Against the backdrop of a growing global population and increasing food security pressure, sustainable agricultural systems are urgently needed. Microalgae are promising alternative food sources due to their rapid growth and high nutritional value, but their food application is limited by undesirable color and odor from high pigment content. In this study, using Chlorella vulgaris as the starting strain, a genetically stable white, low-pigment mutant designated C5 was successfully obtained through zeocin-induced mutagenesis followed by targeted screening. The mutagenesis conditions were: zeocin concentration of 350 mg L−1, treatment time 2 h, with a lethality rate of approximately 95%. The mutant exhibited superior growth performance to the wild-type under heterotrophic conditions. Key parameters (carbon/nitrogen sources, phosphate, magnesium, pH, temperature) were optimized in shake flasks: glucose (100 g L−1), NaNO₃ (1.5 g L−1), pH 7.0, and 25°C. An enriched BG11 medium suitable for high-density fermentation was formulated accordingly. Fed-batch fermentation in a 5 L stirred-tank bioreactor demonstrated that mutant C5 achieved a maximum biomass of 105 g L−1 and a peak growth rate of 0.49 g L−1 h−1. Intracellular protein and lipid contents were comparable to those of the wild-type approximately 25% and 18–30%, respectively, while starch accumulation potential was notably high up to 40% of biomass, with a productivity of 0.14 g L−1 h−1. This study reports the successful generation of a low-pigment Chlorella vulgaris mutant via zeocin mutagenesis for the first time, and systematically validates both the stability of its mutational traits and its fermentation viability, thereby offering a potential new direction for developing microalgae-based food ingredients with improved color properties.

The plastisphere is a novel anthropogenic habitat in the global nitrogen cycle, yet how agricultural nutrient pollution, acidification, and warming combinedly affect its nitrous oxide (N2O) fluxes remains unknown. We hypothesized that these stressors amplify emissions from plastic biofilms. A factorial mesocosm experiment exposed biodegradable (PLA) and non-biodegradable (PE) plastics to potassium (K-70 mg/L), acidification (pH 6.0, 6.5), and warming (23°C, 28 °C) under hypoxic conditions, using inhibitors and genomic profiling to identify pathways. PLA consistently sustained higher N2O emissions than PE, dominated by bacterial denitrification. Potassium and warming elicited a synergistic response, increasing N2O flux by 58%. While acidification combined with potassium and warming suppressed key functional genes (nirS, nosZ), it selected stress-tolerant consortia, including resilient nirK-type denitrifiers, that sustained the genetic potential for N2O production. This community adaptation and reduced N2O reduction capacity (lower nosZ) explain persistent emissions under acidic conditions. Abiotic chemo-denitrification occurred but was an order of magnitude slower than in pure chemical systems. Polymer-specific restructuring occurred, with PLA supporting more diverse consortia and higher genetic potential for nitrogen transformations. Three-way ANOVA confirmed that potassium × warming synergy is significantly modulated by pH (p < 0.001). These findings establish the plastisphere as a significant, unquantified N2O source, creating a feedback loop between plastic pollution, agriculture, and climate change, necessitating its inclusion in global nitrogen and climate models.

The current phosphorus recovery process in wastewater treatment plants faces several challenges, including process complexity and low recovery efficiency. This study examined applying the sequencing batch biofilm reactor (SBBR) and fluidized bed crystallization (FBC) processes to achieve high-P enrichment. Subsequently, the key environmental factors for phosphorus removal and recovery by the SBBR process were investigated. The concept of phosphorus storage was introduced, and a novel phosphorus harvesting control strategy was developed. The redox conditions in the phosphorus-rich solution generated by the SBBR process are compatible with those required for vivianite formation in the FBC process. The two processes were successfully integrated, enabling direct vivianite formation in the liquid phase, which led to stable phosphorus crystallization recovery efficiency and high purity of vivianite. This study offers both technical and theoretical foundations for achieving efficient phosphorus recovery from mainstream processes as well as enhanced vivianite recovery.

Biomass burning in mainland Southeast Asia frequently produces smoke plumes that are transported across national borders, deteriorating air quality in downwind regions. To elucidate the monsoon-related impacts of transboundary biomass burning from Southeast Asia, we conducted a year-long investigation of molecular characteristics of PM2.5-bound organic aerosols at a tropical rainforest site in Southwest China. The results showed distinct seasonal variations in all measured chemical components, with a marked pollution enhancement (February to April) during the late dry season, coinciding with extensive upwind fires and prevailing southwesterly air mass transport. Sugars dominated the quantified organics, and levoglucosan was consistently the most abundant single compound. It exhibited pronounced increases during the late dry season, reflecting intensified smoke influence during the peak burning period. Source apportionment results revealed that direct plant emissions were the major source of organic aerosols in early dry season (46%) and wet season (58%), indicating a limited role of biomass burning during these periods. In contrast, biomass burning became the dominant contributor (54%) in late dry season, largely associated with transboundary transport from Southeast Asia. These results demonstrate that episodic transboundary biomass burning can dominate organic aerosol loading in southwestern China, highlighting the importance of coordinated regional mitigation during the peak dry-season burning period.

Municipal wastewater holds substantial potential for phosphorus recovery, and mainstream biofilm phosphorus recovery has emerged as a promising strategy. However, this process often requires upstream removal of organics and ammonia to create conditions favorable for polyphosphate-accumulating organisms (PAOs). Therefore, developing a front-end process that can achieve advanced nitrogen removal while maximizing liquid-phase phosphorus retention is critical. Unlike conventional activated sludge (CAS) systems, in which high sludge production leads to significant phosphorus loss, this study evaluated a pilot-scale integrated fixed-film activated sludge (IFAS) system as a front-end configuration to enhance phosphorus retention for downstream recovery. Compared with CAS, IFAS increased phosphorus retention efficiency to 78.6%, representing a 1.7 times improvement, while maintaining 83.6% nitrogen removal under low-temperature conditions. Mass balance analysis showed that IFAS reduced both sludge production and sludge phosphorus content, thereby weakening sludge-associated phosphorus removal and increasing phosphorus in the liquid phase. Microbial and functional analyses further indicated that canonical EBPR-associated PAOs were not identified as dominant taxa in either system, whereas IFAS favored a denitrifying community with broader metabolic adaptability. Intracellular polymer and functional gene patterns suggested that carbon was preferentially stored and subsequently mobilized for endogenous denitrification rather than phosphorus uptake. These results demonstrate the technical potential of IFAS as an energy-efficient and environmentally friendly strategy for upgrading WWTPs toward resource recovery.

Climate warming, acidification, and plastic pollution converge to create unrecognized feedback in the nitrogen cycle. Here, we demonstrate that these anthropogenic pressures synergistically amplify emissions of nitrous oxide (N2O), from plastic waste in a lake ecosystem. A factorial mesocosm study reveals that combined warming (28 °C) and acidification (pH 6.0) synergistically enhance N2O emissions from plastic substrates by accelerating nitrogen transformations, depleting ammonium and nitrate while transiently accumulating nitrite. This response is governed by polymer type, with the plastisphere assembled on polylactic acid (PLA) sustains significantly higher (up to 78%) emissions than on polyethylene (PE). A significant temperature and acidification interaction (p < 0.001) confirms synergism, with the combined effect exceeding additivity by 132 μg N g-1 MLVSS h-1 for PLA and 36.2 μg N g-1 MLVSS h-1 for PE. Bacterial-dominated communities produce the highest N2O (1182.9 μg N g-1 MLVSS h-1 from PLA at pH 6.0 and 28 °C), while acetylene inhibition corroborates this trend, with PLA emissions 49% higher than PE. Mechanistically, the synergy reassembles the plastisphere microbiome into efficient, cooperative networks, enriching keystone N2O-producing denitrifiers (e.g., Thauera (Aminoaromatica MZ1T), Pseudomonas Stutzeri) and enhancing electron transfer efficiency. This community shift creates a decisive genetic constriction, upregulating the nirS gene while suppressing the N2O-reducing nosZ gene. Our findings position plastic waste as a climate-sensitive biogeochemical reactor, creating feedback between plastic pollution and anthropogenic climate forcing.

This study systematically investigated the phosphorus (P) adsorption and release behaviors of biofilm extracellular polymeric substances (EPS) in a sequencing batch biofilm reactor (SBBR). Batch experiments, enzyme activity assays, P forms, and spectral characterizations (3D-EEM, FTIR, XPS) were integrated to elucidate the independent role of EPS in biofilm P metabolism. The results quantified the independent P adsorption and release capacities of EPS as 1.68 mg/g and 2.46 mg/g, respectively. Different from cell-dependent biological P metabolism, EPS-mediated P transformation was insensitive to dissolved oxygen variation and carbon addition, and was mainly dominated by physicochemical adsorption. EPS-derived orthophosphate (Orth-P) and polyphosphate (Poly-P) contributed over 67% and less than 12% to the total Orth-P and Poly-P metabolism of biofilms, respectively. Although polyphosphate kinase (PPK) and polyphosphate hydrolase (PPX) activities were detected in EPS, the lack of effective carbon utilization capacity restricted their involvement in Poly-P transformation. Metal-mediated complexation served as the core immobilization pathway, in which Ca2⁺ and Mg2⁺ bound with phosphate groups, as well as carboxyl and amino functional groups of tryptophan- and tyrosine-rich proteins in EPS. Beyond the inherent physicochemical adsorption properties of EPS, microbial cells further regulated EPS content by aerobic biosynthesis and anaerobic biodegradation. Such microbial regulation synergistically optimized the P adsorption-release performance of EPS, verifying that EPS acts as the dominant functional component responsible for P transformation in biofilm systems. This study clarifies the intrinsic mechanisms underlying EPS-mediated P adsorption and release, and provides a theoretical basis for the development of low-carbon and high-efficiency P recovery technologies.

Plastic pollution in inland aquatic ecosystems fosters unique microbial biofilms, termed the “plastisphere”, act as a potent mediator of biogeochemical cycles. This systematic review synthesizes evidence that the plastisphere disrupts nitrogen (N) cycle and amplifies emissions of nitrous oxide (N2O). By creating stratified microenvironments with sharp oxygen gradients, microplastics selectively enrich microbial guilds responsible for N transformations. Conventional polymers (polyethylene, polyvinyl chloride) enrich nitrifying bacteria (Nitrosomonas and Nitrospira), increasing the abundance of functional marker genes for ammonia oxidation (amoA) and nitrite oxidation (nxrB). Simultaneously, these and other polymers (polystyrene) promote denitrifying taxa (Dechloromonas, Thauera, and Flavobacterium), elevating genes for nitrite reduction (nirK, nirS), a key step in N2O production. The gene responsible for N2O reduction (nosZ) is frequently suppressed. This imbalance is quantified by the (nirK+nirS)/nosZ ratio, where a higher value indicates a greater genetic potential for N2O to be produced rather than reduced to N2, is a primary mechanism for N2O accumulation. Biodegradable polymers introduce a complex paradox: while they may inhibit classic nitrifiers, they create anoxic microinches that favor alternative pathways like nitrifier-denitrification and support distinct denitrifier communities, resulting in substantial N2O yields. The direction and magnitude of these effects are critically determined by polymer chemistry and size. We identify research priorities, including long-term field studies and advanced isotopic methods, essential for developing predictive models and effective mitigating strategies.

The industrialization of microalgae cultivation urgently requires cost-effective, reliable, and robust cell monitoring techniques. To address the modeling limitations due to variations in cell morphology and the accumulation of specific products in existing optical methods, this study proposed a simplified and robust cell monitoring approach based on ionic consumption caused by microalgal growth. By modeling a foundational framework based on the nitrate-based photoautotrophic batch cultivation system, clustering metal cations and their associated anions into the "Ion-set" assigned to biomass prediction, and attributing changes in ionic strength during cultivation to the changes in nitrate, bicarbonate, and "Ion-set", the monitoring was simplified. Key parameters of the "Ion-set"-its average molar conductivity coefficient (103.87 mu S cm- 1 mmol- 1 L) and average charge number (1.35)-were quantified via Monte Carlo simulations using literature data. Tribonema minus cultivation demonstrated that with only online conductivity and nitrate electrodes and a moving time-window algorithm to calculate robust change rates, the system accurately tracked biomass (R2 = 0.96) and protein concentration (R2 = 0.99), while identifying process events such as metabolic shifts and bicarbonate accumulation (ca. 6 mmol L- 1). This approach is simplified, robust, and economical, and has extremely strong potential for industrial deployment.

The sustainable transformation of waste activated sludge (WAS) into value-added resources is crucial for circular bioeconomy. This study conducted a systematic, long-term comparison of three types of sludge derived from WAS treatment process as raw materials: secondary sedimentation tank sludge (SSTS), anaerobic digestion sludge (ADS), and dewatered sludge (DS). Over 220 days, a clear trade-off between enrichment rate and operational stability was observed. DS facilitated the fastest anammox enrichment and functional establishment (78 days), while SSTS, despite a longer enrichment period (146 days), achieved the most stable performance with higher biodiversity. Conversely, ADS yielded the highest Candidatus_Brocadia abundance (6.51 %) but suffered from severe nitrate accumulation due to nitrite-oxidizing bacteria (NOB) competition. Mechanistic analysis revealed that endogenous organic matter generation potential of the sludge governed this trade-off by mediating heterotrophic-autotrophic competition, as reflected in initial MLVSS/MLSS ratio, dehydrogenase (DH) activity, and microbial community structure. Significant positive correlation between Candidatus_Brocadia and Bryobacter (p < 0.05) was observed in all reactors. When combined with NOB inhibition strategies, DS would hold significant potential as a rapid enrichment raw material for anammox. This study validates a strategy for upgrading WAS into biological inoculum within wastewater treatment plants, providing valuable insights for sustainable sludge management and anammox applications.

As a primary pathway for mitigating the global phosphorus pollution crisis, widely used conventional activated sludge phosphorus recovery processes in municipal wastewater treatment plants (WWTPs) are facing increasing challenges due to continuously declining influent carbon and phosphorus concentrations. This review systematically compares activated sludge processes with emerging biofilm processes, highlighting a conceptual shift from the biomass growth driven enhanced biological phosphorus removal theory to the novel DAM theory centered on microbial metabolism in biofilms. The DAM theory conceptualizes the biofilm as a reusable, tunable phosphorus reservoir, where periodic accumulation in biofilms promotes liquid phase recovery even under low carbon source conditions. In terms of mechanism, extracellular polymeric substances are examined for their roles in phosphorus transfer, storage, and transformation. Microbial interactions are analyzed, with particular emphasis on the functional roles of glycogen-accumulating organisms in different processes and their implications for system stability. Ultimately, this review proposes a novel phosphorus recovery paradigm based on biofilm processes to circumvent the operational bottlenecks associated with insufficient influent carbon in WWTPs, providing a theoretical framework and technical guidance for sustainable nutrient management.

Brown carbon (BrC) is an important type of organic aerosol that can significantly affect the climate and air quality because of its important role in radiation balance and visibility impairment. Despite its importance, the optical properties and sources of BrC remain poorly characterized, especially in tropical rainforest regions. Here, we collected yearlong PM2.5 samples from a typical tropical forest site in southwest China. We combined optical measurements and chemical analyses to investigate the optical properties and sources of water-soluble BrC. We show that the average absorbance coefficient of BrC (Abs(365)) was higher in the dry season than wet season, coinciding with increased water-soluble organic carbon concentrations during the dry season. Correlation analyses revealed a strong association between Abs(365) and biomass-burning (BB) organic markers (R-2 > 0.6), along with a moderate correlation with secondary organic aerosol (SOA) markers (R-2 > 0.3) in the dry season, indicating that enhanced biomass-burning activities substantially increased BrC levels. However, such a clear association was not observed in the wet season. These results suggest that biomass burning was the major source of BrC in the dry season, followed by secondary formation, while no single dominant source of BrC was apparent in the wet season. The estimation of the contribution of solar absorption by BrC relative to elemental carbon shows that BrC contributed over 29 % of light absorption in the near-UV range in both seasons, indicating an important role of BrC in solar absorption. Overall, our work gains insights into the optical properties and possible sources of BrC in tropical forest regions.

Lipids derived from algal biomass are important constituents of biofuels, nutraceuticals, cosmeceuticals, and animal feed, inter alia. This necessitates the identification and large-scale production of microalgal species that can serve as the biomass based raw material for the above-mentioned categories of bio-products. In this vein, this review sifts through the literature and describes the most promising microalgal species that synthesize lipids and, when subjected to specific conditions, show enhanced lipid production. Currently, Chlorella sp., Cyclotella sp., Neochloris oleoabundans, and Isochrysis galbana are the species with the highest lipid contents. The review mentions and discusses various bioreactor configurations that can be used for large-scale culturing of these microalgae in a comparative aspect. Various configurations of photobioreactors are suitable for high biomass and lipid productivity. Further, prominent strategies of lipid extraction from microalgae have been elaborated, from conventional techniques to the latest ones, comparing and contrasting their advantages and disadvantages. While solvent-based extractions may have their advantages, it would be prudent to explore more eco-friendly techniques for scale-up. Lastly, the review gives a comprehensive account of the biorefinery approach to culturing microalgae, emphasising the assessment of their economic performance using different software and models, such as the techno-economic assessment model. The application of tools such as multi-criteria decision analysis that assess energy technology could enable better optimization. Microalgae have the potential to be used as a renewable source of fuel and feed; therefore, it is incumbent on the scientific community to significantly reduce production costs while ensuring sustainability.

Landfills are significant reservoirs of chlorinated organophosphorus flame retardants (Cl-OPFRs) and microplastics (MPs), yet their interactions remain unclear. This study systematically revealed that MPs in landfill soils significantly inhibited the release of Cl-OPFRs, with a dose-dependent effect (up to 27.69% reduction). Release kinetics followed the pseudo-second-order kinetics (R2 = 0.747-0.986), indicating chemically controlled processes. Molecular modeling confirmed that polar interactions governed the adsorption of Cl-OPFRs onto polar MPs (PA, PVC), while hydrophobic interactions prevailed for non-polar MPs (PE, PP). Ionic strength showed a non-monotonic effect, with low levels (0.01-0.1 M NaCl) enhancing the release process through competitive adsorption, whereas a high levels suppressed it via salting-out and double-layer compression. Both acidic and alkaline conditions promoted the release of Cl-OPFRs, likely resulting from changes surface charges and competitive ion effects. Fulvic acid showed a concentration-dependent dual effect. Critically, structural equation modeling identified ionic strength and soil organic matter as the primary factor governing the release of hydrophilic and hydrophobic Cl-OPFRs, respectively. These findings provide mechanistic insights essential for assessing the mobility and risks of Cl-OPFRs in MPs-contaminated landfills.

Atmospheric secondary organic aerosols (SOAs) play a significant role in climate change, air quality, and human health, yet their formation mechanisms and influencing factors in the field environment are not fully understood. This study conducted a one-year-long observation of specific organic tracers of SOAs derived from isoprene (SOAI), α/β-pinene (SOAP), β-caryophyllene (SOAC), and aromatics (SOAA) oxidation in PM2.5 at a tropical rainforest site in Xishuangbanna, Southwest China. All the SOA tracers presented obviously higher concentrations in dry season than in wet season. The ratio of 2-methylglyceric acid (2-MGA) to 2-methyltetrols (2-MTs) in dry season (0.49) was around 3 times higher than that in wet season (0.17), because the higher NOx concentrations (36.18 µg m−3 in dry season vs. 22.96 µg m−3 in wet seasons) enhanced the 2-MGA formation in dry season. The ratios of 3-methyl-1,2,3-butanetricarboxylic acid to the sum of cis-pinonic and pinic acids (M/P) were above 2 in both seasons, suggesting that the organic aerosols in the tropical rainforest region have undergone a significant degree of oxidation. The concentration of β-caryophyllene was approximately 18 times higher in the dry season (9.18 ± 10.23 ngm−3) than in the wet season (0.49 ± 0.35 ng m−3), which is related to the seasonal activity of biomass burning. In dry season, levoglucosan exhibited significant correlations with SOAP, SOAC, and SOAA, indicating that they were likely influenced by biomass burning. Backward trajectory analysis and potential source contribution factor analyses revealed that the sources of all the SOA tracers are likely influenced by biomass burning from the south and northwest directions in dry season, whereas in wet season they are likely affected by the transport from the southwest and northeast directions. This study highlights the important contribution of biomass burning in Southeast Asia on the SOA formation in the tropical rainforest region of Southwest China.

Phosphorus (P) recovery in municipal sewage from sludge via enhanced biological P removal process is an effective solution to P shortage. However, low influent P concentration (Pinfluent) makes it difficult to obtain highconcentration P-enriched liquid from sludge. This study examined applying a sequencing batch biofilm reactor (SBBR) to remove and enrich low-concentration P from municipal wastewater concurrently. The results demonstrated that the SBBR could efficiently remove and enrich low-concentration P with low carbon consumption. When the phosphate (PO4 3--P) concentration in the influent was 2.5 mg/L, the aerobic effluent met discharge standards. After anaerobic recycling enrichment, the average PO4 3--P concentration of the recovered solution reached 75.8 mg/L, with an enrichment factor of 30.3 times. The average total P recovery rate was 72.8 %, with a carbon consumption of 37.3 mg-P/mg-COD. This is mainly attributed to the recycling operation mode of the P-enriched recovery solution. Even when the Pinfluent is low, it can create conditions for the biofilm to be exposed to a high-P environment. This situation ensures the P absorption by extracellular polymeric substances, enabling the P storage capacity reached 55 mg-P/g-MLSS, and the P mainly exists in the form of PO4 3--P, which is the key to achieving high-efficiency P enrichment in the recovery solution under low carbon consumption. In addition, the decrease in Pinfluent did not alter the dominant role of polyphosphate-accumulating organisms in the biofilm. This study provides theoretical support and a technical approach for the simultaneous removal and enrichment of low-concentration phosphate in municipal wastewater.

The gas-particle partitioning of carbonyl compounds through reversible and irreversible pathways constitutes a critical route for secondary organic aerosol formation. This study simultaneously observed distribution of formaldehyde (FA), acetaldehyde (AA), glyoxal (GLY), and methylglyoxal (MGLY) in both gas and particle phases, as well as concentration and stable carbon isotope (δ¹³C) of oxalic acid. The results show that in the reversible partitioning process, the carbonyl compounds during clean period are mainly partitioned into organic phase, and the salt-in effect exhibits kinetic limitations. However, they are mainly partitioned into aerosol liquid water during haze periods with lower partitioning coefficients, and there is a significant salt-in effect. The carbonyls present different irreversible partitioning pathways to contribute oxalic acid formation in haze periods. In Haze I (O3: 24 ± 11 ppb), the carbonyl compounds are mainly partitioned into aqueous phase and reacted with water to form polymers or undergoing self-polymerization. The large multifunctional compounds decomposed to yield oxalic acid, leading to progressive enrichment of δ¹³C. In Haze II (O3: 41 ± 13 ppb), the elevated atmospheric oxidation capacity promoted aqueous-phase oxidation of the carbonyls to generate intermediate products and ultimately forming oxalic acid. Under these conditions, oxalic acid-C exhibited a depleted δ¹³C signal.

Methanogens play a crucial role in Earth's carbon biogeochemical cycle, and changes in total nitrogen (TN) may have particular effects on methanogenic communities. However, our understanding of the response of cavedwelling methanogens and methane (CH4) generation to TN variation remains limited. To address this, we collected weathered rock and sediment samples from three oligotrophic karst caves in southwestern China, and conducted high-throughput sequencing of the methyl coenzyme M reductase alpha subunit (mcrA) gene. We investigated how TN regulates CH4 production by methanogens, and how TN affects the assembly and network stability of methanogens within the cave ecosystem. Our results indicated that elevated TN levels significantly increased the absolute abundance of methanogens and the relative abundance of core taxa, further enhanced the CH4 production. This was because TN input alleviated nitrogen limitation in the caves and increased the availability of substrates for CH4 metabolism by methanogens. Stochastic processes, especially drift and dispersal limitation, governed methanogen assembly. TN mediated the balance between deterministic and stochastic processes, and its increase resulted in a V-shaped pattern of stochastic process contribution. Elevated TN significantly disrupted methanogen network stability. Our study provides new understanding of nutrientmicrobe-climate interactions in subsurface ecosystems.