Mixed Liquor Research Articles

A new efficient paradigm of energy and resource recovery from sewage: AnMBR treating chemically pre-precipitated concentrate in sidestream

Urged by the requirement for sustainable development, the recovery of energy and resources from sewage is imperative. In this study, a lab-scale anaerobic membrane bioreactor (AnMBR) treating chemically pre-concentrated real sewage with a high content of carbon, phosphorus, and iron in sidestream was established, and its performance at organic loading rate (OLR) varied from 0.67 to 2 g-COD/(L⋅d) was assessed comprehensively. When OLR ≤ 1.33 g-COD/(L⋅d), it achieved high COD removal (∼99 %), and around 60 % of the total influent COD was converted to methane (0.21 L-CH4/g-CODinf). Gaseous methane accounted for up to 95 % of the biogas. Only 1.5 % of yield methane was lost in permeate, far less than the dissolved methane in AnMBR treating sewage in mainstream. Considerable phosphorus (85 %-98 %) was retained in AnMBR. When OLR reached 2 g-COD/(L⋅d), the treatment performance was exacerbated with volatile fatty acids accumulation. The sludge flocs disintegrated with smaller particle sizes. The microbial community of mixed liquor shifted towards that of the pre-concentrated sewage. A specific relative abundance of Epsilonbacteraeota (a biomarker in this research) can be set as a warning of overloading. Compared with AnMBRs treating sewage in the mainstream, this sidestream AnMBR provided a new perspective and paradigm for treating sewage in an energy-efficient, resource-recovered, and low-carbon way.

Enhanced methanogenic degradation and membrane fouling associated with protein-EPS by extending sludge retention time in a high-solid anaerobic membrane bioreactor treating concentrated organic sludge

The improvement of organic sludge destruction efficiency and methanogenic performance is a key concern during anaerobic digestion toward maximum energy recovery. In this study, a high-solid anaerobic membrane bioreactor (AnMBR) was operated continuously for the treatment of organic sludge from Japanese small-scale collective wastewater treatment facility (Johkasou), and digestion efficiency was enhanced by the optimizing solid retention time (SRT). Degradation efficiency of the substrate improved from 36 % to 52 % and the biogas yield was enhanced from 0.37 to 0.51 L/g-VSfed when the SRT was extended from 30 to 60 d. The net energy yield of AnMBR at SRT 60 days was 9.83 kJ/g-VSfed, and the corresponding energy sufficiency ratio was 181 %, indicating that SRT extension could enhance substrate destruction with significant energy recovery potential. However, a long SRT is characterized by high mixed liquor total solids (MLTS), small particle size, high extracellular polymeric substances content, and poor filterability, which exert detrimental effects on membrane operation. Membrane fouling was effectively controlled by regulating the flux at a sustainable rate. The low fouling region and transition region of operating flux were determined as 0.21–4.6 L/m2/h (LMH) and 1.5–5.7 LMH, respectively, when MLTS was 25–50 g/L, and the main contributors to membrane fouling were high protein fractions and small sludge flocs. The current study proposes a promising method to promote digestion efficiency and provided adequate guidance for membrane operation at super-high MLTS by presenting practical engineering applications of AnMBRs in solid waste treatment.

Pilot study on ceramic flat membrane bioreactor in treatment of coal chemical wastewater

Some toxic and refractory pollutants in coal chemical wastewater can penetrate the biochemical treatment systems and cause high concentrations of suspended solids in the effluent, which may obstruct the subsequent advanced treatment. In this project, a submerged ceramic plate membrane system was integrated to the last oxic corridor of an existing multistage anoxic/oxic tank. In the ceramic flat membrane bioreactor, the influent chemical oxygen demand (COD) was 102.24–178.88 mg/L, with a removal ratio of approximately 30%. The NH3–N concentration in the effluent was relatively stable with an average value of 1.76 mg/L. The turbidity of the effluent was in the range of 0.235–0.852 NTU and was stable below 1 NTU. A flux of 30 L m−2·h−1 could meet the requirements of the pilot test. A gas-water ratio of 50:1 was found optimal. When the concentration of mixed liquor suspended solids (MLSS) was >3769 mg/L, the extracellular polymeric substance in the mixed solution was utilized by microorganisms as a substrate. High MLSS decreased membrane fouling rate. NaClO backwashing can effectively remove pollutants without adversely affecting the treatment efficiency of membrane bioreactors.

Insights into the adsorption of perfluoroalkyl substances (PFASs) on excess sludge from an on-site leachate treatment plant

The disposal and reduction of excess sludge is one of the most challenging aspects of wastewater treatment. Recycling excess sludge as functional materials is an innovative approach that has garnered broad attention, as it can address environmental concerns and reduce the consumption of valuable materials. However, this approach is still challenging due to the low mixed liquor suspended solids in sewage treatment plants and the high synthesis costs involved. In this study, we proposed the application of excess sludge from an on-site leachate treatment plant for the efficient removal of perfluoroalkyl substances (PFASs) from wastewater. A simple thermal treatment was conducted and the obtained sludge-based adsorbents enable effective PFASs removal. Through the use of low field nuclear magnetic resonance and structural characterizations, results demonstrated that denitrifying sludge had higher hydrophobicity and specific surface area (30.85 m2/g) than nitrifying sludge, resulting in enhanced PFASs adsorption capacity and initial adsorption rates. Kinetic and isotherm simulations indicated that the adsorption was efficient and controlled by surface and intraparticle diffusion. Characterization and regulation results showed that the adsorption was dominated by hydrophobic and electrostatic interactions. These findings suggest a promising recycling approach of excess sludge while elucidating the dominant mechanisms involved.

The effect of fine grits and fine debris concentrations on the MLVSS/MLSS ratio of an activated sludge system

This study embarks on an explorative investigation into the effects of typical concentrations and varying particle sizes of fine grits (FG, the involatile portion of suspended solids) and fine debris (FD, the volatile yet unbiodegradable fraction of suspended solids) within the influent on the mixed liquor volatile suspended solids (MLVSS)/mixed liquor suspended solids (MLSS) ratio of an activated sludge system. Through meticulous experimentation, it was discerned that the addition of FG or FD, the particle size of FG, and the concentration of FD bore no substantial impact on the pollutant removal efficiency (denoted by the removal rate of COD and ammonia nitrogen) under constant operational conditions. However, a notable decrease in the MLVSS/MLSS ratio was observed with a typical FG concentration of 20 mg/L, with smaller FG particle sizes exacerbating this reduction. Additionally, variations in FD concentrations influenced both MLSS and MLVSS/MLSS ratios; a higher FD concentration led to an increased MLSS and a reduced MLVSS/MLSS ratio, indicating FD accumulation in the system. A predictive model for MLVSS/MLSS was constructed based on quality balance calculations, offering a tool for foreseeing the MLVSS/MLSS ratio under stable long-term influent conditions of FG and FD. This model, validated using data from the BXH wastewater treatment plant (WWTP), showcased remarkable accuracy.

Enhancing anammox bacteria enrichment in integrated fixed-film activated sludge partial nitritation/anammox process via floc retention control

A promising technology for partial nitritation/anammox (PN/A) processes to treat ammonium wastewater is integrated fixed-film activated sludge (IFAS). For practical applications, achieving efficient enrichment of anammox bacteria (AnAOB) remains a challenge. In this study, membranes were temporarily used to separate solid and liquid components to induce changes in the mixed liquor suspended solids of the flocs. With membrane separation, AnAOB proliferated rapidly with a seven-fold increase in the maximum specific growth rate (μ) (from 0.009 to 0.072 d−1) and a three-fold increase in the nitrogen removal rate (from 0.91 to 3.20 kg N/(m3·d)). Moreover, microbial community analysis showed significant changes in bacterial species richness and diversity with and without membrane separation. Overall, the regulation of flocs significantly influenced the microbial community structure of both flocs and biofilms leading to improved nitrogen removal efficiency in the IFAS-PN/A system.

Application of Anaerobic-Aerobic Combined Bioreactor in Phosphorus Removal

A two-stage anaerobic-aerobic sequencing reactor system was developed in order to enhance the removal of biological phosphorus in the sequencing of combined reactors. Combining both aerobic and anaerobic designs in one reactor improved the efficiency and reduced the construction and operating costs. The combination of an upflow anaerobic fixed bed (UAFB) and a floating activated sludge aerobic bioreactor was designed with respective Kaldnes packing ratios of 90 and 30% for the anaerobic and aerobic sections. The controlled parameters were pH levels within a neutral range, a temperature of 37°C, mixed liquor suspended solids (MLSS) of 1220 and 1030 mg/L for the aerobic and anaerobic sections, respectively, and an attached growth that was equal of 743 and 1190 mg/L for the aerobic and anaerobic sections, respectively. Tests were conducted for three different initial phosphorus concentrations (12.8, 32.0, and 44.8 mg/L), two different volumes for each section, and four chemical oxygen demands (CODs) (500, 1000, 1200, and 1400 mg/L). The results demonstrated that, generally, the phosphorus removal in the anaerobic section fell significantly by increasing the inlet COD, and the maximum removal occurred at COD = 500 mg/L. More than 90% of the phosphorus was removed in the aerobic section at COD = 500 mg/L. In other words, the best performance of the reactor was when the ratio of the COD : N : P = 100 : 5 : 2, composition of phosphorus in industrial wastewater.

Biological degradation of leachate from household and similar waste pre‐treated by electro‐Fenton process

AbstractThis study's purpose is to confirm the feasibility and performance of the combination between ‘electro‐Fenton’ process and the ‘activated sludge’ biological process, in order to remove the organic matter contained in ‘intermediate’ leachates from technical landfill centre of Hamici (Algiers). This leachate was initially electrochemically pre‐treated until the ratio of BOD5/chemical oxygen deman (COD) = 0.41, then an optimization of the parameters significantly influencing the biological degradation was carried. The results obtained after 13 h of biological treatment show the removal of 97% of the initial COD, with a mixed liquor composed of 700 mL of pre‐treated leachate and 300 mL of activated sludge, a dissolved oxygen concentration of 3.5 mg O2/L and a pH of 7, which allows the effluent to discharge directly into the environment. The conclusions of this work are promising because it was demonstrated that if the operating parameters are well controlled concerning these treatments, its sequence and the referred pre‐treatment, the treatment efficiency is very high to the point of direct discharge of the leachate. However, in future studies, the combination of the both processes should be more explored in order to reduce the treatment time and to scale‐up the process.

Exposure of the static magnetic fields on the microbial growth rate and the sludge properties in the complete-mix activated sludge process (a Lab-scale study)

BackgroundIn this study, the effect of static magnetic fields (SMFs) on improving the performance of activated sludge process to enhance the higher rate of microbial growth biomass and improve sludge settling characteristics in real operation conditions of wastewater treatment plants has been investigated. The effect of SMFs (15 mT), hydraulic retention time, SRT, aeration time on mixed liquor suspended solids (MLSS) concentrations, mixed liquor volatile suspended solids (MLVSS) concentrations, α-factor, and pH in the complete-mix activated sludge (CMAS) process during 30 days of the operation, were evaluated.ResultsThere were not any differences between the concentration of MLSS in the case (2148.8 ± 235.6 mg/L) and control (2260.1 ± 296.0 mg/L) samples, however, the mean concentration of MLVSS in the case (1463.4 ± 419.2 mg/L) was more than the control samples (1244.1 ± 295.5 mg/L). Changes of the concentration of MLVSS over time, follow the first and second-order reaction with and without exposure of SMFs respectively. Moreover, the slope of the line and, the mean of α-factor in the case samples were 6.255 and, − 0.001 higher than the control samples, respectively. Changes in pH in both groups of the reactors were not observed. The size of the sluge flocs (1.28 µm) and, the spectra of amid I' (1440 cm−1) and II' (1650 cm−1) areas related to hydrogenase bond in the case samples were higher than the control samples.ConclusionsSMFs have a potential to being considered as an alternative method to stimulate the microbial growth rate in the aeration reactors and produce bioflocs with the higher density in the second clarifiers.

Study on the formation process and mechanism of aerobic granular sludge in the sequencing batch biofilter granular reactor.

Sequencing batch biofilter granular reactor (SBBGR) is a promising wastewater treatment technology owing to its low sludge yield and good toxicity tolerance. However, little attention has been paid to the formation process and mechanism of aerobic granular sludge in SBBGR. This study systematically investigated the formation process and mechanism of aerobic granular sludge in an SBBGR to provide a theoretical basis for optimizing the culture of aerobic granular sludge. Aerobic granular sludge with good performance was successfully cultivated after 40 days of incubation using synthetic wastewater as feed: the mixed liquid suspended solids and mixed liquor volatile suspended solids increased from 3.85 and 1.85 g/L to 31.38 and 24.74 g/L respectively, and the COD, TN, and TP removal efficiencies were 91.21%, 84.99%, and 58.14%, respectively. The experimental results showed that Amoebacteria and Bacteroides played an important role in the formation of aerobic granular sludge, filamentous bacteria acted as a three-dimensional skeleton surrounded by filling bacilli and rod-shaped bacteria, and proteins played a dominant role in promoting granulation during the culture process.

Saline wastewater treatment by bioelectrochemical process (BEC) based on Al-electrocoagulation and halophilic bacteria: optimization using ANN with new approach

ABSTRACT In the present study, a bioelectrochemical reactor (BEC) was utilized to treat two types of real saline produced water (PW). BEC was designed based on the combination of electrocoagulation (EC) process with halophilic microorganisms, and it was assessed in terms of biodegradation of hydrocarbons. The effects of various operating parameters including the current density, electrical contact time (On/Off), hydraulic retention time (HRT), and total dissolved solids (TDS) at different levels on the chemical oxygen demand (COD) removal efficiency, settleability, and performance of isolated halophilic microorganisms were examined. Additionally, a novel neural network (ANN) approach modelling using adaptive factors was used to predict and optimize the effects and interactions between operating parameters during BEC process by predicting complicated mechanisms and variations associated with microorganisms. In addition, a new algorithm was developed for the sensitivity analysis to achieve the optimum operating conditions and obtain maximum efficiency in COD removal, sludge volume index (SVI), mixed liquor suspended solids (MLSS), and specific electrical energy consumption (SEEC), simultaneously. BEC was found to be significantly more effective at removing most hydrocarbons, particularly pristine and phytane. In addition, the results showed a significant improvement in settling ability of the biological flocs with average SVI of 91.5 mL/g and a size of 178.25 μm using BEC. Based on estimated operating costs and energy consumption, BEC was more cost-effective and efficient than other bioelectrochemical systems.

Investigation of a membrane bioreactor's performances in treating sunflower oil refinery wastewater containing high oleic acid at different SRTs.

This study investigated the MBR performance, sludge morphology, and membrane fouling potential in treating sunflower oil refinery wastewater containing high oleic acid at three different SRTs of 10days, 40days, and infinite. The analysis of mixed liquor morphology including sludge volume index, PSD, EPS, and SMP showed that the sludge flocs compressibility and bioflocculation considerably improved at 40-days SRT. Additionally, at this SRT, the mixed liquor O&G, COD, and SMP accumulation were low, and the microbial activity and COD removal were enhanced. The gas chromatography/mass spectrometry analysis results confirmed the formation of three different new compounds related to non-readily biodegradable recalcitrant oily compounds and SMP at all SRTs. The analysis of mixed liquor EPS, PSD, SMP, and effluent COD at three different SRTs suggests that under the industrial conditions of MBR operation treating SORW with high oleic acid, the optimal operating conditions are predicted to be at 40-days SRT.

Selective leaching of V, W and recycling of TiO2 carrier from waste V2O5-WO3/TiO2 catalysts by mixed alkali liquor

Recovery of selective catalytic reduction (SCR) denitrification catalysts is important to reduce costs and environmental pollution. To recover and reuse the metal resources in the waste V2O5 - WO3/TiO2 catalyst, a mixed alkaline leaching system of NH3·H2O and sodium compounds was used. The method keeps the carrier composition and structure unchanged while achieving the separation of V and W. The effects of three additives, NaOH, Na2CO3 and NaCl, were investigated after determining the optimum leaching concentration of NH3·H2O at 6.0 mol‧L−1. The results showed the most superior leaching efficiency of V and W in NH3·H2O - NaOH solution. Next, the effects of additive concentrations and process parameters on the leaching of V and W were systematically investigated. Under optimum leaching conditions, 77.47%V and 47.7%W were leached without destroying the carrier. Moreover, this method showed similar separation of valuable metals from different components of waste catalysts, demonstrating its versatility. Meanwhile, the TiO2 carriers with undamaged structure can be directly prepared as new denitrification catalysts. Finally, the comprehensive utilization of 92.84%W, 91.94%V and 92.17%Ti resources in the waste denitrification catalyst is realized. Overall, the method may be an environmentally friendly solution for resource recovery of waste SCR catalysts.

Superior performance of a membrane bioreactor through innovative in-situ aeration and structural optimization using computational fluid dynamics.

The optimization of membrane bioreactors (MBRs) involves a critical challenge in structural design for mitigation of membrane fouling. To address this issue, a three-dimensional computational fluid dynamics (CFD) model was utilized in this study to simulate the hydrodynamic characteristics of a flat sheet (FS) MBR. The optimization of the membrane module configuration and operating conditions was performed by investigating key parameters that altered the shear stress and liquid velocity. The mixed liquor suspended solids (MLSS) concentration was found to increase the shear stress, leading to a more uniform distribution of shear stress. By optimizing the appropriate bubble diameter to 5mm, the shear stress on the membrane surface was optimized with relatively uniform distribution. Additionally, extending the side baffle length dramatically improved the uniformity of the shear stress distribution on each membrane. A novel in-situ aeration method was also discovered to promote turbulent kinetic energy by 200 times compared with traditional aeration modes, leading to a more uniform bubble streamline. As a result, the novel in-situ aeration method demonstrated superior membrane antifouling potential in the MBR. This work provides a new approach for the structural design and optimization of MBRs. The innovative combination of the CFD model, optimization techniques, and novel in-situ aeration method has provided a substantial contribution to the advancement of membrane separation technology in wastewater treatment.

Enhanced nutrients removal and microbial mechanisms in a pilot-scale anaerobic-oxic-anoxic (A/O/A) system: Synergistic roles of denitrifying polyphosphate accumulating organisms and endogenous denitrifiers

The realization of low-cost and high-standard nutrients removal are not acquired effectively in conventional pre-denitrification biological nitrogen removal processes (e.g., anaerobic/anoxic/oxic (A/A/O) process) for the treatment of domestic sewage. In this study, a pilot-scale bioreactor system based on the synergism of denitrifying phosphorus removal (DPR) and endogenous denitrification (ED) was proposed for advanced nutrients removal, which was operated under alternating anaerobic/oxic/anoxic (A/O/A) mode with no extracellular carbon source in the anoxic stage. The results showed that A/O/A and A/A/O systems were successfully established and operated in four stages with different mixed liquor suspended solid (MLSS, I: 3.32 ± 0.25 g/L, II: 5.89 ± 0.94 g/L, III: 8.66 ± 0.51 g/L, IV: 9.11 ± 5.72 g/L). Compared with the A/A/O system, the A/O/A system showed significantly higher nitrogen and phosphorus removal effectiveness within hydraulic retention time of 10 h. At MLSS of 8.66 ± 0.51 g/L, the A/O/A system could achieve simultaneously efficient removal of COD (91.47% ± 2.06%, 2.97 ± 0.26 mg COD/(g MLSS·h)), NH4+-N (97.27% ± 1.23%, 0.37 ± 0.06 mg NH4+-N/(g MLSS·h)), TN (89.94% ± 1.47%, 0.45 ± 0.03 mg TN/(g MLSS·h)), and PO43--P (96.67% ± 0.88%, 0.04 ± 0.01 mg PO43--P/(g MLSS·h)), and the effluent concentrations of COD, NH4+-N, TN, and PO43--P were 24.0 ± 3.1, 0.9 ± 0.4, 4.4 ± 0.6, and 0.13 ± 0.03 mg/L, respectively. In addition, microbial community results indicated that denitrifying polyphosphate accumulating organisms and endogenous denitrifiers synergistically enhanced the nutrients removal capacity in the A/O/A system. Overall, this work provides new insight for further scaling and optimization of the A/O/A system.

Hospital wastewater treatment coupling electrochemical coagulation and activated sludge process

Abstract Dual treatment of raw hospital wastewater (RHWW) is investigated by coupling electrochemical coagulation (ECC) with the activated sludge process (ASP) to achieve the goal of partial mineralization and reclaim quality water. The quality parameters of focus were chemical oxygen demand (COD), color, mixed liquor suspended solids (MLSS), total dissolved solids (TDS), chloride, total alkalinity, and fecal coliform. The initial ECC process with short hydraulic retention time (HRT) could remove 75–82% of the insoluble constituents in <60 min, while the HRT for ASP was >7–8 h. The combined ECC + ASP hybrid treatment process showed effective removal of COD, color, TDS, and fecal coliform by 98.5, 99.6, 83.1, and 97.9%, respectively, from its initial values of 4,000, 2,200, 77, and 2,400 MPN/100 mL, respectively. By coupling ECC and ASP, both the insoluble and soluble pollutants/contaminants in the RHWW were removed effectively. The ECC–ASP dual treatment offers a small energy and spatial footprint for mineralizing RHWW.

Assessment of Wastewater Treatment Plant Upgrading with MBR Implementation.

Modernization of wastewater treatment plants is usually caused by their significant wear and changes in the flow rate and concentration of pollutants. If there is no initial data on the flow or pollution, their determination by calculation is required, which may lead to an increase in concentration. Within the study, the modernization of treatment facilities was estimated under conditions of reduced flow and increased pollution concentration. Calculations were carried out both manually and using the CapdetWorks software package. The focus was on secondary treatment facilities as the main element of the municipal wastewater treatment plant within their upgrade from only organic pollutants removal (plug-flow reactor) to removal of both organic pollutants and nutrients (technology of the University of Cape Town). The calculations of tank volumes have shown that the concentration of pollutants has a much greater impact on them than the change in flow, especially when improvement in the treatment quality is required. The study revealed that membrane sludge separation allows tanks to be reduced in volume by 1.5-2.5 times (depending on the value of mixed liquor suspended solids) in comparison with gravity separation, which means smaller capital costs. However, membrane application requires significant energy costs for membrane aeration. For the initial data of the study, the specific energy costs for aeration before the upgrade, after the upgrade (gravity separation), and after the upgrade (membrane separation) were 0.12 kWh/m3, 0.235 kWh/m3, and 0.3 kWh/m3, respectively. If the membrane lifetime is 10 years, membrane costs were determined to be 10-15% of the energy costs for aeration.

A Hybrid Ultrasonic Membrane Anaerobic System (UMAS) Development for Palm Oil Mill Effluent (POME) Treatment

The high chemical oxygen demand (COD) and biochemical oxygen demand (BOD) levels in palm oil mill effluent (POME) wastewater make it an environmental contaminant. Moreover, conventional POME wastewater treatment approaches pose economic and environmental risks. The present study employed an ultrasonic membrane anaerobic system (UMAS) to treat POME. Resultantly, six steady states were procured when a kinetic assessment involving 11,800–21,700 mg·L−1 of mixed liquor suspended solids (MLSS) and 9800–16,800 mg·L−1 of mixed liquor volatile suspended solids (MLVSS) was conducted. The POME treatment kinetics were explained with kinetic equations derived by Monod, Contois and Chen and Hashimoto for organic at loading rates within the 1–11 kg·COD·m−3·d−1 range. The UMAS proposed successfully removed 96.6–98.4% COD with a 7.5 day hydraulic retention time. The Y value was 0.67 g·VSS/g·COD, while the specific micro-organism decay rate, b was 0.24 day−1. Methane (CH4) gas production ranged from 0.24 to 0.59 litres per gram of COD daily. Once the initial steady state was achieved, the incoming COD concentrations increased to 88,100 mg·L−1. The three kinetic models recorded a minimum calculated solids retention time of 12.1 days with maximum substrate utilization rate, K values ranging from 0.340 to 0.527 COD·g−1·VSS·d−1 and maximum specific growth rate, µmax from 0.248 to 0.474 d−1. Furthermore, the solids retention time (SRT) was reduced from 500 to 12.1 days, resulting in a 98.4% COD level reduction to 1400 mg·L−1.

Enhancement of nutrient removal in an activated sludge process using aerobic granular sludge augmentation strategy with ammonium-based aeration control

To enhance nutrient removal from low-strength municipal wastewater in a continuous-flow activated sludge (CFAS) process using aerobic granular sludge (AGS) augmentation strategy, a pilot-scale demonstration was configured with a mainstream reactor (anaerobic/aerobic process) and a sidestream sequencing batch reactor for AGS production. The aeration of the mainstream reactor was controlled based on dissolved oxygen (DO) and ammonium concentrations during Phases I and II–III, respectively. During Phase III, an anoxic zone was created in the mainstream aerobic tank. Throughout the demonstration period, excellent sludge settleability in the mainstream reactor (SVI30 ≤ 80 mL g−1) under long sludge retention time conditions (≥12 d) allowed the maintenance of a high mixed liquor suspended solids concentration (≥3000 mg L−1). The total nitrogen (TN) removal ratio improved significantly during Phases II and III (49.3 ± 4.1% and 50.1 ± 10.2%, respectively) compared to Phase I (43.2 ± 5.5%). Low DO concentration (< 0.5 mg L−1) by the ammonium-based aeration tended to increase the simultaneous nitrification and denitrification efficiency (> 40%), enhancing TN removal (> 50%). The reduction of DO and nitrate concentrations in the returning sludge liquor can stabilize phosphorus removal (approximately 80% of the 25th percentile). In addition, the aeration efficiency during Phase III decreased by 26–29% compared to Phase I. These results suggest that the introduction of ammonium-based aeration control to the CFAS using the AGS augmentation strategy could contribute to superior sewerage treatment, including nutrient removal and a low carbon footprint.

Does quorum quenching matter to microbial community dynamics in long-term membrane bioreactor operation?

Quorum quenching (QQ) has effectively prevented biofouling in membrane bioreactors (MBRs) employing isolated QQ bacterial strains. However, the influence of QQ on the microbial population still needs to be fully understood. This research aims to analyze the microbial population in MBRs over an extended period (>250 days) under different conditions, such as varying aeration intensities and doses of QQ bacteria, QQ media, and types of feed. Results show that no significant changes occurred in the structure and diversity of the microbial community in the mixed liquor and biofilm due to QQ treatment. Canonical correspondence analysis did reveal that the microbial communities were strongly influenced by feed types and phases. The microbial community composition varied between bacterial habitats (i.e., mixed liquor and biofilm), showing the two dominant phyla Proteobacteria and Bacteroidota in the former and Proteobacteria and Chloroflexi in the latter. The co-occurrence network analysis indicated that the biofilm (with 163 edges) in the MBR fed with real wastewater exhibited a more intricate network than the biofilm (with 53 edges) in the MBR fed with synthetic wastewater. With QQ, the biofilm exhibited more positive edges than negative ones. The phylogenetic investigation of communities showed that QQ barely affects functional gene-related quorum sensing (e.g., bacterial chemotaxis, motility proteins, and secretion) in mixed liquor but in biofilms at relatively large QQ doses (> 75 mg/L BH4). This research sheds light on the bacterial QQ's role in reducing MBR biofouling and provides crucial insights into its underlying mechanisms.