Activated Sludge Research Articles

Predicting the removal efficiency of titanium dioxide nanoparticles in an activated sludge system using fate modeling depending on the operating conditions

Wastewater treatment plants (WWTPs) are a major discharge pathway for engineered nanoparticles (ENPs) that can potentially impact aquatic systems, making it crucial to understand ENP behavior in these facilities. In this study, we developed a fate model for titanium dioxide (TiO2) nanoparticles (NPs) to predict their removal efficiency (RE) in activated sludge (AS) systems. The model, based on material balance equations for free and sludge-attached TiO2 NPs, incorporated a linear-adsorption partition coefficient (Kd) and pseudo-second-order kinetics for TiO2 NP attachment to the activated sludge. Validated with data from three WWTPs, the model investigated RE correlations with inflow TiO2 NP concentration, sludge retention time (SRT), hydraulic retention time (HRT), mixed liquor suspended solid (MLSS) concentration, and water temperature. The model reasonably predicted the comparative performance of the WWTPs but underestimated the RE by up to ∼29 %, probably due to system simplification, limited Kd data, the presence of other Ti-containing NPs besides TiO2 NPs, and unincorporated removal mechanisms such as sweeping in the secondary clarifier. The model revealed favorable design/operating conditions for increasing the TiO2 NP RE of the AS system: shortening the SRT, increasing the MLSS concentration, and increasing the water temperature. The developed model could be useful for estimating and comparing the expected TiO2 NP REs across different WWTPs under varying operating conditions or for tracing the material flow and fate of TiO2 NPs in environmental compartments involving WWTPs, both regionally and country-wide.

Enhancement of livestock wastewater treatment by a novel wooden-modified biocarrier

Intensive livestock wastewater poses threat to ecosystem. A novel wooden-modified biocarrier was applied in this study to enhance the livestock wastewater treatment in anoxic-aerobic systems. Compared to the ordinary polyethylene (PE) biocarrier, the novel wooden-modified biocarrier improved the biomass owing to its rough surface and porous side wall, and had better nitrogen removal ability. The biomass of wooden-modified biocarrier was 6.3 ± 1.1 and 36.4 ± 17.0 times that of PE biocarrier in anoxic and aerobic condition, respectively. The removal rates of ammonia nitrogen and total nitrogen of this novel biocarrier on specific biofilm's aera eventually stabilized at 0.64 ± 0.10 and 0.94 ± 0.21 g N/m2/d, respectively. Notably, this wooden-modified biocarrier was conducive to increase nitrogen removal by simultaneous nitrification and denitrification to some extent. The biofilm on novel modified biocarrier had higher extracellular polymeric substances (EPS) contents than activated sludge (AS), and the proportions of polysaccharides (PS) in EPS from biocarrier were more than those from AS. Compared to PE biocarrier and AS, the wooden-modified biocarriers enhanced the enrichment of nitrifying and denitrifying bacteria, and promoted the membrane transport and aerobic nitrogen metabolism. This study confirmed the superiority of wooden-modified biocarrier and provided reference for the treatment of high concentration sewage in full-scale project.

Method evaluation for viruses in activated sludge: Concentration, sequencing, and identification

Activated sludge (AS) in wastewater treatment plants is one of the largest artificial microbial ecosystems on earth and it makes enormous contributions to human societies. Viruses are an important component in AS with a high abundance. However, their communities and functionalities have not been as widely explored as those of other microorganisms, such as bacteria. This gap is mainly due to technical challenges in effective viral concentration, extraction, and sequencing. In this study, we compared four kinds of concentration methods, two sequencing approaches, and four identification bioinformatic tools to evaluate the whole analysis workflow for viruses in AS. Results showed flocculation, filtration, and resuspension (FFR) could get the longest DNA lengths and ultracentrifugation obtained the highest DNA yields for viruses in AS. Based on the results of present study, FFR and tangential flow filtration with the membrane pore size of 100 kDa were most recommended to concentrate viruses in AS samples with huge volumes. Besides, different concentration methods could get different viral catalogs and thus multiple methods should be combined to get the whole picture of viruses in the system. In addition, geNomad was the most recommended identification tool for viruses in the present study and the long-read sequencing could improve the assembly statistics of viruses when compared with the short-read sequencing. For the 8192 viral operational taxonomic units in this study, 95.1 % of them were phages and belonged to the same lineage at the order level of Caudovirales. Virulent phages dominated the AS system and Pseudomonadota were the main host. Taken together, this study provides new insights into methods selection for virus research of AS.

Combined activated sludge and sand filtration for purification of UASB effluent with high suspended solids from water hyacinth juice

Rapid biogasification of water hyacinth, a globally overgrown species, using compression and up-flow anaerobic sludge blanket (UASB) treatment of the juice has recently been proposed. This study aimed to establish a post-purification system for UASB-treated juice to effectively utilize the remaining nutrients for valuable products, such as vegetables and microalgae. To easily remove hard-to-degrade suspended solids (SS) and organic matter from UASB-treated juice, the activated sludge (AS) and sand filtration processes—conventional biological treatments—were introduced, with a focus on their physical treatment properties.Over 76% of SS and 43% of the organic carbon were removed from UASB-treated juice during the process. The hydraulic retention time of the AS was reduced to one day, indicating the potential of minimizing the facility size. The light transmittance, which is crucial for microalgae mediums, improved sevenfold. Even after most of the SS was removed by the AS, the sand filtration further increased the light transmittance by 1.4 times. The AS effectively removed most of the SS and organic matter, whereas sand filtration enhanced the treatment stability and further improved the light transmittance. NH4+ was mostly oxidized to NO3-, which is less toxic to plants. The total inorganic nitrogen content remained high after treatment, suggesting that UASB effluents from water hyacinth can be used as a nutrient source for hydroponics and microalgae cultivation in developing countries.

Unveiling the potential role of virus-encoded polyphosphate kinases in enhancing phosphorus removal in activated sludge systems

While microbial phosphate removal in activated sludge (AS) systems has been extensively studied, the role of viruses in this process remains largely unexplored. In this study, we identified 149 viral auxiliary metabolic genes associated with phosphorus cycling from 2,510 viral contigs (VCs) derived from AS systems. Notably, polyphosphate kinase 1 (ppk1) and polyphosphate kinase 2 (ppk2) genes, which are primarily responsible for phosphate removal, were found in five unclassified VCs. These genes exhibited conserved protein structures and active catalytic sites, indicating a pivotal role of viruses in enhancing phosphorus removal. Phylogenetic analysis demonstrated a close relationship between viral ppk genes and their bacterial counterparts, suggesting the occurrence of horizontal gene transfer. Furthermore, experimental assays validated that viral ppk genes enhanced host phosphate removal capabilities. VCs carrying ppk genes were observed across diverse ecological and geographical contexts, suggesting their potential to bolster host functions in varied environmental and nutrient settings, spanning natural and engineered systems. These findings uncover a previously underappreciated mechanism by which viruses enhance phosphate removal in wastewater treatment plants. Overall, our study highlights the potential for leveraging virus-encoded genes to improve the efficiency of biological phosphorus removal processes, offering new insights into the microbial ecology of AS systems and the role of viruses in biogeochemical cycling.

Two-way role of iron-carbon in biochemical reactions: microelectrolysis and enhanced activity of aerobic granular sludge for efficient refractory wastewater treatment

Industrial wastewater contained a large amount of refractory organics, and single treatment processes had limitations. This study investigated the mechanism of refractory organics removal using iron-carbon built-in coupled activated sludge (ICAS) and explored the role and function of iron-carbon (IC) within the ICAS system. The aerobic granular sludge (AGS) cultivated with IC exhibited a loose surface and a tight interior structure. Iron in the AGS concentrated near the outer layer to form a crust, which protected the inner microorganisms. IC promoted EPS secretion and regulated the abundance of positive and negative signaling molecules to maintain AGS stability. Experiments using quinoline as a model refractory organic showed that both physical adsorption by IC and biological adsorption by sludge rapidly fixed a large amount of pollutants, providing a buffer capacity for the system. The iron mineral crust on the AGS surface enhanced quinoline adsorption. Hydroxylation was the first step in quinoline degradation, with IC upregulating the genes iorA/B, qorB, and wrbA involved in this process, and the relative abundances of quinoline-degrading bacteria. Both pyridine ring opening and benzene ring cleavage occurred in the single IC system, and the microelectrolysis process produced •OH and [H], which made degradation pathway for quinoline through IC more complex than microbial degradation. Although the IC-mediated pathway accounted for only a small part of overall quinoline removal in the ICAS system, the ICAS system not only preserved the microelectrolysis process but also enhanced microbial metabolic activity. This work provided insights into the synergistic removal of pollutants and maintenance of AGS stability by the ICAS process, ensuring efficient treatment of refractory organic wastewater.

Response to shock load of titanium dioxide nanoparticles on aerobic granular sludge and algal-bacterial granular sludge processes

Titanium dioxide nanoparticles (TiO2 NPs) are extensively used in various fields and can consequently be detected in wastewater, making it necessary to study their potential impacts on biological wastewater treatment processes. In this study, the shock-load impacts of TiO2 NPs were investigated at concentrations ranging between 1 and 200 mg L−1 on nutrient removal, extracellular polymeric substances (EPSs), microbial activity in aerobic granular sludge (AGS), and algal-bacterial granular sludge (AB-AGS) bioreactors. The results indicated that low concentration (≤10 mg L−1) TiO2 NPs had no effect on microbial activity or the removal of chemical oxygen demand (COD), nitrogen, and phosphorus, due to the increased production of extracellular polymeric substances (EPSs) in the sludge. In contrast, the performance of both AGS and AB-AGS bioreactors gradually deteriorated as the concentration of TiO2 NPs in the influent increased to 50, 100, and 200 mg L−1. Specifically, the ammonia‑nitrogen removal rate in AGS decreased from 99.9 % to 88.6 %, while in AB-AGS it dropped to 91.3 % at 200 mg L−1 TiO2 NPs. Furthermore, the nitrate‑nitrogen levels remained stable in AB-AGS, while NO3-N was detected in the effluent of AGS at 100 and 200 mg L−1. Microbial activities change similarly as smaller decrease in the specific ammonia uptake rate (SAUR) and specific nitrate uptake rate (SNUR) was found in AB-AGS compared to those in AGS. Overall, the algal-bacterial sludge exhibited higher resilience against TiO2 NPs, which was attributed to a) higher EPS volume, b) smaller decrease in LB-EPS, and c) the favorable protein to polysaccharide (PN/PS) ratio. This in turn, along with the symbiotic relationship between the algae and bacteria, mitigates the toxic effects of nanoparticles.

Intelligent optimal control model of selection pressure for rapid culture of aerobic granular sludge based on machine learning and simulated annealing algorithm

Aerobic Granular Sludge (AGS) has advantages over Activated sludge (AS) but faces challenges with long granulation periods. In this study, a novel grey-box model is devised to optimize the cultivation of AGS to shorten the formation time. This model is based on an existing white-box model. The modeling process starts with the application of four sensitivity analysis methods to assess the 12 model metrics selected. Subsequently, 12 prediction models were constructed by combining the six Machine learning (ML) algorithms and integrated algorithms, with the best performance selected (R2 = 0.98). Finally, an AGS selection pressure planning model was designed in conjunction with a simulated annealing (SA) algorithm to guide AGS training. The results demonstrate that AGS formation could be achieved within four days under the model’s optimal control. Therefore, the establishment of this model provides a new technique for the cultivation of AGS.

Investigating potential auxiliary anaerobic digestion activity of phage under polyvinyl chloride microplastic stress

Polyvinyl chloride (PVC) microplastics present in sewage were trapped in sludge, thereby hindering anaerobic digestion performance of waste active sludge (WAS). Phages regulate virocell metabolism by encoding auxiliary metabolic genes (AMGs) related to energy acquisition and material degradation, supporting hosts survive in harsh environments and play a crucial role in biogeochemical cycles. This study investigated the potential effects of phages on the recovery of WAS anaerobic digestion under PVC stress. We observed a significant alteration in the phage community induced by PVC microplastics. Phages encoded AMGs related to anaerobic digestion and cell growth probably alleviate PVC microplastics inhibition on WAS anaerobic digestion, and 54.2 % of hydrolysis-related GHs and 40.8 % of acidification-related AMGs were actively transcribed in the PVC-exposed group. Additionally, the degradation of chitin and peptidoglycan during hydrolysis and the conversion of glucose to pyruvate during acidification were more susceptible to phages. Prediction of phage-host relationship indicated that the phyla Pseudomonadota were predominantly targeted hosts by hydrolysis-related and acidification-related phages, and PVC toxicity had minimal impact on phage-host interaction. Our findings highlight the importance of phages in anaerobic digestion and provide a novel strategy for using phages in the functional recovery of microplastic-exposed sludge.

Technical feasibility and modeling of enzymatic pre-treatments of organic fraction of municipal solid waste to improve anaerobic digestion

The study explored the combined effects of enzymatic pre-treatment and anaerobic digestion (AD) on the organic fraction of municipal solid wastes (OFMSW) through experimental and multicriteria decision-making approaches. Five enzymes (UPP2, MPCS, USC4, USE2, and A. niger) and their dosages were studied. AD parameters included two inoculum origins (waste active sludge - WAS - and cow-agricultural sludge - CAS), the substrate: inoculum (SI) ratio, and inoculum incubation time (INOC). Desirability functions were used to optimize the multiple experimental responses simultaneously by converting each of them into values from 0 (unacceptable) to 1 (completely acceptable) and then combining these into a global desirability (D). D highlighted that higher enzyme dosages, INOC, and SI, improved AD performances, with optimal DOSE (at the highest level adopted for each enzyme) and INOC (5–10 d). AD tests with the five enzymes increased CH4 production by 10–13%v/v compared to untreated OFMSW. For UPP2 and MPCS, increasing DOSE boosted the biogas production, while increasing INOC enhanced the CH4 content. MPCS reached the highest efficiency (478. 43 NL CH4/kg VS with CAS, SI = 2:1, INOC = 10 d), followed by UPP2. Furthermore, higher INOC reduced A. niger doses, increasing CH4 production by 9%v/v compared to literature, with 5–10 d INOC (452.86 NL s/kg VS with WAS, SI = 2:1).

Studying the productivity of sewage sludge (SS) components for photocatalytic CO2 transformation to CO and methane

AbstractEnergy-efficient photocatalytic CO2 conversion to sustainable solar fuels is a promising approach for simultaneously resolving energy and environmental concerns. The increased growth of sewage sludge necessitates research and innovation to propose more commercially viable options for lowering the socioeconomic and environmental complications associated with its current treatment. Sewage sludge can be applied to valuable products or used as a feedstock for energy production. According to the characterization results, the sewage sludge contains several metallic oxides (M), including Ni, Al, Mn, and Cu, and semiconductors (Fe2O3 and ZnO). According to the proposed mechanism, ZnO acts as an electron conductor between the Fe2O3 and the active sewage sludge due to forming an n–n type heterojunction. Under visible-light irradiation, photocatalytic CO2 reduction of sewage sludge was investigated using a fixed bed reactor. The CO2 reduction produced CO and CH4, with production rates of 9.76 and 4.20 µmol g−1 h−1, respectively, via the electrical conductivity in the sewage sludge elements. Furthermore, the impacts of photocatalyst loading, system reforming, light effect and pressure range were examined, where the methane yield at 0.1 g was 4.23 and 2.26 times significantly higher than at 0.05 and 0.2 g, correspondingly. With catalyst loadings of 0.1 and 0.2 g, the mono-oxide productivity was 1.69 and 2.58, notably greater, respectively. Moreover, the best yield of the CO and methane was obtained by using 0.3 bar as pressure and 10% methanol in H2O/CO2 as a reducing agent. Finally, using sewage sludge to produce a solar fuel based on the presence of active metallic oxide and semi-conductor heterojunctions provides novel insights from molecular and engineering perspectives into converting CO2 to a green fuel using wastewater sludge. Graphical abstract

High-throughput single-cell sequencing of activated sludge microbiome

Wastewater treatment plants (WWTPs) represent one of biotechnology's largest and most critical applications, playing a pivotal role in environmental protection and public health. In WWTPs, activated sludge (AS) plays a major role in removing contaminants and pathogens from wastewater. While metagenomics has advanced our understanding of microbial communities, it still faces challenges in revealing the genomic heterogeneity of cells, uncovering the microbial dark matter, and establishing precise links between genetic elements and their host cells as a bulk method. These issues could be largely resolved by single-cell sequencing, which can offer unprecedented resolution to show the unique genetic information. Here we show the high-throughput single-cell sequencing to the AS microbiome. The single-amplified genomes (SAGs) of 15,110 individual cells were clustered into 2,454 SAG bins. We find that 27.5% of the genomes in the AS microbial community represent potential novel species, highlighting the presence of microbial dark matter. Furthermore, we identified 1,137 antibiotic resistance genes (ARGs), 10,450 plasmid fragments, and 1,343 phage contigs, with shared plasmid and phage groups broadly distributed among hosts, indicating a high frequency of horizontal gene transfer (HGT) within the AS microbiome. Complementary analysis using 1,529 metagenome-assembled genomes from the AS samples allowed for the taxonomic classification of 98 SAG bins, which were previously unclassified. Our study establishes the feasibility of single-cell sequencing in characterizing the AS microbiome, providing novel insights into its ecological dynamics, and deepening our understanding of HGT processes, particularly those involving ARGs. Additionally, this valuable tool could monitor the distribution, spread, and pathogenic hosts of ARGs both within AS environments and between AS and other environments, which will ultimately contribute to developing a health risk evaluation system for diverse environments within a One Health framework.

Leaching behavior of microplastics during sludge mechanical dewatering and its effect on activated sludge

Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2–25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

Microbial core communities in activated sludge plants are strongly affected by immigration and geography

BackgroundThe microbiota in wastewater treatment plants (WWTPs) and incoming wastewater is critical for the treatment process, the preservation of natural ecosystems and human health, and for the recovery of resources and achievement of sustainability goals. Both core species and conditionally rare and abundant taxa (CRAT) are considered process-critical but little is known about identity as well as true functional and ecological importance. Here, we present a comprehensive investigation of the microbiota of 84 municipal activated sludge (AS) plants with nutrient removal treating ~ 70% of all wastewater within a confined geographical area, Denmark (43,000 km2). With the use of an ecosystem-specific database (MiDAS 5.2), species-level classification allowed us to investigate the core and CRAT species, whether they were active, and important factors determining their presence.ResultsWe established a comprehensive catalog of species with names or placeholder names showing each plant contained approx. 2,500 different species. Core and CRAT represented in total 258 species, constituting around 50% of all reads in every plant. However, not all core and CRAT could be regarded as process-critical as growth rate calculations revealed that 43% did not grow in the AS plants and were present only because of continuous immigration from the influent. Analyses of regional microbiota differences and distance decay patterns revealed a stronger effect for species than genera, demonstrating that geography had a clear effect on the AS microbiota, even across a limited geographical area such as Denmark (43,000 km2).ConclusionsThe study is the first comprehensive investigation of WWTPs in a confined geographical area providing new insights in our understanding of activated sludge microbiology by introducing a concept of combining immigration and growth calculation with identifying core and CRAT to reveal the true ecosystem-critical organisms. Additionally, the clear biogeographical pattern on this scale highlights the need for more region-level studies to find regional process-critical taxa (core and CRAT), especially at species and amplicon sequence variant (ASV) level.

Aerobic granular sludge inoculant for enhancing high salinity wastewater treatment: Performance and value-added biopolymer recovery

In this study, two lab-scale aerobic granular sludge (AGS) systems, seeded with intertidal wetland sediment (IWS) and activated sludge (AS), were constructed to compare their treatment performances and alginate-like exopolymers (ALE) recovery potential in high salinity wastewater treatment. Both reactors (RIWS and RAS) exhibited excellent total organic carbon (TOC) reduction rates > 95.0 %, while RIWS exhibited an improved total nitrogen (TN) removal than RAS (84.4 % vs 75.7 %). The presence of several inorganic particulates (acted as nucleus) in IWS accelerated the formation of granules in RIWS. The ALE yield of RIWS reached 466.6 ± 52.2 mg/g VSS, which was 1.6 times higher than that of RAS (286.2 ± 5.2 mg/g VSS). Moreover, to illustrate the different ALE recovery potentials, the proposed ALE biosynthesis pathway was also assessed. It was observed that the abundance of function genes encoding ALE biosynthesis of RIWS was significantly higher than that of RAS, revealing its superior ALE recovery potential. This study proposed a novel and effective treatment method for high-salinity wastewater with high potential resource recovery.

Enhancing biofilm formation with powder carriers for efficient nitrogen and phosphorus removal

This study assesses the improvement in nitrogen and phosphorus removal from wastewater achieved through the integration of zeolite and attapulgite carrier materials into the activated sludge (AS) process. It was found that the addition of these materials significantly enhanced the processing performance of the reactor. Specifically, the use of zeolite and attapulgite powders increased sludge particle sizes to averages of 231.56 μm and 219.62 μm, respectively. This facilitated micro-granule formation, substantially improving the settling characteristics of the sludge and boosting the activity and proliferation of essential microbes. Illumina MiSeq sequencing demonstrated significant accumulations of DGAOs (Candidatus_Competibacter) and DPAOs (Candidatus_Accumulibacter). Furthermore, these carriers augmented the protein content in extracellular polymers, enhancing the hydrophobicity of the sludge and promoting aggregation. Comparative analysis based on the extended Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory indicated a preferential adhesion affinity of sludge for zeolite compared to attapulgite, attributed primarily to Lewis acid-base and electric double-layer interactions. These findings underscore zeolite's enhanced efficacy in biomass fixation and suggest significant potential for the technological advancement of wastewater treatment plants.

Characteristics and nontargeted metabolomics analysis of anammox granular sludge under short-term exposure to polypropylene and polylactic acid microplastics

A significant quantity of microplastics (MPs) is concealed within biological sludge. Current research predominantly examines the effects of non-biodegradable MPs on traditional sludge. However, the influence of biodegradable MPs on the functional microbial activity of anaerobic ammonium oxidation granular sludge (AnGS) remains inadequately explored. This study specifically investigated the effects of non-biodegradable polypropylene (PP) MPs and biodegradable polylactic acid (PLA) MPs on AnGS under short-term stress. The study found that PP MPs inhibited nitrogen removal performance, reducing nitrogen removal efficiency by 1.14% (100 mesh) and 5.77% (1000 mesh) respectively, along with decreased hydrazine dehydrogenase (HDH) activity. Conversely, PLA promoted denitrification performance, increasing efficiency by 8.21% (100 mesh) and 6.54% (1000 mesh). In response to MPs-induced environmental stress, the secretion of extracellular polymeric substances (EPS) increased in all experimental groups. Additionally, non-targeted metabolomic analysis revealed a decrease in the abundance of KEGG pathways related to carbon and amino acid metabolism in the experimental groups, while the enrichment of terephthalate and benzamide in the PLA groups significantly impacted its process. These findings offered valuable insights into the impact of MPs on anaerobic ammonium oxidation (anammox) and could potentially enhance its application.

Morphological characteristics of activated sludge recovered from biological reactors impact on the energy requirement for centrifugal dewatering

The effect of sludge dewatering on handling and transport costs as well as the impact of various parameters like sludge characteristics, the used dewatering equipment and the adopted specific operating conditions, on the efficiency of this step, were considered in the present study. The influence of a laboratory-scale centrifugation for dewatering activated sludge (AS) was also investigated. Additionally, models to describe the relationships between independent variables like centrifugation speed, AS volume and fixed time and dependent variables like the percentage of solid cake (% GS). The used approach was based on the response surface methodology (RSM) along with a central composite design experiment, considering three distinct types of AS: healthy (BS), partially bulking (BF), and deflocculated (BD) sludges. The morphological characteristics of the sludge do have an effect on the operating conditions for the centrifugation, hence the energy consumption for a desired dewatering level. For the case of BS sludge, a centrifugation at 2600 rpm for 10 min, using a 10.3 mL plug, led to a solid cake of 12.65 %, whereas for BD sludge, with a higher centrifugation at 3000 rpm for 17.30 min and a smaller plug volume (8 mL) led to 6.82 %, roughly half of the previous percentage.

Lab-scale evaluation of Microalgal-Bacterial granular sludge as a sustainable alternative for brewery wastewater treatment

Microalgal-bacterial granular sludge (MBGS) could offer a sustainable alternative to traditional aerobic methods in brewery wastewater (BWW) treatment. This study compared MBGS with conventional activated sludge (AS) in treating real BWW and highlighted its advantages and challenges. MBGS achieved comparable chemical oxygen demand removal efficiency (93%) compared to AS (89%). Additionally, MBGS exhibited higher phosphate removal capabilities than AS. Extra nitrogen was added to influent to balance C/N ratio of BWW. MBGS was robust in handling C/N ratio fluctuations with an 82% total nitrogen removal efficiency. Metagenomic analysis further indicated that most of the genes involved in carbon, nitrogen and phosphorus metabolism were up-regulated in MBGS compared to AS. Despite changes in the microbial community and settling ability due to high starch and sugar content in BWW, MBGS demonstrated high efficiency and sustainability. Further research should optimize MBGS operation strategies to fully realize its potential for sustainable BWW treatment.

Activated sludge microbial community assembly: the role of influent microbial community immigration.

Wastewater treatment plants (WWTPs) are host to diverse microbial communities and receive a constant influx of microbes from influent wastewater. However, the impact of immigrants on the structure and activities of the activated sludge (AS) microbial community remains unclear. To gain insight on this phenomenon known as perpetual community coalescence, the current study utilized controlled manipulative experiments that decoupled the influent wastewater composition from the microbial populations to reveal the fundamental mechanisms involved in immigration between sewers and AS-WWTP. The immigration dynamics of heterotrophs were analyzed by harvesting wastewater biomass solids from three different sewer systems and adding to synthetic wastewater. Immigrating influent populations were observed to contribute up to 14% of the sequencing reads in the AS. By modeling the net growth rate of taxa, it was revealed that immigrants primarily exhibited low or negative net growth rates. By developing a protocol to reproducibly grow AS-WWTP communities in the lab, we have laid down the foundational principles for the testing of operational factors creating community variations with low noise and appropriate replication. Understanding the processes that drive microbial community diversity and assembly is a key question in microbial ecology. In the future, this knowledge can be used to manipulate the structure of microbial communities and improve system performance in WWTPs.IMPORTANCEIn biological wastewater treatment processes, the microbial community composition is essential in the performance and stability of the system. This study developed a reproducible protocol to investigate the impact of influent immigration (or perpetual coalescence of the sewer and activated sludge communities) with appropriate reproducibility and controls, allowing intrinsic definitions of core and immigrant populations to be established. The method developed herein will allow sequential manipulative experiments to be performed to test specific hypothesis and optimize wastewater treatment processes to meet new treatment goals.