Co-contamination bynitrate-nitrogen (NO3--N)and heavy metals (HMs) can impair biological nitrogen removal. This study investigated whether powdered activated carbon (PAC) derived from coconut shell, applied at a trace dose, could enhance denitrification, manganese oxidation, and metal immobilization by Zoogloea sp. MFQ7 under HM stress. Under the selected conditions of pH 7.0, a carbon-to-nitrogen ratio of 1.5, and an initial Mn(II) concentration of 10.0 mg L-1, strain MFQ7 removed 92.89 % of NO3--N and 89.12 % of Mn(II). Addition of 0.8 mg L-1 PAC increased these removal efficiencies to 97.02 % and 97.11 %, respectively, while nitrite remained below 0.01 mg L-1. Under combined zinc (Zn(II)), copper (Cu(II)), and nickel (Ni(II)) stress, PAC maintained NO3--N and Mn(II) removal efficiencies at 75.93 % and 69.00 %, respectively, and achieved Zn(II), Cu(II), and Ni(II) immobilization efficiencies of 79.22 %, 78.65 %, and 71.34 %, respectively. PAC also increased electron transport system activity to a level 9.66 % above that of the unstressed control and helped preserve a matrix of extracellular polymeric substances (EPS) rich in proteins. Analyses of the solid phase showed that PAC introduced additional carbonaceous interfaces containing oxygen functional groups, while EPS, biogenic Mn precipitates, and metal carbonate phases contributed to metal immobilization. Overall, trace PAC derived from coconut shell alleviated inhibition caused by HMs through a combination of physiological protection and immobilization in the solid phase, supporting its exploratory application as an amendment derived from waste for complex wastewater treatment at the batch scale.
Nitrogen removal mechanisms of marine anammox bacteria (MAB) induced by zero-valent iron (ZVI) were investigated to reveal the differences resulting from nitrate or nitrite under high-salinity (3.5 %) and low-temperature (15 ± 1 °C) stress. The one-time addition of ZVI (20 g) altered the microbial energy metabolism and electron transfer pathways. When nitrate served as the electron acceptor, ZVI-based autotrophic denitrification (ZVI-AD) served as the "engine", providing essential nitrite for MAB through partial nitrate reduction, achieving a total nitrogen removal efficiency (TNRE) of 31.5 %. Conversely, when nitrite was the electron acceptor, marine anammox dominated nitrogen removal, while ZVI-AD acted as a recycler of the anammox by-product (nitrate), establishing a self-coupled nitrogen cycle with a superior TNRE of 94.0 %. Sulfurimonas and Candidatus Scalindua were the core functional microbes, exhibiting different preferences for nitrate and nitrite. Compared to the nitrite-added reactor, Sulfurimonas was enriched more in the nitrate-added reactor. Nevertheless, ZVI significantly promoted the enrichment of Candidatus Scalindua in the nitrite-added reactor, with its relative abundance increasing to 31.3 %. Furthermore, Feammox may have contributed to ammonium removal during the later stage. Overall, the selection of electron acceptors regulated the nitrogen removal mechanisms of ZVI-induced MAB consortia, providing new insights into intensifying nitrogen removal in high-salinity and low-temperature wastewater treatment.
Environmental nitrogen pollution resulting from various sources (e.g., industrial/municipal wastewater and agricultural runoff) poses a tough global challenge. Traditional approaches for transforming nitrogenous contaminants to inert N2 are often restricted by large operational costs, high energy dependence, and severe reaction bottlenecks. Recently, the discovery of direct mechanobiological activation has inspired a new frontier emerged, highlighting the potential to promote nitrogen conversion via an unprecedented abiotic-biotic synergy enabled by ferroelectric and piezoelectric materials. While previous reviews have focused on either bioelectrochemical nitrogen transformation or piezocatalytic nitrogen conversion, there is no comprehensive discussion that integrates these two domains and elucidates their interfacial coupling mechanisms. This review is aimed to fill this gap by critically examining this synergistic paradigm. We dissect how these materials function dually: they act as abiotic catalysts that form localized electric fields and reactive species, directly activating nitrogen molecules, and simultaneously as biotic stimulators that electronically interface with microbes, enhancing their metabolic denitrification pathways. How this synergy breaks conventional limitations is elaborated. The abiotic pathway can generate favorable microenvironments or intermediates used by the biotic pathway, while microbial activity in turn prevents catalyst fouling. However, practical application requires addressing the critical challenge of energy mismatch with ambient environments. Thus, key emerging strategies are assessed, including photo-mechanical synergy using sunlight as the primary power source while weak mechanical forces restrict charge recombination, and flexoelectric effects that harvest energy from low-frequency non-uniform strains. Harnessing this abiotic-biotic synergy through next-generation concepts can offer a transformative method for sustainable nitrogen remediation.
Carnosine is increasingly needed in pharmaceutical, nutraceutical, and cosmetic industries, but its production in bacteria is severely hampered. In this study, Escherichia coli Nissle 1917 has been engineered for efficient carnosine production. Firstly, the peptidase PepD that degrades carnosine was identified, and its mutant WYT03 was constructed. Secondly, an aspartate α-decarboxylase PanD from Bacillus subtilis and ATP phosphoribosyltransferase HisG from Bacteroides thetaiotaomicron were identified for optimum synthesis of β-alanine and l-histidine in E. coli, respectively; plasmid pWT-Y2DG which overexpress BsPanD, BtHisG, and l-amino acid ligase BsBacDN108E H378K was constructed and transformed in WYT03, resulting in carnosine production. Thirdly, a point mutation W332F in BsBacDN108E H378K that can increase the carnosine yield by 51% was identified through saturation mutagenesis. Fourthly, an optimum combination of the promoter and RBS, Ptac-R2, was screened out and used to replace the leader peptide hisL of his operon and to activate prs expression; the genes edd, amn, and purF were deleted, resulting in WYT10 producing more l-histidine; WYT09 was further modified by replacing purF with Cgppk2 with Ptac-R2, and replacing ldha with BsrocG with Ptac-R2, inserting Ptac-R2 upstream of yfcc, deleting pitA resulting WYT17. Finally, plasmid pWT-Y3DG which overexpress BsPanD, BtHisG, and BsBacDN108E H378K W332F was transformed in WYT17, and the final strain WYT17/pWT-Y3DG could produce 14.39 g/L carnosine in a 5-L fed-batch fermentation with a yield of 0.145 g/g glucose and a productivity of 0.133 g/(L·h). To the best of our knowledge, this represents the highest carnosine titer from microbial fermentation reported to date.
This study investigated how ethanol pretreatment (EP) enhances the resilience of high-solid anaerobic digestion against rapid organic loading shocks. Semi-continuous reactors fed with either untreated or EP-treated food waste were compared, and the underlying mechanisms were elucidated by integrating thermodynamic calculations with metagenomic analyses. At an organic loading rate of 6.0 g VS/(Lˑd), the control group (untreated) collapsed due to the accumulation of propionate and other longer-chain volatile fatty acids (VFAs), resulting in a methane yield decrease exceeding 70%. In contrast, the EP group maintained stability, exhibiting a methane yield decrease of less than 5%, with VFAs dominated by readily degradable acetate. Thermodynamic analysis confirmed that EP significantly lowered the energy barriers for VFA degradation. Metagenomic analysis revealed that both propionate/butyrate activation pathways (with lower energy cost or independence from acetyl-CoA) and syntrophic acetate oxidation were activated in the EP group, thereby avoiding the VFA metabolic stress observed in the control group. Furthermore, higher abundances of conductive type IV pili genes, Complex II, and archaeal V/A-type ATPase were detected in the EP group, suggesting the establishment of direct interspecies electron transfer and enhanced electron flux and energy capture efficiency. Moreover, under high loading conditions, only a few high-abundance metagenome-assembled genomes (MAGs) were detected in the control group, while multiple MAGs carrying identical VFA-degrading enzyme systems were identified in the EP group. The functionally redundant microbiota, unobstructed VFA metabolic pathways, and efficient electron transfer and energy supply collectively sustained the stability of the EP group under loading shocks.
The conversion of agro-industrial residues into biohydrogen (BioH2) represents a promising strategy for waste valorization and renewable energy generation. This study evaluated cashew apple bagasse-derived streams, including enzymatic hydrolysate (CAB-EH) and fermentation vinasse (CABV), as feedstocks for photofermentative H2 production by Rhodopseudomonas palustris ATCC 17001. Cheese whey (CW) was included as a comparative substrate. R. palustris consumed 22.6 ± 0.2 % of the lactose present in CW and produced 1.4 ± 0.4 mmol H2⋅g-1 carbon. In comparison, CAB-EH resulted in the highest volumetric production, reaching 1654.2 ± 37.7 mL H2⋅L-1 medium, corresponding to a BioH2 yield of 10.6 ± 3.0 mmol H2 g-1 carbon and a carbon consumption of 81.2 ± 0.7 %. Furthermore, CABV produced 50.0 ± 1.1 mL H2⋅L-1 medium, demonstrating its potential as a feedstock for H2 production despite residual ethanol (19.7 g L⁻1). Based on initial feedstock mass, CW provided the highest BioH2 yield based on the initial feedstock mass, reaching 8910.0 L H2⋅t-1. These findings demonstrate, for the first time, the feasibility of converting cashew apple bagasse-derived stream into BioH2 through photofermentation, highlighting their potential for integrated residue valorization.
Municipal solid waste (MSW) valorization is constrained by the mismatch between heterogeneous feedstock properties and the operating requirements of individual conversion technologies. This review synthesizes integrated thermochemical and biochemical pathways and treats MSW valorization as a system design problem organized around carbon cascading, in which each carbon fraction is routed to the process able to convert it and performance is governed by interactions between processes rather than by individual process yields. Four hybrid routes are examined: gasification-syngas fermentation, pyrolysis-anaerobic digestion, hydrothermal processing-anaerobic digestion, and reverse configurations in which digestion precedes thermochemical conversion. Across these routes, intermediate quality rather than process yield governs feasibility. Tar (1-150 g/Nm3), ammonia (up to 14,000 ppmv), and sulfur species must be reduced by two to three orders of magnitude before downstream bioconversion, relocating the critical engineering problem from the reactor to the interface. Environmental and economic evidence indicates that integration benefits are real but conditional. Coupling anaerobic digestion with pyrolysis approximately doubled the climate mitigation of standalone digestion, yet the advantage is not uniform across impact categories, and one configuration achieved the greatest climate benefit while increasing freshwater ecotoxicity 52-fold. Reported production costs for integrated routes ($0.31-1.95/L ethanol) exceed those of standalone biochemical conversion, though integrated systems convert carbon that cheaper routes cannot access, and scale and product value influence viability more than process configuration. Integration is therefore justified by feedstock coverage and interface management rather than by coupling processes as such, and full-chain demonstration on real MSW remains the principal research challenge.
Converting non-food cellulosic sugars into programmable amylose offers a route to higher-value carbohydrate materials. α-Glucan phosphorylase (αGP) controls glucose-1-phosphate (G-1-P)-dependent chain elongation in cellobiose-to-amylose cascades. Here, Nicotiana attenuata αGP (NicαGP) was engineered by integrating AlphaFold3-based structural modeling, ProteinMPNN, EVcouplings, structural priors, and DynaMut2 filtering. Of 916 candidate substitutions, 37 were selected for experimental validation, and combinatorial screening identified L226Y/V437L/F751H as the optimal triple mutant, with 2.10-fold higher relative activity than the same-batch wild-type (WT) control and clear positive epistasis. The mutant further shifted the optimal temperature from 40 to 45 °C, increased thermal transition midpoint from 56.2 to 58.8 °C, and enhanced catalytic efficiency toward both maltotetraose and G-1-P. In the Clostridium thermocellum cellobiose phosphorylase (CtCBP)-NicαGP cascade, L226Y/V437L/F751H reached 38.86 ± 2.06 % conversion at 72 h versus the previously reported WT value of 35.84 ± 1.04 % at 84 h, increasing apparent productivity by 26.5 %. Docking, CAVER, and molecular dynamics (MD) analyses suggested that these gains may be associated with optimization of structural regions surrounding the conserved catalytic core. This work provides an engineered αGP for amylose synthesis from cellobiose and supports peripheral regulatory engineering as a practical strategy for improving phosphorylase-based biocatalytic cascades.
Ammonium persulfate (APS)-assisted hydrothermal pretreatment (HP) is an emerging method for xylan depolymerization, yet its potential for integrated valorization of all biomass fractions remains underexplored. This study aimed to selectively produce xylo-oligosaccharides (XOS) and xylose from corncob via controlled APS-HP, evaluate XOS bioactivity, and ferment xylose hydrolysate to xylonic acid without detoxification, while assessing enzymatic digestibility of solid residues. Under 0.5 % APS at 150 °C for 90 min, an optimal XOS yield reached 40.90 % (based on xylan in corncob), whereas 1 % APS gave a maximal xylose yield of 56.34 %. The XOS hydrolysate at 50 mg/L improved Chinese cabbage (Brassica rapa L. var. pekinensis) seed germination, plant height, root elongation, and fresh biomass, revealing its agricultural bioactivity. Notably, the xylose hydrolysate without detoxification was converted to xylonic acid with a yield of 90.32 % within 24 h, and even a 2.15-fold concentrated hydrolysate achieved 90.36 %, demonstrating process robustness. Solid residues from XOS and xylose production exhibited excellent enzymatic digestibility, with glucose yields of 96.89 % and 99.03 %, respectively, at 20 FPU/g glucan. Preliminary techno-economic analysis and qualitative life cycle assessment are used to assess economic theoretical basis for practical industrial production. Collectively, this study presents a novel integrated biorefinery strategy enabling sequential production of bioactive XOS, fermentable xylose, and highly digestible solid residues from corncob via APS-HP, offering a promising route for comprehensive lignocellulosic carbohydrates utilization without requiring a separate detoxification step.
This review seeks to compile Polyhydroxyalkanoates (PHAs) degradation studies published over the past 20 years. It highlights the effect of physical properties, such as crystallinity and molecular weight, on the decomposition rate of these molecules. Both biotic processes, mediated by bacteria, fungi, and enzymes, as well as abiotic processes, such as hydrolysis and thermal degradation, are analyzed. A repertoire of diverse microorganisms, including their metabolic pathways and enzymes for PHA breakdown, is presented. Furthermore, this review presents the decomposition of PHAs in various environments, such as soil and seawater, highlighting their potential as a sustainable alternative. Finally, the resulting degradation products are described, emphasizing their potential applications in medicine and industry. Although degradation of PHAs has been extensively studied through these years, several knowledge gaps remain undisclosed, including the degradation of diverse polyester monomers. PHAs comprise numerous monomer compositions with variable properties, which present opportunities for different applications but pose a challenge in their degradation. The reader of this review can extract useful information for both the production of PHAs and their potential applications.
Chemo-biological valorization of CO2 into value-added chemicals, such as the biodegradable plastic monomer glycolic acid (GA), represents a promising frontier in sustainable manufacturing. However, the realization of this synergistic loop is hindered by the low carbon efficiency of C1 bioconversion. Herein, we address this challenge by engineering an efficient methanol bioconversion platform that selectively upgrades CO2-derived methanol into GA. To address metabolic redox constraints inherent to methanol assimilation that severely limit carbon yield, we reprogrammed Komagataella phaffii by constructing a cofactor-neutral biosynthetic route that couples NADPH generation directly to GA formation. Combined with the elimination of competing carbon sinks, this design eradicates the redox constraints that typically limit C1 assimilation. As a result, carbon flux toward GA surged by 4.6-fold while maintaining cellular fitness. Translating this rewired module to a 5-L bioreactor establishes a benchmark, achieving a titer of 41.2 g/L and the highest reported yield of 0.41 g/g for methanol-only bioconversion. Life-cycle assessment (LCA) reveals a 59.0% lower global warming potential (GWP) relative to fossil-based routes. This study establishes a high-efficiency methanol bioconversion platform for GA production, completing the CO2-to-GA loop and providing a sustainable route for the utilization of CO2-derived carbon resources.
Efficient pretreatment that enables selective fractionation, structural preservation, and coordinated downstream utilization remains a major challenge for lignocellulosic biorefineries. Herein, an alkaline deep eutectic solvent composed of triethylbenzylammonium chloride and ethanolamine was adopted for the integrated biorefinery of bamboo shoot shells. The pretreatment afforded 92.14-95.20 % delignification and 89.61-94.00 % hemicellulose removal across four feedstocks, while largely preserving cellulose integrity. Meanwhile, the recovered lignin retained substantial β-O-4 linkages, showed reduced condensation, narrowed molecular-weight distribution, and enhanced chemical reactivity, indicating its suitability for downstream valorization. Owing to the improved accessibility of the cellulose-rich residues, enzymatic hydrolysis delivered glucose yields of 92.06-96.70 % after 48 h. In addition to enzymatic saccharification, the fractionated components were further upgraded into lignin-containing cellulose nanofibrils, lignin nanoparticles, and nitrogen-doped carbon dots from the recovered spent solvent, demonstrating downstream utilization within one process. Overall, this work adopted an alkaline DES-based pretreatment strategy that integrates efficient fractionation, high enzymatic digestibility, and cascade valorization of major biomass components, demonstrating the potential of this strategy for integrated lignocellulosic biorefining.
Cultivation conditions are known to affect the structural organization of microbial cell walls. However, the impact of these structural variations on protein release following mild cell disruption remains largely unknown. Therefore, this study investigated the effects of cultivation conditions on the Saccharomyces cerevisiae cell wall. Its robustness and apparent protein permeability were assessed indirectly through, respectively, zymolyase susceptibility and intracellular protein release following hydrophobic deep eutectic solvent assisted membrane-permeabilization. More specifically, the influences of cultivation pH, glucose-limitation, growth phase and cultivation mode were evaluated. Shake-flask experiments demonstrated that cultivation conditions associated with different physiological states strongly affected cell wall structural organization, since a shift from glucose-limitation to glucose-abundance increased zymolyase susceptibility by 5-fold, and increased protein release by up to 3.8-fold. Therefore, the effects of growth phase and cultivation mode were further investigated in controlled bioreactors, resulting in more profound differences. Biomass harvested from exponentially growing batch cultures exhibited a 5.7-fold higher soluble protein release than low-rate fed-batch cultures, while zymolyase susceptibility increased by 19.4-fold. Moreover, strong correlations were found between physiological state, zymolyase susceptibility and protein permeation behaviour, suggesting that cultivation-dependent physiological states impact cell wall characteristics and intracellular protein release. Finally, apparent molecular size analysis demonstrated that the released material obtained from permeabilized biomass was enriched with components smaller than 100 kDa. Overall, this study demonstrates that cultivation-driven modulations in cell wall characteristics strongly affect mild disruption yields, thereby highlighting the importance of integrating upstream and downstream processes for efficient recovery of intracellular proteins.
Metal hyperaccumulators are promising plants for phytoextraction, but the root traits that help them grow toward metal-rich soil remain unclear. Metal-directed root foraging has been proposed as a unique trait of hyperaccumulators, yet inconsistent observations have obscured its functional significance. Here, we combined a meta-analysis of 128 published observations with split-root experiments in Sedum alfredii to evaluate the recurrence, environmental sensitivity, and physiological relevance of metal-directed root foraging. A meta-analysis showed a broad but context-dependent tendency for hyperaccumulators to allocate more roots to metal-enriched patches, and this response was positively associated with shoot metal accumulation and biomass. However, this response was strongly shaped by soil conditions, particularly soil texture and soil source. Split-root experiments further revealed a clear ecotype-specific response in hydroponics. The hyperaccumulating ecotype (HE) allocated more than 60 % of its root biomass to the Cd-enriched compartment, whereas the non-hyperaccumulating ecotype (NHE) showed reduced root allocation to this compartment. This ecotype-specific contrast was not fully retained in the tested soil system: Cd-directed foraging by HE was no longer detectable, whereas Cd avoidance by NHE persisted. These findings identify metal-directed root foraging as a recurrent but soil-dependent trait of hyperaccumulators. By showing that soil conditions can constrain the detectability of this trait, our study reconciles inconsistent observations and points to soil management as a potential strategy to strengthen root foraging and enhance phytoextraction in contaminated soils.
Enhancing lake carbon sequestration is a vital nature-based climate solution, whereas the degradation of submerged macrophytes seriously threatens this potential. Plant growth-promoting rhizobacteria (PGPR) are capable of accelerating the stress recovery of submerged macrophytes and enhancing the greenhouse gas (GHG) absorption for single-species macrophyte. Here, four-species submerged macrophyte communities (Potamogeton wrightii, Myriophyllum spicatum, Vallisneria denseserrulata, and Hydrilla verticillata) were established under simulated underwater low-light conditions and inoculated with a high-efficiency PGPR consortium (Pseudomonas vancouverensis, Pseudomonas plecoglossicida, and Enterobacter ludwigii). Treatments included inoculation applied to 0, 1, 2, 3, and 4 species treatments, respectively. Over an annual timescale, inoculation of all four plant species resulted in the highest monthly biomass increment (19 % above control) and increased the system's CO2-equivalent sink by 336 %, yielding the lowest global warming potential (GWP, -7939.91 ± 96.73 g CO2-eq m-2 yr-1). These results indicate a strong synergy between growth promotion and carbon sink enhancement. CO2-equivalent uptake during the overwintering stage significantly exceeded that during the rapid growth stage, likely because low temperatures suppress biological metabolic activities while simultaneously enhancing physicochemical absorption, thereby enhancing net CO2 sequestration. Methodologically, the conventional 1-hour morning sampling overestimated CO2-equivalent fluxes by 3.54 to 6.28 times compared to 24-hour continuous monitoring. These findings demonstrate the dual capacity of PGPR to boost macrophyte productivity and GHG sink functions under low-light stress. The results underscore the necessity of 24-hour continuous sampling for accurate GHG flux assessment in aquatic ecosystems and provide a scientific basis for developing low-carbon lake restoration and carbon-neutral management strategies.
This eight-year study characterized trace compounds in grid-injected biomethane from methanization using a multi-analytical strategy combining broad thermal desorption gas chromatography-mass spectrometry (TD-GC/MS) screening with targeted quantitative methods. Between 2016 and 2023, 75 sampling campaigns were conducted at 40 French biomethane injection plants, covering diverse feedstocks and upgrading technologies. 530 organic compounds across nine chemical families were identified by TD-GC/MS. Of these, 65 calibrated compounds were quantified and 465 non-target compounds were semi-quantitatively estimated as order-of-magnitude concentrations. Most compounds occurred sporadically and at low levels: only 100 were detected in more than ten samples, whereas 207 appeared only once, with an average of 48 trace compounds per sample. Average concentrations were generally low, with only 13 % exceeding 100 µg/Nm3. Hydrocarbons were dominant, followed by oxygenated compounds, while terpenes, organic sulfur compounds, siloxanes, halocarbons and amines occurred less frequently. Chemometric analysis of 45 selected TD-GC/MS compounds showed broadly similar biomethane trace profiles, with no robust clustering by feedstock or upgrading technology. Targeted analyses quantified compounds of regulatory or operational relevance, including monoaromatic hydrocarbons, terpenes, sulfur species, ammonia, mercury and trace elements. Regulated sulfur species, ammonia, mercury and siloxanes remained below current injection requirements, and compounds shared with conventional natural gas were generally comparable to or lower than natural-gas reference levels. This information-rich dataset demonstrates the complementarity of analytical strategies and shows that grid-injected biomethane contains a chemically diverse but low-abundance trace-compound fraction, supporting secure grid integration and future monitoring, standardization and specification evolution.
Partial substitution of chemical fertilizers with organic amendments is a promising strategy to sustain soil productivity while reducing chemical inputs. However, the ecological mechanisms by which organic substitution and inorganic reduction reshape soil microbial community assembly, life‑history strategies, and nutrient cycling potential remain poorly understood. A 43-year field experiment with different proportions of organic fertilizer substituting for inorganic nitrogen was conducted. Microbial community structure, assembly processes, keystone taxa, and functional genes involved in nitrogen (N) and sulfur (S) cycles were investigated with high-throughput amplicon and metagenomic sequencing. Our results showed that organic substitution significantly reshapes microbial community composition, increasing community evenness while maintaining species richness. It significantly reduced the proportion of transient and persistent microorganisms while increasing intermittent taxa. Organic substitution significantly reduced (p < 0.05) the contribution of stochastic processes in soil microbes in comparison to those treated only with chemical fertilizers. This shift was accompanied by the enrichment of specific functional phyla such as Actinomycetota (class Thermoleophilia), Myxococcota, and Gemmatimonadota, which served as keystone species in co‑occurrence networks. Functionally, organic substitution significantly upregulated genes involved in organic nitrogen mineralization (glnAB&ureABC&gdhA&GLUL) and anaerobic ammonium oxidation (anammox), while downregulating nitrification, dissimilatory nitrate reduction to ammonium (DNRA), and assimilatory nitrate reduction. Likewise, organic substitution reduced organic sulfur mineralization and hydrogen sulfide production (sreAB) but enhanced assimilatory sulfate reduction. The findings of this study provide new insights into the ecological mechanisms through which organic substitution regulates soil microbiomes and nutrient cycling.
The sustainable treatment of surfactant-rich wastewater in anaerobic systems is often hindered by the biochemical recalcitrance of linear alkylbenzene sulfonate (LAS) and its inhibitory effects on methanogenesis. This study investigated controlled microaeration under two hydraulic retention time (HRT) and organic loading rate (OLR) regimes as a strategy to intensify LAS degradation and energy recovery in upflow anaerobic sludge blanket (UASB) reactors. Four configurations were evaluated: R1 (anaerobic, 8-h HRT), R2 (microaerated, 8-h HRT), R3 (anaerobic, 16-h HRT), and R4 (microaerated, 16-h HRT). Results demonstrated that under strictly anaerobic conditions, operating at a 16-h HRT and the corresponding lower OLR resulted in higher chemical oxygen demand (COD) removal than at 8-h HRT (87.4% vs. 65.7%). In contrast, microaeration played an important role in enhancing surfactant biotransformation. R4 achieved the highest LAS removal (64.0 ± 6.2%), significantly outperforming the strictly anaerobic R3. The 16-h HRT/lower-OLR configuration provided operational conditions that may have favored the progression of successive LAS biotransformation steps, including oxygenase-mediated ω-oxidation and the transformation of aromatic compounds under microaerated conditions. Notably, R4 exhibited a remarkable specific methane yield of 0.28 ± 0.01 LCH4/gCODapp, doubling the efficiency of the other reactors. Microbial analysis indicated that microaeration was associated with a more diverse consortium in which potentially oxidative bacteria (Smithella and Thauera) coexisted with acetoclastic methanogens (Methanosaeta). These findings indicate that microaeration, when combined with the longer HRT tested, enhanced LAS degradation and process performance compared with the 8-h condition, highlighting the potential of this strategy for process intensification in treatment plants.
