Metagenomic insights into the mechanism for the rapid enrichment and high stability of Candidatus Brocadia facilitated by Fe(â ¢).

The rapid enrichment of anammox bacteria and its fragile resistance to adverse environment are the critical problems facing of anammox processes. As an abundant component in anammox bacteria, iron has been proved to promote the activity and growth of anammox bacteria in the mature anammox systems, but the functional and metabolic profiles in Fe(III) enhanced emerging anammox systems have not been evaluated. Results indicated that the relative abundance of functional genes involved in oxidative phosphorylation, nitrogen metabolism, cofactors synthesis, and extracellular polymers synthesis pathways was significantly promoted in the system added with 5 mg/L Fe(III) (R5). These enhanced pathways were crucial to energy generation, nitrogen removal, cell activity and proliferation, and microbial self-defense, thereby accelerating the enrichment of anammox bacteria Ca. Brocadia and facilitating their resistance to adverse environments. Microbial community analysis showed that the proportion of Ca. Brocadia in R5 also increased to 64.42 %. Hence, R5 could adapt rapidly to the increased nitrogen loading rate and increase the nitrogen removal rate by 108 % compared to the system without Fe(III) addition. However, the addition of 10 and 20 mg/L Fe(III) showed inhibitory effects on the growth and activity of anammox bacteria, which exhibited the lower relative abundance of Ca. Brocadia and unstable or even collapsed nitrogen removal performance. This study not only clarified the concentration range of Fe(III) that promoted and inhibited the enrichment of anammox bacteria, but also deepened our understanding of the functional and metabolic mechanisms underlying enhanced enrichment of anammox bacteria by Fe(III), providing a potential strategy to hasten the start-up of anammox from conventional activated sludge.

Efficient phosphate elimination from aqueous media by La/Fe bimetallic modified bentonite: Adsorption behavior and inner mechanism.

Nowadays, eutrophication problem in surface waterbodies has attracted specific attention. Herein, we reported facile synthesis and application of La/Fe engineered bentonite (LFB) for efficient phosphate elimination. Results indicated that bimetallic modified LFB composite could achieve efficient phosphate removal at pH 2-6, and satisfactory selectivity was implied by stable phosphate capturing within the interference of competing species (Cl-, NO3-, HCO3-, SO42-, F- and HA). Pseudo-second-order model could satisfactorily depict the kinetic behavior at different initial concentrations, indicating chemisorption of phosphate on LFB surface. Isotherm study suggested that phosphate adsorption behavior could be fitted well with Sips isotherm equation, indicating that both homogeneous monolayer adsorption and heterogeneous multilayer coverage of phosphate on LFB surface occurred within the investigated conditions. Adsorption thermodynamics implied the spontaneous and endothermic feature of phosphate loading on LFB composite. Characterization analysis confirmed successful La and Fe loading on bentonite, and electrostatic attraction and ligand exchange were the main adsorption mechanism. The high adsorption capacity, cost-effective feature and strong affinity towards phosphate demonstrated certain potential of as-prepared LFB composite for phosphate separation from eutrophic water.

Aerobic granulation and microbial community succession in sequencing batch reactors treating the low strength wastewater: The dual effects of weak magnetic field and exogenous signal molecule.

The application of magneto-biological effects in wastewater treatment has been brought under the spotlight recently. This work explored the dual effects of magnetic field (MF) and exogenous N-hexanoyl-l-homoserine lactone (C6-HSL) on activated sludge granulation. Results showed that exposure to MF and C6-HSL obviously accelerated the aerobic granulation process and promoted the secretion of extracellular polymeric substances, especially polysaccharides, humic acid-like substances, aromatic proteins, and tryptophan-like substrates. Illumina MiSeq sequencing results indicated that the introduction of MF and C6-HSL can increase the diversity and richness of microbial community without antagonism, and the biological basis for rapid granulation process in this study was the enrichment of slow-growing bacteria Candidatus_Competibacter. Besides, the overgrowth of filamentous bacteria Thiothrix could be suppressed due to the presence of MF, improving the stabilities of aerobic granular sludge. This study provides a new understanding of the MF and C6-HSL effects on rapid aerobic granulation when treating the low-strength wastewater.

Role of weak magnetic strength in the operation of aerobic granular reactor for wastewater treatment containing ammonia nitrogen concentration gradient.

Weak magnetic field (WMF) and aerobic granular sludge (AGS) technology were both robust technologies in wastewater treatments. In this study, the AGS characteristics and nutrient removal performances were all estimated at the load of 20 to 40 mg/L ammonia nitrogen (NH4+-N) and 0 to 40mT magnetic field. Results showed that 10mT was beneficial for keeping stable structure of granules when increasing NH4+-N load, accompanied with increasing protein (PN) secretion in EPS. Besides, all the total nitrogen (TN) removal rate under 10mT reached above 90%, while they were all less than 80% under other WMF strength when loading with 40 mg/L NH4+-N. Moreover, the simultaneous nitrification and denitrification (SND) efficiency could be enhanced by WMF of 10mT. Illumina MiSeq sequencing showed that NH4+-N load changed the bacterial richness and diversity when the magnetic strength was 10mT. And Candidatus_Competibacter was identified as the main functional genes for effective operation in this system.

Novel talc encapsulated lanthanum alginate hydrogel for efficient phosphate adsorption and fixation.

In the present work, talc (a low-cost clay) encapsulated salts alginate (TAL) beads were synthesized by cross-linking with lanthanum ion and tested for phosphate adsorption. Multiple methods were applied for the characterization of composites. The combined effect of talc and lanthanum improved phosphate removal performance of TAL beads. Factors such as talc content, La3+ concentration, adsorbent dosage, pH, co-existing ions (Cl-, NO3- and SO42-) were studied in batch experiments. The optimized TAL-7 beads exhibited satisfactory selectivity towards phosphate in the coexistence of competing anions and could remain efficient phosphate removal in the pH range of 4-6. The phosphate removal efficiency reached to 95% with a maximum uptake of 16.4 mg P/g obtained at the optimal pH 4. Further experiments suggested that Langmuir isotherm model and the pseudo-second-order kinetic model could well describe the phosphate adsorption process of TAL-7 beads. Moreover, TAL-7 beads exhibited superior phosphate fixation performance in the long-term experiment. The results from adsorption experiment and characterization analysis demonstrated that TAL-7 beads could be a cost-effective and promising biosorbent for phosphate adsorption and fixation in the aqueous environment.

A comprehensive comparison between non-bulking and bulking aerobic granular sludge in microbial communities.

Filamentous sludge bulking poses great threats to operational stability of aerobic granular sludge. Exploration of the microbial community aids knowledge of the causative factors to sludge bulking and guides directions for corresponding actions for prevention and controlling. Detailed changes of bacterial community within the non-bulking and bulking were performed and compared with a non-specific method through 1‰ (v/v) hydrogen peroxide (H2O2) addition. Results revealed that non-bulking/bulking granules maintained effective carbon and nitrogen removal, while bulking completely deteriorated enhanced biological phosphorus removal (EBPR). Excess extracellular polymeric substances (EPS) especially polysaccharide (PS) were directly linked with sludge bulking and abundant PS contributed to subsequent granular re-stability. Filamentous bulking dramatically altered the bacterial populations and 1‰ H2O2 effectively controlled bulking by eliminating causative filaments Singulisphaera and Thiothrix. Together, this study provides new insights into the non-bulking/bulking granules and could direct the prevention and control of filamentous bulking in aerobic granules.

Highly efficient removal of Cr(VI) and Cu(II) by biochar derived from Artemisia argyi stem.

In this work, a novel biochar was prepared from the Artemisia argyi stem at 300 °C (AS300), 450 °C (AS450), and 600 °C (AS600). The structural properties of these biochars were characterized with various tools. The sorption kinetic processes of Cr(VI) and Cu(II) onto these biochars were better described by the pseudo-second order. The sorption isotherm processes of Cr(VI) onto these biochars were better described by the Freundlich model while the adsorption processes of Cu(II) were consistent with the Langmuir model. Batch sorption experiments showed that AS600 had the maximum adsorption capacity to Cr(VI) and Cu(II) with 161.92 and 155.96 mg/g, respectively. AS600 was selected for the follow-up batch and dynamic adsorption experiments. Results showed that AS600 had larger adsorption capacity for Cr(VI) at lower pH while the larger adsorption capacity for Cu(II) was found at higher pH. The effect of ionic strength on the adsorption of Cu(II) by AS600 was greater than that on the adsorption of Cr(VI). Dynamic adsorption experiments showed that Cu(II) had a higher affinity for the adsorption sites on the AS600 compared with Cr(VI). The adsorption mechanisms mainly involved electrostatic attraction, ion exchange, pore filling, and chemical bonding effect. Graphical abstract.

Hydrodynamic shear force shaped the microbial community and function in the aerobic granular sequencing batch reactors for low carbon to nitrogen (C/N) municipal wastewater treatment.

The lab-scale aerobic granules process was applied for low carbon to nitrogen (C/N < 4) wastewater treatment under different hydrodynamic shear forces. Results revealed that aerobic granules exhibited strong adaptability and stability. The aerobic granules might adopt an extracellular polymeric substances (EPS) regulating mechanism to address the changes in operational conditions, especially through growing secretion of fluorescence protein. The hydrodynamic shear force determinedly shaped and regulated the diversity and structure of dominant microbial community, briefly, reduced aeration intensity with increased time led to higher microbial richness, lower diversity and evenness, and shifts of predominant microorganisms. Phylogenetic classification of the key functional groups including bacteria related to carbon and nutrients removal, EPS production and quorum sensing (QS) presented much more differences among the reactors subject to different conditions. Therefore, the present work adds insight into the comprehensive understanding of the effect of aeration induced hydrodynamic shear force on aerobic granules.

Natural sunlight induced rapid formation of water-born algal-bacterial granules in an aerobic bacterial granular photo-sequencing batch reactor.

Wastewater treatment by means of algal-bacterial granules has become a hot topic worldwide recently. Rapid granulation of algal-bacterial granules was achieved in an aerobic bacterial granular sequencing batch reactor (SBR) under natural sunlight exposure. Occurrence of abundant filamentous bacteria bridging the water-born algae, and overproduction of extracellular polymeric substances (EPS) (especially polysaccharides (PS), tryptophan & protein-like, and humic acid-like substances) were observed on the first 3 days, while the algae grew into the inner side of the granules and mature granules were obtained on day 7. The growth of the water-born algae slightly decreased the settleability, mean sizes of the granules, but stimulated the bioactivity significantly. Whereas, the biomass retention decreased before day 3, and got stable soon with the maturation period with symbiotic growth of algal-bacterial biomass. Illumina results revealed that the introduction of algae reduced the richness and diversity of bacterial community. Besides, few changes in structure and some compositions shifts in bacterial communities were found, while the predominant algae shifted from Diatomea to green algae Chlorophyceae. The possible mechanism for natural sunlight induced granulation of algal-bacterial granules was thus proposed based on the interactions between algae and bacteria.