Bioconversion of high concentrations of hydrogen sulfide to elemental sulfur in airlift bioreactor

Biochemical engineering for elemental sulfur from flue gases through multi-enzymatic based approaches - A review

Flue gases are the gases which are produced from industries related to chemical manufacturing, petrol refineries, power plants and ore processing plants. Along with other pollutants, sulfur present in the flue gas is detrimental to the environment. Therefore, environmentalists are concerned about its removal and recovery of resources from flue gases due to its activation ability in the atmosphere to transform into toxic substances. This review is aimed at a critical assessment of the techniques developed for resource recovery from flue gases. The manuscript discusses various bioreactors used in resource recovery such as hollow fibre membrane reactor, rotating biological contractor, sequential batch reactor, fluidized bed reactor, entrapped cell bioreactor and hybrid reactors. In conclusion, this manuscript provides a comprehensive analysis of the potential of thermotolerant and thermophilic microbes in sulfur removal. Additionally, it evaluates the efficacy of a multi-enzyme engineered bioreactor in this process. Furthermore, the study introduces a groundbreaking sustainable model for elemental sulfur recovery, offering promising prospects for environmentally-friendly and economically viable sulfur removal techniques in various industrial applications.

The effect of biofilm growth on the sulfur oxidation pathway and the synergy of microorganisms in desulfurization reactors under different pH conditions

Biofilm growth affects the oxygen transfer in biofilm and thus the oxidation pathway of sulfur and the synergy of microorganisms. In this study, the effect of biofilm growth on the oxidation pathway of H₂S and the synergy of microorganisms in desulfurization reactors under different pH conditions was first discussed to enhance the understanding of desulfurization process. A biotrickling filter (BTF) was operated for 168 days under acidic condition (pH<4.7) and 32 days under alkaline condition (7.0 <pH<10.2). In acidic period, the average growth mass (AGM) of biofilm was 0.04 g/L-BTF/d, and most of S-H₂S was converted to S-SO₄^2- (>89.0%). In alkaline period, the AGM raised to 0.97 g/L-BTF/d, and 77.0% of S-H₂S was transferred to elemental sulfur (S⁰) and polysulfanes (R-S_x-R) accumulated in biofilm. The increase of biofilm and sulfur-oxidizing bacteria activity limited the oxygen transfer in alkaline biofilm, leading to the accumulation of S⁰ and the emergence of an obligate anaerobe- Acetoanaerobium (8.1%). The formation of R-S_x-R may be due to the reaction of S⁰ with thiols produced by a thiol-producing bacterium- Pseudomonas (6.7%). The uneven distribution of oxygen in biofilm caused by biofilm growth complicated the transfer pathway of sulfur and the synergy of microorganisms in desulfurization system.

Extremely acidic condition (pH<1.0) as a novel strategy to achieve high-efficient hydrogen sulfide removal in biotrickling filter: Biomass accumulation, sulfur oxidation pathway and microbial analysis

Extremely acidic conditions (pH < 1.0) during hydrogen sulfide (H₂S) biotreatment significantly reduce the cost of pH regulation; however, there remain challenges to its applications. The present study investigated the H₂S removal and biomass variations in biotrickling filter (BTF) under long-term highly acidic conditions. A BTF operated for 144 days at pH 0.5-1.0 achieved an H₂S elimination capacity (EC) of 109.9 g/(m³·h) (removal efficiency = 97.0%) at an empty bed retention time of 20 s, with an average biomass concentration at 20.6 g/L-BTF. The biomass concentration at neutral pH increased from 22.3 to 49.5 g/L-BTF within 28 days. In this case, elemental sulfur (S⁰) accumulated due to insufficient oxygen transfer in biofilm, which aggravated the BTF blockage problem. After long-term domestication under extremely acidic conditions, a mixotrophic acidophilic sulfur-oxidizing bacteria (SOB) Alicyclobacillus (abundance 55.4%) were enriched in the extremely acidic biofilm, while non-aciduric bacteria were eliminated, which maintained the balance of biofilm thickness. Biofilm with optimum thickness ensured oxygen transfer and H₂S oxidation, avoiding the accumulation of S⁰. The BTF performance improved due to the enrichment of active mixotrophic SOB with high abundance under extremely acidic conditions. The mixotrophic SOB is expected to be further enriched under extremely acidic conditions by adding carbohydrates to enhance H₂S removal.