Can different inoculum sources influence the biodegradation of sulfamethoxazole antibiotic during anaerobic digestion?

Sulfamethoxazole (SMX) is one of the antibiotics most frequently detected in effluents from conventional wastewater treatment plants, which increases the concern about the possible impacts on the aquatic biota and public health regarding the emergence of bacteria resistant to this drug. Anaerobic fixed bed reactors are supposed to enhance antibiotic biodegradation due to the biofilm formation in the reactor. In this context, this study evaluated the dynamics of the microbial community in the biofilm of three inoculum sources taken from Upflow Anaerobic Sludge Blanket (UASB) reactors for the biodegradation of SMX in anaerobic structured bed biofilm reactor (ASBBR) with: poultry slaughterhouse sludge (PS), brewery sludge (BS) and domestic sewage sludge (SS). The ASBBR reached high COD (Chemical Oxygen Demand) removal (> 84%) and biomethane yield (> 276 mLCH4 g−1 CODremoved) for all inocula. The bioreactor operation with PS inoculum presented the best SMX removal (90 ± 5%), while the BS and SS inocula resulted in 84 ± 6% and 70 ± 5% removal, respectively. The kinetic profiles of COD and SMX removal indicated the occurrence of cometabolic biodegradation of sulfonamide. The molecular biology analysis showed that the microbial community of the SS inoculum suffered significant changes during the ASBBR operation for the Archaea and Bacteria domains and the biomass of PS presented more similarity to the inoculum, indicating a better SMX adaptation, in agreement with the higher SMX removal. Furthermore, the diversity of the Archaea domain (mainly Methanosaeta and Methanosarcina) increased in the biomass after each reactor operation compared to the raw inocula, indicating that the methanogenic pathway was favored during the anaerobic digestion. The experimental results showed that the inoculum source plays an important role in the SMX biodegradation during the biological wastewater treatment.