On-line monitoring of gas-phase bioreactors for biogas treatment: hydrogen sulfide and sulfide analysis by automated flow systems

Biogas is produced by biological processes under anaerobic conditions and may contain up to 20,000 ppm(v) hydrogen sulfide (H2S), a corrosive substance that attacks power engines and can affect the health of the industrial staff. H2S must be removed from the biogas, especially in co-generation facilities where the biogas is burnt for energy production. Nowadays, biofiltration is being studied and considered as an interesting alternative for removing H2S from the biogas besides classical chemical processes. The novelty of this work is the design and construction of an automated H2S on-line analyser to assess the composition of the liquid and gas phases of gas-phase bioreactors. The analyser is made of two parallel flow configurations which share the same detection device. The first configuration is a single-channel flow injection analyser (FIA) to detect S-2-in the liquid phase. The second configuration is a continuous flow analyser (CFA) with a gaseous diffusion step (GD CFA) for detecting H2S in the gas phase. The diffusion step enables separation of the H2S(g) from the sample and its conversion into a detectable chemical species (S2-). S-2-detection was performed with an Ag2S ion-selective electrode (ISE) selective to S-(aq)(2)-. The main response parameters of the FIA system are a linear range between 3 x 10(-5) and 1 x 10(-1) mol L-1 S-2-(0.61 -3,200 mg L-1), with a sensitivity of 27.9 mV decade(-1) and a detection limit of 1.93 x 10(-5) mol L-1 S2-. The GD -CFA configuration presents a linear range between 400 and 10,000 ppmv H2S(g) with a sensitivity of 26.1 mV decade(-1) and a detection limit of 245 ppmv H2S. The proposed analyser was used by analysing real gas and liquid samples with optimal results at a full-scale biotrickling filter for biogas treatment at a municipal wastewater treatment plant.