Simultaneous removal of NOX and SO2 from flue gas in an integrated FGD-CABR system by sulfur cycling-mediated Fe(II)EDTA regeneration

N2O recovery from wastewater and flue gas via microbial denitrification: Processes and mechanisms

Nitrous oxide (N2O) is increasingly regarded as a significant greenhouse gas implicated in global warming and the depletion of the ozone layer, yet it is also recognized as a valuable resource. This paper comprehensively reviews innovative microbial denitrification techniques for recovering N2O from nitrogenous wastewater and flue gas. Critical analysis is carried out on cutting-edge processes such as the coupled aerobic-anoxic nitrous decomposition operation (CANDO) process, semi-artificial photosynthesis, and the selective utilization of microbial strains, as well as flue gas absorption coupled with heterotrophic/autotrophic denitrification. These processes are highlighted for their potential to facilitate denitrification and enhance the recovery rate of N2O. The review integrates feasible methods for process control and optimization, and presents the underlying mechanisms for N2O recovery through denitrification, primarily achieved by suppressing nitrous oxide reductase (Nos) activity and intensifying competition for electron donors. The paper concludes by recognizing the shortcomings in existing technologies and proposing future research directions, with an emphasis on prioritizing the collection and utilization of N2O while considering environmental sustainability and economic feasibility. Through this review, we aim to inspire interest in the recovery and utilization of N2O, as well as the development and application of related technologies.

Delayed Shift in Microbiota Composition in a Marine Microcosm Pollution Experiment

Benthic habitats are the largest habitats on Earth, being essential for marine ecosystem functioning. Benthic habitats are particularly vulnerable towards pollution and anthropogenetic influence due to general oligotrophic nature. We, therefore, simulated pollution events involving nitrate and sulphate, in combination with organic carbon. We then observed the microbiota composition the following month. Surprisingly, upon nitrate addition, an abrupt response was observed between two and three weeks after the pollution event. We observed a threefold reduction in species richness, with a dominance of the genus Pseudarchobacter within the Campylobacteriota phylum, concurring with a decrease in nitrification potential and an increase in Dissimilatory Nitrate Reduction to Ammonium (DNRA) and a regain in denitrification. Likewise, addition of sulphate contributed to a delayed response with reduction in species richness albeit weaker than for nitrate, leading to a shift towards potential spore-forming Firmicutes. There was also an increase in DNRA, but only for the oxic conditions, concurring with a regain in sulphate reductio and denitrification. For the nitrate addition experiments, the delay in response could potentially be attributed to the genus Pseudarchobacter which rely on sulphides for denitrification, while for the sulphate addition experiments, the delayed response might be explained by the germination of spores. The late increase of DNRA may indicate a shift towards a different metabolic regime for nitrogen. In conclusion, our microcosm experiments revealed delayed abrupt microbiota shifts resembling tipping points that can potentially be overlooked in natural ecosystems.

A novel simultaneous short-course nitrification, denitrification and fermentation process: bio-enhanced phenol degradation and denitrification in a single reactor

The feasibility of a simultaneous nitrification, denitrification and fermentation process (SNDF) under electric stirrer agitation conditions was verified in a single reactor. Enhanced activated sludge for phenol degradation and denitrification in pharmaceutical phenol-containing wastewater under low dissolved oxygen conditions, additional inoculation with Comamonas sp. BGH and optimisation of co-metabolites were investigated. At a hydraulic residence time (HRT) of 28 h, 15 mg/L of substrate as strain BGH co-metabolised substrate degraded 650 ± 50 mg/L phenol almost completely and was accompanied by an incremental increase in the quantity of strain BGH. Strain BGH showed enhanced phenol degradation. Under trisodium citrate co-metabolism, strain BGH combined with activated sludge treated phenol wastewater and degraded NO2--N from 50 ± 5 to 0 mg/L in only 7 h. The removal efficiency of this group for phenol, chemical oxygen demand (COD) and TN was 99.67%, 90.25% and 98.71%, respectively, at an HRT of 32 h. The bioaugmentation effect not only promotes the degradation of pollutants, but also increases the abundance of dominant bacteria in activated sludge. Illumina MiSeq sequencing research showed that strain BGH promoted the growth of dominant genera (Acidaminobacter, Raineyella, Pseudarcobacter) and increased their relative abundance in the activated sludge system. These genera are resistant to toxicity and organic matter degradation. This paper provides some reference for the activated sludge to degrade high phenol pharmaceutical wastewater under the action of biological enhancement.

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.

Modeling based on machine learning to investigate flue gas desulfurization performance by calcium silicate absorbent in a sand bed reactor

Flue gas desulfurization (FGD) is a critical process for reducing sulfur dioxide (SO2) emissions from industrial sources, particularly power plants. This research uses calcium silicate absorbent in combination with machine learning (ML) to predict SO2 concentration within an FGD process. The collected dataset encompasses four input parameters, specifically relative humidity, absorbent weight, temperature, and time, and incorporates one output parameter, which pertains to the concentration of SO2. Six ML models were developed to estimate the output parameters. Statistical metrics such as the coefficient of determination (R2) and mean squared error (MSE) were employed to identify the most suitable model and assess its fitting effectiveness. The random forest (RF) model emerged as the top-performing model, boasting an R2 of 0.9902 and an MSE of 0.0008. The model's predictions aligned closely with experimental results, confirming its high accuracy. The most suitable hyperparameter values for RF model were found to be 74 for n_estimators, 41 for max_depth, false for bootstrap, sqrt for max_features, 1 for min_samples_leaf, absolute_error for criterion, and 3 for min_samples_split. Three-dimensional surface plots were generated to explore the impact of input variables on SO2 concentration. Global sensitivity analysis (GSA) revealed absorbent weight and time significantly influence SO2 concentration. The integration of ML into FGD modeling offers a novel approach to optimizing the efficiency and effectiveness of this environmentally crucial process.

Large-Scale Integration of Amplicon Data Reveals Massive Diversity within Saprospirales, Mostly Originating from Saline Environments

The order Saprospirales, a group of bacteria involved in complex degradation pathways, comprises three officially described families: Saprospiraceae, Lewinellaceae, and Haliscomenobacteraceae. These collectively contain 17 genera and 31 species. The current knowledge on Saprospirales diversity is the product of traditional isolation methods, with the inherited limitations of culture-based approaches. This study utilized the extensive information available in public sequence repositories combined with recent analytical tools to evaluate the global evidence-based diversity of the Saprospirales order. Our analysis resulted in 1183 novel molecular families, 15,033 novel molecular genera, and 188 K novel molecular species. Of those, 7 novel families, 464 novel genera, and 1565 species appeared in abundances at ≥0.1%. Saprospirales were detected in various environments, such as saline water, freshwater, soil, various hosts, wastewater treatment plants, and other bioreactors. Overall, saline water was the environment showing the highest prevalence of Saprospirales, with bioreactors and wastewater treatment plants being the environments where they occurred with the highest abundance. Lewinellaceae was the family containing the majority of the most prevalent species detected, while Saprospiraceae was the family with the majority of the most abundant species found. This analysis should prime researchers to further explore, in a more targeted way, the Saprospirales proportion of microbial dark matter.

Effects of salinity on the performance, microbial community, and functional genes among 4-chlorophenol wastewater treatment

Chlorophenols frequently occur alongside salinity in industrial wastewater; thus, the effects of low concentrations of salinity (NaCl, 100 mg/L) on sludge performance, microbial community, and functional genes were deeply analyzed among 4-chlorophenol (4-CP, 2.4-4.0 mg/L) wastewater treatment. The influent 4-CP was effectively degraded, but the efficiencies for PO₄^3--P, NH₄⁺-N, and organics reduction were slightly inhibited by NaCl stress. Long-term NaCl and 4-CP stress significantly stimulated the secretion of extracellular polymeric substances (EPS). The abundances of predominant microbes at different taxonomic levels were affected by NaCl, and the increased relative abundances of functional genes encoding proteins contributed to resist NaCl and 4-CP stress. The functional genes associated with phosphorus metabolism and nitrogen metabolism in nitrification were unaffected, but the functional genes in denitrification increased in diversity under NaCl stress in 4-CP wastewater treatment. This finding acquires useful insight into the wastewater treatment with low chlorophenols and low salinity.

A review: Biological technologies for nitrogen monoxide abatement

Nitrogen oxides (NOx), including nitrogen monoxide (NO) and nitrogen dioxide (NO2), are among the most important global atmospheric pollutants because they have a negative impact on human respiratory health, animals, and the environment through the greenhouse effect and ozone layer destruction. NOx compounds are predominantly generated by anthropogenic activities, which involve combustion processes such as energy production, transportation, and industrial activities. The most widely used alternatives for NOx abatement on an industrial scale are selective catalytic and non-catalytic reductions; however, these alternatives have high costs when treating large air flows with low pollutant concentrations, and most of these methods generate residues that require further treatment. Therefore, biotechnologies that are normally used for wastewater treatment (based on nitrification, denitrification, anammox, microalgae, and combinations of these) are being investigated for flue gas treatment. Most of such investigations have focused on chemical absorption and biological reduction (CABR) systems using different equipment configurations, such as biofilters, rotating reactors, or membrane reactors. This review summarizes the current state of these biotechnologies available for NOx treatment, discusses and compares the use of different microorganisms, and analyzes the experimental performance of bioreactors used for NOx emission control, both at the laboratory scale and in industrial settings, to provide an overview of proven technical solutions and biotechnologies for NOx treatment. Additionally, a comparative assessment of the advantages and disadvantages is performed, and special challenges for biological technologies for NO abatement are presented.

Complexing agents-free bioelectrochemical trickling systems for highly-efficient mesothermal NO removal: The role of extracellular polymer substances

The biological treatments are promising for nitric oxide (NO) reduction, however, the biotechnology has long suffered from high demands of NO-complexing agents (i.e., Fe(II)EDTA), leading to extra operation costs. In this study, novel complexing agents-free bioelectrochemical systems have been developed for direct NO reduction. The electricity-driven bioelectrochemical trickling system (ED-BTS, a denitrifying biocathode driven by the external electricity and an acetate-consuming bioanode) achieved approximately 68% NO removal without any NO-complexing agents, superior to the bioanode-driven BTS and open-circuit BTS. The extracellular polymeric substances from the biofilms of ED-BTS contained more polysaccharides, humic substrates, and hydrophobic tryptophan that were beneficial for NO reduction. Additionally, the external electricity altered the microbial community toward more denitrifying bacteria and a higher abundance of NO reduction genes (nosZ and cnorB). This study provides a comprehensive understanding of microbial behaviors on the adsorption and reduction of NO and proposes a promising strategy for mesothermal NO biotreatment.

Enhancement of desulfurization by hydroxyl ammonium ionic liquid supported on active carbon

Power plants emit sulfur dioxide (SO₂) during combustion, which is typically removed via wet flue gas desulfurization, but this process produces numerous secondary pollutants. Ionic liquids (ILs) can potentially be used to remove SO₂, but they suffer from poor mass transfer rates. Hydroxyl ammonium ILs are classical cheap ILs that contain electron-rich O and N sites that favor high absorption capacities. To accelerate mass transfer, two hydroxyl ammonium ILs, triethanolamine citrate and triethanolamine lactate, were immobilized on activated carbon (SILs) and used to capture SO₂ from simulated flue gas. They exhibited excellent adsorption at low SO₂ partial pressures due to the presence of a large gas-liquid interface. The molar adsorption ratios reached 7.65 and 2.40 mol/mol at 10 kPa SO₂. The SILs possessed good SO₂ selectivity in SO₂/CO₂ and SO₂/O₂ mixtures, because of the only 8% reduction in the total adsorption of SILs at 60 °C. And they exhibited excellent reversibility in which their total adsorption capacities were unaffected after 5 adsorption-desorption cycles. The mechanism analysis revealed that chemical adsorption was the major adsorption route, although physical adsorption also occurred. The main reactive sites included C-O and N-H groups in the ionic liquid. These SILs may potentially replace traditional chemical absorption materials for the separation of SO₂ from flue gas.

Antagonistic effects of surfactants and CeO2 nanoparticles co-occurrence on the sludge fermentation process: Novel insights of interaction mechanisms and microbial networks

Various pollutants commonly co-exist in the waste active sludge (WAS), but the interactive effects and mechanisms of co-occurrence pollutants on the WAS treatment remain unclear. This work mainly investigated the impacts of different surfactants (i.e., HTAB and SDBS) and CeO₂ nanoparticles (NPs) co-occurrence on the WAS fermentation for short-chain fatty acids (SCFAs) production, and found that the CeO₂ NPs coexisting with surfactants caused antagonistic effects on the SCFAs generation (10.7% and 33.9% inhibition by HTAB and SDBS, respectively). The surfactants and CeO₂ NPs co-occurrence restrained the solubilization, hydrolysis, and acidification steps simultaneously. Moreover, the functional hydrolytic-acidogenic bacterial (e.g., Haliangium and Bacteroidetes sp.) and the microbial metabolic networks involved in extracellular hydrolysis (e.g., pepd and NEU1), substrate metabolism (e.g., ALDO and asdA), and fatty acid biosynthesis (e.g., aarC and pct) were all downregulated by 4.3-53.8% in the reactors with surfactants and CeO₂ NPs co-occurrence. The presence of surfactants enhanced the dispersibility and stability of CeO₂ NPs and the Ce dissolution (1.5-3.0 times higher). Also, surfactants contributed to the WAS disintegration, which could improve the interactive chances of microorganisms entrapped in WAS and CeO₂ NPs by promoting the transportation channels, and therefore aggravated the toxicity towards anaerobic species.

Nitrogen and sulfamethoxazole removal in a partially saturated vertical flow constructed wetland treating synthetic mariculture wastewater

This study investigated the removal of nitrogen and sulfamethoxazole (SMX), and the microbial communities in a partially saturated vertical flow constructed wetland (PS-VFCW) fed with synthetic mariculture wastewater operated at different saturated zone depths (SZDs), i.e. 51, 70, and 60 cm. Removal efficiencies were 99.8%-100.0% for COD, 34.1%-100.0% for NH4+-N, 67.8%-97.3% for total inorganic nitrogen (TIN), and 29.8%-57.2% for SMX. Excellent nitrification performance was achieved at the SZDs of 51 and 60 cm. Denitrification performed well at 70 and 60 cm SZDs. The highest TIN removal efficiency (97.3%) was achieved as the SZD was 60 cm. SMX removal was significantly influenced by SZD and was promoted by higher SZD. The removal of organics, nitrogen, and SMX mainly occurred in the unsaturated zone. Ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, denitrifying bacteria, and SMX-degrading bacteria were detected in the unsaturated and saturated zones, and showed an increasing trend in abundance along the depth.

Antibiotics and microbial community-induced antibiotic-resistant genes distribution in soil and sediment in the eastern coastline of China

The health risk of antibiotic-resistant genes (ARGs) has been a global concern, while the report on occurrence and prevalence of ARGs in coastal zone is relatively scarce. This study investigated typical ARGs in soil and sediment in coastal line of eastern China and assessed its relationship with antibiotics and heavy metals as well as microbial community. Results showed that eight ARGs were all detected in the samples, and β-lactam resistance gene blaTEM reached the highest absolute abundance (6.28 × 10⁷ ~ 6.48 × 10⁸ copies/g) and relative abundance (2.3 × 10^-2 copies/16S rRNA) among samples. Amoxicillin and tetracycline were most frequently detected with the average concentration of 2.28 μg/kg and 3.48 μg/kg, respectively. Cr and Zn were found to be most abundant heavy metals with average value of 82.1 and 59.1 mg/kg, respectively. Proteobacteria, Campilobacterota, Bacteroidota, and Firmicutes were dominant phyla in most samples, while bacterial community varied significantly among samples. Redundancy analyses (RDA) showed that microbial community and antibiotics (amoxicillin and tetracycline) were driving factors of ARGs distribution, while heavy metals were not significantly correlated with ARGs. This study is helpful to understand the fate of ARGs in coastal zone.