Biological mechanism of alleviating membrane biofouling by porous spherical carriers in a submerged membrane bioreactor

Synthetic microbial community maintains the functional stability of aerobic denitrification under environmental disturbances: Insight into the mechanism of interspecific division of labor

Understanding how synthetic microbial community (SMC) respond to environmental disturbances is the key to realizing SMC engineering applications. Here, dibutyl phthalate (DBP) and levofloxacin (LOFX) were used as environmental disturbances to study their effects on the aerobic denitrification functional stability of SMC composed of Pseudomonas aeruginosa N2 (PA), Acinetobacter baumannii N1(AC) and Aeromonas hydrophila (AH). The results showed that aerobic denitrification efficiency could be maintained at about 93 % under DBP or LOFX disturbance, and interspecific communication was mainly carried out through N-butyryl-L-homoserine lactone (C4-HSL) and N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), correspondingly. DBP and LOFX induced the acceleration of tricarboxylic acid (TCA) cycle, which facilitated the energy flux and extracellular polymeric substances (EPS) production, thereby allowing SMC to adapt to disturbances. Under DBP disturbance, DBP stimulated phenazine-1-carboxylic acid production to accelerate electron transfer from the quinone pool to complex III, resulting in an increase in electron transfer activity. Up-regulation of complex I, complex III and heme synthesis genes under LOFX disturbance led to enhanced denitrification enzymes expression and electron transfer efficiency. SMC re-regulated different metabolic pathways to build metabolic networks to maintain normal metabolic activity under different disturbances. Overall, SMC maintained functional stability through the labor division in modulation of interspecific communication, formation of defensive barriers, promotion of energy flux, directional transfer of electron flux, and reconstruction of metabolic networks. DBP stimulated AH and PA to occupy functional dominance, while LOFX induced AC and PA to play a major role. The understanding of the stability mechanism under different environmental disturbances provides valuable guidance for stability maintenance and engineering applications of SMC.

Inoculation with Acinetobacter indicus CZH-5 in internal circulation airlift zeolite spheres sequencing batch reactor to augment simultaneous removal of nitrogen, phosphorus, and tetracycline

Inoculating functional bacterial strains is a cost-effective strategy for enhancing treatment of anaerobic digestion liquids in swine wastewater. This study systematically evaluated inoculation of heterotrophic nitrification aerobic denitrification strain Acinetobacter indicus CZH-5 in an internal circulation airlift zeolite sphere-based sequencing batch reactor (IR) for aerobic removal of nitrogen (N), phosphorus (P), and tetracycline (TEC). Inoculation with CZH-5 promoted secretion of quorum sensing signaling molecules, specifically N-acyl-homoserine lactones (C6-HSL and C10-HSL). These signaling molecules enhance quorum sensing and reinforce cooperation among functional bacteria. Under optimal conditions, average removal efficiencies of total nitrogen, total phosphate, and TEC were 92.8 %, 88.4 %, and 93.1 %, respectively. The removal performance in IR exceeded that of the control by 26 %-71 %. N removal involved complete nitrification-denitrification, while accumulated P was transformed into phosphate monoesters within biofilm. Metagenomic analysis identified Thauera and Acinetobacter as the dominant genera, and Acinetobacter indicus as predominant species. Inoculation enhanced microbial richness and diversity to improve system operational stability. The abundance of functional genes associated with N, P, and TEC transformations significantly increased compared to the control. This study aimed to investigate the characteristics and mechanisms of inoculating a heterotrophic nitrification aerobic denitrification strain into an aerated biofilm system for swine wastewater remediation.

Development of a novel membrane-based quorum-quenching microbial isolator for biofouling control: Process performance and microbial mechanism

Quorum quenching (QQ) can mitigate biofouling in membrane bioreactors (MBRs) by inhibiting cell-to-cell communication. However, it is difficult to maintain long-term QQ activity. Here, a novel microbial isolator composed of tubular microfiltration membranes was developed to separate QQ bacteria (Rhodococcus sp. BH4) from sludge. The time to reach a transmembrane pressure of 50 kPa was delayed by 69.55 % (p = 0.002, Student's t test) in MBR with QQ microbial isolator (MBR-Q), compared to that in the control MBR (MBR-C) during stable operation. The concentration of proteins in the extracellular polymeric substances of sludge was reduced by 20.61 % in MBR-Q relative to MBR-C. The results of the bacterial community analyses indicated less enrichment of fouling-associated bacteria (e.g., Acinetobacter) but a higher abundance of QQ enzymes in MBR-Q than in MBR-C. This environmentally friendly technique can decrease the cleaning frequency and increase the membrane lifespan, thus improving the sustainability of MBR technology.

Deciphering the potential role of quorum quenching in efficient aerobic denitrification driven by a synthetic microbial community

Low efficiency is one of the main challenges for the application of aerobic denitrification technology in wastewater treatment. To improve denitrification efficiency, a synthetic microbial community (SMC) composed of denitrifiers Acinetobacter baumannii N1 (AC), Pseudomonas aeruginosa N2 (PA) and Aeromonas hydrophila (AH) were constructed. The nitrate (NO3--N) reduction efficiency of the SMC reached 97 % with little nitrite (NO2--N) accumulation, compared to the single-culture systems and co-culture systems. In the SMC, AH proved to mainly contribute to NO3--N reduction with the assistance of AC, while PA exerted NO2--N reduction. AC and AH secreted N-hexanoyl-DL-homoserine lactone (C6-HSL) to promote the electron transfer from the quinone pool to nitrate reductase. The declined N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), resulting from quorum quenching (QQ) by AH, stimulated the excretion of pyocyanin, which could improve the electron transfer from complex III to downstream denitrifying enzymes for NO2--N reduction. In addition, C6-HSL mainly secreted by PA led to the up-regulation of TCA cycle-related genes and provided sufficient energy (such as NADH and ATP) for aerobic denitrification. In conclusion, members of the SMC achieved efficient denitrification through the interactions between QQ, electron transfer, and energy metabolism induced by N-acyl-homoserine lactones (AHLs). This study provided a theoretical basis for the engineering application of synthetic microbiome to remove nitrate wastewater.

Insight of the bio-cathode biofilm construction in microbial electrolysis cell dealing with sulfate-containing wastewater

Signaling molecules are useful in biofilm formation, but the mechanism for biofilm construction still needs to be explored. In this study, a signaling molecule, N-butyryl-l-Homoserine lactone (C₄-HSL), was supplied to enhance the construction of the sulfate-reducing bacteria (SRB) bio-cathode biofilm in microbial electrolysis cell (MEC). The sulfate reduction efficiency was more than 90% in less time under the system with C₄-HSL addition. The analysis of SRB bio-cathode biofilms indicated that the activity, distribution, microbial population, and secretion of extracellular polymers prompted by C₄-HSL, which accelerate the sulfate reduction, in particular for the assimilatory sulfate reduction pathway. Specifically, the relative abundance of acidogenic fermentation bacteria increased, and Desulfovibrio was co-metabolized with acidogenic fermentation bacteria. This knowledge will help to reveal the potential of signaling molecules to enhance the SRB bio-cathode biofilm MEC construction and improve the performance of treating sulfate-containing wastewater.

Ferruginibacter albus sp. nov., isolated from a mountain soil, and Mucilaginibacter robiniae sp. nov., isolated from a black locust flower, Robinia pseudoacacia

Two bacterial strains, designated KIS38-8T and F39-2T, were isolated from a mountain soil sample and a black locust flower (Robinia pseudoacacia) in Republic of Korea, respectively. The phylogenetic tree based on 16S rRNA gene sequences showed that strain KIS38-8T was classified into the genus Ferruginibacter with the highest sequence similarity to Ferruginibacter lapsinanis HU1-HG42T (96.6 %), and strain F39-2T was grouped into the genus Mucilaginibacter with the highest sequence similarity to Mucilaginibacter daejeonensis Jip 10T (97.6 %). Orthologous average nucleotide identity and digital DNA–DNA hybridization values between strain KIS38-8T and closely related Ferruginibacter strains were less than 72 and 19 %, respectively, while those values between strain F39-2T and closely related Mucilaginibacter strains were less than 73 and 21 %, respectively. The DNA G+C contents of strain KIS38-8T and F39-2T were 36.4 and 41.4 mol%, respectively. On the basis of the phenotypic and genotypic evidence, strains KIS38-8T and F39-2T are considered to represent novel species of the genus Ferruginibacter and Mucilaginibacter , respectively, for which the names Ferruginibacter albus sp. nov. (type strain KIS38-8T=KACC 17328T=NBRC 113101T) and Mucilaginibacter robiniae sp. nov. (type strain F39-2T=KACC 19733T=JCM 33062T) have been proposed.

Applications of submerged and staged membrane systems for pollutant removal from effluents and mechanism studies - a review

Membrane based filtration is one of the promising technologies for rehabilitation of wastewater streams for reuse and recycle. Many advancements have emerged with the use of novel materials and innovative integrated technologies. The present investigation focuses on the treatment methods based on submerged and stages systems of membranes for water purification. Ceramic, polymeric and mixed matrix type of membranes fabricated for specific type of effluents, their modification methods for accelerating the rejection efficiency, permeability, durability, stability and antifouling properties are detailed in this review. Graphene oxide is the most considered membrane material for adsorption purposes as it exhibits larger surface area, abundant functional groups contain oxygen and has good supply of ligands which is responsible in metal adsorption as it enhances electrostatic interaction by bonding metal ions with graphene oxide nanosheets. Energy derivation in terms of biogas production was also reported in some integrated methods. In many cases, embedded nanomaterial matrices yielded maximum efficiencies in both the submerged and staged operations. However, submerged type of membranes are reported more than the staged type due to simpler configuration with relatively lesser equipment, operational and maintenance issues. In treatment of a low strength wastewater, aluminum oxide based membrane in fluidized bed assembly was reported to yield promising results with reduced power requirement.