Biostimulation of anaerobic digested wastewater using magnetic nanoparticles and an external magnetic field for biogas enhancement

Energy-driven wastewater treatment plants (WWTP) have become an interesting research focus for environmental and process engineers. To meet the rigorous discharge limit standards imposed by the environmental protection agency (EPA) and South African national standards (SANS), the conventional treatment method has been improved and advanced technologies have been adapted. As such, studies on magnetized anaerobic digestion systems for wastewater treatment with the concept of energy generation have been explored. The present study evaluated the effect of an external magnetic field (MF) on biochemical methane potential (BMP) tests using magnetic nanoparticles (MNP) for wastewater treatment. Two BMP systems were compared, where both systems were dosed with Fe₃O₄ (MNP) and operated at 35 °C for 10 days. One of the systems (control) was not exposed to the magnetic field while the other system had 3 h of 20 mT magnetic field exposure on daily basis. The system exposed to the magnetic field showed better performance in terms of biogas enhancement and the treatability of the wastewater. About 85% chemical oxygen demand (COD) of the wastewater (350 mg.L^–1 COD remaining) was degraded by the MF, which resulted in 72% color removal, 210 mL.day^–1 biogas produced and 97% methane. On other hand, 75% COD was degraded by the control system, which resulted in 175 mL.day^–1 biogas and 94% methane. Exposing the BMP system coupled with MNPs to an external magnetic field was found to be feasible and promising in terms of biogas production and color removal.