Lower C/N ratio induces prior utilization of soluble microbial products with more dramatic variability and higher biodegradability in denitrification by strain YSF15

Unraveling stress responses of microalgal-bacterial granular sludge when treating ciprofloxacin-laden wastewater

Unraveling the potential of microalgal-bacterial granular sludge (MBGS) technology for sustainable treatment of ciprofloxacin (CIP)-laden wastewater and mitigation of antibiotic resistance genes (ARGs) remains limited. This study evaluated the performance of bacterial granular sludge (BGS) and MBGS systems in terms of nutrient and CIP removal, granular stability, and ARG attenuation under long-term exposure to CIP for the first time. While both systems achieved effective pollutant removal at low CIP concentrations (0.1 and 0.5 mg/L), MBGS demonstrated superior resilience and efficiency under high CIP loads (10 mg/L). Notably, MBGS improved phosphorus removal by 32.71 %, achieved a 70.42 μg/(g-SS)/d greater CIP removal and maintained structural integrity, unlike BGS, which disintegrated under oxidative stress. The microalgae species (Pseudoneochloris and Chlamydopodium) could effectively resist various concentrations of CIP. Additionally, the relative abundance of ARGs in MBGS was 30.91 % lower than that in BGS, suggesting that microalgae in MBGS system could reduce ARG production. Overall, these findings improve our understanding of the role of microalgae in enhancing CIP remediation and controlling ARG propagation in MBGS systems.

Degradation-Resistant Biochar Improves Soil Organic Carbon Storage: Promoting Autotrophic Metabolism & Increasing Refractory Organic Carbon

Biochar, as a soil amendment to enhance soil carbon sink, is a dual-effect carbon neutralization technology. However, the dissolved solids released from biochar not only shorten the duration of carbon sequestration but also diminish its efficacy on improving soil carbon fixation. In this study, biochar prepared from cellulase-treated lignocellulose (BC-SR) was utilized to address the defect. After one year, BC-SR promoted a net increase of 4.39 mg C/g in soil (equivalent to fixing 16.10 mg CO2/g), which was 28 % higher than ordinary biochar. The role of BC-SR was primarily achieved by three aspects: (1) Enhance microbial autotrophic metabolism; (2) Promote the formation of soil macroaggregates to protect easily degradable organic carbon; (3) Increase the proportion of refractory organic matter. This study demonstrated that compared with ordinary biochar, BC-SR exerted a stronger effect on autotrophic metabolism, and the newly generated organic matter persisted in the soil for a longer time.

Exposure to zinc and dialkyldimethyl ammonium compound alters bacterial community structure and resistance gene levels in partial sulfur autotrophic denitrification coupled with the Anammox process

Dialkyldimethyl ammonium compound (DADMAC) is widely used in daily life as a typical disinfectant and often co-exists with the heavy metal zinc in sewage environments. This study investigated the effects of co-exposure to zinc (1 mg/L) and DADMAC (0.2-5 mg/L) on the performance, bacterial community, and resistance genes (RGs) in a partial sulfur autotrophic denitrification coupled with anaerobic ammonium oxidation (PSAD-Anammox) system in a sequencing batch moving bed biofilm reactor for 150 days. Co-exposure to zinc and low concentration (0.2 mg/L) DADMAC did not affect the nitrogen removal ability of the PASD-Anammox system, but increased the abundance and transmission risk of free RGs in water. Co-exposure to zinc and medium-to-high (2-5 mg/L) DADMAC led to fluctuations in and inhibition of nitrogen removal, which might be related to the enrichment of heterotrophic denitrifying bacteria dominated by Denitratisoma. Co-exposure to zinc and high concentration DADMAC (5 mg/L) stimulated the secretion of extracellular polymeric substances and increased the proliferation risk of intracellular RGs in sludge. This study provided insights into the application of PSAD-Anammox system and the ecological risks of wastewater containing zinc and DADMAC.

Enhanced denitrification and p-nitrophenol removal performance via hydrophilic sponge carriers fixed with dual-bacterial: Optimization, performance, and enhancement mechanism

Effective treatment of industrial wastewater containing complex pollutants, such as nitrate (NO3--N) and organic pollutants, remains a significant challenge to date. Here, a strain Nocardioides sp. ZS2 with denitrification and degradation of p-nitrophenol (PNP) was isolated and its culture conditions were optimized by kinetic analysis. Hydrophilic sponge carriers were prepared using polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and chitosan (CS) to construct bioreactors. Furthermore, to further enhance the PNP degradation and denitrification performance of bioreactors, Pseudomonas stutzeri GF2 with denitrification capability was introduced. The results revealed that the removal efficiencies of PNP and NO3--N reached 97.9 % and 91.9 %, respectively, when hydraulic retention time (HRT) of 6 h, C/N of 2.0, and pH of 6.5. The bioreactor exhibited stable denitrification performance even with fluctuations in the influent PNP concentration. The potential functional prediction results revealed that the abundance of amino acids, fatty acids, and carbohydrates increased as the influent C/N decreased, reflecting a tendency of the microbial community to adjust carbon source utilization to maintain cell growth, metabolic balance, and resist adverse C/N environments. This research provides new insights into the effective removal of organic pollutants and NO3--N in wastewater treatment.

Chemical characteristics of dissolved organic matter in effluent from sludge alkaline fermentation liquid-fed sequencing batch reactors

Sludge alkaline fermentation liquid (SAFL) is a promising alternative to acetate for improving biological nitrogen removal (BNR) from wastewater. SAFL inevitably contains some refractory compounds, while the characteristics of dissolved organic matter (DOM) in effluent from SAFL-fed BNR process remain unclear. In this study, the molecular weight distribution, fluorescent composition and molecular profiles of DOM in effluent from SAFL and acetate-fed sequencing batch reactors (S-SBRs and A-SBRs, respectively) at different hydraulic retention time (12 h and 24 h) was comparatively investigated. Two carbon sources resulted in similar effluent TN, but a larger amount of DOM, which was bio-refractory or microorganisms-derived, was found in effluent of S-SBRs. Compared to acetate, SAFL increased the proportion of large molecular weight organics and humic-like substances in effluent DOM by 74.87%-101.3% and 37.52%-48.35%, respectively, suggesting their bio-refractory nature. Molecular profiles analysis revealed that effluent DOM of S-SBRs exhibited a more diverse composition and a higher proportion of lignin-like molecules. Microorganisms-derived molecules were found to be the dominant fraction (71.51%-72.70%) in effluent DOM (<800 Da) of S-SBRs. Additionally, a prolonged hydraulic retention time enriched Bacteroidota, Haliangium and unclassified_f_Comamonadaceae, which benefited the degradation of DOM in S-SBRs. The results help to develop strategies on reducing effluent DOM in SAFL-fed BNR process.

Ozone Micronano-bubble-Enhanced Selective Degradation of Oxytetracycline from Production Wastewater: The Overlooked Singlet Oxygen Oxidation

The efficient and selective removal of refractory antibiotics from high-strength antibiotic production wastewater is crucial but remains a substantial challenge. In this study, a novel ozone micronano-bubble (MNB)-enhanced treatment system was constructed for antibiotic production wastewater treatment. Compared with conventional ozone, ozone MNBs exhibit excellent treatment efficiency for oxytetracycline (OTC) degradation and toxicity decrease. Notably, this study identifies the overlooked singlet oxygen (1O2) for the first time as a crucial active species in the ozone MNB system through probe and electron paramagnetic resonance methods. Subsequently, the oxidation mechanisms of OTC by ozone MNBs are systematically investigated. Owing to the high reactivity of OTC toward 1O2, ozone MNBs enhance the selective and anti-interference performance of OTC degradation in raw OTC production wastewater with complex matrixes. This study provides insights into the mechanism of ozone MNB-enhanced pollutant degradation and a new perspective for the efficient treatment of high-concentration industrial wastewater using ozone MNBs. In addition, this study presents a promising technology with scientific guidance for the treatment of antibiotic production wastewater.

Regulating mechanism of denitrifier Comamonas sp. YSF15 in response to carbon deficiency: Based on carbon/nitrogen functions and bioaggregation

There is an urgent demand to investigate mechanisms for the improvement of denitrification in carbon-deficient environment, which will effectively reduce the eutrophication in water bodies polluted by nitrate. In this study, denitrifying bacterium Comamonas sp. YSF15 was used to explore the differences in different carbon source concentrations, with the complete genome, metabolomics, and other detecting methods. Results showed that strain YSF15 was able to achieve efficient denitrification, with complete pathways for denitrification and central carbon metabolism. The carbon deficiency prompted the bacteria to use extracellular amino acid-like metabolites initially, to alleviate inhibition and maintain bioactivity, which also facilitated glycogen storage. The biogenic inhibitors (tautomycin, navitoclax, and glufosinate) at extremely low level potentially favored the competitiveness and intraspecific utilization of extracellular polysaccharides (PS). Optimal solutions for bioaggregation in carbon-deficient condition are achieved by regulating the hydrophobicity, and hydrogen bond in extracellular metabolites. The strategy contributes to the maintenance of bioactivity and adaptation to carbon deficiency. Overall, this study provides a new perspective on understanding the denitrification strategies in carbon-deficient environment, and helps to improve the nitrate removal in low-carbon wastewater treatment.

Acute impact of salinity and C/N ratio on the formation and properties of soluble microbial products from activated sludge

The present study investigated the shock of NaCl and C/N ratio on properties of soluble microbial products (SMPs), focusing on their sized fractions. The results indicated that the NaCl stress increased the content of biopolymers, humic substances, building blocks, and LMW substances in SMPs, while the addition of 40 g NaCl L^-1 significantly changed their relative abundance in SMPs. The acute impact of both N-rich and N-deficient conditions accelerated the secretion of SMPs, but the characteristics of LMW substances differed. Meanwhile, the bio-utilization of SMPs has been enhanced with the increase of NaCl dosage but decreased with the increase of the C/N ratio. The mass balance of sized fractions in SMPs + EPS could be set up when NaCl dosage <10 g/L and C/N ratio >5, which indicates the hydrolysis of sized fractions in EPS mainly compensated for their increase/reduction in SMPs. Besides, the results of the toxic assessment indicated that the oxidative damage caused by the NaCl shock was an important factor affecting the property of SMPs, and the abnormal expression of DNA transcription cannot be neglected for bacteria metabolisms with the change of C/N ratio.

Impacts of exogenous quorum sensing signal molecule-acylated homoserine lactones (AHLs) with different addition modes on Anammox process

Anammox was proved having the quorum sensing ability, and several acylated homoserine lactones (AHLs) signal molecules were detected in the system. In this study, the impact of exogenous N-dodecanoyl homoserine lactone (C12-HSL) with different addition modes on the nitrogen removal, key enzymes' activity, and microbial revolution were investigated in Anammox system. Results showed that once-addition of C12-HSL had no obvious impact on Anammox. Daily-addition with 40 nM slightly improved the TN removal from 71.1 % to 74.5 %, while 80 and 200 nM significantly decreased it to 62.7 % and 61.8 %, respectively. The enzyme activity of ammonia monooxygenase increased from 0.015 to 0.068, nitrite reductase increased from 0.25 to 1.23, and nitrate reductase increased from 0.05 to 0.11 μg NO₂^--N mg^-1 Protein min^-1. Arenimonas abundance showed positive correlation with TN removal while Candidatus Kuenenia was continuously suppressed. C12-HSL was beneficial for partial nitrification, and it could be adopted for regulating the nitrite production.

Synergistic removal of nitrate by a cellulose-degrading and denitrifying strain through iron loaded corn cobs filled biofilm reactor at low C/N ratio: Capability, enhancement and microbiome analysis

Optimization of nitrate removal rate under low carbon-to-nitrogen ratio has always been one of the research hotspots. Biofilm reactor based on functional carrier and using interspecific synergic effect of strains provides an insight. In this study, iron-loaded corn cob was used as a functional carrier that can contribute to the cellulose degradation, iron cycling, and collaborative denitrification process of microorganisms. During biofilm reactor operation, the maximum nitrate removal efficiency was 99.30% and could reach 81.73% at no carbon source. Dissolved organic carbon and carrier characterization showed that strain ZY7 promoted the release of carbon source. The crystallinity of cellulose I and II in carrier of experimental group increased by 31.26% and decreased by 21.83%, respectively, in comparison to the control group. Microbial community showed the synergistic effect among different strains. The vitality and metabolic activity of the target microorganisms in bioreactor were increased through interspecific bacterial cooperation.

Enhanced denitrification of dispersed swine wastewater using Ca(OH)2-pretreated rice straw as a solid carbon source

In a pilot-scale packed bed reactor, the denitrification performance and microbial community structure of the dispersed swine wastewater treatment using calcium hydroxide (Ca(OH)₂) pretreated rice straw as a carbon source were investigated. In a Ca(OH)₂-pretreated rice straw supported denitrification system (Ca(OH)₂-RS), the removal efficiency of NO₃^--N was 96.39% at an influent NO₃^--N load of 0.04 kg/(m³•d). Meanwhile, there was no obvious accumulation of NO₂^--N or chemical oxygen demand (COD) in the effluent of Ca(OH)₂-RS. The contents of soluble microbial byproduct-like substances and tryptophan-like substances in the effluent of Ca(OH)₂-RS were reduced by 46.2% and 43.4%, respectively, compared with the influent. Overall, the Ca(OH)₂-pretreated rice straw system had a strong resistance to fluctuations in water quality conditions, such as influent NO₃^--N and COD concentrations. According to the microbial assay results, the Ca(OH)₂ pretreatment enriched more denitrifying bacteria. Among them, Proteobacteria (42.33%) and Bacteroidetes (35.28%) were the dominant bacteria. Moreover, the main denitrifying functional bacteria, generanorank_f_Saprospiraceae (13.32%), norank_f_Porphyromonadaceae (4.22%), and Flavobacterium (3.25%), were enriched in Ca(OH)₂-RS. This suggested that using Ca(OH)₂-pretreated rice straw as a carbon source was a stable and efficient technology to enhance the denitrification performance of dispersed swine wastewater.

Nitrogen removal from low C/N wastewater in a novel Sharon&DSR (denitrifying sulfide removal) reactor

Denitrification reactions commonly remove nitrate and other reactive nitrogen (Nr) from wastewater. The C/N ratio indicates the sufficiency of organic carbons to drive heterotrophic denitrification; a low C/N ratio frequently leads to poor denitrification performance in wastewater treatment. This study proposed and tested a novel Sharon&DSR (denitrifying sulfide removal) process, with nitrite generated by the Sharon reactions and sulfide from sulfur-reducing reactions for promoting the following nitrite-based denitrification and denitrifying sulfide removal (DSR) process. The present reactor can remove nitrate at an efficiency of 97.7 %-93.5 % at an influent C/N ratio of 0.646-0.737 over a 96-d continuous-flow test. The microbial community study reveals the functional strains corresponding to individual groups of critical reactions. The stoichiometry analysis reveals the potential to apply the nitrite-based DSR process for Nr removal from ultra-low C/N (<0.64) wastewaters, experimentally demonstrated in the present study with a C/N ratio of 0.16-0.39.

Hydrophilic spongy biochar crosslinked with starch and polyvinyl alcohol biocarrier for nitrate, phosphorus, and cadmium removal in low carbon wastewater: Enhanced performance mechanism and detoxification

This study aims to develop a functional biocarrier with hydrophilic spongy biochar crosslinked with starch and polyvinyl alcohol (WSB/starch-PVA) for simultaneous removal of NO₃^--N, total phosphorus (TP) and Cd²⁺ in low carbon wastewater. Results showed that the WSB/starch-PVA bioreactor achieved the maximum NO₃^--N removal efficiency in subphase 1.2 with 98.07 % (3.64 mg L^-1h^-1) versus control (75.30 %, 2.81 mg L^-1h^-1), and removed 54.84 % and 73.97 % of TP and Cd²⁺. Material characterization suggested that functional groups (related to C, N and O) on biocarrier and biofilm, and biogenic co-precipitation facilitated TP and Cd²⁺ removal. The WSB made the biocarrier pores larger and regular, and decreased fluorescent soluble microbial products. The predicted metagenome further suggested that central citrate cycle, oxidative phosphorylation of bio-community, and NO₃^--N removal were enhanced. Functions for microbial induced co-precipitation, Cd²⁺ transport/efflux, antioxidants, and enhanced biofilm formation favored the NO₃^--N/TP removal and Cd²⁺ detoxification.

Performance and enhancement mechanism of redox mediator for nitrate removal in immobilized bioreactor with preponderant microbes

The acceleration of nitrate removal in wastewater treatment by redox mediator (RM) is greatly weakened due to wash-out loss and mass transfer resistance (low hydrophilia) of RM during operation. In this study, an RM reactor with the fixed 1-Amino-4-hydroxyanthraquinone (AHAQ) and three core strains was established and achieved high nitrate removal efficiency (NRE) under low carbon to nitrogen ratio (C/N) and short hydraulic retention time (HRT) conditions, with the maximum efficiency of 99.41% (14.00 mg L-1 h-1) and average improvement by 11.97% (1.41 mg L-1 h-1). This acceleration led to more proportion of carbon consumption by denitrifying bacteria and improved their competitiveness against others in carbon deficiency, although resulting in nitrite accumulation (NIA) in lower C/N. The RM reactor induced the decorrelation tendencies between NRE and active extracellular organics and more sensitive denitrification toward C/N, which favored the stability of effluent organics and biological activities. The increase of oxidative phosphorylation and ubiquinone and other terpenoid-quinone biosynthesis pathway suggested electron transport activity was potentially enhanced by AHAQ. Although the lower C/N deteriorated the reactor NRE, the abundances of amino acids-, fatty acids- and carbohydrate-related metabolisms (45% of the total up-regulating pathways) were enhanced to utilize carbon source effectively. Meanwhile, the enhanced phosphotransferase system facilitated the balance between carbon and nitrogen metabolism. These indicated the changes in biological strategy to grow better and resist the adverse condition. This study highlighted the superior NRE by AHAQ in an immobilized reactor with core strains and more importantly, extended the RM application in wastewater treatment.