Removal of antibiotic and disinfectant compounds from digested pig manure by an aerobic hybrid biofilm process

Using nutrient-rich manure as fertiliser on agricultural land improves crop yield, biodiversity, soil structure, water and nutrient availability. However, manure often contains high levels of antibiotics, as only 10-30 % are metabolised by the animal, thus, soil application contributes to the spread of antibiotics and antibiotic-resistant genes (ARGs). As anaerobic digestion fails to remove the antibiotics and ARGs completely, this study investigates aerobic moving bed biofilm reactors (MBBRs) as post-treatment. The dissipation of sulfadiazine, sulfamethoxazole, ofloxacin, ciprofloxacin, roxithromycin, erythromycin, tylosin, tetracycline, chlortetracycline, benzalkonium chloride C12 and -C14 (BAC-12 and -14) was observed in small laboratory batch MBBRs with digested pig manure. Proficiency testing resulted in an overall removal of 92 %. Sulfamethoxazole and erythromycin were removed by >99 % within 12 and 23 days, respectively. The digestate exhibited high concentrations of benzalkonium biocides, i.e., BAC-12 and -14 (800 μg/L and 172 μg/L, respectively), highlighting the necessity for post-treatment before application to agricultural soil. Within 23 days, the aerobic MBBRs achieved 89 % and 93 % degradation of BAC-12 and -14, respectively. The biofilms improved the total removal by 19 % and BAC degradation by 61-68 % while increasing bacterial diversity. The MBBR-operation increased the abundance of the genera Paracoccus, Parvibaculum, and Clostridium sensu stricto 1. The sulfonamide-resistance genes were the most abundant ARGs (96 % and 98 % in the sludge and carrier biofilm, respectively). The ARG-abundance increased after antibiotic spiking and declined during incubation, reducing direct ARG spread to the environment by degrading antimicrobial concentrations. We, therefore, propose to treat anaerobically digested manure by aerobic biofilm treatment for antibiotic removal.