Precise portrayal of microscopic processes of wastewater biofilm formation: Taking SiO2 as the model carrier

Advance nitrogen removal from anaerobic sludge digestion liquor using partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification process

A novel two-stage continuous-flow partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) process was developed to treat anaerobic sludge digestion liquor. During the stable phase, the total nitrogen and chemical oxygen demand (COD) removal efficiencies were 93 ± 3 % and 59 ± 7 %, respectively. Free ammonia suppression (26.2 ± 12.7 mg/L) and low dissolved oxygen (DO, 0.12 ± 0.07 mg/L) were key factors in the operation of the PND process, while the SNAD process was restricted successfully by limited oxygen (DO < 0.1 mg/L) and short solids retention time (9.7 d). The PND process was an important pretreatment process that could remove biodegradable dissolved COD by denitrification and supply ammonium-oxidizing bacteria (AOB) to the SNAD process. Nitrosomonas and Ca. Brocadia were the dominant AOB and anammox bacteria, respectively. Overall, this research presents a distinctive SNAD combined process for anaerobic sludge digestion liquor treatment.

Microalgae cell adhesions on hydrophobic membrane substrates using quartz crystal microbalance with dissipation

Microalgal cell adhesion and biofilm formation are affected by interactions between microalgae strains and membrane materials. Variations of surface properties of microalgae and membrane materials are expected to affect cell-membranes and cell-cell interactions and thus initial microalgal cell adhesion and biofilm formation rates. Hence, it should be possible to identify the dominant mechanisms controlling microalgal cell adhesion and biofilm formation. The effects of surface properties of three different microalgal strains and three different types of membrane materials on microalgal cell adhesion and biofilm formation were systematically investigated in real time by monitoring changes in the oscillation frequency and dissipation of the quartz crystal resonator (QCM-D). The results revealed that in general a higher surface free energy, more negative zeta potential, and higher surface roughness of membrane materials positively correlated with a larger quantity of microalgae cell deposition, while a more hydrophilic microalgae with a larger negative zeta potential preferred to attach to a more hydrophobic membrane material. The adhered microalgal layers exhibited viscoelastic properties. The relative importance of these mechanisms in controlling microalgae cell attachment and biofilm formation might vary, depending on the properties of specific microalgae species and hydrophobic membrane materials used.

Adaptive Evolution Laws of Biofilm under Emerging Pollutant-Induced Stress: Community Assembly-Driven Structure Response

The widely used biofilm process in advanced wastewater treatment is currently challenged by numerous exotic emerging pollutants (EPs), and the underlying principle of the challenge is the adaptive evolution laws of biofilm under EP stress. However, there is still a knowledge gap in exploration of the biofilm adaptive evolution theory. Herein, we comprehensively analyzed the morphological variation, community succession, and assembly mechanism of biofilms to report the mechanism underlying their adaptive evolution under sulfamethoxazole and carbamazepine stress for the first time. The ecological role of the dominant species was driven as a pioneer and assembly hub by EP stress, and the deterministic processes indicated the functional basis of the transformation. In addition, the characteristic responses of dispersal limitation and homogenizing dispersal adequately revealed the assembly pathways in adaptive evolution and the resulting structural variation. Therefore, the "interfacial exposure-structural variation-mass transfer feedback" mechanism was inferred to underly the adaptive evolution process of biofilms. Overall, this study highlighted the internal drivers of the adaptive evolution of the biofilm at the phylogenetic level and deepened our understanding of the mechanism of biofilm development under EP stress in advanced wastewater purification.

Research advances in application of mainstream anammox processes: Roles of quorum sensing and microbial metabolism

Anaerobic ammonium oxidation (anammox) is a low-carbon biological nitrogen removal process, that has been widely applied to treat high-strength wastewater. However, the practical application of mainstream anammox treatment is limited due to the slow growth rate of anammox bacteria (AnAOB). Therefore, it is important to provide a comprehensive summary of the potential impacts and regulatory strategies for system stability. This article systematically reviewed the effects of environmental fluctuations on anammox systems, summarizing the bacterial metabolisms and the relationship between metabolite and microbial functional effects. To address the shortcoming of mainstream anammox process, molecular strategies based on quorum sensing (QS) were proposed. Sludge granulation, gel encapsulation and carrier-based biofilm technologies were adopted to enhance the QS function in microbial aggregation and reduction of biomass loss. Furthermore, this article discussed the application and progress of anammox-coupled processes. Valuable insights were provided for the stable operation and development of mainstream anammox process from the perspectives of QS and microbial metabolism.