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Hydrogen sulfide removal from synthetic biogas using anoxic biofilm reactors

Abstract : The aim of this work was to develop and study anoxic bioreactors for the removal of re-duced inorganic sulfur compounds from liquid and gaseous waste streams. In addition, the aim was to enable process integration for the simultaneous treatment of H2S con-taminated gas streams and NO3--containing wastewater. The experiments related to sulfide oxidation in the liquid phase were conducted in two different attached growth bioreactors, i.e. a fluidized-bed reactor (FBR) and a moving bed biofilm reactor (MBBR), inoculated with the same mixed culture of sulfur-oxidizing nitrate-reducing (SO-NR) bacteria. The bioreactors were operated under different nitro-gen-to-sulfur (N/S) molar ratios using S2O32- and NO3- as an energy source and electron acceptor, respectively. Results revealed that both the FBR and MBBR achieved S2O32- removal efficiencies (RE) >98% and completely removed NO3- at an N/S ratio of 0.5. Under severe nitrate limitation (N/S ratio of 0.1), the S2O32- RE in the MBBR (37.8%) was higher than that observed in the FBR (26.1%). In addition, the MBBR showed better resilience to nitrate limitation than the FBR as the S2O32- RE was recovered to 94% with-in 1 day after restoring the feed N/S ratio to 0.5, while it took 3 days to obtain 80% S2O32- RE in the FBR. Artificial neural network models were successfully used to predict the FBR and MBBR performance, i.e. S2O32- and NO3- RE as well as sulfate production. The SO-NR biomass from the MBBR was used to inoculate an anoxic biotrickling filter (BTF), which was studied for simultaneous treatment of H2S and NO3- containing waste streams. In the anoxic BTF, a maximum H2S elimination capacity (EC) of 19.2 g S m-3 h-1 (99% RE) was obtained at an inlet H2S load of 20.0 g S m-3 h-1 (~500 ppmv) and an N/S ratio of ~1.7. As some NO3--containing wastewaters can also contain organic com-pounds, the anoxic BTF inoculated with Paracoccus versutus strain MAL 1HM19 was studied for the simultaneous treatment of H2S, NO3- and organic carbon containing waste streams. With this BTF, NO3- and acetate removal rates of 16.7 g NO3--N m-3 h-1 and 42.0 g acetate m-3 h-1, respectively, were achieved, which was higher than the val-ues observed in the BTF inoculated with the mixed culture of autotrophic SO-NR bacte-ria (11.1 g NO3--N m-3 h-1 and 10.2 g acetate m-3 h-1). Anoxic BTFs were operated under several transient conditions (i.e. varied gas and trickling liquid flow rates, intermittent NO3- supply and H2S shock loads) to evaluate the impacts of sudden changes that usu-ally occur in practical applications. The different transient conditions significantly affect-ed the H2S EC of the anoxic BTF. After applying H2S shock loads, the H2S RE fully re-covered to >99% within 1.7 days after resuming normal operation.In summary, the MBBR was more effective for the removal of S2O32- than the FBR, especially under nitrate limited conditions. Based on the short recovery times after expo-sure to transient-state conditions, the anoxic MBBR and BTF were found to be resilient and robust systems for removal of reduced sulfur compounds under autotrophic and mixotrophic conditions
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Ramita Khanongnuch. Hydrogen sulfide removal from synthetic biogas using anoxic biofilm reactors. Environmental Engineering. Université Paris-Est; Tampereen yliopisto, 2019. English. ⟨NNT : 2019PESC2053⟩. ⟨tel-02481161⟩

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