Recent advances in biocatalysts engineering for polyethylene terephthalate plastic waste green recycling

The massive waste of poly(ethylene terephthalate) (PET) that ends up in the landfills and oceans and needs hundreds of years for degradation has attracted global concern. The poor stability and productivity of the available PET biocatalysts hinder their industrial applications. Active PET biocatalysts can provide a promising avenue for PET bioconversion and recycling. Therefore, there is an urgent need to develop new strategies that could enhance the stability, catalytic activity, solubility, productivity, and re-usability of these PET biocatalysts under harsh conditions such as high temperatures, pH, and salinity. This has raised great attention in using bioengineering strategies to improve PET biocatalysts' robustness and catalytic behavior. Herein, historical and forecasting data of plastic production and disposal were critically reviewed. Challenges facing the PET degradation process and available strategies that could be used to solve them were critically highlighted and summarized. In this review, we also discussed the recent progress in enzyme bioengineering approaches used for discovering new PET biocatalysts, elucidating the degradation mechanism, and improving the catalytic performance, solubility, and productivity, critically assess their strength and weakness and highlighting the gaps of the available data. Discovery of more potential PET hydrolases and studying their molecular mechanism extensively via solving their crystal structure will widen this research area to move forward the industrial application. A deeper knowledge of PET molecular and degradation mechanisms will give great insight into the future identification of related enzymes. The reported bioengineering strategies during this review could be used to reduce PET crystallinity and to increase the operational temperature of PET hydrolyzing enzymes

Solubility of H2S under Haloalkaliphilic Conditions: Experimental Measurement and Modeling with the Electrolyte NRTL Equation

Haloalkaliphilic biological desulfurization has been recognized as a promising technology due to its remarkable economy and good performance. The process removes H2S from gases using aqueous solutions of alkali carbonates. In this study, the solubility of H2S in an aqueous Na2CO3-NaHCO3 solution was first experimentally measured by a static analysis method at an operating pressure and temperature of biological desulfurization. An accurate and comprehensive thermodynamic model was developed based on the electrolyte nonrandom two-liquid model for the solubility of H2S in aqueous solutions of alkali carbonates. The solubility of H2S in pure water is predicted and compared favorably to previous literature, with the temperature varying from 298.16 to 377.45 K and pressure up to 39.6 bar. The average deviation of the model predictions compared to all experimental data is 0.95% for the solubility of H2S in an aqueous Na2CO3-NaHCO3 solution. This study will provide a valuable reference for the process design, simulation, and optimization of haloalkaliphilic biological desulfurization in the future

Recent advances in microbial capture of hydrogen sulfide from sour gas via sulfur-oxidizing bacteria

Biological desulfurization offers several remarkably environmental advantages of operation at ambient temperature and atmospheric pressure, no demand of toxic chemicals as well as the formation of biologically re-usable sulfur (S-0), which has attracted increasing attention compared to conventionally physicochemical approaches in removing hydrogen sulfide from sour gas. However, the low biomass of SOB, the acidification of process solution, the recovery of SOB, and the selectivity of bio-S-0 limit its industrial application. Therefore, more efforts should be made in the improvement of the BDS process for its industrial application via different research perspectives. This review summarized the recent research advances in the microbial capture of hydrogen sulfide from sour gas based on strain modification, absorption enhancement, and bioreactor modification. Several efficient solutions to limitations for the BDS process were proposed, which paved the way for the future development of BDS industrialization

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 0.D-600 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

Rate-based model for predicting and evaluating H2S absorption in the haloalkaliphilic biological desulfurization process

The highly efficient performance of H2S absorption is the crucial indicator for haloalkaliphilic biological desulfurization (HBDS) because it immediately concerns the H2S removal efficiency and pH change of alkaline solutions. Therefore, we investigated the effect of operating parameters on the H2S absorption's performance under haloalkaline conditions. The gas-liquid ratio and packing height significantly improve H2S removal efficiency, from 80% to 90% and 66% to 99%, respectively. The absorption temperature had a trivial impact on the H2S removal efficiency, and the maximum value appeared at 45 degrees C. Additionally, all operating parameters caused pH changes that varied in the acceptable range (0.1 to 0.5) during the absorption process. A rate-based model was successfully developed to predict the haloalkaliphilic H2S absorption process accurately. Moreover, this model could be implemented to effectively evaluate the HBDS system's stability and provide reliable theoretical guidance for the industrial HBDS process to ensure good process stability. (C)2022 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved

Rate-based model for predicting and evaluating H2S absorption in the haloalkaliphilic biological desulfurization process

The highly efficient performance of H2S absorption is the crucial indicator for haloalkaliphilic biological desulfurization (HBDS) because it immediately concerns the H2S removal efficiency and pH change of alkaline solutions. Therefore, we investigated the effect of operating parameters on the H2S absorption's performance under haloalkaline conditions. The gas-liquid ratio and packing height significantly improve H2S removal efficiency, from 80% to 90% and 66% to 99%, respectively. The absorption temperature had a trivial impact on the H2S removal efficiency, and the maximum value appeared at 45 degrees C. Additionally, all operating parameters caused pH changes that varied in the acceptable range (0.1 to 0.5) during the absorption process. A rate-based model was successfully developed to predict the haloalkaliphilic H2S absorption process accurately. Moreover, this model could be implemented to effectively evaluate the HBDS system's stability and provide reliable theoretical guidance for the industrial HBDS process to ensure good process stability. (C)2022 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved

Enhanced Biodesulfurization with a Microbubble Strategy in an Airlift Bioreactor with Haloalkaliphilic Bacterium Thioalkalivibrio versutus D306

Biodesulfurization under haloalkaline conditions requires limiting oxygen and additional energy in the system to deliver high mixing quality control. This study considers biodesulfurization in an airlift bioreactor with uniform microbubbles generated by a fluidic oscillation aeration system to enhance the biological desulfurization process and its hydrodynamics. Fluidic oscillation aeration in an airlift bioreactor requires minimal energy input for microbubble generation. This aeration system produced 81.87% smaller average microbubble size than the direct aeration system in a bubble column bioreactor. The biodesulfurization phase achieved a yield of 94.94% biological sulfur, 84.91% biological sulfur selectivity, and 5.06% sulfur oxidation performance in the airlift bioreactor with the microbubble strategy. The biodesulfurization conditions of thiosulfate via Thioalkalivibrio versutus D306 are revealed in this study. The biodesulfurization conditions in the airlift bioreactor with the fluidic oscillation aeration system resulted in the complete conversion of thiosulfate with 27.64% less sulfate production and 10.34% more biological sulfur production than in the bubble column bioreactor. Therefore, pleasant hydrodynamics via an airlift bioreactor mechanism with microbubbles is favored for biodesulfurization under haloalkaline conditions

Enhanced Biodesulfurization with a Microbubble Strategy in an Airlift Bioreactor with Haloalkaliphilic Bacterium Thioalkalivibrio versutus D306

Biodesulfurization under haloalkaline conditions requires limiting oxygen and additional energy in the system to deliver high mixing quality control. This study considers biodesulfurization in an airlift bioreactor with uniform microbubbles generated by a fluidic oscillation aeration system to enhance the biological desulfurization process and its hydrodynamics. Fluidic oscillation aeration in an airlift bioreactor requires minimal energy input for microbubble generation. This aeration system produced 81.87% smaller average microbubble size than the direct aeration system in a bubble column bioreactor. The biodesulfurization phase achieved a yield of 94.94% biological sulfur, 84.91% biological sulfur selectivity, and 5.06% sulfur oxidation performance in the airlift bioreactor with the microbubble strategy. The biodesulfurization conditions of thiosulfate via Thioalkalivibrio versutus D306 are revealed in this study. The biodesulfurization conditions in the airlift bioreactor with the fluidic oscillation aeration system resulted in the complete conversion of thiosulfate with 27.64% less sulfate production and 10.34% more biological sulfur production than in the bubble column bioreactor. Therefore, pleasant hydrodynamics via an airlift bioreactor mechanism with microbubbles is favored for biodesulfurization under haloalkaline conditions

Improving confirmed nanometric sulfur bioproduction using engineered Thioalkalivibrio versutus

Complicated production procedures and superior characteristics of nano-sized sulfur elevate its price to 25-40 fold higher than micrograde kind. Also, natural gas hydrogen sulfide levels are restricted because of its toxic environmental consequences. Thioalkalivibrio versutus is a polyextremophilic industrial autotroph with high natural gas desulfurization capability. Here, nanometric ( > 50 nm) sulfur bioproduction using T. versutus while desulfurizing natural gas was validated. Also, this production was enhanced by 166.7% via lowering sulfate production by 55.1%. A specially-developed CRISPR system, with 42% editing efficiency, simplified the genome editing workflow scheme for this challenging bacterium. In parallel, sulfur metabolism was uncovered using proteins mining and transcriptome studies for defining sulfate-producing key genes (heterodisulfide reductase-like complex, sulfur dioxygenase, sulfite dehydrogenase and sulfite oxidase). This study provided cost-effective nanometric sulfur production and improved this production using a novel CRISPR strategy, which could be suitable for industrial polyextremophiles, after uncovering sulfur pathways in T. versutus