Sludge Settleability Research Articles

Analysis on pollutants removal and sludge characteristics of a novel two-phase anaerobic/aerobic/integrated deoxygenated and anoxic reactor associated with membrane process for treating pesticide wastewater

Most frequently used biological method was improved anaerobic/anoxic/aerobic (A/A/O) process for treating actual pesticide wastewater presently. However, the effluent results were far away from what the national standard expects due to pesticide wastewater characteristics of high COD concentration, high total nitrogen (TN) concentration and high toxicity. In this study, a novel two-phase anaerobic/aerobic/integrated deoxygenated and anoxic reactor associated with membrane process (P1) were regarded as excellent candidates for the treatment of pesticide wastewater, compared the removal efficiency of pollutants with improved A/A/O process (P2) under different hydraulic retention times (HRTs). Effluent ethylene thiourea (ETU) concentration was reduced effectively by 67.1 % in P1. The average cyanide (CN−) effluent concentration in P1 and P2 was 0.40 mg/L and 6.67 mg/L, respectively. During the entire HRT change period, P1 significantly increased the biological oxygen demand (BOD5) removal efficiency by 12.98 %. The average effluent COD concentration of P1 was 36.41 mg/L, while that of P2 was 984.42 mg/L. In addition, TN removal efficiency of P1 exhibited distinct superiority. When HRT was 72 h, the average TN effluent concentration of P1 and P2 was 12.67 mg/L and 67.66 mg/L. The sludge performance indicators have been determined and results showed that the sludge viscosity of the membrane reactor in P1 had merely 32.6 % higher than that of the secondary sedimentation tank in P2, and the average vertical displacement of sludge settleability in P1 was 23.0 % slight lower than that of P2. The overall sludge performance proved that higher sludge concentration was allowed in P1. Moreover, experiment improved nitrite reductase (NIR) and nitrate reductase (NAR) in P1 were less susceptible to be suppressed by ETU and CN− increase compared with P2. Finally, the positive correlation relationship of sludge settleability with ETU and CN− has been identified successfully in P1.

Integrated urban wastewater management through on-site generation and application of ferrous carbonate

Integrated urban water management is an increasingly popular concept that cost-effectively maximizes system-wide performance by holistically considering all aspects of water and wastewater sectors. An innovative technology enabling production of high-quality bioenergy and an iron salt, ferrous carbonate (FeCO3), represents a significant opportunity for integrated urban water management. This study experimentally evaluates the effect of in-sewer FeCO3 dosing on the performance of sewers and the downstream wastewater treatment plants. Two continuous-flow laboratory-scale urban wastewater systems, each consisting of sewer reactors, a sequencing batch wastewater treatment reactor, and an anaerobic digester, were operated in parallel. After establishing comparable performance, one served as the control without any chemical dosing, while the other received a dosing of 10mgFe/L of FeCO3 in its sewer reactors. Compared to the control, the FeCO3-dosed experimental system reduced dissolved sulfide concentrations by 32.2±3.3% (at 0.58±0.05mgS/mgFe, or 1.0molFe/molS) in sewer reactors, decreased phosphate concentrations by 38.3%±3.2% (at 0.37±0.04mgP/mgFe, or 1.5molFe/molP) in sequencing batch reactors, and lowered dissolved sulfide concentrations by 72.0±4.2% (18.9±2.4mgS/L) in the anaerobic sludge digester. Iron accumulated in the sludge and improved sludge settleability by 33.9±5.5% and enhanced dewaterability of anaerobically digested sludge by 15.9±2.0%. The findings indicate multiple benefits from the integrated use of FeCO3, potentially being as a substitute for the currently used iron salts in urban wastewater systems.

Synthesis and Characterization of an Alkali-Activated Binder from Blast Furnace Slag and Marble Waste.

This study reports an alkali-activated binder including blast furnace slag (BFS) together with marble waste (MW). Cement is an industrial product that emits a significant amount of CO2 during its production and incurs high energy costs. MW is generated during the extraction, cutting, and processing of marble in production facilities, where dust mixes with water to form a settling sludge. This sludge is an environmentally harmful waste that must be disposed of in accordance with legal regulations. In this study, a substantial amount of MW, a by-product with considerable environmental and economic impacts worldwide, was utilized in the production of a binder through the alkaline activation of BFS. In doing this, different experimental parameters were tested to obtain the best binder samples according to workability and mechanical properties. Then, some experiments such as drying shrinkage determination, strength testing, and microstructure analyses were fulfilled through samples with the best values. The findings supported the improvement of the rapid-setting property of BFS by means of the addition of MW. MW reduced the time-dependent drying shrinkage values of BFS by 55%, especially in slag alkaline activation systems with a low or moderate alkali activator content. The substitution of MW (≤50%) in BFS increased flexural and compressive strengths (4.5 and 61.7 MPa), while a reference sample contained BFS only. Although the use of MW did not create a new phase, it contributed to a C-S-H bonding structure during the alkali activation of BFS in a microstructure analysis.

Removal of nitrate nitrogen by aerobic denitrification granular sludge under strongly alkaline conditions: Performance and mechanism

Aerobic granular sludge (AGS) technology faces challenges in treating strongly alkaline wastewater because high pH affects sludge settleability and microbial metabolic activity. In this study, aerobic denitrification granular sludge (ADGS) was cultivated with strongly autoaggregating aerobic denitrifying bacteria as the sludge source at an influent pH of 11.0 under aerobic conditions. The formation characteristics of ADGS and its pollutant removal efficiency under strongly alkaline conditions were explored. Compared with ADGS cultivated under neutral conditions, ADGS cultivated under strongly alkaline conditions resulted in superior particle formation rates, settleability, particle strengths and particle stabilities. Nitrate nitrogen was almost completely removed at a pH of 11.0 under aerobic conditions. Protein, polysaccharides and humic acid in extracellular polymeric substances (EPS) under strongly alkaline conditions were involved in the ADGS formation process. In addition, the presence of metallic elements in the EPS and inorganic nuclei in the sludge facilitated the formation of ADGS. The strongly alkaline environment enriched the alkali-resistant aerobic denitrifying bacteria, such as unclassified_f__Rhodobacteraceae, Tessaracoccus, Halomonas, and Pseudofulvimonas, as well as specialized alkali-resistant genera. Furthermore, the strongly alkaline environment increased the abundance of key enzymes involved in carbon metabolism and upregulated the expression of nitrogen metabolism genes in the ADGS to maintain their metabolic activity. In addition, the microorganisms upregulated genes that encoded reverse transporter protein genes (mnhACEFG, nhaACP, and phaACDEFG) and K+ uptake protein genes (trkAHG) and secreted greater amounts of acidic functional groups and free amino groups to help maintain intracellular and extracellular osmolality and acid–base homeostasis under strongly alkaline stress. This research provides a possible option and innovative strategy for the management of highly alkaline nitrate-containing wastewater.

Nanostructured materials as hazardous wastewater micropullutants: Sources, behavior, and impact on functional bacterial community of activated sludge

Unique properties of nanoscale materials make them attractive for industrial, medical, agricultural, and environmental applications. Nevertheless, the release of nanoparticles into the environment is a major concern due to the lack of knowledge about their behavior in the environment and potential widespread environmental impacts. On the one hand, nanomaterials are perceived as pollutants that may affect activated sludge microorganisms and, consequently, the efficiency of wastewater treatment processes. On the other hand, some nanomaterials can be intentionally added to activated sludge systems to improve their performance in terms of, e.g., sludge settling and removing heavy metals or organic pollutants. As a result, nanoparticles are frequently accumulated in wastewater, which is considered to be a major source of nanoparticle release to the surrounding environment. Processes that involve the action of activated sludge are used worldwide in wastewater treatment plants due to their excellent capacity of removing nutrients, degrading toxins, and retaining biomass. High concentrations of nanoparticles entering activated sludge systems can affect their growth and metabolism. The research studies, which are reviewed in the present article, show that nanoparticles significantly reduce the relative abundance of the activated sludge microbial community associated with nitrification, denitrification, and phosphorus removal. The knowledge about the structure of the activated sludge microbial community with an assessment of nanomaterial toxicity can contribute to optimizing the sludge population and improving the performance of wastewater treatment plants.

Response of aerobic granular sludge to salinity fluctuations in formation, stability and microbial community structures

Aerobic granular sludge (AGS) exhibits excellent resistance to adverse environment due to its unique layered structure. However, the mechanism about how salinity fluctuations in municipal wastewater impact AGS formation and its physicochemical properties has not been thoroughly revealed. In this study, AGS was cultivated under additional 0 % salinity (R1), additional 1.5 % constant salinity (R2), and additional 0–1.5 % fluctuant salinity (R3), respectively. The results indicate that increased salinity can enhance extracellular polymeric substances (EPS) production and improve sludge settleability, thereby facilitate AGS formation. However, the AGS experienced frequent environmental conversion between dehydration and swell due to salinity fluctuations, resulting in higher content of loosely-bond EPS and low settleability, which delayed the maturation of AGS for over 14 days. Additional salinity significantly inhibited the nitrification process, but the formation of AGS promoted the recovery of ammonia oxidation activity and facilitated the construction of short-range nitrification denitrification processes, resulting in over 16.0 % higher total nitrogen removal efficiency than R1. The microbial community analysis revealed that Thauera played an important role in the granulation process under salinity stress, due to its salt tolerance and EPS secretion abilities. As expected, the formation of AGS enhanced the salt resistance of microorganisms, allowing for the enrichment of functional bacteria, such as Flavobacterium and Candidatus_Competibacter. Generally, microorganisms required extended adaptation periods to cope with salinity fluctuations. Nevertheless, the resulting AGS proved stable and efficient wastewater treatment performance.

Olive oil waste treatment: A review

The most intriguing results were obtained on UASB reactors, both at laboratory and pilot scale, fed on diluted waste, and the most promising results were obtained on UASB reactors, both at laboratory and pilot scale, fed on diluted waste. With these digesters, volumetric loading rates were observed and 70 percent removal efficiency was achieved. The start-up of UASB reactors fed with waste from olive oil mills is a complicated process that must be carefully monitored and optimized. Starting with very diluted trash yielded the greatest results. Granulation of the sludge, as seen in UASB digesters fed on sugar beet wastewaters, was not attained; however, the sludge's settleability was observed to be excellent. Since the olive oil industry has been blamed for a lot of pollution, there has been a lot of pressure to improve olive oil waste treatment facilities. Bioremediation (ex-situ, in-situ), thermal processes (incineration, pyrolysis, gasification), evaporation, membrane processes, electrolysis, ozonation, digestion, Coagulation/flocculation/precipitation, and distillation are among the many methods currently in use. Per the waste treatment approach, both advantages and downsides were described, along with the methodology and explicit flow diagrams. Furthermore, the most recent studies were provided, with around twenty–five figures primarily illustrating the efficacy of current waste treatment procedures versus time or temperature. The comparison of the various olive oil waste treatment approaches revealed that, while bioremediation is the most environmentally beneficial option, it is not the only one.

Synergetic association of hydroxyapatite-mediated biofilm and suspended sludge enhances resilience of partial nitrification/anammox (PN/A) system treating high-strength anaerobic membrane bioreactor (AnMBR) permeate

A single-stage partial nitrification/anammox (PN/A) system with biocarriers was used to treat the permeate from an anaerobic membrane reactor (AnMBR) processing organic fraction of municipal solid wastes. The suitable Ca/P ratio and high pH in the AnMBR permeate facilitated hydroxyapatite (HAP) formation, enhancing the biofilm attachment and the settleability of suspended sludge. This maintained sufficient biomass and a stable microbial structure after flushing to mitigate the free nitrous acid inhibition. Robust anammox bacteria in the biofilm and ammonia-oxidizing bacteria in the suspended sludge ensured that the PN/A system achieved an 87.3 % nitrogen removal efficiency at an influent NH4+-N concentration of 1802 mg/L. This study demonstrates that AnMBR permeate with high Ca, P and NH4+-N content is suitable for single-stage PN/A system with biocarriers due to the high resilience enhanced by HAP, offering a reference for the treatment of high-strength AnMBR permeate.

Mechanisms underlying the detrimental impact of micro(nano)plastics on the stability of aerobic granular sludge: Interactions between micro(nano)plastics and extracellular polymeric substances

Microplastics (MPs) and nanoplastics (NPs) present in wastewater can pose a negative impact to aerobic granular sludge (AGS). Herein, this study found that MPs and NPs (20 mg/L) deteriorated the sludge settleability and granule integrity, resulting in a 15.7 % and 21.9 % decrease in the total nitrogen removal efficiency of the AGS system, respectively. This was possibly due to the reduction of the extracellular polymeric substances (EPS) content. The subsequent analysis revealed that tyrosine, tryptophan, and humic acid-like substances in EPS exhibited a higher propensity for chemisorption and inhomogeneous multilayer adsorption onto NPs compared to MPs. The binding of EPS onto the surface of plastic particles increased the electronegativity of the MPs, but facilitated the aggregation of NPs through reducing the electrostatic repulsion, thereby mitigating the adverse effects of MPs/NPs on the AGS stability. Additionally, comprehensive analysis of the extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the suppressed aggregation of microorganisms was the internal mechanisms contributing to the inadequate stability of AGS induced by MPs/NPs. This study provides novel insights into the detrimental mechanisms of MPs/NPs on the AGS stability, highlighting the key role of EPS in maintaining the structural stability of AGS when exposed to MPs/NPs.

Optimized wastewater management utilizing multivariate statistical analysis: a case study of the Mascara wastewater treatment plant, Algeria.

Effective wastewater management is crucial in regions experiencing water scarcity and environmental stressors, such as pollution and climate change. Optimizing treatment processes is essential for achieving environmental sustainability. This study aims to highlight the importance of effective wastewater management strategies, particularly in regions facing water scarcity. Our objective was to identify key factors influencing the treatment process. Therefore, we evaluated associations between physicochemical parameters using multivariate statistical methods, including Principal Component Analysis (PCA) and Hierarchical Ascendant Classification (HAC). Our findings categorize the monthly water samples into three distinct groups based on levels of organic pollution: the first group (July, August, and September) is characterized by high oxygenation levels and significantly low organic pollution, indicating optimal system operation. The second group (April, October, November, and December) exhibits low oxygenation and low organic pollution, promoting sludge settling and pollutant reduction. The third group (January, February, March, May, and June) shows significantly high organic pollution and low oxygenation, which corresponds to unfavorable environmental conditions. Our study demonstrates the effectiveness of multivariate statistical methods in optimizing wastewater treatment processes, providing crucial insights for environmental sustainability and water resource management.

Treatment of Synthetic Wastewater Containing Polystyrene (PS) Nanoplastics by Membrane Bioreactor (MBR): Study of the Effects on Microbial Community and Membrane Fouling.

The persistent presence of micro- and nanoplastics (MNPs) in aquatic environments, particularly via effluents from wastewater treatment plants (WWTPs), poses significant ecological risks. This study investigated the removal efficiency of polystyrene nanoplastics (PS-NPs) using a lab-scale aerobic membrane bioreactor (aMBR) equipped with different membrane types: microfiltration (MF), commercial ultrafiltration (c-UF), and recycled ultrafiltration (r-UF) membranes. Performance was assessed using synthetic urban wastewater spiked with PS-NPs, focusing on membrane efficiency, fouling behavior, and microbial community shifts. All aMBR systems achieved high organic matter removal, exceeding a 97% COD reduction in both the control and PS-exposed reactors. While low concentrations of PS-NPs did not significantly impact the sludge settleability or soluble microbial products initially, a higher accumulation increased the carbohydrate concentrations, indicating a protective bacterial response. The microbial community composition also adapted over time under polystyrene stress. All membrane types exhibited substantial NP removal; however, the presence of nano-sized PS particles negatively affected the membrane performance, enhancing the fouling phenomena and increasing transmembrane pressure. Despite this, the r-UF membrane demonstrated comparable efficiency to c-UF, suggesting its potential for sustainable applications. Advanced characterization techniques including pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) were employed for NP detection and quantification.

A Critical Review of Systems for Bioremediation of Tannery Effluent with a Focus on Nitrogenous and Sulfurous Species Removal and Resource Recovery

Tanneries generate copious amounts of potentially toxic sludge and effluent from the processing of skins and hides to leather. The effluent requires remediation before discharge to protect the receiving environment. A range of physicochemical methods are used for pre- and post-treatment, but biological secondary remediation remains the most popular choice for the reduction of the organic and macronutrient fraction of tannery effluent. This review provides an update and critical discussion of biological systems used to remediate tannery effluent. While the conventional activated sludge process and similar technologies are widely used by tanneries, they have inherent problems related to poor sludge settling, low removal efficiencies, and high energy requirements. Treatment wetlands are recommended for the passive polishing step of beamhouse effluent. Hybrid systems that incorporate anoxic and/or anaerobic zones with sludge and/or effluent recycling have been shown to be effective for the removal of organics and nitrogenous species at laboratory scale, and some have been piloted. Novel systems have also been proposed for the removal and recovery of elemental sulfur and/or energy and/or process water in support of a circular economy. Full-scale studies showing successful long-term operation of such systems are now required to convince tanneries to modernize and invest in new infrastructure.

Unravelling the impact of oxic-settling-anaerobic cycle implementation and solid retention time on sludge generation, membrane operation, and contaminant removal in membrane bioreactors

Sewage sludge production represents a critical issue nowadays. The oxic-settling-anaerobic (OSA) system is a promising strategy for reducing sludge production during biological wastewater treatment. However, the distinct effect of OSA process and solid retention time (SRT) on sludge production has not been clarified yet. Therefore, during this study, the impacts of OSA system implementation at different SRT on sludge generation, membrane operation, and contaminant removal were elucidated in two lab-scale membrane bioreactors working at 20 d (MBR20) and 60 d (MBR60). After OSA implementation, the MBR-OSA20 and MBR-OSA60 were operated at a hydraulic retention time in the sludge holding tank (HRTSHT) of 6–12 h and of 6–24 h, respectively. The estimated observed sludge yield (Yobs) showed a reduction of 38–48 % for the MBR-OSA20, but no beneficial effect was observed for MBR-OSA60 at 6 h of HRTSHT. At the HRTSHT of 24 h, Yobs decreased by 17 % due to hydrolysis and acidogenic biomass fermentation. OSA implementation and long SRT had no negative effects on organic carbon and ammonium removal (96(±3) % and 100 %, respectively) and improved total nitrogen (TN) reduction by 19–41 %. Membrane fouling and sludge filterability were not significantly affected, whereas sludge settleability worsened after the implementation of the OSA cycle. This activity provided additional insights about the distinct impact of the OSA process and SRT on sludge production and characteristics, confirming the OSA process as a valid solution for reducing sludge production under a moderate SRT, but revealing a negligible effect on Yobs under a prolonged SRT and a short HRTSHT.

Development of an integrated fixed-film activated sludge (IFAS) reactor treating landfill leachate for the biological nitrogen removal through nitritation-denitritation

The current work investigated the performance of an Integrated Fixed-Film Activated Sludge Sequencing Batch Reactor (IFAS-SBR) for Biological Nitrogen Removal (BNR) from mature landfill leachate through the nitritation-denitritation process. During the experimental period two IFAS-SBR configurations were examined using two different biocarrier types with the same filling ratio (50%). The dissolved oxygen (DO) concentration ranged between 2 and 3 mg/L and 4–6 mg/L in the first (baseline-IFAS) and the second (S8-IFAS) setup, respectively. Baseline-IFAS operated for 542 days and demonstrated a high and stable BNR performance maintaining a removal efficiency above 90% under a Nitrogen Loading Rate (NLR) up to 0.45 kg N/m3-d, while S8-IFAS, which operated for 230 days, was characterized by a limited and unstable BNR performance being unable to operate sufficiently under an NLR higher than 0.20 kg N/m3-d. It also experienced a severe inhibition period, when the BNR process was fully deteriorated. Moreover, S8-IFAS suffered from extensive biocarrier stagnant zones and a particularly poor sludge settleability. The attached biomass cultivated in both IFAS configurations had a negligible content of nitrifying bacteria, probably attributed to the insufficient DO diffusion through the biofilm, caused by the low DO concentration in the liquid in the baseline case and the extensive stagnant zones in the S8-IFAS case. As a result of the high biocarrier filling ratio, the S8-IFAS was unstable and low. This was probably attributed to the mass transfer limitations caused by the biocarrier stagnant zones, which hinder substrate and oxygen diffusion, thus reducing the biomass activity and increasing its vulnerability to inhibitory and toxic factors. Hence, the biocarrier filling fraction is a crucial parameter for the efficient operation of the IFAS-SBR and should be carefully selected taking into consideration both the media type and the overall reactor configuration.

Significant in situ sludge yield reduction in an acidic activated sludge system

Minimizing sludge generation in activated sludge systems is critical to reducing the operational cost of wastewater treatment plants (WWTPs), particularly for small plants where bioenergy is not recovered. This study introduces a novel acidic activated sludge technology for in situ sludge yield reduction, leveraging acid-tolerant ammonia-oxidizing bacteria (Candidatus Nitrosoglobus). The observed sludge yield (Yobs) was calculated based on the cumulative sludge generation and COD removal during 400 d long-term operation. The acidic process achieved a low Yobs of 0.106 ± 0.004 gMLSS/gCOD at pH 4.6 to 4.8 and in situ free nitrous acid (FNA) of 1 to 3 mg/L, reducing sludge production by 58 % compared to the conventional neutral-pH system (Yobs of 0.250 ± 0.003 gMLSS/gCOD). The acidic system also maintained effective sludge settling and organic matter removal over long-term operation. Mechanism studies revealed that the acidic sludge displayed higher endogenous respiration, sludge hydrolysis rates, and higher soluble microbial products and loosely-bounded extracellular polymer substances, compared to the neutral sludge. It also selectively enriched several hydrolytic genera (e.g., Chryseobacterium, Acidovorax, and Ottowia). Those results indicate that the acidic pH and in situ FNA enhanced sludge disintegration, hydrolysis, and cryptic growth. Besides, a lower intracellular ATP content was observed for acidic sludge than neutral sludge, suggesting potential decoupling of catabolism and anabolism in the acidic sludge. These findings collectively demonstrate that the acidic activated sludge technology could significantly reduce sludge yield, contributing to more cost- and space-effective wastewater management.

Treatment of high ammonia anaerobically digested molasses wastewater using aerobic granular sludge reactor

This study addressed the treatment of high ammonia, low biodegradable chemical oxygen demand (bCOD) anaerobically digested molasses wastewater, utilizing an aerobic granular sludge (AGS) reactor. The AGS achieved 99 % ammonia removal regardless of the bCOD supplementation. By adding low ammonia (<60 mg/L), high bCOD raw molasses wastewater (before anaerobic digestion) as a carbon source, enhanced nitrogen removal, increasing from 10 % to 97 %, and improved sludge settleability via bio-induced calcite precipitation were observed. Functional genes prediction suggested two potential denitrification pathways, including heterotrophic denitrification by Paracoccus and Thauera, and autotrophic denitrification, specifically sulfide-oxidizing autotrophic denitrification by Thiobacillus. An increase in the relative abundance of microorganisms involved in heterotrophic denitrification was observed with the addition of high bCOD raw molasses wastewater. Consequently, incorporating raw molasses wastewater into the AGS presents a sustainable approach to achieve mixotrophic denitrification, maintain stable granular sludge and ensure stable treatment performance when treating anaerobically digested molasses wastewater.

Evaluation of activated sludge settling characteristics from microscopy images with deep convolutional neural networks and transfer learning

Timely assessment and prediction of changes in microbial compositions leading to activated sludge settling problems, such as filamentous bulking (FB), can reduce water resource recovery facilities (WRRFs) upsets, operational challenges, and negative environmental impacts. This study presents a computer vision approach to assess activated sludge-settling characteristics based on Microscopy Images (MIs). We utilize MIs to train deep convolutional neural networks (CNN) using transfer learning to investigate the morphological properties of flocs and filaments. The methodology was tested on the offline MI dataset collected over two years at a full-scale industrial WRRF in Belgium. Various CNN architectures were tested, including Inception v3, ResNet18, ResNet152, ConvNeXt-nano, and ConvNeXt-S. The sludge volume index (SVI) was used as the final prediction variable, but the method can be easily adjusted to predict any other settling metric of choice. The best-performing CNN, ConvNeXt-nano, could predict SVI values with MAE (37.51 ± 4.02), MTD (11.65 ± 1.94), MAPE (0.18 ± 0.02), and R2 (0.75 ± 0.05). The model was tested in real-life FB events, where it identified early indicators of bulking by predictive surges in SVI values. We used an explainable AI technique, Eigen-CAM, to discover key morphological indicators of sludge bulking transitions. The findings highlight the SVI multimodality issue, where SVI readings as a unidimensional metric could not capture delicate shifts from good to poor sludge settling, while the model detected these subtle changes. The key morphological attributes of threshold conditions leading to FB were identified, which can provide actionable insight for preemptive WRRF management.

Advancing the treatment of low carbon-to-nitrogen ratio municipal wastewater using a novel microaerobic sludge bed approach: Insights into enhanced performance and functional microbial community

Microaerobic sludge bed systems could align with low-energy, reasonable carbon-nitrogen (C/N) ratio, and synchronous removal objectives during wastewater treatment. However, its ability to treat municipal wastewater (MW) with varying low C/N ratio, low NH4+ concentration, along with managing sludge bulking and loss are still unclear. Against this backdrop, this study investigated the performance of an Upflow Microaerobic Sludge Bed Reactor (UMSR) treating MW characterized by varying low C/N ratios and low NH4+ concentrations. The study also thoroughly examined associated sludge bulking and loss, pollutant removal efficiencies, sludge settleability, microbial community structures, functional gene variations, and metabolic pathways. Findings revealed that the effluent NH4+-N concentration gradually decreased to 0 mg/L with a decrease in the C/N ratio, whereas the effluent COD was unaffected by the influent, maintaining a concentration below 50 mg/L. Notably, TN removal efficiency reached 90% when C/N ratio was 3. The decrease in the C/N ratio (C/N ratio was 1) increased microbial community diversity, with abundances of AOB, AnAOB, aerobic denitrifying bacteria, and anaerobic digestion bacteria reaching 8.34%, 0.96%, 5.07%, and 9.01%, respectively. Microorganisms' metabolic pathways significantly shifted, showing increased carbohydrate and cofactor/vitamin metabolism and decreased amino acid metabolism and xenobiotic biodegradation. This study not only provides a solution for the effluent of different pre-capture carbon processes but also demonstrates the UMSR's capability in managing low C/N ratio municipal wastewater and emphasizes the critical role of microbial community adjustments and functional gene variations in enhancing nitrogen removal efficiency.

Granular sludge characterization and microbial response in a hydroxyapatite (HAP)- anammox coupled process at different nitrogen loading rates

To enhance the treatment capacity and operational stability of the anammox process for nutrient-rich wastewater disposal, a hydroxyapatite (HAP)-anammox coupled process was developed in a granular sludge-based upflow bioreactor. The impact of nitrogen loading rate (NLR) on process performance was investigated by gradually increasing the NLR from 1 to 1.5, 3, and 5 kgN/m3/d for 264 days continuous operation. TN and TP removal rates of 82.51 ± 3.58 % and 60.49 ± 2.82 % were achieved at the NLR of 5 kgN/m3/d. The precipitation of Ca and phosphorus resulted in HAP crystals formation evidenced by sludge morphology and component analysis, which enhanced sludge settling properties and facilitated biomass enrichment. The HAP-anammox granular sludge was characterized by the outer layer HAP crystals formed on inner anammox granules, while highly mineralized granular sludge with higher density distributed at the bottom of the reactor is conducive to HAP-based phosphorus recovery. After a long-term accumulation, the abundance of Planctomycetota phylum gradually increased (from 7.7 % to 14.1 %), consisting of three species of anammox bacteria, namely Candidatus_Brocadia_sapporoensis, Candidatus_Brocadia_sinica and Candidatus_Kuenenia_stuttgartiensis. Nitrogen metabolic pathway analysis illustrated that denitrification was also present except the anammox reaction, synergistically contributing to superior nitrogen removal in the HAP-anammox process.

Management strategy of granular sludge settleability in saline denitrification: Insights from machine learning

The settleability of granular sludge is a crucial factor in maintaining an adequate amount of granules in the wastewater treatment process (WWTP). However, Accurate measurement of settleability is challenging due to the complex interactions in WWTP. To address this issue, an intelligent strategy for controlling the settleability of granular sludge is required. This study developed a machine learning (ML)-based model to predict the sludge volume index (SVI30). Three ML models, namely artificial neural networks (ANNs), random forest (RF), and support vector machine (SVM) models, were employed with an ANNs-based mixed liquor suspended solids (MLSS) soft sensor, which served as input data for predicting SVI30 using ML. The combination of the soft sensor’s output and ANNs yielded the highest performance with R2 and mean absolute error (MAE) of 0.8946 and 5.5 mL/g, respectively. The Shapely Additive Explanations (SHAP) analysis revealed that MLSS, salinity, glucose loading rate, and pH were significant factors influencing SVI30. The surrogate model-based optimization strategy of SVI30 was conducted using core control parameters (CCPs), namely glucose loading rate, effluent pH, and salinity. It was suggested that a glucose loading rate over 3.0 kg-N/m3-d and an effluent pH exceeding 9.0 can deteriorate the SVI30. To the best of our knowledge, this is the first study on the surrogate model-based suggestion of the management strategy in the granular sludge process under saline denitrification conditions.