Biogas production from wastewater treatment: Evaluating anaerobic and biomagnetic systems

Abstract

Biogas, a green and sustainable form of energy produced during the degradation of organic waste anaerobically comes with ecological and economic paybacks when compared to a comprehensive fossil fuel-based energy system. However, the biodiversity of microorganisms and chemical loads for enzymatic and bioconversion reactions impedes the anaerobic digester’s (AD) practicality for commercialization. Hence, this study examined the application of titanium dioxide magnetite (Fe-TiO2) (F) via a synthetic route in AD + F and a biomagnetic system (BMs) as a collective pathway to maximize methane potentials, wastewater treatment, and improve biogas production. The AD + F and BM systems were operated at a working volume of 0.8 L (inoculum to wastewater ratio of 0.6), the mesophilic temperature of 35 °C for an incubation period of 30 days. The results showed in-situ Fe-TiO2 facilitated the bio-electrolysis and bio-methanation reactions in the AD process which improved its performance as compared to the control (AD only). Above 75% of chemical oxygen demand (1600 ± 16.2 mg/L), Total Kjeldahl Nitrogen (76 ± 6.4 mg/L), total solids (135 ± 12 mg VS/L), volatile solids (94 ± 6.8 mg VS/L), and other inorganic contaminants (28 elementals) contained in the wastewater were removed by the BMs at a pH of 6.5 followed by the AD + F (65–75%) and the AD only (50–65%). On the 20th day, the control system (AD only) had a maximum daily biogas yield of 50 mL/COD.d, whereas the AD + F gave 90 mL/d and BMs 120 mL/d. Compared to the control with a methane yield of 66%, the addition of the Fe-TiO2 to AD + F and BMs increased the methane yield to 100%. Synergistically, the catalytic and biomagnetic activity of Fe-TiO2 in the BMs heightened the adsorption and reaction pathway of the contaminant’s transformations and degradation. Amidst two kinetic models investigated, the cumulative biogas yield followed the Gompertz kinetic model. In conclusion, combining the magnetic effect with green magnetic catalyst (Fe-TiO2) in AD and adsorption–based wastewater settings have viable prospects towards environmental purification.