Application of the redox potential for controling a sulfide oxidizing bioreactor

Abstract

Abstract:The investigations described show that the formation of elemental sulfur from the biological oxidation of sulfide can be optimized by controling the redox state of the solution. The nonsoluble sulfur can be removed by gravity sedimentation and re-used as a raw material, i.e., in bioleaching processes. It was shown that, by supplying an almost stoichiometrical amount of oxygen to the recirculated gas phase, the formation of sulfate is minimized. The redox potential is mainly determined by the sulfide concentration because this compound has a high standard exchange current density with the platinum electrode surface. By maintaining a particular redox setpoint value, in fact, the reactor becomes a ''sulfide-stat.'' It was shown that in a sulfide-oxidizing bioreactor the measured redox potential, using a polished redox electrode, is kinetically determined rather than thermodynamically. The optimal redox value for sulfur formation is between −147 and −137 mV (H 2 reference electrode, 30°C, pH 8). The presented results are currently used for controling several full-scale installations, which desulfurize biogas and high-pressure natural gas.

Hydrogen sulphide removal from biogas by an anoxic biotrickling filter packed with Pall rings

“…In the controlled regime the ORP was measured on-line. Sulphide accumulation produced a significant decrease in the ORP [12,13] and M3 solution (NaNO 3 concentration of 5 g L À1 ) was added between the following setpoints:…”

Challenges of a feasible route towards sustainability in environmental protection

“…Undoubtedly, the major innovative development of the Ae micro WT-system lies in its capacity to convert reduced Scompounds into elementary sulfur [31][32][33][34][35][36][37]; the system enables a high rate and low-cost bio-conversion of volatile S-compounds like H 2 S and methanethiol from polluted gases, e.g., from Liquefied petroleum gas (LPG) [38][39][40][41] and from natural gas and/or biogas. The system is effective up to removal capacities of 50 tons H 2 S/day; for higher loads tentatively the well-proven amine/Claus process still looks more attractive [40].…”

Biotechnological removal of H2S and thiols from sour gas streams under haloalkaline conditions

“…Formation of sulfur and sulfate in the bioreactor is related to the O2/H2S supply ratio resulting in a certain equilibrium sulfide concentration, which, in turn, results in a particular value of oxidation-reduction potential (ORP) of the process liquid [90]. In the final section, elemental sulfur is separated from the solvent in the sulfur settler (Fig.…”

“…In case of gas biodesulfurization processes, it is known that the production of biosulfur is strongly correlated with the sulfide concentration and the availability of oxygen [86,90]. Therefore, the application of a sulfide sensor in control systems could be beneficial.…”

“…For example, selective ion electrodes and amperometric sensors are characterized by temperature and ionic strength sensitivity, and have a short lifetime [114][115][116]. Because in the absence of other strong reductants the ORP is mainly determined by the sulfide concentration [90], ORP sensors are commonly applied instead of sulfide sensors. The ORP sensor is often used in combination with a proportional-integral-derivative (PID) controller to control the oxygen supply ( Fig.…”