C. vulgaris has a positive effect on the removal of nutrients from pig farm biogas slurry. However, swine wastewater often contains heavy metal ions, such as Cu (II), which may have impacts on the nutrient removal performance of C. vulgaris. Additionally, the heavy metal ions in wastewater can be adsorbed by microalgae. In this study, the stress effect of Cu (II) on the growth of Chlorella vulgaris, the Cu (II) removal by microalgae, and the effect of different concentrations of Cu (II) on the nutrient removal efficiency of C. vulgaris in biogas slurries were explored. The results showed that the microalgae biomass of microalgae on the sixth day of the experiment was the highest in the treatment with a Cu (II) concentration of 0.5 mg/L, which was 30.1% higher than that of the 2.5 mg/L group. C. vulgaris had higher removal efficiencies of Cu (II) at a Cu (II) concentration of 0.1~1.5 mg/L. The–OH, C=O, –COOH, and C–O groups on the surface of the algal cells play a significant role in the removal of Cu (II). The removal rates of COD, NH₃–N, TN, and TP by C. vulgaris at a Cu (II) concentration of 0.5 mg/L were the highest, which were 89.0%, 53.7%, 69.6%, and 47.3%, respectively.

The long multiplication time and extremely demanding enrichment environment requirements of Anammox bacteria (AAOB) have led to difficult reactor start-ups and hindered its practical dissemination. Few feasibility studies have been reported on the recovery of AAOB activity initiation after inlet substrate disconnection caused by an unfavorable condition, and few factors, such as indicators of the recovery process, have been explored. Therefore, in this experiment, two modified expanded granular sludge bed reactors (EGSB) were inoculated with 1.5 L anaerobic granular sludge (AGS) + 1 L Anammox sludge (AMS) (R1) and 2.5 L anaerobic granular sludge (AGS) (R2), respectively. After a long-term (140 days) starvation shock at a high temperature (38 °C), the bacteria population activity recovery experiments were conducted. After 160 days, both reactors were successfully started up, and the total nitrogen removal rates exceeded 87%. Due to the experimental period, the total nitrogen removal rate of R2 was slightly higher than that of R1 in the final stage. However, it is undeniable that R2 had a relatively long activity delay during startup, while R1 had no significant activity delay during startup. The sludge obtained from R1 had a higher specific anammox activity (SAA). Analysis of the extracellular polymer substances (EPS) results showed that the extracellular polymer content in R1 was higher than that in R2 throughout the recovery process, indicating that R1 had higher sludge stability and denitrification performance. Scanning electron microscopy (SEM) analysis showed that more extracellular filamentous bacteria could be seen in the R1 reactor with better morphology of Anammox bacteria. In contrast, the R2 reactor had fewer extracellular hyphae and micropores as a percentage and higher filamentous bacteria content. The results of microbial 16SrDNA analysis showed that R1 used AAOB as inoculum to initiate Anammox, and the reactor was enriched with Anammox bacteria earlier and in much greater abundance than R2. The experimental results indicated that inoculating mixed anaerobic granular sludge and Anammox sludge to initiate an anammox reactor was more effective.

Environmental health and biosecurity in pig farms and surroundings are increasingly threatened by pathogenic bacteria carried by fine particulate matter with an aerodynamic diameter of 2.5 μm or less (PM_2.5) in enclosed piggeries. However, limited attention has been given to these pathogens and their association with the respiratory microbiome of pigs. Using high-throughput sequencing, we investigated the overall and pathogenic bacterial communities attached to PM_2.5 in pig houses, as well as those in the upper (URT) and lower respiratory tracts (LRT) of healthy fattening pigs. Concentrations of PM_2.5, particulate matter with an aerodynamic diameter of 10 μm or less (PM₁₀), ammonia (NH₃), total volatile organic compounds (TVOCs), and hydrogen sulfide (H₂S) were significantly higher inside the piggery than in the surrounding environment. The composition of PM_2.5-associated bacteria varied with sampling height and showed greater similarity to the microbiota of the URT, particularly the oropharynx, than to that of the LRT. Additionally, 140 core potential bacterial pathogens were identified via Venn analysis in both PM_2.5 and respiratory tracts. Co-occurrence network analysis and community assembly patterns revealed that microbial communities in PM_2.5 and the respiratory tract exhibit distinct interaction and assembly characteristics. These findings highlight the potential role of PM_2.5 as a vector for respiratory pathogens and underscore the importance of air quality management in pig farming to safeguard environmental health.

ZnO and CuO nanoparticles (NPs) are ubiquitous emerging contaminants in wastewater treatment systems. They dose-dependently impair biological nitrogen removal by targeting denitrifying microorganisms, representing a critical environmental challenge for wastewater treatment. Herein, we report that Fe²⁺ is correlated with alleviated NPs toxicity, which may be attributed to modulated NPs physicochemical behavior and enhanced microbial metabolic resilience. At 20 mg/L NPs, Fe²⁺ elevated NO₂^- removal efficiency of strain Y-11 from 38.22% to 59.20% (ZnO-NPs) and from 1.66% to 29.70% (CuO-NPs). Fe²⁺ reduced Zn²⁺ dissolution from ZnO-NPs by 15.7% (10 mg/L ZnO-NPs) and promoted aggregation of both NPs (hydrodynamic diameter increased 2-3 fold) by compressing the electric double layer and lowering surface zeta potential. Fe²⁺ was associated with preserved activities of key denitrifying enzymes (nitrate reductase, nitrite reductase) and electron transport chain complexes I-IV. Fe²⁺ restrained intracellular reactive oxygen species within 80%-150% of the control and reduced lactate dehydrogenase release to maintain cell membrane integrity. Fe²⁺ also strengthened antioxidant enzyme activities (superoxide dismutase, catalase, peroxidase) by up to 56.7-fold and stimulated extracellular polymeric substance secretion to form a physical barrier against NPs. Fe²⁺ provides a practical strategy to enhance the stability of biological nitrogen removal processes under NPs stress.