Methane Production From Antibiotic Bearing Swine Wastewater Using Carbon-Based Materials As Electrons' Conduits During Anaerobic Digestion

The impact of granular-activated carbon (GAC), graphite felt (GF), and activated carbon cloth (ACC), and two veterinary antibiotics, oxytetracycline (OTC) and enrofloxacin (ERX), was evaluated during the production of methane from the anaerobic digestion of swine effluent. The results showed that GAC (10 g/L) increased 3.0-fold the methane production and 1.4-fold the organic matter removal efficiency, with respect to the control in the presence of OTC (10 mg/L). With ERX, GAC also increases the production of methane with respect to ACC and GF. Adsorption experiments reveal the affinity of antibiotics to carbon materials; nonetheless, even though GAC adsorbed lesser antibiotics, which would mean that antibiotic toxicity remained, the production of methane with GAC was higher. The microbial electron-accepting capacity of GAC (0.57 mmol/g) indicates that electrons from organic matter's oxidation are driven to the material and, subsequently, may act as an electron donor for methanogens to promote methane production. Finally, ERX showed the capacity to act as a redox mediator to reduce Fe(III) up to 1.6-fold higher than the control; nonetheless, it was not reflected in improving the production of methane.