Effect of applying a magnetic field on the biofiltration of hexane over long-term operation period

The present study reports on the effect of magnetic field (MF) intensity on the biofiltration of hexane vapors. MF ranging from 0 to 30 mT (millitesla) was used to evaluate the biofiltration of hexane for 191 days under a fixed inlet load of 40 g m^-3 h^-1. A homogeneous MF generated by Helmholtz coils was used. The performance of the reactors was evaluated in terms of removal efficiency (RE), elimination capacity (EC), biomass content, and exopolysaccharide (EPS) production. Maximal removal efficiencies of 25%, 36%, and 40% were found for the control (H₀), 10 mT (H₁₀), and 30 mT (H₃₀) reactors, corresponding to ECs of 14.2, 15, and 18 g m^-3 h^-1, respectively. In the last period (days 94 to 162), H₁₀ and H₃₀ showed 40% of RE improvement compared with H_o. Also, the removal occurred all along the bioreactor height for biofilters exposed to MF. Reactors achieved a total biomass content of 152, 180, and 147 mg _{VS (volatile solids)} g^-1 dry perlite for H₀, H₁₀, and H₃₀, correspondingly, associated with EPS production of 30, 30, and 40 mg EPS g^-1 _VS. The main components of EPS affected by the MF were carbohydrates and glucuronic acid; proteins were slightly affected. Experiments with MF pulses of 4 and 2 h confirmed that MF exposure improved the removal efficiency of hexane, and after the pulse, removal enhancement was maintained for 5 days. Thus, the MF application by pulses could be an economically and friendly technology to improve the RE of volatile organic compounds (VOCs).