Microbiome structure and function in parallel full-scale aerobic granular sludge and activated sludge processes.

Aerobic granular sludge (AGS) and conventional activated sludge (CAS) are two different biological wastewater treatment processes. AGS consists of self-immobilised microorganisms that are transformed into spherical biofilms, whereas CAS has floccular sludge of lower density. In this study, we investigated the treatment performance and microbiome dynamics of two full-scale AGS reactors and a parallel CAS system at a municipal WWTP in Sweden. Both systems produced low effluent concentrations, with some fluctuations in phosphate and nitrate mainly due to variations in organic substrate availability. The microbial diversity was slightly higher in the AGS, with different dynamics in the microbiome over time. Seasonal periodicity was observed in both sludge types, with a larger shift in the CAS microbiome compared to the AGS. Groups important for reactor function, such as ammonia-oxidising bacteria (AOB), nitrite-oxidising bacteria (NOB), polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs), followed similar trends in both systems, with higher relative abundances of PAOs and GAOs in the AGS. However, microbial composition and dynamics differed between the two systems at the genus level. For instance, among PAOs, Tetrasphaera was more prevalent in the AGS, while Dechloromonas was more common in the CAS. Among NOB, Ca. Nitrotoga had a higher relative abundance in the AGS, while Nitrospira was the main nitrifier in the CAS. Furthermore, network analysis revealed the clustering of the various genera within the guilds to modules with different temporal patterns, suggesting functional redundancy in both AGS and CAS. KEY POINTS: • Microbial community succession in parallel full-scale aerobic granular sludge (AGS) and conventional activated sludge (CAS) processes. • Higher periodicity in microbial community structure in CAS compared to in AGS. • Similar functional groups between AGS and CAS but different composition and dynamics at genus level.

A novel carbon emission evaluation model for anaerobic-anoxic-oxic urban sewage treatment.

The proposal of the dual carbon goal and the blue economy in China has sparked a keen interest in carbon emissions reduction from sewage treatment. Carbon accounting in urban sewage plants serves as the foundation for carbon emission reduction in sewage treatment. This paper re-evaluated carbon accounting in the operational processes for urban sewage treatment plants to develop a novel carbon emission evaluation model for anaerobic-anoxic-oxic treatment plants. The results show that the carbon emissions generated by non-carbon dioxide gases far exceed the carbon emissions from carbon dioxide alone. Moreover, the recycling of sewage leads to carbon emissions reduction that offsets the carbon emissions generated during the operation of the sewage plant. Also, the carbon emissions generated by sewage treatment plants are lower than those generated by untreated sewage. The findings and insights provided in this paper provide valuable references for carbon accounting and the implementation of low-carbon practices in urban sewage treatment plants.

Anaerobic membrane bioreactors for municipal wastewater: Progress in resource and energy recovery improvement approaches.

Anaerobic membrane bioreactor (AnMBR) offer promise in municipal wastewater treatment, with potential benefits including high-quality effluent, energy recovery, sludge reduction, and mitigating greenhouse gas emissions. However, AnMBR face hurdles like membrane fouling, low energy recovery, etc. In light of net-zero carbon target and circular economy strategy, this work sought to evaluate novel AnMBR configurations, focusing on performance, fouling mitigation, net-energy generation, and nutrients-enhancing integrated configurations, such as forward osmosis (FO), membrane distillation (MD), bioelectrochemical systems (BES), membrane photobioreactor (MPBR), and partial nitrification-anammox (PN/A). In addition, we highlight the essential role of AnMBR in advancing the circular economy and propose ideas for the water-energy-climate nexus. While AnMBR has made significant progress, challenges, such as fouling and cost-effectiveness persist. Overall, the use of novel configurations and energy recovery strategies can further improve the sustainability and efficiency of AnMBR systems, making them a promising technology for future sustainable municipal wastewater treatment.

Effluent parameters prediction of a biological nutrient removal (BNR) process using different machine learning methods: A case study.

This paper proposes a novel targeted blend of machine learning (ML) based approaches for controlling wastewater treatment plant (WWTP) operation by predicting distributions of key effluent parameters of a biological nutrient removal (BNR) process. Two years of data were collected from Plajyolu wastewater treatment plant in Kocaeli, Türkiye and the effluent parameters were predicted using six machine learning algorithms to compare their performances. Based on mean absolute percentage error (MAPE) metric only, support vector regression machine (SVRM) with linear kernel method showed a good agreement for COD and BOD5, with the MAPE values of about 9% and 0.9%, respectively. Random Forest (RF) and EXtreme Gradient Boosting (XGBoost) regression were found to be the best algorithms for TN and TP effluent parameters, with the MAPE values of about 34% and 27%, respectively. Further, when the results were evaluated together according to all the performance metrics, RF, SVRM (with both linear kernel and RBF kernel), and Hybrid Regression algorithms generally made more successful predictions than Light GBM and XGBoost algorithms for all the parameters. Through this case study we demonstrated selective application of ML algorithms can be used to predict different effluent parameters more effectively. Wider implementation of this approach can potentially reduce the resource demands for active monitoring the environmental performance of WWTPs.

Efficient nitrogen removal from municipal wastewater using an integrated fixed-film activated sludge process in a novel air-lifting loop reactor: A pilot-scale demonstration.

A novel air-lifting loop reactor combines anoxic, oxic, and settling zones to achieve organic and nutrient removal, as well as solid-liquid separation. To address sludge settling ability and operation stability issues caused by low dissolved oxygen in aerobic zones, this study proposes using modified polypropylene carriers to establish a fixed-film activated sludge (IFAS) system. A pilot-scale demonstration of the IFAS-based air-lifting loop reactor is conducted, and the results show successful operation for approximately 300 days. The pilot-scale reactor achieves a maximum aerobic granulation ratio of 16% in the bulk liquid. The IFAS system contributes to efficient removal of organic matter (96%) and nitrogen (94%) by facilitating simultaneous nitrification and denitrification, as well as fast solid-liquid separation with a low sludge volume index of 34 mL/g. Microbial analysis reveals enrichment of functional bacteria involved in nitrification, denitrification, and flocculation throughout the operation process.

Metal-phenolic network as precursor complex coating for forward osmosis membrane with enhanced antifouling property.

In this study, a multi-functional layer was developed based on the commercially available cellulose triacetate (CTA) forward osmosis (FO) membrane to improve its antifouling property. Tannic acid/ferric ion (TA/Fe3+) complexes were firstly coated as a precursor layer on the membrane surface via self-assembly. Afterwards, the tannic acid/diethylenetriamine (TA/DETA) hydrophilic functional layer was further coated, following Ag/polyvinylpyrrolidone (PVP) anti-bacterial layer was formed in situ through the reducibility of TA to obtain TA/Fe3+-TA/DETA-Ag/PVP-modified membrane. The optimized precursor layer was acquired by adjusting the buffer solution pH to 8, TA/Fe3+ ratio to 4 and the number of self-assembled layers to 5. The permeability testing results illustrated that the functional layer had an insignificant effect on the membrane transport parameters. The TA/Fe3+-TA/DETA-Ag/PVP-modified membrane simultaneously exhibited excellent physical and chemical stability. The coated membrane also demonstrated enhanced anti-bacterial properties, achieving 98.63 and 97.30% inhibition against Staphylococcus aureus and Escherichia coli, respectively. Furthermore, the dynamic fouling experiment showed a 12% higher water flux decrease for the TA/Fe3+-TA/DETA-Ag/PVP CTA membrane compared to the nascent CTA membrane, which proved its excellent antifouling performance. This work provides a feasible strategy to heighten the antifouling property of the CTA FO membrane.

A short bibliographic review concerning biomethane production from wastewater sludge.

Biomethane production by anaerobic digestion (AD) of sludge from municipal wastewater treatment is a viable practice to valorise the residues of these plants. However, although the relevant literature is abundant, no comprehensive reviews have been recently published on this topic. Detailed information concerning the factors influencing the AD process and values of biomethane production from the sludge from municipal wastewater treatment plants (MWWTPs) on the global scale may support technicians and researchers in both the planning and the design steps of an AD process. This study proposes a systematic review and a meta-analysis of the factors that noticeably influence biomethane yield deriving from AD of sludge from MWWTP. The reported values were systematically analysed compared to the main factors driving AD, including publication year, geographical area of each study, type of digested sludge, treatment in the water line of the MWWTP, possible sludge pre-treatments, type of digestion process, hydraulic retention time (HRT) and temperature regime of the AD process. A higher biomethane production was registered in North American plants compared to countries in other continents. Older studies published between 2001 and 2005 reported lower mean values compared to the more recent experiments. A gradient of 'primary sludge' > 'mixed sludge' > 'wastewater activated sludge' was found for the mean biomethane yield in relation to the digested sludge type. The mean biomethane yields for different types of sludge on a global scale are 0.425, 0.296 and 0.176 Nm3 kg VS-1 for primary sludge, mixed sludge and waste activated sludge, respectively. Overall, the study demonstrates: (i) the very large variability of biomethane yields from AD of the residues from MWWTPs (mainly due to the different characteristics of sludge) and (ii) the non-significance of some factors (i.e. treatment in the water line, pre-treatments, type of process, HRT and temperature regime) on energy yields from the AD process.

Combination of Sequencing Batch Operation and A/O Process to Achieve Partial Mainstream Anammox: Pilot-Scale Demonstration and Microbial Ecological Mechanism.

In this study, sequencing batch operation was successfully combined with a pilot-scale anaerobic biofilm-modified anaerobic/aerobic membrane bioreactor to achieve anaerobic ammonium oxidation (anammox) without inoculation of anammox aggregates for municipal wastewater treatment. Both total nitrogen and phosphorus removal efficiencies of the reactor reached up to 80% in the 250-day operation, with effluent concentrations of 4.95 mg-N/L and 0.48 mg-P/L. In situ enrichment of anammox bacteria with a maximum relative abundance of 7.86% was observed in the anaerobic biofilm, contributing to 18.81% of nitrogen removal, with denitrification being the primary removal pathway (38.41%). Denitrifying phosphorus removal (DPR) (40.54%) and aerobic phosphorus uptake (48.40%) played comparable roles in phosphorus removal. Metagenomic sequencing results showed that the biofilm contained significantly lower abundances of NO-reducing functional genes than the bulk sludge (p < 0.01), favoring anammox catabolism in the former. Interactions between the anammox bacteria and flanking community were dominated by cooperation behaviors (e.g., nitrite supply, amino acids/vitamins exchange) in the anaerobic biofilm community network. Moreover, the hydrolytic/fermentative bacteria and endogenous heterotrophic bacteria (Dechloromonas, Candidatus competibacter) were substantially enriched under sequencing batch operation, which could alleviate the inhibition of anammox bacteria by complex organics. Overall, this study provides a feasible and promising strategy for substantially enriching anammox bacteria and achieving partial mainstream anammox as well as DPR.

Carbon-Restricted Anoxic Zone as an Overlooked Anammox Hotspot in Municipal Wastewater Treatment Plants.

The anoxic zone serves as the core functional unit in municipal wastewater treatment plants (MWWTPs). Unfortunately, in most cases, the downstream range of the anoxic zone is severely lacking in available organic carbon and thus contributes little to the removal of nutrients. This undesirable range is termed the "carbon-restricted anoxic zone", representing an insurmountable drawback for traditional MWWTPs. This study uncovers a previously overlooked role for the carbon-restricted anoxic zone: a hotspot for anaerobic ammonium oxidation (anammox). In a continuous-flow pilot-scale plant treating municipal wastewater (55 m3/d), virgin biocarriers were introduced into the carbon-restricted anoxic zone (downstream 25% of the anoxic zone with BOD5 of 5.9 ± 2.3 mg/L). During the 517-day monitoring, anammox bacteria highly self-enriched within the biofilms, with absolute and relative abundance reaching up to (9.4 ± 0.1) × 109 copies/g-VSS and 6.17% (Candidatus Brocadia), respectively. 15N isotopic tracing confirmed that anammox overwhelmingly dominated nitrogen metabolism, responsible for 92.5% of nitrogen removal. Following this upgrade, the contribution ratio of the carbon-restricted anoxic zone to total nitrogen removal increased from 9.2 ± 4.1% to 19.2 ± 4.2% (P < 0.001), while its N2O emission flux decreased by 84.5% (P < 0.001). These findings challenge stereotypes about the carbon-restricted anoxic zone and highlight the multiple environmental implications of this newfound anammox hotspot.

Step-feeding food waste fermentation liquid as supplementary carbon source for low C/N municipal wastewater treatment: Bench scale performance and response of microbial community.

Municipal wastewater treatment often lacks carbon source, while carbon-rich organics in food waste are deficiently utilized. In this study, the food waste fermentation liquid (FWFL) was step-fed into a bench-scale step-feed three-stage anoxic/aerobic system (SFTS-A/O), to investigate its performance in nutrients removal and the response of microbial community as a supplementary carbon source. The results showed that the total nitrogen (TN) removal rate increased by 21.8-109.3% after step-feeding FWFL. However, the biomass of the SFTS-A/O system was increased by 14.6% and 11.9% in the two phases of the experiment, respectively. Proteobacteria was found to be the dominant functional phyla induced by FWFL, and the increase of its abundance attributed to the enrichment of denitrifying bacteria and carbohydrate-metabolizing bacteria was responsible for the biomass increase. Azospira belonged to Proteobacteria phylum was the dominant denitrifying genera when step-fed with FWFL, its abundance was increased from 2.7% in series 1 (S1) to 18.6% in series 2 (S2) and became the keystone species in the microbial networks. Metagenomics analysis revealed that step-feeding FWFL enhanced the abundance of denitrification and carbohydrates-metabolism genes, which were encode mainly by Proteobacteria. This study constitutes a key step towards the application of FWFL as a supplementary carbon source for low C/N municipal wastewater treatment.

Realizable wastewater treatment process for carbon neutrality and energy sustainability: A review.

Despite a quick shift of global goals toward carbon-neutral infrastructure, activated sludge based conventional systems inhibit the Green New Deal. Here, a municipal wastewater treatment plant (MWWTP) for carbon neutrality and energy sustainability is suggested and discussed based on realizable technical aspects. Organics have been recovered using variously enhanced primary treatment techniques, thereby reducing oxygen demand for the oxidation of organics and maximizing biogas production in biological processes. Meanwhile, ammonium in organic-separated wastewater is bio-electrochemically oxidized to N2 and reduced to H2 under completely anaerobic conditions, resulting in the minimization of energy requirements and waste sludge production, which are the main problems in activated sludge based conventional processes. The anaerobic digestion process converts concentrated primary sludge to biomethane, and H2 gas recovered from nitrogen upgrades the biomethane quality by reducing carbon dioxide in biogas. Based on these results, MWWTPs can be simplified and improved with high process and energy efficiencies.

The responding mechanism of indigenous bacteria in municipal wastewater inoculated with different concentrations of exogenous microalgae.

Indigenous bacteria popularly exist in real wastewater. Therefore, the potential interaction between bacteria and microalgae is inevitable in microalgae-based wastewater treatment systems. It is likely to affect the performance of systems. Accordingly, the characteristics of indigenous bacteria is worth serious concerning. Here we investigated the response of indigenous bacterial communities to variant inoculum concentrations of Chlorococcum sp. GD in municipal wastewater treatment systems. The removal efficiency of COD, ammonium and total phosphorus were 92.50%-95.55%, 98.00%-98.69%, and 67.80%-84.72%, respectively. The bacterial community responded differently to different microalgal inoculum concentrations, which was mainly affected by microalgal number, ammonium and nitrate. Besides, there were differential co-occurrence patterns and carbon and nitrogen metabolic function of indigenous bacterial communities. All these results indicated that bacterial communities responded significantly to environmental changes caused by the change of microalgal inoculum concentrations. The response of bacterial communities to different microalgal inoculum concentrations was beneficial for forming a stable symbiotic community of both microalgae and bacteria to remove pollutants in wastewater.

Abundance, characteristics, fate, and removal of microplastics during municipal wastewater treatment plant in the west of Iran: the case of Kermanshah city.

The threat of microplastics (MPs) in aquatic systems is almost a new challenge in environmental management. The municipal wastewater treatment plants (WWTPs) act both as collectors of MPs from anthropic use and as a source to natural environments. This study is aimed to determine the abundance, characteristics, and removal of MPs in a municipal WWTP with conventional activated sludge process. Particle size/type, influent loads, and removal rate of MPs in bar screen, grit chamber, primary sedimentation, returned activated sludge, and secondary clarification units of this WWTP were studied by collecting composite samples from wastewater and sludge over a 3-month sampling campaign. Suspected MP particles were counted by light microscopy and characterized using SEM, EDS, FTIR, and TGA-DSC techniques. The mean total MPs, fibers, and fragment concentration after the grit chamber were 6608, 3594, and 3014 which were reduced to 1855, 802, and 1053 particles/L in the effluent, respectively. The sludge retention of total MPs, fibers, and fragments were 8001, 3277, and 4719 particles/L, respectively. The overall efficiency of WWTP with an activated sludge process to remove MPs was 64% and it removed 66.6% and 60% of fibers and fragments, respectively. Fibers were the dominant shape for the collected samples after the grit chamber and fragments were prevalent in the effluent. Polyethylene polymer was detected in most wastewater samples. Existing treatment processes are effective in the removal of MP particles but still act as a potential source to the aquatic ecosystem.

Ecological and human health risk assessment of heavy metals in sewage sludge produced in Silesian Voivodeship, Poland: a case study.

This study aimed to assess the potential risks posed by heavy metals in sewage sludge (SS) produced by municipal wastewater treatment plants (WWTPs) in the most industrialized region in Poland, the Silesian Voivodeship. The ecological risk was assessed using three indices: the Geoaccumulation Index (Igeo), Potential Ecological Risk Factor (ER), and Risk Assessment Code (RAC), while the health risk was estimated by using carcinogenic and non-carcinogenic risk indices. The average concentrations of metals in the sludge samples were determined revealing that Zn was the predominant element, whereas Cd and Hg were present in the lowest concentrations. The study showed that the processes used in wastewater treatment plants influenced the overall metal content and chemical speciation. According to Igeo values, the dewatered sludge samples exhibited higher contamination levels of Cd and Zn, while Cu and Pb were upon to a lesser extent. The ER values suggest that Cd and Hg present the highest ecological risk. Considering the chemical forms and RAC values, Ni (26.8-37.2%) and Zn (19.8-27.0%) were identified to cause the most significant risks. The non-carcinogenic risk for adults and children was below acceptable levels. However, the carcinogenic risk associated with Ni (WWTP1) for both demographic groups and Cr and Cd (WWTP2), specifically for children, exceeded the acceptable threshold. Ingestion was the primary route of exposure. Although the dewatered SS met the standards for agricultural use, there is still a risk of secondary pollution to the environment and possible adverse health effects.

Exploring the Limits of Polyhydroxyalkanoate Production by Municipal Activated Sludge.

Municipal activated sludge can be used for polyhydroxyalkanoate (PHA) production, when supplied with volatile fatty acids. In this work, standardized PHA accumulation assays were performed with different activated sludge to determine (1) the maximum biomass PHA content, (2) the degree of enrichment (or volume-to-volume ratio of PHA-accumulating bacteria with respect to the total biomass), and (3) the average PHA content in the PHA-storing biomass fraction. The maximum attained biomass PHA content with different activated sludge ranged from 0.18 to 0.42 gPHA/gVSS, and the degree of enrichment ranged from 0.16 to 0.51 volume/volume. The average PHA content within the PHA-accumulating biomass fraction was relatively constant and independent of activated sludge source, with an average value of 0.58 ± 0.07 gPHA/gVSS. The degree of enrichment for PHA-accumulating bacteria was identified as the key factor to maximize PHA content when municipal activated sludge is directly used for PHA accumulation. Future optimization should focus on obtaining a higher degree of enrichment of PHA-accumulating biomass, either through selection during wastewater treatment or by selective growth during PHA accumulation. A PHA content in the order of 0.6 g PHA/g VSS is a realistic target to be achieved when using municipal activated sludge for PHA production.

Optimal sensor placement method for wastewater treatment plants based on discrete multi-objective state transition algorithm.

Parameters monitoring is essential to maintain the stability and efficiency of the wastewater treatment process, which has spurred ubiquitous installation of sensors in wastewater treatment plants (WWTPs). As the rich process data of WWTPs is not effectively transformed into actionable knowledge for system optimization due to improper sensor installation, the sensor placement scheme needs to be optimized. In this paper, a weighted sensor placement optimization model based on sensor cost, information richness and reliability is established to transform the sensor optimization problem to a nonlinear mathematical programming problem. Then a discrete multi-objective state transition algorithm is proposed to find the Pareto optimal solutions. Finally, an evaluation strategy is designed to select the most suitable solution for industrial application. The results of simulation experiments on three different WWTPs demonstrate the validity and superiority of the proposed method, increasing the degree of variable observability and measurement redundancy while keeping the sensor cost at a low level.

Reuse-focused selection of appropriate technologies for municipal wastewater treatment: a multi-criteria approach.

Wastewater treatment technologies (WWTTs) are employed across the world, and the selection is mainly based on 'past experiences' aimed at 'pollution prevention' in the receiving water bodies. This paper aims to develop a methodology for the selection of an appropriate wastewater treatment chain that produces effluent suitable for the defined reuse. Adopting the least weighted cost approach, four decision criteria: Capital cost, Operation and Maintenance cost, Land requirement, and Energy requirement, have been used and the Full Consistency Method (FUCOM) has been employed for obtaining weights. Quality expectations for 14 reuses have been enlisted, and 25 WWTTs have been evaluated in a total of 360 combinations. In Kanpur city, for water reuse in industrial cooling under restricted land and challenging influent quality conditions, a combination of Membrane Bioreactor (MBR) with Wuhrmann process (WP) is obtained as the most preferred suggestion. For non-potable domestic reuse, Anaerobic Anoxic Oxic (A2O) with Ultrafiltration (UF) and Reverse Osmosis (RO) is the most preferred combination. In Varanasi city, for vehicular washing operations and for flow augmentation (inland surface water), under energy-constraint scenario, high-rate activated sludge-based biological filtration and oxygenated reactor (BIOFOR-F) is suggested. For technology supplementation to existing ASP-based STPs in the city to obtain effluent for inland surface water augmentation, WP in combination with microfiltration (MF) and reverse osmosis (RO) is suggested. Thus, the developed model may be used as a decision-making tool for planning a reuse-focused water reclamation program or for upgradation of existing STPs as per resource availability and target reuse objectives.

Direct Evidence for Deterministic Assembly of Bacterial Communities in Full-Scale Municipal Wastewater Treatment Facilities.

In this study, we investigated whether bacterial community composition in full-scale wastewater treatment bioreactors can be better explained by niche- or neutral-based theory (deterministic or stochastic) and whether bioreactor design (continuous flow versus fill and draw) affected community assembly. Four wastewater treatment facilities (one with quadruplicated continuous-flow bioreactors, two with one continuous-flow bioreactor each, and one with triplicate fill-and-draw bioreactors) were investigated. Bioreactor community composition was characterized by sequencing of PCR-amplified 16S rRNA gene fragments. Replicate bioreactors at the same wastewater treatment facility had largely reproducible (i.e., deterministic) bacterial community composition, although bacterial community composition in continuous-flow bioreactors was significantly more reproducible (P < 0.001) than in fill-and-draw bioreactors (Bray-Curtis dissimilarity, µ = 0.48 ± 0.06 versus 0.58 ± 0.08). Next, we compared our results to previously used indirect methods for distinguishing between deterministic and stochastic community assembly mechanisms. Synchronicity was observed in the bacterial community composition among bioreactors within the same metropolitan region, consistent with deterministic community assembly. Similarly, a null model-based analysis also indicated that all wastewater bioreactor communities were controlled by deterministic factors and that continuous-flow bioreactors were significantly more deterministic (P < 0.001) than fill-and-draw bioreactors (nearest-taxon index, µ = 3.8 ± 0.6 versus 2.7 ± 0.8). Our results indicate that bacterial community composition in wastewater treatment bioreactors is better explained by deterministic community assembly theory; simultaneously, our results validate previously used but indirect methods to quantify whether microbial communities were assembled via deterministic or stochastic mechanisms. IMPORTANCE Understanding the mechanisms of bacterial community assembly is one of the grand challenges of microbial ecology. In environmental systems, this challenge is exacerbated because replicate experiments are typically impossible; that is, microbial ecologists cannot fabricate multiple field-scale experiments of identical, natural ecosystems. Our results directly demonstrate that deterministic mechanisms are more prominent than stochastic mechanisms in the assembly of wastewater treatment bioreactor communities. Our results also suggest that wastewater treatment bioreactor design is pertinent, such that the imposition of feast-famine conditions (i.e., fill-and-draw bioreactors) nudge bacterial community assembly more toward stochastic mechanisms than the imposition of stringent nutrient limitation (i.e., continuous-flow bioreactors). Our research also validates the previously used indirect methods (synchronous community dynamics and an application of a null model) for characterizing the relative importance of deterministic versus stochastic mechanisms of community assembly.

Tropical and temperate wastewater treatment plants assemble different and diverse microbiomes.

The diversity and assembly of activated sludge microbiomes play a key role in the performances of municipal wastewater treatment plants (WWTPs), which are the most widely applied biotechnological process systems. In this study, we investigated the microbiomes of municipal WWTPs in Bangkok, Wuhan, and Beijing that respectively represent tropical, subtropical, and temperate climate regions, and also explored how microbiomes assembled in these municipal WWTPs. Our results showed that the microbiomes from these municipal WWTPs were significantly different. The assembly of microbiomes in municipal WWTPs followed deterministic and stochastic processes governed by geographical location, temperature, and nutrients. We found that both taxonomic and phylogenetic α-diversities of tropical Bangkok municipal WWTPs were the highest and were rich in yet-to-be-identified microbial taxa. Nitrospirae and ß-Proteobacteria were more abundant in tropical municipal WWTPs, but did not result in better removal efficiencies of ammonium and total nitrogen. Overall, these results suggest that tropical and temperate municipal WWTPs harbored diverse and unique microbial resources, and the municipal WWTP microbiomes were assembled with different processes. Implications of these findings for designing and running tropical municipal WWTPs were discussed. KEY POINTS: • Six WWTPs of tropical Thailand and subtropical and temperate China were investigated. • Tropical Bangkok WWTPs had more diverse and yet-to-be-identified microbial taxa. • Microbiome assembly processes were associated with geographical location.

Microbial invasions in sludge anaerobic digesters.

Among processes that control microbial community assembly, microbial invasion has received little attention until recently, especially in the field of anaerobic digestion. However, knowledge of the principles regulating the taxonomic and functional stability of microbial communities is key to truly develop better predictive models and effective management strategies for the anaerobic digestion process. To date, available studies focus on microbial invasions in digesters feed with activated sludge from municipal wastewater treatment plants. Herein, this review summarizes the importance of invasions for anaerobic digestion management, the ecological theories about microbial invasions, the traits of activated sludge microorganisms entering the digesters, and the resident communities of anaerobic reactors that are relevant for invasions and the current knowledge about the success and impacts of invasions, and discusses the research needs on this topic. The initial data indicate that the impact of invasions is low and only a small percentage of the mostly aerobic microorganisms present in the activated sludge feed are able to become stablished in the anaerobic digesters. However, there are still numerous unknowns about microbial invasions in anaerobic digestion including the influence of anaerobic feedstocks or process perturbances that new approaches on microbial ecology could unveil. KEY POINTS: • Microbial invasions are key processes to develop better strategies for digesters management. • Knowledge on pathogen invasions can improve anaerobic digestion microbial safety. • To date, the number of successful invasions on anaerobic digesters from activated sludge organisms is low. • Feed organisms detected in digesters are mostly inactive residual populations. • Need to expand the range of invaders and operational scenarios studied.