Biogas desulphurization at technical scale by lithotrophic denitrification: Integration of sulphide and nitrogen removal

Biogas desulphurization was carried out in a continuous bioscrubber with a volume of 5 m³ using aerobically treated wastewater containing activated sludge and mixture of nitrate (NO₃^-) and nitrite (NO₂^-) as electron acceptors in industrial relevant conditions. Both nitrate and nitrite were provided from full-scale activated sludge treatment plant operated and controlled using dissolved oxygen and redox sensors to make sure nitrification performed and biogas was provided from anaerobic digester. The biogas flowrate changed from 5 to 25 m³/h and wastewater flowrate from 2.5 to 15 m³/h. The volumetric sulphide loading rates ranged between 2 and 22 kg S^2- m^-3 d ^-1. The optimum wastewater/biogas ratio observed for maximum H ₂S removal rates was in the range of 2-3 m³/m³ and minimum empty bed residence time (EBRT) determined was around 10 min. Nitrogen removal in the form of nitrate and nitrite was found to be proportional to sulphide removal. The redox potential of the effluent was also monitored and related to the wastewater/biogas ratio. More than 95% of H₂S has been removed from biogas in this study when the volumetric sulphide loading rates were between 2 and 4 kg S^2- m^-3 d^-1. This work reveals that sulphide removal can successfully be integrated to biological nitrogen removal (BNR) in industrial wastewater treatment systems.