Effects of different carriers on biogas production and microbial community structure during anaerobic digestion of cassava ethanol wastewater

In this study, an anaerobic bioreactor (AB) with no added fillers (ABWF), a packed-bed bioreactor with a porous ceramic filler (ABCF), and another packed-bed bioreactor filled with graphite felt (ABGF) were established for anaerobic digestion of cassava ethanol wastewater. The results showed that ABCF exhibited excellent wastewater treatment performance in a stable process that was superior to ABWF and ABGF, with the following characteristics: a high chemical oxygen demand removal efficiency of 98.06% and maximum biogas production of 3200mL/d at a total reactor volume of 3.46L. Illumina MiSeq sequencing analysis revealed that differences existed among the microbial communities of the three ABs that were in accordance with the operational characteristics. The ABCF system displayed maximum bacterial diversity, whereas the ABWF system exhibited moderate richness and the ABGF system possessed the lowest species richness. The ABCF system was more stable than the ABWF and ABGF systems during anaerobic digestion of cassava ethanol wastewater. Different functional microbial communities that are responsible for the degradation of certain compounds were also identified in the ABCF and ABGF systems. Our results demonstrate that ceramic materials should be considered an appropriate support for the immobilization of cells.