Simultaneous veterinary antibiotics reduction and biomass production from pig slurry by microalgae co-immobilization in Moving Bed Biofilm Reactors

The objective of the study was to assess, for the first time, the effectiveness of using either freely suspended or co-immobilized microalgae on Moving Bed Biofilm Reactor carriers in removing lincomycin from the liquid fraction of pig slurry, while ensuring the safe production of biomass. To this end, continuous-mode (HRT = 8 d) and batch-mode (10 d) experiments were conducted on bench-scale reactors. In the continuous-mode experiment, co-immobilized microalgae removed 99% of lincomycin and 94% of ammonium, whereas the control reactors and free-microalgae reactors showed significantly lower ammonium removals (69% and 87%, respectively). The removal rates for lincomycin and ammonium in co-immobilized microalgae reactors were higher (0.85 and 0.32 d-1, respectively) than the removal rates of the free-microalgae reactors (0.32 and 0.19 d-1) and control reactor (0.18 and 0.12 d-1). Furthermore, the microalgae reactors were linked with the production of lincomycin transformation products following ammonium and nitrate removal. In contrast to the control reactors, the suspended biomass of both free microalgae and co-immobilized microalgae reactors showed no accumulation of lincomycin. This characteristic makes this biomass particularly appealing in the context of a circular economy. The study introduces an innovative method for producing biomass from pig slurry, with the goal of obtaining high-value products while minimizing pollutant content.