Search Results (58)

Wastewater treatment plants (WWTPs) face increasing pressure to handle higher volumes of water due to climate change causing storm surges, which current infrastructure cannot handle. Aerobic granular sludge (AGS) is a promising alternative to activated sludge systems due to their improved settleability property, lowering the land footprint and improving efficiency. This research investigates the optimisation of a lab-scale sequencing batch reactor (SBR) into a continuous flow reactor through mathematical modelling, sensitivity analysis, and a computational fluid dynamic model. This is all applied for the future goal of scaling up the model designed to a full-scale continuous flow reactor. The mathematical model developed analyses microbial kinetics, COD degradation, and mixing flows using Reynolds and Froude numbers. To perform a sensitivity analysis, a Python code was developed to investigate the stability when influent concentrations and flow rates vary. Finally, CFD simulations on ANSYS Fluent evaluated the mixing within the reactor. An 82% COD removal efficiency was derived from the model and validated against the SBR data and other configurations. The sensitivity analysis highlighted the reactor’s inefficiency in handling high-concentration influents and fast flow rates. CFD simulations revealed good mixing within the reactor; however, they did show issues where biomass washout would be highly likely if applied in continuous flow operation. All of these results were taken under deep consideration to provide a new reactor configuration to be studied that may resolve all these downfalls. Full article

This study examines the effects of polyester and denim microfibers (MFs) on aerobic granular sludge (AGS) over a 42-day period. Treatment performance, granulation, and microbial community changes were assessed at 0, 10, 70, 210, and 1500 MFs/L. Reactors with 70 MFs/L achieved rapid granulation and showed improved settling by day 9, while 0 and 10 MFs/L reactors showed delayed granule formation, which was likely due to limited nucleation and weaker shear conditions. Severe clogging and frequent maintenance occurred at 1500 MFs/L. Despite > 98% MF removal in all reactors, treatment performance declined at higher MF loads. Nitrogen removal dropped from 93% to 68%. Phosphate removal slightly increased in reactors with no or low microfiber loads (96–99%), declined in reactors with 70 or 210 MFs/L (92–91%, 89–88%), and dropped significantly in the reactor with1500 MFs/L (86–70%, p < 0.05). COD removal declined with increasing MF load. Paracoccus (denitrifiers) dominated low-MF reactors; Acinetobacter (associated with complex organic degradation) and Nitrospira (nitrite-oxidizing genus) were enriched at 1500 MFs/L. Performance decline likely stemmed from nutrient transport blockage and toxic leachates, highlighting the potential threat of MFs to wastewater treatment and the need for upstream MF control. Full article

The widely utilized TiO₂ nanoparticles (NPs) tend to accumulate in wastewater and affect microbial growth. This work investigated the impacts of prolonged TiO₂ NP addition to filamentous aerobic granular sludge (AGS) using two identical sequencing batch reactors (SBRs, R1 and R2). R1 (the control) had no TiO₂ NP addition. In this reactor, filamentous bacteria from large AGS grew rapidly and extended outward, the sludge volume index (SVI₃₀) quickly increased from 41.2 to 236.8 mL/g, mixed liquid suspended solids (MLSS) decreased from 4.72 to 0.9 g/L, and AGS disintegrated on day 40. Meanwhile, the removal rates of COD and NH₄⁺-N both exhibited significant declines. In contrast, 5–30 mg/L TiO₂ NPs was added to R2 from day 21 to 100, and the extended filamentous bacteria were effectively controlled on day 90 under a 30 mg/L NP dosage, leading to significant reductions in COD and NH₄⁺-N capabilities, particularly the latter. Therefore, NP addition was stopped on day 101, and AGS became dominant in R2, with an SVI₃₀ and MLSS of 48.5 mL/g and 5.67 g/L on day 130. COD and NH₄⁺-N capabilities both increased to 100%. Microbial analysis suggested that the dominant filamentous bacteria—Proteobacteria, Bacteroidetes, and Acidobacteria—were effectively controlled by adding 30 mg/L TiO₂ NPs. XRF analysis indicated that 11.7% TiO₂ NP accumulation made the filamentous bacteria a framework for AGS recovery and operation without NPs. Functional analysis revealed that TiO₂ NPs had stronger inhibitory effects on nitrogen metabolism compared to carbon metabolism, and both metabolic pathways recovered when NP addition was discontinued in a timely manner. These findings offer critical operational guidance for maintaining the stable performance of filamentous AGS systems treating TiO₂ NP wastewater in the future. Full article

Industrial activated sludge plants in many sectors, including the dairy industry, face sludge separation problems caused by sludge bulking. Aerobic granular sludge (AGS) could be a solution by forming well-settling granules. The key to successful granulation is the microbial selection of slow-growing glycogen-accumulating organisms (GAOs) by introducing an anaerobic feeding/reaction step. The objective of the current study was to investigate the impact of two slow feeding strategies to achieve granulation in existing sequencing batch reactors treating real dairy wastewater, by microbial selection only. The first strategy consisted of slow 90 min mixed feeding. The second strategy combined 45 min static and 45 min mixed feeding to build up a substrate gradient. The feeding strategies did not affect the effluent quality, but significantly impacted the sludge morphology, settling properties, and microbial community composition. Mixed feeding led to filamentous overgrowth by Thiothrix species, up to 45% abundance, and deteriorating settling, with sludge volume index (SVI) values up to 125 mL/g. In contrast, static feeding yielded densified sludge with SVI values below 45 mL/g and up to 35% GAO abundance. In conclusion, the results show successful granulation when using a simple static slow feeding mode, which could benefit the industrial application of AGS technology. Full article

In recent years, there has been an increase in the emission of tire wear particle (TWP) microplastics from wastewater treatment plants into the environment. The aim of this study was to determine the effect of TWPs in wastewater flowing into a biological reactor on the transcription of the 16S rRNA gene and the key genes responsible for nitrogen metabolism, amoA, nirK and nosZ, in aerobic granular sludge. The laboratory experiment was carried out in sequencing aerobic granular sludge reactors operated in an 8 h cycle into which TWP microplastics were introduced with municipal wastewater at a dose of 50–500 mg TWPs/L. The ammonia removal rate and the production of oxidized forms of nitrogen increased with the TWP dose. Gene transcript abundance analysis showed that the presence of rubber and substances leached from it promoted the activity of ammonium-oxidizing bacteria (160% increase), while the transcription of genes related to denitrification conversions was negatively affected. The activity of nitrite reductase gradually decreased with increasing TWP concentration in wastewater (decreased by 33% at 500 mg TWPs/L), while nitric oxide reductase activity was significantly inhibited even at the lowest TWP dose (decreased by 58% at 500 mg TWPs/L). The data obtained indicate that further studies are needed on the mechanisms of the effects of TWPs on the activities of the most important groups of microorganisms in wastewater treatment to minimize the negative effects of TWPs on biological wastewater treatment. Full article

Aerobic granular sludge (AGS) is a promising technology for wastewater treatment. Granules have a compact microbial structure and a high potential for pollutant removal. Despite its advantages, the impact of microplastics (MPs) on AGS remains poorly understood, posing a potential risk to the stability and efficiency of biological wastewater treatment processes. This study investigates the effects of polyethylene terephthalate (PET) MPs on AGS structure and extracellular polymeric substance (EPS) composition, providing new insights into the interaction between MPs and AGS. Four granular sequencing batch reactors (GSBRs) were operated with varying concentrations of PET MPs in the influent wastewater (0, 1, 10, 50 mg/L). Key findings include MP-induced changes in granule size distribution, with an increase in smaller granules (<90 µm) observed in reactors exposed to PET MPs. EPS concentrations (51–77 mg/L) exhibited significant differences among reactors, with notable shifts in protein (PN) and polysaccharide (PS) fractions. A higher PET MP dose resulted in an increased PN/PS ratio (from 1.96 to 5.40) and elevated hydrophobicity of AGS. These changes suggest that MPs can alter AGS structure and EPS composition, potentially affecting granule stability and treatment performance. This study provides novel evidence on the disruptive effects of MPs in wastewater treatment systems, emphasizing the need to address MP pollution in the context of biological treatment processes. The results contribute to a deeper understanding of the interactions between MP and AGS and form the basis for strategies to mitigate their adverse effects. Full article

This study presents an automated control system for wastewater treatment, developed using machine learning (ML) models integrated into a Supervisory Control and Data Acquisition (SCADA) framework. The experimental setup focused on a laboratory-scale Aerobic Granular Sludge (AGS) reactor, which utilized synthetic wastewater to model real-world conditions. The machine learning models, specifically N-BEATS and Temporal Fusion Transformers (TFTs), were trained to predict Biological Oxygen Demand (BOD₅) values using historical data and real-time influent contaminant concentrations obtained from online sensors. This predictive approach proved essential due to the absence of direct online BOD₅ measurements and an inconsistent relationship between BOD₅ and Chemical Oxygen Demand (COD), with a correlation of approximately 0.4. Evaluation results showed that the N-BEATS model demonstrated the highest accuracy, achieving a Mean Absolute Error (MAE) of 0.988 and an R² of 0.901. The integration of the N-BEATS model into the SCADA system enabled precise, real-time adjustments to reactor parameters, including sludge dose and aeration intensity, leading to significant improvements in granulation stability. The system effectively reduced the standard deviation of organic load fluctuations by 2.6 times, from 0.024 to 0.006, thereby stabilizing the granulation process within the AGS reactor. Residual analysis suggested a minor bias, likely due to the limited number of features in the model, indicating potential improvements through additional data inputs. This research demonstrates the value of machine learning-driven predictive control for wastewater treatment, offering a resilient solution for dynamic environments. By facilitating proactive management, this approach supports the scalability of wastewater treatment technologies while enhancing treatment efficiency and operational sustainability. Full article

The work presents the concept of aerobic granular sludge (AGS) and its potential for wastewater treatment. The work also evaluates the condition of the SBR (Sequencing Batch Reactor) type of municipal wastewater-treatment plant (WWTP) after its reconstruction into a system with AGS. The WWTP parameters achieved before and after reconstruction were compared. Operational measurements of the process during the individual phases of the treatment process showed a balanced concentration profile of the monitored parameters in the span of the semicontinuous cycle. Laboratory tests showed that the sludge from the WWTP has nitrification and denitrification rates comparable to the rates achieved for flocculent sludge, and it is also comparable to the nitrification and denitrification rates of AGS with size of granules below 400 µm. Despite the fact that complete sludge granulation was not achieved, the results measured at the WWTP confirmed the advantages of the AGS concept. Neither anaerobic nor anoxic conditions were identified in the SBR during the individual phases of operation, yet high removal efficiencies of ammonia and nitrate nitrogen and orthophosphate phosphorus were achieved. The concentration of ammonia and nitrate nitrogen at the WWTP effluent was below 5 mg/L, and the concentration of phosphorus was below 0.5 mg/L. Full article

This study investigates the densification/granulation of activated sludge with poor settleability, treating real industrial wastewater from a tank truck cleaning company. The wastewater is low in nutrients, acidic in nature, and high and variable in chemical oxygen demand (COD, ranging from 2770 mg·L⁻¹ to 14,050 mg·L⁻¹). A microbial selection strategy was applied to promote slow-growing glycogen-accumulating microorganisms (GAO) by the implementation of an anaerobic feast/aerobic famine strategy in a sequencing batch reactor (SBR). After 60 to 70 days, the uptake of carbon during the anaerobic phase exceeded 80%, the sludge morphology improved, and the sludge volume index (SVI) dropped below 50 mL·g⁻¹. 16S rRNA gene sequencing showed the enrichment of the GAOs Defluviicoccus and Candidatus Competibacter. Stable sludge densification was maintained when using a constant organic loading rate (OLR) of 0.85 ± 0.05 gCOD·(L·d)⁻¹, but the sludge quality deteriorated when switching to a variable OLR. In view of the integration of densified/granular sludge in a membrane bioreactor configuration, the filtration properties of the densified SBR sludge were compared to the seed sludge from the full-scale plant. The densified sludge showed a significantly lower resistance due to pore blockage and a significantly higher sustainable flux (45 vs. 15 L·(m²·h)⁻¹). Full article

Aerobic granules are small, dense aggregates of microbial cells that form naturally in aerobic wastewater treatment systems. They are characterized by their spherical shape, strong structural integrity, and ability to rapidly settle. These granules are formed through a self-immobilization process where different microbial species coalesce to degrade organic and inorganic compounds in wastewater. This study summarizes the development of aerobic granulation technology in wastewater treatment and the mechanism of aerobic granules’ formation, analyzes the characteristics and the factors affecting the aerobic granules’ formation, and presents practical engineering examples of its application from pilot-scale to full-scale operation. Full article

This study aimed to investigate the influencing factors and characteristics of granule morphology through approximately 500 d of long-term monitoring of two types of anaerobic–aerobic phosphorus-accumulating organism (PAO) and anaerobic–anoxic denitrifying PAO (DPAO) sequencing batch reactors (SBRs). The results show that granules were present in the DPAO SBR and PAO SBR after 200 d and 250 d of operation, respectively. The average diameters of the granules were 2.2 ± 0.7 mm in the DPAO SBR and 0.4 ± 0.3 mm in the PAO SBR, respectively. The DPAO granular sludge contained rod-shaped microorganisms, whereas the PAO granular sludge contained cocci-type microorganisms. A precipitated core consisting of hydroxyapatite was found in the DPAO granules. A comparative analysis conducted under various operating conditions revealed that the availability and type of the electron acceptors (EAs) may have a significant impact on granulation. This observation suggests that the presence and diversity of EAs are crucial factors for the development of different granule sizes and morphologies. Full article

Aerobic granulation is an emerging process in wastewater treatment that has the potential to accelerate sedimentation of the microbial biomass during secondary treatment. Aerobic granulation has been difficult to achieve in the continuous flow reactors (CFRs) used in modern wastewater treatment plants. Recent research has demonstrated that the alternation of nutrient-abundant (feast) and nutrient-limiting (famine) conditions is able to promote aerobic granulation in a CFR. In this study, we conducted a metagenomic analysis with the objective of characterizing the bacterial composition of the granular biomass developed in three simulated plug flow reactors (PFRs) with different feast-to-famine ratios. Phylogenetic analyses revealed a clear distinction between the bacterial composition of aerobic granules in the pilot simulated PFRs as compared with conventional activated sludge. Larger and denser granules, showing improved sedimentation properties, were observed in the PFR with the longest famine time and were characterized by a greater proportion of bacteria producing abundant extracellular polymeric substances (EPS). Functional metagenomic analysis based on KEGG pathways indicated that the large and dense aerobic granules in the PFR with the longest famine time showed increased functionalities related to secretion systems and quorum sensing, which are characteristics of bacteria in biofilms and aerobic granules. This study contributes to a further understanding of the relationship between aerobic granule morphology and the bacterial composition of the granular biomass. Full article

Aerobic granular sludge is an interesting alternative to the conventional activated sludge (CAS) system and modified-Ludzack–Ettinger (MLE) process for biological wastewater treatment, as it allows a more cost-effective and simultaneous removal of carbon (C) and nitrogen (N) compounds in a single stage. In this study, (micro)aerobic C and N removal from synthetic urban wastewater was investigated in a continuous-double-column-upflow aerobic granular sludge blanket (UAGSB) system. The UAGSB reactor was operated under different dissolved oxygen (DO) ranges (0.01–6.00 mg∙L⁻¹), feed C/N ratios (4.7–13.6), and hydraulic retention times (HRTs) (6–24 h). At a DO range of 0.01–0.30 mg∙L⁻¹, feed C/N ratio of 13.6, and HRT of 24 h, the UAGSB achieved the highest chemical oxygen demand (COD), N-NH₄⁺, and total inorganic nitrogen (TIN) removal efficiencies of 86, 99, and 84%, respectively. A preliminary assessment of the energy and economic savings associated with the process investigated was also carried out. The impact of capital and operating costs mainly related to the energy consumption of the aeration was taken into account. The assessment reveals that the capital and energy expenses of the UAGSB reactor would result in cost savings of around 14 and 7%, respectively, compared with a MLE system. Full article

This review paper provides an overview of various types of photobioreactors (PBRs) that could be used for the production of polyhydroxyalkanoates (PHAs) using anoxygenic photoheterotrophs, with a focus on the design and operation of these systems. The paper highlights the potential of different PBRs based on reactor geometry and growth mode, and also examines the advantages and disadvantages of each PBR type and summarizes their suitability for PNSB-PHA production. The optimization of reactor design and operation is crucial for maximizing PNSB growth and PHA productivity. The self-immobilization of bacteria in granular sludge is a promising technology for wastewater treatment and the production of PHAs, while grooved-surface PBRs and porous-substrate PBRs have limitations due to difficult biomass harvesting in the former and the presence of aerobic conditions incongruent with PNSB culturing in the latter. Limitations exist with all solutions for maximizing rapid growth and maintaining high biomass concentrations due to the requirements of phototrophic growth. Full article

The most common technology for the recovery of energy and valuable materials from sewage sludge is anaerobic digestion (AD). Ensuring thermophilic conditions during AD has been proven to cause process intensification and an improvement in its final outcomes. Nonetheless, the search is underway for other methods to bolster the effectiveness of the AD of aerobic granular sludge (AGS), which is characterized by a compact and complex structure. A prospective AGS pre-treatment technology entails the use of solidified carbon dioxide (SCO₂). The present study focused on an evaluation of the AGS pre-treatment with SCO₂ on the thermophilic AD technological effects. It evaluated the effect of the SCO₂ pre-treatment method on changes in the concentrations of organic and biogenic compounds in the dissolved phase and the yield and kinetics of biogas and methane production in periodical reactors, as well as enabled the development of an empirical organizational model of biogas production. SCO₂ introduced to AGS caused an increase in the content of COD, N-NH₄⁺, and P-PO₄³⁻ in the AGS dissolved phase at SCO₂/AGS volumetric ratios ranging from 0 to 0.3. A further increase in the SCO₂ dose did not cause any statistically significant differences in this respect. The highest biogas and methane yields were obtained at SCO₂/AGS of 0.3 and reached 482 ± 21 cm³/gVS and 337 ± 14 cm³/gVS, respectively. The higher SCO₂ doses used led to a significant decrease in the pH value of the AGS, which, in turn, contributed to a decreasing CH₄ concentration in the biogas. Full article