Biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapolitanus in an internal airlift loop reactor

Impact of p-cresol on hydrogen sulfide and ammonia treatment by biotrickling filter and the production of nitrous oxide

Biotrickling filter (BTF) is often used for purification of waste gas from swine houses, with vital information still needed regarding interaction effects among multiple gas pollutants removal and also the formation of byproducts especially nitrous oxide (N2O, a strong greenhouse gas) due to the relative high NH3 concentration level compared to other gases. In this study, gas removal and N2O production were compared between two BTFs, where the inlet gas of BTF-1 contained NH3 and H2S while p-cresol was additionally supplied to BTF-2. At inlet load (IL) between 3.67 and 18.91 g m-3 h-1, removal efficiencies of NH3 exceeded 95% for both BTFs. As alternative strategy, adding thiosulfate improved H2S removal. Interestingly, presence of p-cresol to some extent promoted H2S removal at IL of 0.56 g m-3 h-1possibly due to effect on pH value of circulating solution. Similar to NH3, removal efficiencies of p-cresol were higher than 95% at an average IL of 2.98 g m-3 h-1. Gas residence time, pH of circulating solution and inlet loading were identified as key factors affecting BTF performance, but the response of individual gas compound to these factors was not consistent. Overall, p-cresol enhanced N2O generation although the effects were not always significant. High-throughput sequencing results showed that Proteobacteria accounted for the largest proportion of relative abundance and BTF-2 had much richer microbial diversity compared to BTF-1. Thermomonas, Comamonas, Rhodanobacter and other bacterial genus capable of denitrification were detected in both BTFs, and their corresponding abundances in BTF-2 (10.9%, 8.7% and 5.2%) were all greater than those in BTF-1 (0.4%, 0.3% and 2.0%), indicating that more denitrification may occur within BTF-2 and higher N2O could have been generated. This study provided evidence that organic gas components, served as carbon source, may increase the N2O production from BTF when treating waste gases containing NH3.

Biodesulfurization of Fossil Fuels: Analysis and Prospective

Biodesulfurization (BDS) of fossil fuels is a promising method for treating the high content of sulfur in crude oils and their derivatives in the future, attributed to its environmental-friendly nature and the technical efficient ability to desulfurize the organosulfur compounds recalcitrant on other techniques. It was found that the bioreaction rate depends on the treated fluid, targeting sulfur compounds, and the microorganism applied. Also, many studies investigated the operation conditions, specificity, and biocatalysts modification to develop BDS efficiency. Furthermore, mathematical kinetics models were formulated to represent the process. In this review, the previous studies are analyzed and discussed. This review article is characterized by a clear picture of all BDS's experimental, industrial, procedural, theoretical, and hypothetical points.

Effects of two plant species combined with slag-sponges on the treatment performance of contaminated saline water in constructed wetland

Constructed wetland (CW), an ecological water treatment system, can purify and repair the damaged saline water body in an open watershed, but its repairing function is limited at low temperature under salt stress. In this study, two different plant species with slag-sponge layer were operated to enhance the purification effect of CW on the damaged saline water body. The results showed that the combination of Scirpus mariqueter and slag-sponges in CW had a better purification effect especially under the condition of salinity of 10‰ (S = 10) with a respective removal efficiency of 91.04% of total nitrogen, 80.07% of total phosphorus, and 93.02% of COD in high temperature (25 ~ 35 °C). Furthermore, ecological traits (enzyme activity and amino acids) of plants, the abundance and distribution of functional microorganisms on the surface of slag-sponges, and the microbial state on the substrate surface of the denitrifying zone of CW were analyzed to explain how exactly the combinations worked. It was found that the enrichment of functional microorganisms in slag-sponge and the anaerobic zone of plants have improved the nitrogen and phosphorus removal. Plants maintained high enzyme activities and the ability to synthesize key amino acids under salt stress to ensure the growth and reproduction of plants and achieve the assimilation function. Scirpus mariqueter combined with slag-sponges in CW effectively improved the purification effect of damaged saline water, indicating that it is an ecological and green saline water treatment way.

Recent advances in biological technologies for anoxic biogas desulfurization

Recovery of the energy contained in biogas will be essential in coming years to reduce greenhouse gas emissions and our current dependence on fossil fuels. The elimination of H₂S is a priority to avoid equipment corrosion, poisoning of catalytic systems and SO₂ emissions in combustion engines. This review describes the advances made in this technology using fixed biomass bioreactors (FBB) and suspended growth bioreactors (SGB) since the first studies in this field in 2008. Anoxic desulfurization has been studied mainly in biotrickling filters (BTF). Elimination capacities (EC) up to 287 gS m^-3 h^-1 have been achieved, with a removal efficiency (RE) of 99%. Both nitrate and nitrite have been successfully used as electron acceptor. SGBs can solve some operational problems present in FBBs, such as clogging or nutrient distribution issues. However, they present greater difficulties in gas-liquid mass transfer, although ECs of up to 194 gS m^-3 h^-1 have been reported in both gas-lift and stirred tank reactors. One of the major disadvantages of using anoxic biodesulfurization compared to aerobic biodesulfurization is the need to provide reagents (nitrates and/or nitrites), with the consequent increase in operating costs. A solution proposed in this respect is the use of nitrified effluents, some ammonium-rich effluents nitrified include landfill leachate and digested effluent from the anaerobic digester have been tested successfully. Among the microbial diversity found in the bioreactors, the genera Thiobacillus, Sulfurimonas and Sedimenticola play a key role in anoxic removal of H₂S. Finally, a summary of future trends in technology is provided.

Bacterial Biological Factories Intended for the Desulfurization of Petroleum Products in Refineries

The removal of sulfur by deep hydrodesulfurization is expensive and environmentally unfriendly. Additionally, sulfur is not separated completely from heterocyclic poly-aromatic compounds. In nature, several microorganisms (Rhodococcus erythropolis IGTS8, Gordonia sp., Bacillus sp., Mycobacterium sp., Paenibacillus sp. A11-2 etc.) have been reported to remove sulfur from petroleum fractions. All these microbes remove sulfur from recalcitrant organosulfur compounds via the 4S pathway, showing potential for some organosulfur compounds only. Activity up to 100 µM/g dry cell weights is needed to meet the current demand for desulfurization. The present review describes the desulfurization capability of various microorganisms acting on several kinds of sulfur sources. Genetic engineering approaches on Gordonia sp. and other species have revealed a variety of good substrate ranges of desulfurization, both for aliphatic and aromatic organosulfur compounds. Whole genome sequence analysis and 4S pathway inhibition by a pTeR group inhibitor have also been discussed. Now, emphasis is being placed on how to commercialize the microbes for industrial-level applications by incorporating biodesulfurization into hydrodesulfurization systems. Thus, this review summarizes the potentialities of microbes for desulfurization of petroleum. The information included in this review could be useful for researchers as well as the economical commercialization of bacteria in petroleum industries.

Unravelling microbial drivers of the sulfate-reduction process inside landfill using metagenomics

Hydrogen sulfide (H₂S) is one of the common landfill odor. This research demonstrates that the sulfate transformation behavior is significantly enhanced during the landfill process, accompanied by a shift in microbial structure. The relative abundance of dissimilatory sulfate reduction (DSR) and thiosulfate oxidation by SOX (sulfur-oxidation) complex gradually decreases through the landfill processes while the assimilatory sulfate reduction (ASR) demonstrates the opposite behavior. The major module for landfill sulfate reduction is ASR, accounting for 31.72% ± 2.84% of sulfate metabolism. Based on the functional genes for the sulfate pathway, the drivers for sulfate biotransformation in landfills were determined and further identified their contribution in the sulfate metabolism during landfill processes. Pseudomonas, Methylocaldum, Bacillus, Methylocystis and Hyphomicrobium were the top 5 contributors for ASR pathway, and only one genus Pseudomonas was found for DSR pathway. Among the 26 high-quality metagenome-assembled genomes of sulfate functional species, 24 were considered novel species for sulfuric metabolism. Overall, this study provides unique insight into the sulfate transformation process related to the H₂S odor control in landfill management.

Nickel-Catalyzed mesoporous biochar for enhanced adsorptive oxidation of aqueous Sulfide: An investigation of influencing factors and mechanisms

Biochar (BC) is a low-cost and electroactive adsorbent for removing sulfide in aqueous media, which toxifies aquatic organisms and corrodes water treatment facilities. However, it lacks a pore structure for sulfide ion (S^2-) mass transfer to active sites. Herein, it is shown that nickel-modified biochar (BC-Ni) adsorbed S^2- 2.72-fold faster than BC alone and attained a 1244 ± 252 mg-sulfide/g maximum adsorption capacity due to markedly increased mesopores, while BC attained 583 ± 250 mg-sulfide/g. Factors influencing S^2-sorption and theoretical sorption kinetics and isotherms models were evaluated. Structural and surface compositions of BC and BC-Ni were examined using state-of-the-art characterizations. The results suggest that S^2- was adsorbed via pore diffusion, pore filling, and cation bridging and oxidized to elemental sulfur and sulfate with quinone and hydrogen peroxide generated from dehydrogenation of hydroquinone on the BC-Ni by metallic nickel in the carbon matrix. This study would spur biomass valorization and desulfurization.

Biodesulfurization of thiosulfate by a Pseudomonas strain PSP1 and the investigation of underlying metabolic mechanisms

The increasing public expectations for good air quality have necessitated the development of biodeodorization technology. Among different malodorous pollutants, H₂S has attracted extensive attention and diverse biodesulfurization technology has been developed for efficient H₂S removal. In this study, a novel heterotrophic Pseudomonas strain, PSP1, was isolated from biogas slurry and its biodesulfurization ability was investigated. Culture conditions of 30 °C and 200 rpm were determined as the optimal for both cell growth and thiosulfate conversion. Under such conditions, the highest OD₆₀₀ value was observed as 6.74 and 50 mM thiosulfate within 10 h. PSP1 was found to convert thiosulfate to sulfane which could be decomposed into elemental sulfur and therefore achieved desulfurization. However, this process was relatively weak as more than 60% thiosulfate was converted into soluble tetrathionate. The whole genome sequencing and functional annotation identified the genes in PSP1 associated with sulfur metabolism and the RT-qPCR analysis quantified the expression level of corresponding genes. The expression level of tsdA, which was responsible for tetrathionate production, was around 60 folds higher than genes for sulfane production (e.g. TST1, cysI). Further research would focus on the enhancement of sulfane production pathway through metabolic engineering tools.

Microbial Communities Involved in Methane, Sulfur, and Nitrogen Cycling in the Sediments of the Barents Sea

A combination of physicochemical and radiotracer analysis, high-throughput sequencing of the 16S rRNA, and particulate methane monooxygenase subunit A (pmoA) genes was used to link a microbial community profile with methane, sulfur, and nitrogen cycling processes. The objects of study were surface sediments sampled at five stations in the northern part of the Barents Sea. The methane content in the upper layers (0-5 cm) ranged from 0.2 to 2.4 µM and increased with depth (16-19 cm) to 9.5 µM. The rate of methane oxidation in the oxic upper layers varied from 2 to 23 nmol CH4 L-1 day-1 and decreased to 0.3 nmol L-1 day-1 in the anoxic zone at a depth of 16-19 cm. Sulfate reduction rates were much higher, from 0.3 to 2.8 µmol L-1 day-1. In the surface sediments, ammonia-oxidizing Nitrosopumilaceae were abundant; the subsequent oxidation of nitrite to nitrate can be carried out by Nitrospira sp. Aerobic methane oxidation could be performed by uncultured deep-sea cluster 3 of gamma-proteobacterial methanotrophs. Undetectable low levels of methanogenesis were consistent with a near complete absence of methanogens. Anaerobic methane oxidation in the deeper sediments was likely performed by ANME-2a-2b and ANME-2c archaea in consortium with sulfate-reducing Desulfobacterota. Sulfide can be oxidized by nitrate-reducing Sulfurovum sp. Thus, the sulfur cycle was linked with the anaerobic oxidation of methane and the nitrogen cycle, which included the oxidation of ammonium to nitrate in the oxic zone and denitrification coupled to the oxidation of sulfide in the deeper sediments. Methane concentrations and rates of microbial biogeochemical processes in sediments in the northern part of the Barents Sea were noticeably higher than in oligotrophic areas of the Arctic Ocean, indicating that an increase in methane concentration significantly activates microbial processes.

Production and characteristics of elemental sulfur during simultaneous nitrate and sulfide removal

The production and characteristics of elemental sulfur were examined during simultaneous sulfide and nitrate removal, with abiotic assays as control. The biotic assay showed good sulfide and nitrate removal, with the respective removal percentage of which were 90.67-96.88% and 100%. Nitrate reduction resulted in the production of nitrogen gas, while sulfate formed due to sulfide oxidation. The concentration of elemental sulfur in the effluent was greater than that in the sludge, which accounted for 73.70-86.28% of total elemental sulfur produced. Furthermore, the elemental sulfur of the effluent and sludge from the biotic assays was orthorhombic crystal S₈. Elemental sulfur was normally distributed in the effluent, but its average diameter increased with the increasing influent sulfide concentration (60-300 mg S/L), where the average diameter increased from 10 (60 mg S/L) to 29 μm (300 mg S/L).

Microbially-driven sulfur cycling microbial communities in different mangrove sediments

Microbially-driven sulfur cycling is a vital biogeochemical process in the sulfur-rich mangrove ecosystem. It is critical to evaluate the potential impact of sulfur transformation in mangrove ecosystems. To reveal the diversity, composition, and structure of sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) and underlying mechanisms, we analyzed the physicochemical properties and sediment microbial communities from an introduced mangrove species (Sonneratia apetala), a native mangrove species (Kandelia obovata) and the mudflat in Hanjiang River Estuary in Guangdong (23.27°N, 116.52°E), China. The results indicated that SOB was dominated by autotrophic Thiohalophilus and chemoautotrophy Chromatium in S. apetala and K. obovata, respectively, while Desulfatibacillum was the dominant genus of SRB in K. obovata sediments. Also, the redundancy analysis indicated that temperature, redox potential (ORP), and SO₄^2- were the significant factors influencing the sulfur cycling microbial communities with elemental sulfur (ES) as the key factor driver for SOB and total carbon (TC) for SRB in mangrove sediments. Additionally, the morphological transformation of ES, acid volatile sulfide (AVS) and SO₄^2- explained the variation of sulfur cycling microbial communities under sulfur-rich conditions, and we found mangrove species-specific dominant Thiohalobacter, Chromatium and Desulfatibacillum, which could well use ES and SO₄^2-, thus promoting the sulfur cycling in mangrove sediments. Meanwhile, the change of nutrient substances (TN, TC) explained why SOB were more susceptible to environmental changes than SRB. Sulfate reducing bacteria produces sulfide in anoxic sediments at depth that then migrate upward, toward fewer reducing conditions, where it's oxidized by sulfur oxidizing bacteria. This study indicates the high ability of SOB and SRB in ES, SO₄^2-_,S₂^- and S^2- generation and transformation in sulfur-rich mangrove ecosystems, and provides novel insights into sulfur cycling in other wetland ecosystems from a microbial perspective.

Insights into microbial community in microbial fuel cells simultaneously treating sulfide and nitrate under external resistance

The effect of electricity, induced by external resistance, on microbial community performance is investigated in Microbial Fuel Cells (MFCs) involved in simultaneous biotransformation of sulfide and nitrate. In the experiment, three MFCs were operated under different external resistances (100 Ω, 1000 Ω and 10,000 Ω), while one MFC was operated with open circuit as control. All MFCs demonstrate good capacity for simultaneous sulfide and nitrate biotransformation regardless of external resistance. MFCs present similar voltage profile; however, the output voltage has positive relationship with external resistance, and the MFC1 with lowest external resistance (100 Ω) generated highest power density. High-throughput sequencing confirms that taxonomic distribution of suspended sludge in anode chamber encompass phylum level to genus level, while the results of principal component analysis (PCA) suggest that microbial communities are varied with external resistance, which external resistance caused the change of electricity generation and substrate removal at the same, and then leads to the change of microbial communities. However, based on Pearson correlation analyses, no strong correlation is evident between community diversity indices (ACE index, Chao index, Shannon index and Simpson index) and the electricity (final voltage and current density). It is inferred that the performance of electricity did not significantly affect the diversity of microbial communities in MFCs biotransforming sulfide and nitrate simultaneously.

Insights to the oxidative desulfurization process of fossil fuels over organic and inorganic heterogeneous catalysts: advantages and issues

Strict environmental laws have been put in place around the world to reduce the amount of sulfur in the fuel to reduce the emissions of harmful gases from fuel combustion and improve air quality. Therefore, extensive researches have been undertaken to devise effective processes or to improve the desulfurization processes. Among the desulfurization processes, the oxidative desulfurization (ODS) process is a promising method to achieve very low and near-zero sulfur content of the fuel. In this process, sulfur compounds are converted to the corresponding sulfone by a catalyst and in the presence of an oxidant. The obtained compounds by polar solvents or adsorbents are removed from the fuel. In recent decades, extensive studies have been carried out on the catalysts used in the oxidative desulfurization process. In this review, a comprehensive survey has been performed on heterogeneous catalysts used in the oxidative desulfurization process. According to the reported researches, the heterogeneous catalysts used can be divided into five groups: ionic liquids, carbon materials, polyoxometalates, transition metal oxides stabilized on porous solid substrates, and metal-organic frameworks. The proposed mechanisms with different catalysts have also been studied in this work.

Application of activated sludge for odor control in wastewater treatment plants: Approaches, advances and outlooks

Odors from wastewater treatment plants (WWTPs) have attracted extensive attention and stringent environmental standards are more widely adopted to reduce odor emissions. Biological odor treatment methods have broader applications than the physical and chemical counterparts as they are environment-friendly, cost-effective and generate low secondary wastes. The aqueous activated sludge (AS) processes are among the most promising approaches for the prevention or end-of-pipe removal of odor emissions and have the potential to simultaneously treat odor and wastewater. However, AS deodorization biotechnologies in WWTPs still need to be further systematically summarized and categorized while in-depth discussions on the characteristics and underlying mechanisms of AS deodorization process are still lacking. Recently, considerable studies have been reported to elucidate the microbial metabolisms in odor control and wastewater treatment. This paper reviews the fundamentals, characteristics, advances and field experiences of three AS biotechnologies for odor treatment in WWTPs, i.e., AS recycling, microaeration in AS digester and AS diffusion. The underlying deodorization mechanisms of typical odors have been revealed through the summary of recent advances on multi-element conversions, metabolic interactions of bacteria, microscopic characterization and identification of functional microorganisms. Future research aspects to advance the emerging deodorization AS process, such as deodorization mechanisms, simultaneous odor and water treatment, synergistic treatment with other air emissions, are discussed.

Enhanced growth-driven stepwise inducible expression system development in haloalkaliphilic desulfurizing Thioalkalivibrio versutus

Highly toxic and flammable H₂S gas has become an environmental threat. Because of its ability to efficiently remove H₂S by oxidation, Thioalkalivibrio versutus is gaining more attention. Haloalkaliphilic autotrophs, like the bio-desulfurizing T. versutus, grow weakly. Weak growth makes any trial for developing potent genetic tools required for genetic engineering far from achieved. In this study, the fed-batch strategy improved T. versutus growth by 1.6 fold in maximal growth rate, 9-fold in O.D₆₀₀ values and about 3-fold in biomass and protein productions. The strategy also increased the favorable desulfurization product, sulfur, by 2.7 fold in percent yield and 1.5-fold in diameter. A tight iron-inducible expression system for T. versutus was successfully developed. The system was derived from fed-batch cultivation coupled with new design, build, test and validate (DPTV) approach. The inducible system was validated by toxin expression. Fed-batch cultivation coupled with DPTV approach could be applied to other autotrophs.