Diffusion of soluble organic substrates in aerobic granular sludge: Effect of molecular weight

Feasibility and application of membrane aerated biofilm reactors for industrial wastewater treatment

Membrane aerated biofilm reactors (MABRs) have emerged as a promising technology for wastewater treatment, offering significant advantages over conventional activated sludge (CAS) systems. Over the past decades, membrane processes have revolutionized municipal water treatment with membrane bioreactors (MBRs) becoming a widely accepted process for municipal and then industrial wastewater (IW) treatment. By the same token, MABR technologies were initially applied to municipal wastewater; however, their application in industrial settings is still emerging. Despite the promise of MABRs due to the biofilm's tolerance to IW toxins, there is a lack of information on their industrial applications. Therefore, this paper critically reviews the feasibility and application of MABRs for IW treatment, including pharmaceutical, chemical, refinery, petrochemical, oilfield, landfill leachate and other complex industrial waters. Three existing technology vendors with full-scale experience were compared; however, additional providers with innovative designs may provide step-changes in performance. Key outcomes highlight the effectiveness of MABRs in reducing carbon, nitrogen, and xenobiotics from high-strength IWs at bench and pilot scales. Critical factors influencing MABR performance, such as biofilm thickness (BT) were correlated to organics and nitrogen removal efficiency in industrial applications. Review of advances in MABR modeling techniques showed that current models lack the needed resolution for large and dynamic industrial systems. Additionally, the review compares municipal and industrial applications of MABRs, emphasizing the unique challenges and innovations required for their adoption in IW treatment. Overall, the MABR process was found to be feasible for industrial applications with pilot and/or demonstration-scale testing being necessary to further optimize process performance.

Insights into the impact of feeding with polymers on aerobic granular sludge development and stability: Performance and mechanisms

In this study, the effect of feeding with polymers on aerobic granular sludge (AGS) formation and stability was comprehensively investigated during 235-day operation. Results showed that the granules developed in starch-fed reactor possessed fluffy surface with overgrowth of granule size, and 60 % flocs were produced in protein-fed reactor, identifying feeding with polymers deteriorated AGS development and stability. Moreover, substrate conversion analysis revealed that ∼ 14 % of the consumed COD was recovered as storage of poly-hydroxybutyrate in polymer-fed reactor, much lower than 63.7 % in acetate-fed reactor. Extended Derjaguin-Landau-Verwey-Overbeek theory analysis showed that feeding with polymers increased the cell-cell energy barriers to 307.8 ∼ 388.8 kT, weakening the microbial aggregation capacity in AGS system. Microbial population results found that the relative abundance of Candidatus_Competibacter in protein- and starch-fed reactor displayed 0.01 ∼ 6.1 % and 0.07 ∼ 3.7 %, much lower than 81 % in acetate-fed reactor. Assembly mechanism analysis demonstrated that feeding with polymers enhanced the stochastic selection in shaping microbial assembly.

Genome-resolved metatranscriptomics unveils distinct microbial functionalities across aggregate sizes in aerobic granular sludge

Microbial aggregates of different sizes in aerobic granular sludge (AGS) systems have been shown to exhibit distinct microbial community compositions. However, studies comparing the microbial activities of different-sized aggregates in AGS systems remain limited. In this study, genome-resolved metatranscriptomics was used to investigate microbial activity patterns within differently sized aggregates in a full-scale AGS plant. Our analysis revealed a weak correlation between the relative abundance of metagenome-assembled genomes (MAGs) and their transcriptomic activity, indicating that microbial abundance does not directly correspond to metabolic activity within the system. Flocculent sludge (FL; <0.2 mm) predominantly featured active nitrifiers and fermentative polyphosphate-accumulating organisms (PAOs) from Candidatus Phosphoribacter, while small granules (SG; 0.2-1.0 mm) and large granules (LG; >1.0 mm) hosted more metabolically active PAOs affiliated with Ca. Accumulibacter. Differential gene expression analysis further supported these findings, demonstrating significantly higher expression levels of key phosphorus uptake genes associated with Ca. Accumulibacter in granular sludge (SG and LG) compared to flocculent sludge. Conversely, Ca. Phosphoribacter showed higher expression of these genes in the FL fraction. This study highlights distinct functional roles and metabolic activities of crucial microbial communities depending on aggregate size within AGS systems, offering new insights into optimizing wastewater treatment processes.

Relaxation-weighted MRI analysis of biofilm EPS: Differentiating biopolymers, cells, and water

Biofilms are a highly complex community of microorganisms embedded in a protective extracellular polymeric substance (EPS). Successful biofilm control requires a variety of approaches to better understand the structure-function relationship of the EPS matrix. Magnetic resonance imaging (MRI) is a versatile tool which can measure spatial structure, diffusion, and flow velocities in three dimensions and in situ. It is well-suited to characterize biofilms under natural conditions and at different length scales. MRI contrast is dictated by T 1 and T 2 relaxation times which vary spatially depending on the local chemical and physical environment of the sample. Previous studies have demonstrated that MRI can provide important insights into the internal structure of biofilms, but the contribution of major biofilm components-such as proteins, polysaccharides, and cells-to MRI contrast is not fully understood. This study explores how these components affect contrast in T 1 -and T 2 -weighted MRI by analyzing artificial biofilms with well-defined properties modeled after aerobic granular sludge (AGS), compact spherical biofilm aggregates used in wastewater treatment. MRI of these biofilm models showed that certain gel-forming polysaccharides are a major source of T 2 contrast, while other polysaccharides show minimal contrast. Proteins were found to reduce T 2 contrast slightly when combined with polysaccharides, while cells had a negligible impact on T 2 but showed T 1 contrast. Patterns observed in the model biofilms served as a reference for examining T 2 and T 1 -weighted contrast in the void spaces of two distinct AGS granules, allowing for a qualitative evaluation of the EPS components which may be present. Further insights provided by MRI may help improve understanding of the biofilm matrix and guide how to better manage biofilms in wastewater, clinical, and industrial settings.

Utilizing anaerobic substrate distribution for growth of aerobic granular sludge in continuous-flow reactors

The development of continuous flow reactors (CFRs) employing aerobic granular sludge (AGS) for the retrofit of existing wastewater treatment plants (WWTPs) using a continuous-flow activated sludge (CFAS) system has garnered increasing interest. This follows the worldwide adoption of AGS technology in sequencing batch reactors (SBRs). The better settleability of AGS compared to AS allows for process intensification of existing wastewater treatment plants without the difficult conversion of often relatively shallow CFRs to deeper AGS-SBRs. To retrofit existing CFAS systems with AGS, achieving both increased hydraulic capacity and enhanced biological nutrient removal necessitates the formation of granular sludge based on the same selective pressures applied in AGS-SBRs. Previous efforts have focussed mainly on the selective wasting of flocculent sludge and retaining granular sludge to drive aerobic granulation. In this study a pilot-scale CFR was developed to best mimic the implementation of the granulation mechanisms of full-scale AGS-SBRs. The pilot-scale reactor was fed with pre-settled municipal wastewater. We established metrics to assess the degree to which the proposed mechanisms were implemented in the pilot-scale CFR and compared them to data from full-scale AGS-SBRs, specifically with respect to the anaerobic distribution of granule forming substrates (GFS). The selective pressures for granular sludge formation were implemented through inclusion of anaerobic upflow selectors with a water depth of 2.5 meters, which yielded a sludge with properties similar to AGS from full-scale SBRs. In comparison to the CFAS system at Harnaschpolder WWTP treating the same pre-settled wastewater, a more than twofold increase in volumetric removal capacity for both phosphorus and nitrogen was achieved. The use of a completely mixed anaerobic selector, as opposed to an anaerobic upflow selector, caused a shift in EBPR activity from the largest towards the smallest size class, while nitrification was majorly unaffected. Anaerobic selective feeding via bottom-feeding is, therefore, favorable for the long-term stability of AGS, especially for less acidified wastewater. The research underlines the potential of AGS for enhancing the hydraulic and biological treatment capacity of existing CFAS systems.

Improving the thermal stability of phytase using core-shell hydrogel beads

A core-shell hydrogel bead system was designed to maintain the catalytic activity of phytase and protect its enzymatic functionality from heat treatment. The designed structure consists of a chitosan-phytase complex core and an alginate-carrageenan hydrogel shell. The core-shell hydrogel was optimized to improve phytase encapsulation efficiency and increase the thermal stability of the encapsulated phytase. After heat treatment, encapsulated phytase retained ∼ 70 % of its catalytic activity and the same secondary structure of free phytase. Fourier transform infrared spectroscopy indicated strong intermolecular interactions between chitosan and phytase in the core, but little interaction between the core and the alginate and κ-carrageenan shell, this supports the structural and functional stability of the phytase. Differential scanning calorimetry confirmed that the designed core-shell structure had a higher melting point. Encapsulating phytase in a core-shell hydrogel bead can enhance the thermal stability of phytase, which broadens the potential applications for phytase delivery.

Environmental and ecological controls of the spatial distribution of microbial populations in aggregates

In microbial communities, the ecological interactions between species of different populations are responsible for the spatial distributions observed in aggregates (granules, biofilms or flocs). To explore the underlying mechanisms that control these processes, we have developed a mathematical modelling framework able to describe, label and quantify defined spatial structures that arise from microbial and environmental interactions in communities. An artificial system of three populations collaborating or competing in an aggregate is simulated using individual-based modelling under different environmental conditions. In this study, neutralism, competition, commensalism and concurrence of commensalism and competition have been considered. We were able to identify interspecific segregation of communities that appears in competitive environments (columned stratification), and a layered distribution of populations that emerges in commensal (layered stratification). When different ecological interactions were considered in the same aggregate, the resultant spatial distribution was identified as the one controlled by the most limiting substrate. A theoretical modulus was defined, with which we were able to quantify the effect of environmental conditions and ecological interactions to predict the most probable spatial distribution. The specific microbial patterns observed in our results allowed us to identify the optimal spatial organizations for bacteria to thrive when building a microbial community and how this permitted co-existence of populations at different growth rates. Our model reveals that although ecological relationships between different species dictate the distribution of bacteria, the environment controls the final spatial distribution of the community.