Wastewater from rare earth smelteries contains large amounts of ammonium nitrogen (NH₄⁺-N), which causes severe environmental problems. In this contribution, the desalination efficiency of reverse osmosis (RO) was investigated in the treatment of NH₄Cl or NaCl solutions from 0.1 to 40 g/L under different operating pressures with a commercial RO membrane. Experimental results showed that when an operating pressure above 30 bar is applied to the 5 g/L NH₄Cl solution, the permeate was found to meet the discharge standards of NH₄⁺-N. Compared to NH₄Cl, the permeate fluxes of NaCl solutions were higher due to the higher net driving force and lower propensity to membrane fouling. Theoretical models indicate a linear relationship between water flux and the net driving force for both NH₄Cl and NaCl solutions. On the contrary, a power function between the salt flux and concentration difference correlated well with the experimental data for salt transport. The equations for water and salt transport obtained by this work would provide a facile and practical means for predicting the membrane performance in design and optimization of RO processes for the treatment of wastewater from the rare earth industry.

Anaerobic ammonium oxidation (anammox), as an efficient and low-carbon method for nitrogen removal from wastewater, faces the challenge of slow enrichment of functional bacteria. In this study, the enrichment of anammox bacteria Candidatus Brocadia was successfully accelerated by co-culturing with the quorum-sensing strain Pseudomonas aeruginosa and anoxic sludge from a pig farm. Experimental results showed that the R2, which had Pseudomonas aeruginosa added, exhibited chemical reaction ratios R_S (NO₂⁻-N consumption/NH₄⁺-N consumption) and R_P (NO₃⁻-N production/NH₄⁺-N consumption) closer to the theoretical values of the anammox reaction since Phase Ⅱ. Bacterial community analysis indicated that the abundance of Candidatus Brocadia in R2 reached 1.63% in cycle 20, significantly higher than the 0.45% in R1. More quorum-sensing signaling molecules, primarily C6-HSL, were detected in R2. C6-HSL was positively correlated with processes such as the secretion of anammox extracellular polymers (EPS) and the regulation of nitric oxide reductase (Nir), which may explain the reason behind the accelerated increase in the abundance of Candidatus Brocadia through co-culturing. Moreover, the metabolism of the dominant genus Paracoccus within the two groups of reactors also showed positive regulation by C6-HSL, with its abundance trend similar to that of Candidatus Brocadia, jointly completing the nitrogen removal process in the reactors. However, it is still unknown which genera secrete large amounts of C6-HSL after inoculation with Pseudomonas aeruginosa. This research provides a novel and low-cost method for the enrichment of anammox bacteria.

This study investigates how 0.8 V applied voltage modulates phenazine biosynthesis, quorum sensing (QS), and microbial interactions in Pseudomonas aeruginosa PAO1-inoculated microbial electrolysis cell (MEC) reactors. Voltage stimulation significantly enhanced phenazine derivatives (PYO: 8.65-fold; 1-OH-PHZ: 14.98-fold) and QS signals (C4-HSL: 2.88-fold; 3-OXO-C12-HSL: 2.21-fold), correlating with upregulated biosynthetic genes (phzG: 14.8-fold; rhlI: 15.2-fold). Electrical stimulation amplified QS cross-regulation, reinforcing Las-mediated positive feedback on Rhl/PQS systems while attenuating Rhl’s inhibition of PQS. Untargeted metabolomic analysis demonstrated significant alterations in bacterial metabolic activity under electrical stimulation, identifying 140 differential metabolites. Among these, indole, a signaling molecule with QS-like functionality, exhibited the highest VIP score as an upregulated metabolite, and another indole derivative, brassicanal A, was also elevated. KEGG pathway enrichment analysis highlighted that these metabolites were primarily associated with amino acid metabolism and transport, while anthranilic acid and L-tryptophan—key metabolites linked to both indole-related pathways and phenazine biosynthesis—were also identified. Correlation analysis between differential metabolites with microbial communities confirmed that Delftia and Burkholderiales were strongly associated with phenazine biosynthesis and QS activity in P. aeruginosa PAO1. These findings highlight voltage as a key driver of metabolic rewiring and microbial niche partitioning, optimizing MEC reactor performance for wastewater treatment. This work provides foundational insights into electro-stimulated biofilm engineering through targeted QS and metabolic pathway regulation.

Nitrous oxide (N₂O) is not only recognized as a potent greenhouse gas, but it is also used in industry as a clean energy source. In this study, different electrode materials of carbon felt and graphite were equipped in the ΔnosZ P. aeruginosa/microbial electrolysis cell (MEC) systems to explore the optimization mechanism for long-term N₂O recovery during incineration leachate treatment. The carbon felt group showed a better performance in N₂O recovery across 45 days of operation. The N₂O conversion efficiency was above 80% and the proportion of N₂O in biogas accounted for 80.6% in the carbon felt group. qRT-PCR analysis was conducted to evaluate the expression of genes involved in denitrification (norB) and electroactivity (phzG, phzM, and phzH) of ΔnosZ P. aeruginosa. The results showed a significant upregulation in the suspended biomass (day 21) and the electron-attached biomass (day 45) from the carbon felt-equipped reactor, which was highly related to the opportunity of biomass exposed to the phenazine derivatives. By the carbon felt optimization in the system, 82.6% of the Pseudomonas genus survived after 45 days of operation. These results indicate that the carbon felt electrode has a more sustainable performance for N₂O recovery in the ΔnosZ P. aeruginosa/MEC system.

Lignocellulosic fruit peel waste represents an abundant, carbon-neutral feedstock for green biohydrogen production via dark fermentation, yet its rigid compact structure and high cellulose crystallinity severely restrict saccharification and fermentative hydrogen yield. In this study, a hydrothermal acidification pretreatment strategy was proposed to boost dark fermentative biohydrogen generation from navel orange peel waste, and systematic investigations were conducted to reveal the regulating mechanisms of key pretreatment parameters (hydrochloric acid concentration, pretreatment temperature, duration) on reducing sugar release and hydrogen-producing performance. Multiscale characterizations including SEM, XRD, FTIR, and TG were integrated to unravel the microstructural and chemical compositional evolution of raw and pretreated substrates. The results demonstrated that hydrothermal acidification effectively disrupted the dense lignocellulosic network of navel orange peel, lowered cellulose crystallinity, and greatly improved substrate accessibility for hydrolytic reactions and microbial adhesion. Under the optimal pretreatment condition (1.0 mol/L HCl, 120 °C, 1 h), the concentration of released reducing sugars reached 10.2 g/L, which was 67.2% higher than that of untreated raw peel. The corresponding maximum cumulative hydrogen yield attained 36.5 mL H₂/g TS, representing a 67.4% improvement relative to the untreated control group. Pearson correlation analysis verified that pretreatment temperature, acid concentration, and duration exhibited strong positive correlations with hemicellulose and cellulose removal efficiencies, while excessive pretreatment (HCl > 1.0 mol/L, temperature > 120 °C, duration > 1 h) generated inhibitory by-products that suppressed microbial hydrogen evolution. This study comprehensively clarifies the structural modification and biohydrogen promotion mechanism of hydrothermal acidification pretreatment on pectin-rich biomass, and delivers a cost-effective, facile technical route for high-value energy valorization and harmless disposal of fruit processing solid wastes.