BACKGROUNDBiological technologies for biogas upgrading such as anoxic biotrickling filters (BTF) and algal-bacterial photobioreactors (PBR) constitute a cost-effective, environmentally friendly alternative to conventional physical-chemical methods. Nonetheless, there is a lack of studies comparing their performance when treating real biogas. RESULTSA H2S removal efficiency >98% was consistently recorded in both systems, with elimination capacities up to 26 and 12.4 g S-H2S m(-3) h(-1) in the BTF and PBR, respectively, at empty bed residence times (EBRTs) of approximate to 30 min. Both bioreactors demonstrated a high robustness towards fluctuations in biogas composition and flowrate, maintaining nearly complete desulfurization despite the variations in sulfur load and EBRT. The BTF also showed an immediate recovery from a 15 days operational shut-down, and the ability to utilize the nutrients from nitrate-supplemented digestate during biogas desulfurization. In addition, the PBR supported an average CO2 removal of 23.011.8%, increasing to 62% at higher pH of 8.1, with a carbon fixation rate of 285 mg CO2 L-1 d(-1). CONCLUSIONSThe BTF was confirmed as a robust technology for the desulfurization of real biogas, even when supplemented with effluent from the digester. High H2S removal was also achieved in the PBR, the CO2 fixation capacity of microalgae enhancing biogas purification. (c) 2015 Society of Chemical Industry