact on the performance of the reactor (Krsmanovic
et al., 2021).
In this study, we investigated the effect of different carriers on the
decolorization efficiency and degradation pathway of Reactive Black 5
(RB5) biofilm reactors inoculated with Shewanella india. We
employed three different types of carriers, namely almond shell biochar,
Moving Bed Biofilm Reactor (MBBR) polyethylene, and Porous Polyurethane
Carrier (PPC), and examined their effectiveness in achieving high and
stable decolorization rates. We analyzed the microbial community
structure and identified highly efficient degradation strains in the
reactors to investigate the variations in microbial composition among
different carriers. Through 16S rDNA community analysis, we explored the
composition of microorganisms on the carrier and highly efficient RB5
degradation bacterial communities in the reactor. The findings from this
study will provide guidance for expanding the selectivity of biofilm
reactor fillers and improving the decolorization efficiency of azo dyes.