A new anaerobic, aerobic, nitrification, anoxic reactor (AANAR) with overlaid biological zones: Sulfide removal from wastewater and biogas

•Overlaid biological zones were efficiently separated.•AANAR was able to simultaneously remove sulfide from wastewater and biogas.•The removal of dissolved sulfide from anaerobic effluent reached 99.8 ± 0.2 %.•The biogas treatment for sulfide removal reached 97 ± 2.0 %. Hydrogen sulfide is a by-product from anaerobic digestion of wastewater that can cause a wide range of inconveniences, such as toxicity, corrosion, and foul odor. In this study, a new Anaerobic, Aerobic, Nitrification, Anoxic Reactor – AANAR (364 L), with overlaid biological zones, separated by a modified three phase separator, was evaluated on a pilot-scale to remove both sulfide from anaerobic effluent and biogas simultaneously, to control the foul odor. The AANAR was operated in three different phases: (i) Wastewater flow of 20 Lh−1 using ethanol supplementation to the denitrification process without biogas recirculation on the anoxic zone, (ii) Wastewater flow of 25 Lh−1 using ethanol supplementation to the denitrification process and biogas recirculation on the anoxic zone, and (iii) Wastewater flow of 25 Lh−1 with biogas recirculation on the anoxic zone without ethanol supplementation. The overlaid biological zone was observed by dissolved oxygen monitoring which was verified to be efficiently separated. The dissolved sulfide removal was 99.6 ± 0.5, 99.6 ± 0.1, and 99.8 ± 0.2 % for phase 1, 2, and 3, respectively. The biogas treatment performance to sulfide removal was 89 ± 7.0, 97 ± 2.0, and 96 ± 3.0 % for phases 1, 2, and 3, respectively. Hence, these results show the possibility of biological zones in an AANAR to efficiently remove sulfide from both anaerobic effluent and biogas generated by anaerobic digestion of wastewater.