Evaluation of a hybrid physicochemical/biological technology to remove toxic H2S from air with elemental sulfur recovery

The efficiency and mechanism of humidity in alleviating CO2 inhibition on H2S adsorption to straw biochars

Adsorption tests were conducted to clarify the impact of carbon dioxide (CO₂) on hydrogen sulfide (H₂S) removal to straw biochars and the role of humidity in affecting the CO₂ impact. When straw biochars were dry, CO₂ proved significantly detrimental to their H₂S adsorption, regardless of the CO₂ contents. In contrast, when adjusting the humidity of the biochars to 20%, the presence of CO₂ promoted the conversion of H₂S into sulfites, though still inhibited the generation of elemental sulfur, through which the original negative CO₂ impact was nearly compensated. The presence of low to medium contents of CO₂ even slightly improved the adsorption capacity and extended the breakthrough time. This phenomenon was ascribed to a favorable carbon surface environment for H₂S dissociation and oxidation, created from the reactions of the major minerals (Ca and Mg) with CO₂ and water. To sum up, the CO₂ inhibition on the H₂S adsorption to biochars was ascribed to the competition of CO₂ for the active sites; however, humidity induced a series of CO₂-participated chemical reactions between H₂S and the minerals, sufficiently alleviating the CO₂ inhibition. The results also highlight the necessity to recognize the most critical biochar properties or an efficient balance of crucial biochar properties in achieving an optimal H₂S removal when CO₂ is present in the syngas.

A Critical Review on the Properties and Applications of Sulfur-Based Concrete

The incessant demand for concrete is predicted to increase due to the fast construction developments worldwide. This demand requires a huge volume of cement production that could cause an ecological issue such as increasing the rates of CO₂ emissions in the atmosphere. This motivated several scholars to search for various alternatives for cement and one of such alternatives is called sulfur-based concrete. This concrete composite contributes to reduce the amount of cement required to make conventional concrete. Sulfur can be used as a partial-alternate binder to Ordinary Portland Cement (OPC) to produce sulfur-based concrete, which is a composite matrix of construction materials collected mostly from aggregates and sulfur. Sulfur modified concrete outperforms conventional concrete in terms of rapid gain of early strength, low shrinkage, low thermal conductivity, high durability resistance and excellent adhesion. On the basis of mentioned superior characteristics of sulfur-based concrete, it can be applied as a leading construction material for underground utility systems, dams and offshore structures. Therefore, this study reviews the sources, emissions from construction enterprises and compositions of sulfur; describes the production techniques and properties of sulfur; and highlights related literature to generate comprehensive insights into the potential applications of sulfur-based concrete in the construction industry today.

Desulfurization of Biogas from a Closed Landfill under Acidic Conditions Deploying an Iron-Redox Biological Process

Desulfurization processes play an important role in the use of biogas in the emerging market of renewable energy. In this study, an iron-redox biological process was evaluated at bench scale and pilot scale to remove hydrogen sulfide (H2S) from biogas. The pilot scale system performance was assessed with real biogas emitted from a closed landfill to determine the desulfurization capacity under outdoor conditions. The system consisted of an Absorption Bubble Column (ABC) and a Biotrickling Filter (BTF) with useful volumes of 3 L and 47 L, respectively. An acidophilic mineral-oxidizing bacterial consortium immobilized in polyurethane foam was utilized to regenerate Fe(III) ion, which in turn accomplished the continuous H2S removal from inlet biogas. The H2S removal efficiencies were higher than 99.5% when H2S inlet concentrations were 120–250 ppmv, yielding a treated biogas with H2S < 2 ppmv. The ferrous iron oxidation rate (0.31 g·L−1·h−1) attained when the system was operating in natural air convection mode showed that the BTF can operate without pumping air. A brief analysis of the system and the economic aspects are briefly analyzed.

Simultaneous Biological and Chemical Removal of Sulfate and Fe(II)EDTA-NO in Anaerobic Conditions and Regulation of Sulfate Reduction Products

In the simultaneous flue gas desulfurization and denitrification by biological combined with chelating absorption technology, SO2 and NO are converted into sulfate and Fe(II)EDTA-NO which need to be reduced in biological reactor. Increasing the removal loads of sulfate and Fe(II)EDTA-NO and converting sulfate to elemental sulfur will benefit the application of this process. A moving-bed biofilm reactor was adopted for sulfate and Fe(II)EDTA-NO biological reduction. The removal efficiencies of the sulfate and Fe(II)EDTA-NO were 96% and 92% with the influent loads of 2.88 kg SO42−·m−3·d−1 and 0.48 kg NO·m−3·d−1. The sulfide produced by sulfate reduction could be reduced by increasing the concentrations of Fe(II)EDTA-NO and Fe(III)EDTA. The main reduction products of sulfate and Fe(II)EDTA-NO were elemental sulfur and N2. It was found that the dominant strain of sulfate reducing bacteria in the system was Desulfomicrobium. Pseudomonas, Sulfurovum and Arcobacter were involved in the reduction of Fe(II)EDTA-NO.