Comparison between two different fixed-bed reactor configurations for nitrogen removal coupled to biogas biodesulfurization

Abstract

A comparison between a mixed aerobic-anoxic horizontal fixed-bed reactor (MAAFBR) and an aerobic horizontal fixed-bed reactor coupled with an anoxic vertical fixed-bed reactor (AHFBR-AVFBR) was made in order to evaluate the nitrogen removal behavior when nitrification and sulfide-driven autotrophic denitrification occurred in a single unit or spatially separated. Both systems achieved Total-N removal efficiencies (RE) higher than 89 %. Moreover, for both reactors, the effluent pH was affected for bicarbonate alkalinities lower than 250 mg CaCO3 L−1, decreasing the biogas desulfurization from 98 to 50 % in the MAAFBR and from 100 to 61 % in the AVFBR. Hydraulic retention times (HRTs) of 6, 8, 10 and 12 h did not affect the nitrification RE on the AHFBR, maintaining values higher than 99 %. In both cases, biogas desulfurization was achieved. However, results suggested that elemental sulfur (S0) was not predominantly formed due to the interference of oxygen. Such interference was more severe for the MAAFBR, in which the results implied diffusion of O2 and H2S between the aerobic and anoxic chambers.