Energy uncoupling inhibits aerobic granulation

Formation of anaerobic granular sludge (AnGS) to treat high-strength perchlorate wastewater via anaerobic baffled reactor (ABR) system: Electron transfer characteristic, bacterial community and positive feedback mechanism

Anaerobic granular sludge (AnGS) was cultured to treat high-strength perchlorate (reaching to 4800 mg/L) wastewater by an anaerobic baffled reactor (ABR) system with five equal-volume compartments (C1-C5 compartments). Inoculated sludge completely granulated on day 104 with granule size of 0.50-0.75 mm and perchlorate removal efficiency reaching to 97% (influent perchlorate of 2000-4800 mg/L). The Cyclic voltammetry (CV) capacitance increased from 487.5, 465.8 and 407.8 μF to 576.5, 552.4, 549.6 μF in C1, C3 and C5 compartments of ABR system, respectively, suggesting the electron transfer capacity was enhanced under high-strength perchlorate stress. Meanwhile, adenosine triphosphate (ATP) value and electron transport system activity (ETSA) increased to 25.05, 22.87, 20.43 and 6.22, 4.87, 3.95 of C1, C3 and C5 compartments, respectively. The results suggested that high-strength perchlorate stress improved the microbial metabolic activity, which promoted secretion of extracellular polymeric substances (EPS). The more EPS could facilitate the formation and stability of AnGS under high-strength perchlorate stress. In addition, more reasonable metabolic division of labor in functional bacterial (Thauera and Comamonas) was beneficial to AnGS formation, which achieved high-strength perchlorate efficient removal. Finally, a positive feedback mechanism between AnGS formation and high-strength perchlorate removal was established through EPS, microbial metabolic activity and electron transfer characteristic in ABR system. However, excessive perchlorate (5800 mg/L) would exceed the treatment capacity of AnGS, which resulted in the deterioration of removal performance. This work provided an effective information for AnGS application to treat high-strength perchlorate wastewater.

Effects of interactions between quorum sensing and quorum quenching on microbial aggregation characteristics in wastewater treatment: A review

Due to the increasingly urgent demand for effective wastewater denitrification and dephosphorization systems, there is a need to improve the performance of existing biological treatment technologies. As a bacteria-level communication mechanism, quorum sensing (QS) synchronizes gene expression in a density-dependent manner and regulates bacterial physiological behavior. On this basis, the QS-based bacterial communication mechanism and environmental factors affecting QS are discussed. This paper reviews the influence of QS on sludge granulation, biofilm formation, emerging contaminants (ECs) removal, and horizontal gene transfer in sewage treatment system. Furthermore, the QS inhibition strategies are compared. Based on the coexistence and balance of QQ and QS in the long-term operation system, QQ, as an effective tool to regulate the growth density of microorganisms, provides a promising exogenous regulation strategy for residual sludge reduction and biofilm pollution control. This paper reviews the potential of improving wastewater treatment efficiency based on QS theory and points out the feasibility and prospect of exogenous regulation strategy. PRACTITIONER POINTS: The mechanism of bacterial communication based on QS and the environmental factors affecting QS were discussed. The application of QS and QQ in improving the sludge performance of biological treatment systems was described. The significance of QS and QQ coexistence in sewage treatment process was described.

Biodegradation of salicylic acid, acetaminophen and ibuprofen by bacteria collected from a full-scale drinking water biofilter

This study examined the biodegradation of two pharmaceuticals-acetaminophen, and ibuprofen, and one natural organic surrogate-salicylic acid, by bacteria seeded from backwash water collected from a full-scale biofiltration plant. The degradation was studied in the presence of oxygen. Complete removal of salicylic acid was observed in 27-66 h depending on the seasonality of the collected backwash water, while 90-92% acetaminophen removal was observed in more than 225 h. Ibuprofen demonstrated poor removal efficiencies with only 50% biodegradation after 230 h. Adenosine tri phosphate (ATP) in the reactor was found to be linked with the biodegradation rate. ATP was found to be correlated with oxygen uptake rate (OUR). ATP also had a correlation with each of extracellular polymeric substances (EPS), protein and polysaccharides. These results highlight the potential for increasing the biodegradation rates to achieve enhanced contaminant removal.

Biological-based control strategies for MBR membrane biofouling: a review

Membrane bioreactor (MBR) technology has been paid extensive attention for wastewater treatment because of its advantages of high effluent quality and minimized occupation space and sludge production. However, the membrane fouling is always an inevitable problem, which causes high operation and maintenance costs and prevents the wide use of MBR technology. The membrane biofouling is the most complicated and has relatively slow progress among all types of fouling. In recent years, many membrane biofouling control methods have been developed. Different from the physical or chemical methods, the biological-based strategies are not only more effective for membrane biofouling control, but also milder and more environment-friendly and, therefore, have been increasingly employed. This paper mainly focuses on the mechanism, unique advantages and development of biological-based control strategies for MBR membrane biofouling such as quorum quenching, uncoupling, flocculants and so on. The paper summarizes the up-to-date development of membrane biofouling control strategies, emphasizes the advantages and promising potential of biological-based ones, and points out the direction for future studies.

Effect of Fe3O4 nanoparticles exposure on the treatment efficiency of phenol wastewater and community shifts in SBR system

Increasing magnetic Fe₃O₄ nanoparticles (Fe₃O₄ NPs) application has aroused concern about its potential environmental toxicity. During acute and chronic exposure, key enzymes involved in phenol biodegradation were promoted at 0-600 mg/L Fe₃O₄ NPs, while were inhibited at 800 mg/L Fe₃O₄ NPs, correspondingly affected phenol degradation efficiency. Lactic dehydrogenase (LDH) increased when Fe₃O₄ NPs exceeded 600 mg/L, indicated the more severe cell rupture at high Fe₃O₄ NPs concentration. At the same Fe₃O₄ NPs concentration, the removal of EPS further inhibited key enzymes, decreased phenol degradation, and increased LDH, indicating that the existence of EPS relieved the adverse effects on microorganisms. Spectroscopic analysis showed that protein and polysaccharide associated bonds in EPS decreased at 0-600 mg/L Fe₃O₄ NPs, while increased when Fe₃O₄ NPs exceeded 600 mg/L, which was in accordance with EPS content. Biopolymer-degrading and phenol-degrading genera increased at 0-600 mg/L Fe₃O₄ NPs, while decreased at Fe₃O₄ NPs exceeded 600 mg/L, which conformed to EPS content and phenol degradation efficiency.

Enhanced treatment performance of phenol wastewater and membrane antifouling by biochar-assisted EMBR

Biochar-assisted EMBR (BC-assisted EMBR) was built to enhance treatment performance of phenol wastewater and membrane antifouling. BC-assisted EMBR significantly increased phenol degradation efficiency, owing to combined effects of biodegradation, adsorption and electro-catalytic degradation. Meanwhile, BC-assisted EMBR obviously mitigated membrane fouling. The coupling effect of BC and voltage led to the lower N-acyl-homoserine lactones (AHLs) and bound extracellular polymeric substances (bound EPS) contents around and on membrane surface. Protein (PN)/polysaccharide (PS) in bound EPS was decreased, led to the increase of negative charge and decrease of hydrophobicity of sludge, which abated bound EPS adsorption on membrane surface. Microbial community analyses revealed that the coupling effect of BC and voltage could enrich phenol-degraders (e.g., Comamonas), electron transfer genus (Phaselicystis), and biopolymer-degraders (Phaselicystis and Tepidisphaera) in BC-assisted EMBR and on its membrane surface, while decrease biofilm-former (e.g., Acinetobacter) and bound EPS-producer (Devosia), which was beneficial to promote phenol treatment and mitigate membrane fouling.

Impacts of long-term electric field applied on the membrane fouling mitigation and shifts of microbial communities in EMBR for treating phenol wastewater

The membrane antifouling and shifts of microbial communities of long-term electric field applied in MBR (EMBR) for treating phenol wastewater was systematically investigated. The increased voltage increased the phenol degradation rate and slowed down the TMP increase rate in EMBR (G1-G4: 1.65 × 10^-3-8.40 × 10^-4 Mpa/d), indicated the enhancement of phenol treatment and mitigation of membrane fouling. Decrease of protein (PN)/polysaccharide (PS) in EPS increased the negative charge and decreased the hydrophobicity of sludge, thus abated its adsorption on membrane surface. The decrease of AHLs concentration attributed to the electrolysis of AHLs by the electro-generated H₂O₂. Besides, the AHLs had significantly negative correlation with QQ bacteria Rhodococcus and Stenotrophomonas enrichment and positive correlation with QS bacteria Aeromonas decrease in EMBRs, suggesting that coupling effects of voltage and QQ bacteria degraded AHLs, thus decreased EPS content which was positively correlated with AHLs concentration. Biopolymer-degrading genera (Clostridium sensu strict etc.) increased in EMBR and on membrane surface, while biofilm-forming genera (Pseudomonas etc.) decreased on membrane surface. These resulted in EPS content decrease and membrane antifouling.

The regulation of N-acyl-homoserine lactones (AHLs)-based quorum sensing on EPS secretion via ATP synthetic for the stability of aerobic granular sludge

According to the relationship among microbial activity, quorum sensing (QS) and structural stability of aerobic granular sludge, the mechanism of QS regulation for microbial activity and granular stability was investigated in AGS process. Results showed that ATP content decreased sharply from 1.8 μmol/gVSS of stable granules to 0.8 μmol/gVSS of disintegrating granules, and the relative abundance of QS-activity microbes, Rhodobacter spp. and Xanthomonadaceae decreased in initially unstable granules compared with stable granules. The main AHLs were detected in this study, and C8-HSL, 3OHC8-HSL and 3OHC12-HSL decreased significantly when structure of granules changed from stability to disintegration. Accompanying with the decrease of AHLs level, the extracellular polymeric substances (EPS) content in initially unstable granules decreased sharply from 226.8 to 163.6 mg/gVSS with the ratio of extracellular protein to exopolysaccharide (PN/PS) decreasing from 3.6 to 2.2, despite EPS-secretion microbes enriched. The effect of QS on microbial activity was proved by AHL add-back study, results indicated that ATP and EPS content in sludge increased significantly (p < 0.05) with AHLs added, but EPS production was limited when ATP synthesis was disrupted. It was concluded that the AHLs-based QS favored the granular stability via the enhancement of ATP synthesis in microbes. This study provides a new perspective for QS regulation in aerobic granular sludge system, because the ATP regulated by QS could be the energy currency for cellular metabolism, such as nutrient removal, degradation of emerging pollutants, microbial growth and other aspects.

Impacts of applied voltage on EMBR treating phenol wastewater: Performance and membrane antifouling mechanism

The impacts of electric field applied in MBR (EMBR) for treating phenol wastewater and membrane antifouling mechanism were systematically investigated. Phenol degradation rate increased from 0 to 0.8 V/cm, while decreased from 0.8 to 1.75 V/cm, which significantly positively correlated with key enzymes. The membrane fouling rate of EMBR gradually slowed down with voltage increasing. The applied voltage significantly reduced EPS contents, and altered its compositions probably due to H₂O₂ oxidation, which were the major reasons for membrane antifouling. Red shift in UV-Vis spectrum at 210-220 nm and reduction of fluorescence emission intensity from tryptophan protein-like substances in EPS reduced the energy requirement for electrons transition of electron-donating groups with voltage increasing. Positively charged bond NH₂ decreased and negatively charged bond COO increased in EPS with voltage increasing, which led to the increase of absolute value of zeta potential and then remarkable augmented of electrostatic repulsion between sludge and membrane.

Assessment of the Sludge Reduction of the Metabolic Uncoupler 3,3',4',5-tetrachlorosalicylanilide (TCS) in Activated Sludge Culture

Batch experiments were completed to assess the sludge reduction of the metabolic uncoupler 3,3',4',5-tetrachlorosalicylanilide (TCS). The effects of various TCS concentrations on sludge yield were evaluated and the mechanisms associated with sludge reduction were assessed. We discovered that TCS addition resulted in a reduction in sludge. Furthermore, a low dose of TCS (≤3 mg/L) resulted in a slight reduction in the efficiency of the wastewater treatment system, while >3 mg/L TCS reduced matrix removal efficiency, with an especially remarkable inhibition effect on ammonia removal. An increase in TCS addition was associated with a gradual decrease in both the electron transport system (ETS) activity and the specific cellular ATP (SATP) in the TCS system. It was demonstrated that TCS plays an important role in metabolic uncoupling. However, with the addition of TCS, both contents and compositions were increased, and the protein content increased more than polysaccharide production in extracellular polymeric substances (EPS). At TCS concentrations of ≤3 mg/L, DNA content was stable, but it increased rapidly from 4.97 mg/L to 15.34 mg/L as the TCS concentration was elevated from 6 mg/L to 12 mg/L. This implied that the mechanisms of sludge reduction were different for different TCS concentrations, including uncoupling metabolism, maintenance metabolism and lysis-cryptic growth.

Effect of metabolic uncoupler, 2,4‑dinitrophenol (DNP) on sludge properties and fouling potential in ultrafiltration membrane process

Energy uncoupling technology was applied to the membrane process to control the problem of bio-fouling. Different dosages of uncoupler (2,4‑dinitrophenol, DNP) were added to the activated sludge, and a short-term ultrafiltration test was systematically investigated for analyzing membrane fouling potential and underlying mechanisms. Ultrafiltration membrane was used and made of polyether-sulfone with a molecular weight cut off (MWCO) of 150 kDa. Results indicated that low DNP concentration (15-30 mg/g VSS) aggravated membrane fouling because more soluble microbial products were released and then rejected by the membrane, which significantly increased cake layer resistance compared with the control. Conversely, a high dosage of DNP (45 mg/g VSS) retarded membrane fouling owing to the high inhibition of extracellular polymeric substances (proteins and polysaccharides) of the sludge, which effectively prevented the formation of cake layer on the membrane surface. Furthermore, analyses of fouling model revealed that a high dosage of DNP delayed the fouling model from pore blocking transition to cake filtration, whereas this transition process was accelerated in the low dosage scenario.

Critical review of fouling mitigation strategies in membrane bioreactors treating water and wastewater

The current research was an effort to critically review all approaches used for membrane fouling control in the membrane bioreactors treating water and wastewater. The first generation of antifouling methods tried to optimize operational conditions, or used chemical agents to control membrane fouling. Despite their positive impacts on the fouling mitigation, these methods did not provide a sustainable solution for the problem. Moreover, chemical agents may affect microorganisms in bioreactors and has some environmental drawbacks. The improved knowledge of membrane fouling mechanism and effective factors has directed the attention of researchers to novel methods that focus on disrupting fouling mechanism through affecting fouling causing bacteria. Employing nanomaterials, cell entrapment, biologically- and electrically-based methods are the latest efforts. The results of this review indicate that sustainable control of membrane fouling requires employing more than one single approach. Large scale application of fouling mitigation strategies should be the focus of future studies.

Exploiting extracellular polymeric substances (EPS) controlling strategies for performance enhancement of biological wastewater treatments: An overview

Extracellular polymeric substances (EPS) are present both outside of the cells and in the interior of microbial aggregates, and account for a main component in microbial aggregates. EPS can influence the properties and functions of microbial aggregates in biological wastewater treatment systems, and specifically EPS are involved in biofilm formation and stability, sludge behaviors as well as sequencing batch reactors (SBRs) granulation whereas they are also responsible for membrane fouling in membrane bioreactors (MBRs). EPS exhibit dual roles in biological wastewater treatments, and hence the control of available EPS can be expected to lead to changes in microbial aggregate properties, thereby improving system performance. In this review, current updated knowledge with regard to EPS basics including their formation mechanisms, important properties, key component functions as well as sub-fraction differentiation is given. EPS roles in biological wastewater treatments are also briefly summarized. Special emphasis is laid on EPS controlling strategies which would have the great potential in promoting microbial aggregates performance and in alleviating membrane fouling, including limitation strategies (inhibition of quorum sensing (QS) systems, regulation of environmental conditions, enzymatic degradation of key components, energy uncoupling etc.) and elevation strategies (enhancement of QS systems, addition of exogenous agents etc.). Those strategies have been confirmed to be feasible and promising to enhance system performance, and they would be a research niche that deserves further study.

Start-up of granule-based denitrifying reactors with multiple magnesium supplementation strategies

In the present work, the effect of Mg(2+) supplementation on the start-up of a denitrification process and the granulation of denitrifying sludge was investigated in three upflow anaerobic sludge blanket (UASB) reactors. The reactors R1 and R2 were continuously and intermittently, respectively, supplied with 50 mg L(-1) Mg(2+), whereas R0 was used as the control. The nitrogen loading rate (NLR) and organic loading rate (OLR) gradually increased, and extremely high values were obtained (36.0 kgN m(-3) d(-1) and 216.0 kgCOD m(-3) d(-1), respectively). Granulation occurred in R1 first, but the reactor capacities were comparable. Suffering from starvation, the R0-R2 performances were comparable. At the end of the experiment, the average diameter of the granules in R0, R1, and R2 were 1.67, 1.72 and 1.68 mm, respectively, and the settling velocities of the granules in R1 and R2 were 1.14-fold the speed of R0. The specific denitrifying activity (SDA) of the sludge from the reactors supplied with Mg(2+) was greater than the reactor without Mg(2+). Intermittent Mg(2+) supplementation was identified as the best choice to be utilized to cultivate denitrifying granules, which was consistent with kinetic analysis.

The effect of seed sludge type on aerobic granulation via anoxic-aerobic operation

The effects of two seed sludge types, namely conventional activated sludge (CAS) and membrane bioreactor sludge (MBS), on aerobic granulation were investigated. The treatment performances of the reactors were monitored during and after the granulation. Operational period of 37 days was described in three phases; Phase 1 corresponds to Days 1-10, Phase 2 (overloading conditions) to Days 11-27 and Phase 3 (recovery) to Days 28-37. Aerobic granules of 0.56 ± 0.23 to 2.48 ± 1.28 mm were successfully developed from both MBS and CAS. First granules appeared on Day 9 in both reactors, indicating that there was no difference between two seed sludge types in terms of the time period for granulation initiation. The results revealed that the granules developed from MBS performed better than CAS in terms of settleability, stability, biomass retention, adaptation, protection of granular structure at high loading rates (0.86 g N/L d and 3.92 g COD/L d) and low COD/TAN ratio (5). Granules of MBS were also found to be capable of providing better protection for nitrifiers at toxic free-ammonia concentrations (38-46 mg/L NH3-N), thus showing better treatment recovery than those of CAS.

Chemically inhibited ATP synthesis promoted detachment of different-age biofilms from membrane surface

This study investigated the response of different-age biofilms developed on membrane surface to a chemical uncoupler 3, 3', 4', 5-tetrachlorosalicylanilide (TCS). Results showed that adenosine triphosphate (ATP) dissipation caused by TCS would promote different-age biofilms detachment, whereas chemically inhibited cellular ATP synthesis subsequently suppressed autoinducer-2 (AI-2) and extracellular polymeric substances (EPS) production. The extent of biofilm detachment was found to be closely related to AI-2-regulated EPS contents of bacteria. It was revealed that energy dissipation induced biofilm detachability was controlled by AI-2 regulated cellular communication via AI-2-mediated EPS secretion. This study would lead to a new cleaning strategy of biologically fouled membrane.

The role of nitrite and free nitrous acid (FNA) in wastewater treatment plants

Nitrite is known to accumulate in wastewater treatment plants (WWTPs) under certain environmental conditions. The protonated form of nitrite, free nitrous acid (FNA), has been found to cause severe inhibition to numerous bioprocesses at WWTPs. However, this inhibitory effect of FNA may possibly be gainfully exploited, such as repressing nitrite oxidizing bacteria (NOB) growth to achieve N removal via the nitrite shortcut. However, the inhibition threshold of FNA to repress NOB (∼0.02 mg HNO2-N/L) may also inhibit other bioprocesses. This paper reviews the inhibitory effects of FNA on nitrifiers, denitrifiers, anammox bacteria, phosphorus accumulating organisms (PAO), methanogens, and other microorganisms in populations used in WWTPs. The possible inhibition mechanisms of FNA on microorganisms are discussed and compared. It is concluded that a single inhibition mechanism is not sufficient to explain the negative impacts of FNA on microbial metabolisms and that multiple inhibitory effects can be generated from FNA. The review would suggest further research is necessary before the FNA inhibition mechanisms can be more effectively used to optimize WWTP bioprocesses. Perspectives on research directions, how the outcomes may be used to manipulate bioprocesses and the overall implications of FNA on WWTPs are also discussed.

Control and cleaning of membrane biofouling by energy uncoupling and cellular communication

This study investigated possible biological control of membrane biofouling and membrane cleaning by disrupting energy metabolism of microorganisms. Results showed that 2,4-dinitrophenol (DNP), a typical uncoupler, could not only significantly inhibit membrane biofouling but also enhance biofilm detachment from nylon membrane. Inhibited ATP synthesis by a chemical uncoupler resulted in lowered production of autoinducer-2 (AI-2). The standard dead-end microfiltration tests further confirmed that the reduced AI-2 was positively correlated to the reduced fouling resistance of nylon membranes. It appears that inhibition of energy metabolism would be a promising alternative for control and cleaning of membrane biofouling.

Development of denitrifying granules in sequencing batch reactors

This study investigated characteristics of denitrifying granules developed in sequencing batch reactors (SBRs) run at different cycle times. The complete denitrification was achieved in the denitrifying granular sludge SBRs. Results showed that the mean size and settleability of denitrifying granules were inversely related to the SBR cycle time, i.e., bigger and faster-settling denitrifying granules were obtained at a shorter cycle time. Meanwhile, a higher initial denitrifying granulation rate was observed at a shorter cycle time, indicating that the shorter cycle time would favor rapid denitrifying granulation. It was found that the content of extracellular polysaccharides in biomass almost remained unchanged in the course of denitrifying granulation, however a substantial increase in the content of extracellular proteins was recorded, i.e. denitrifying granulation would be more related to extracellular proteins instead of polysaccharides. Furthermore, denitrifying granules cultivated at the shorter cycle time exhibited higher mechanical strength which was found to be determined by cell surface charge density. This study offer insights on the characteristics of denitrifying granules, which indeed are essential for actual application of denitrifying granular sludge bioreactor for nitrogen removal from wastewater.

Control of microbial attachment by inhibition of ATP and ATP-mediated autoinducer-2

In this study, 2,4-dinitrophenol (DNP), a typical chemical uncoupler, was employed to investigate the possible roles of ATP and autoinducer-2 (AI-2) of suspended microorganisms in attachment onto nylon membrane and glass slide surfaces. Results showed that DNP could disrupt ATP synthesis, subsequently led to a reduced production of AI-2 which is a common signaling molecule for cellular communication. Attachment of suspended microorganisms exposed to DNP was significantly suppressed as compared to microorganisms without contact with DNP. These suggest that an energized state of suspended microorganisms would favor microbial attachment to both nylon membrane and glass slide surfaces. The extent of microbial attachment was found to be positively related to the AI-2 content of microorganisms. This study offers insights into the control of biofouling by preventing initial microbial attachment through inhibition of energy metabolism.