The Impact of Operating Parameters on the Gas-Phase Sulfur Concentration after High Temperature Sulfur Sorption on a Supported Mo-Mn Sorbent

The impact of operating parameters on H2S capture from a syngas mixture by a Mo-promoted Mn-based high-temperature sorbent was investigated. The parameters investigated included temperature, space velocity, H2S concentration in the feed gas, and steam content. The H2S and SO2 concentrations in the gas after passing over a bed of the sorbent were analyzed and compared with thermodynamic calculations. The results confirmed that low temperature, low space velocity, low H2S concentration, and a dry feed were favorable for achieving a low residual concentration of sulfur compounds in the effluent gas. The sorbent was able to reduce the residual H2S concentration to below 1 ppm under all tested conditions. However, the unavoidable steam content in the gas phase had a significant adverse effect on sulfur removal from the gas. An empirical model, containing the three variables, i.e., temperature, space velocity, and H2S concentration in the feed, was developed and can be used to predict the effluent H2S residual concentration after treatment by the 15Mn8Mo sorbent.

Poly-β-Hydroxybutyrate Production by Rhodopseudomonas sp. Grown in Semi-Continuous Mode in a 4 L Photobioreactor

The synthesis of polyhydroxybutyrate (PHB) by photosynthetic non-sulfur bacteria is a potential approach for producing biodegradable plastics. In this work, acetate was used as a single carbon source to study the effect on PHB formation in Rhodopseudomonas sp. cultured in a cylindrical four-liter photobioreactor under semi-continuous mode. The cultivation process is divided into a symmetrical growth phase and a PHB accumulation phase separated temporally. The symmetrical growth phase (nutrient sufficient conditions) was followed by a sulfur-limited phase to promote PHB accumulation. The main novelty is the progressive lowering of the sulfur concentration into Rhodopseudomonas culture, which was obtained by two concomitant conditions: (1) sulfur consumption during the bacterial growth and (2) semi-continuous growth strategy. This caused a progressive lowering of the sulfur concentration into Rhodopseudomonas culturedue to the sulfur-free medium used to replace 2 L of culture (50% of the total) that was withdrawn from the photobioreactor at each dilution. The PHB content ranged from 9.26% to 15.24% of cell dry weight. At the steady state phase, the average cumulative PHB was >210 mg/L. Sulfur deficiency proved to be one of the most suitable conditions to obtain high cumulative PHB in Rhodopseudomonas culture.

Influence of Sulfur and Light Intensity in Nutrient Removal, and Hydrogen and Ethanol Production by Optimized Biomass of Chlamydomonas Reinhardtii in Batch Anaerobic Photobioreactors

Hydrogen is a renewable fuel that can be biologically produced by green algae in closed anaerobic photobioreactors with light and organic carbon as energy sources. This research aimed to investigate the influence of sulfur concentration and light intensity on hydrogen and ethanol production, as well as on nutrient removal by Chlamydomonas reinhardtii (CC425) in batch cultures. The strain was cultivated in two phases: in the first step, the cultures were maintained under aerobic conditions to obtain biomass; in the second step, the biomass was transferred to closed anaerobic photobioreactors for gas generation under continuous illumination. A factorial design was accomplished to optimize the biomass production in the first step, with light variation, pH, and glucose addition. Afterward, light intensity and sulfur concentration were varied to test hydrogen production in the second step. The best production occurred in photobioreactors without sulfur addition (average increase of 7 times in the production) and under higher light intensity the production was 37% higher than lower light (39.64 ± 2.44 µmol H2 L-1 h-1). There was an effect of sulfur concentration in the ethanol production and under higher light intensity the production was higher (203.20 ± 31.49 mg L-1). In addition, in general, under conditions with the presence of sulfur, there was greater removal of ammoniacal nitrogen (5.3%), phosphate (85.0%), COD (9.1%) and acetic acid (97.2%). This research demonstrates the efficient production of hydrogen and ethanol by C. reinhardtii and it shows that the process can be associated with nutrient removal.

Effect of abiotic factors on sulfidogenic activity of bacteria Desulfuromonas sp.

Sulfur-reducing bacteria are promising agents for the development of new methods of wastewater treatment with the removal of ions of heavy metals and organic compounds. Study of the effect of various environmental factors on the growth and sulfidogenic activity of sulfur-reducing bacteria allows one to investigate the adaptability of these microorganisms to stress factors. The paper deals with the effect of рН, different concentrations of elemental sulfur, hydrogen sulfide and presence of various electron acceptors on the growth and sulfidogenic activity of bacteria Desulfuromonas sp. YSDS-3. The calculation of C/S ratio for sulfur-reducing bacteria Desulfuromonas sp. YSDS-3 was made, with the comparison with similar parameters of sulfate-reducing bacteria. In the medium with elemental sulfur, concentration of hydrogen sulfide increased with the concentration of elemental sulfur. Bacteria Desulfuromonas sp. YSDS-3 accumulated their biomass in the most effective way at the concentration of elemental sulfur of 10–100 mM. In the medium with polysulfide form of sulfur at the neutral pH, bacteria produced hydrogen sulfide and accumulated biomass the best. Hydrogen sulfide at the concentration of 3 mM did not inhibit the bacterial growth, but further increase in the hydrogen sulfide concentration inhibited the growth of bacteria. The bacteria did not grow at the hydrogen sulfide concentration of 25 mM and above. As the concentration of elemental sulfur and cell density increases, sulfidogenic activity of the bacteria grows. Presence of two electron acceptors (S and K2Cr2O7, S and MnO2, S and Fe (III)) did not affect the accumulation of biomass of the bacteria Desulfuromonas sp. YSDS-3. However, under such conditions the bacteria accumulated 1.5–2.5 times less hydrogen sulfide than in the test medium. After 12–24 h of cultivation, different concentrations of elemental sulfur had a significant effect on the sulfidogenic activity. However, during 3–16 days of cultivation, the percentage of effect of elemental sulfur concentration decreased to 31%, while the percentage of effect of cell density increased threefold. Presence in the medium of the electron acceptors (Cr (VI), MnO2, Fe (III)) alternative to elemental sulfur led to a significant decrease in the content of hydrogen sulfide produced by sulfur-reducing bacteria.