Dominance of candidate Saccharibacteria in a membrane bioreactor treating medium age landfill leachate: Effects of organic load on microbial communities, hydrolytic potential and extracellular polymeric substances

A comparison study on membrane fouling in A/O-MBR and A/A-MBR at different mixed liquor-suspended solids concentrations

Membrane fouling leads to decreased membrane flux, increases the frequency of membrane tissue replacement and membrane cleaning, and increases the operating cost of membrane bioreactor. In this study, the pollutant removal effects, membrane fouling differences and microbial characteristics of anaerobic/aerobic MBR (A/O-MBR) and anaerobic/anoxic MBR (A/A-MBR) were investigated at different mixed liquor suspended solids (MLSS) concentrations. The results showed that the chemical cleaning cycle of membrane contamination was 12, 28, 44 h and 24, 40, 104 h, respectively, and the cycle was prolonged with the increase of MLSS concentration (from 6000 to 9000 mg L-1). A/O-MBR was 1.4-2.4 times the rate of membrane fouling of A/A-MBR. In irreversible resistance, extracellular polymer substances (EPS) were the most significant contributors to membrane fouling. EPS concentration in A/A-MBR (118.33, 73.75, 54.26 mg/gMLSS) was lower than that in A/O-MBR (171.68, 91.92, 62.33 mg/gMLSS). Therefore, increasing MLSS concentration could mitigate membrane fouling. 16S rRNA high-throughput sequencing demonstrated that filamentous bacteria was the primary reason for the membrane fouling difference. Filamentous bacteria were more likely to be attached to the surface of the membrane, causing membrane fouling. The abundance percentage of filamentous bacteria in A/A-MBR was smaller than that in A/O-MBR. In summary, The excellent performance of A/A-MBR in membrane fouling behaviour, resistance analysis, EPS and microorganisms proved that A/A-MBR is more promising than A/O-MBR in wastewater nitrogen and phosphorus removal. This study can provide a theoretical basis for the application of MBR in the field of sewage treatment.

Semi-supervised learning-based identification of the attachment between sludge and microparticles in wastewater treatment

Monitoring the microparticle transfer process in wastewater treatment systems is crucial for improving treatment performance. Supervised deep learning methods show high performance to automatically detect particles, but they rely on vast amounts of labeled data for training. To overcome this issue, we proposed a semi-supervised learning (SSL) method based on the Simple framework for Contrastive Learning of visual Representations (SimCLR), to detect microparticles free from sludge and attached to sludge. First, we pre-trained a ResNet50 backbone by SimCLR, to extract features from much unlabeled data (1,000 images). Then, we constructed a Mask R-CNN architecture based on the pre-trained ResNet50, and fine-tuned it on a small quantity of labeled data (≈200 images with ≈600 annotated particles) in supervised learning fashion. We showcased its performance and practical applicability for microscopy images obtained from the water lab of TU Delft. The results demonstrate that the SSL methods obtain a significant improvement in mean average precision of up to 5% compared to the conventional supervised learning method, when a limited amount of labeled data is available (e.g., 91 labeled images). Furthermore, these methods improve the average precision for detecting attached particles by over 12%. With the detection results from the SSL methods, we measured the attachment efficiency of microparticles to sludge under varying mixed liquor suspended solids concentration and aeration intensity. The precise measurements demonstrate the effectiveness and practical applicability of the SSL method in facilitating long-term monitoring of particle transfer processes in biological wastewater treatment systems.

Exploring the effects of polyethylene and polyester microplastics on biofilm formation, membrane Fouling, and microbial communities in Modified Ludzack-Ettinger-Reciprocation membrane bioreactors

Microplastics (MPs) inevitably enter wastewater treatment plants (WWTPs), yet their impacts remain poorly understood. This study investigates the effects of MPs on system performance and membrane fouling in a Modified Ludzack-Ettinger (MLE)-Reciprocation Membrane Bioreactor (rMBR), an energy-efficient alternative to conventional membrane bioreactors. Additionally, the study examines changes in microbial community induced by different types and shapes of MPs-polyethylene (PE) pellets and polyester (PES) fibers- as well as biofilm formation on MPs, using next-generation sequencing. Results revealed that transmembrane pressure (TMP) increased 2-3 times faster in the presence of PE pellets, while TMP remained stable during the PES stage, implying that MP type and shape could influence biofouling behaviors. Furthermore, enhanced nitrate removal was observed in the aerobic tank due to denitrifying biofilm formation on MPs. However, PES MPs reduced nitrate removal efficiency from 99.6 ± 0.3 % to 90.9 ± 7.9 % and decreased the relative abundance of denitrifying bacteria. Numerous taxa showed affinity to PE pellets, including some pathogens, e.g., Norcadia and Mycobacterium. Notably, an uncultured phylum Candidatus Saccharibacteria dominated in membrane biofilm and MPs, reaching up to 37 % relative abundance. This study is the first to explore how different types and shapes of MPs affect membrane bioreactor systems, particularly with respect to microbial community structure and biofilm formation. The findings offer new insights into the influence of MPs on wastewater treatment processes and highlight the significance of the uncultured phylumCandidatus Saccharibacteriain membrane fouling.

Efficient PPCPs removal from wastewaters via a novel A/O-MBBR system: Transition towards circular economy in the water sector

As industrial and agricultural production depends on water supply, it is crucial for economic development. The available freshwater reserves on Earth are insufficient to meet humanity's growing demands. This study establishes a three-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR) system. The study evaluated the wastewater purification capacity of the system in summer and winter, examined the system's removal efficiency of 10 pharmaceuticals and personal care products (PPCPs) from the water, and analyzed the composition of microbial communities. Results indicate that the system effectively removes pollutants and PPCPs, with the aerobic tanks in the first two A/O stages playing a significant role in PPCP removal. The system is effective in removing four kinds of pollutants: AMP, IBU, CLR, and CAF, and the removal efficiency of CAF is up to 99.2%. Seasonal variations significantly affect the removal of PPCPs and bacterial growth, leading to changes in bacterial species. At the genus level, 41 bacterial types presented different effects in response to temperature changes, with Trichoderma and c_OM190_unclassified being the most affected. This study provides essential theoretical support for reducing pollutant levels and improving water recycling and economic efficiency.

Novel insights into the co-metabolism of pyridine with different carbon substrates: Performance, metabolism pathway and microbial community

Pyridine is a widely employed nitrogen-containing heterocyclic organic, and the discharge of pyridine wastewater poses substantial environmental challenges due to its recalcitrance and toxicity. Co-metabolic degradation emerged as a promising solution. In this study, readily degradable glucose and the structurally analogous phenol were used as co-metabolic substrates respectively, and the corresponding mechanisms were thoroughly explored. To treat 400 mg/L pyridine, all reactors achieved remarkably high removal efficiencies, surpassing 98.5%. And the co-metabolism reactors had much better pyridine-N removal performance. Batch experiments revealed that glucose supplementation bolstered nitrogen assimilation, thereby promoting the breakdown of pyridine, and resulting in the highest pyridine removal rate and pyridine-N removal efficiency. The high abundance of Saccharibacteria (15.54%) and the enrichment of GLU and glnA substantiated this finding. On the contrary, phenol delayed pyridine oxidation, potentially due to its higher affinity for phenol hydroxylase. Nevertheless, phenol proved valuable as a carbon source for denitrification, augmenting the elimination of pyridine-N. This was underscored by the abundant Thauera (30.77%) and Parcubacteria (7.21%) and the enriched denitrification enzymes (narH, narG, norB, norC, and nosZ, etc.). This study demonstrated that co-metabolic degradation can bolster the simultaneous conversion of pyridine and pyridine-N, and shed light on the underling mechanism.

Global landfill leachate characteristics: Occurrences and abundances of environmental contaminants and the microbiome

Landfill leachates are complex mixtures containing very high concentrations of biodegradable and recalcitrant toxic compounds. Understanding the major contaminant components and microbial community signatures in global landfill leachates is crucial for timely decision-making regarding contaminant management and treatment. Therefore, this study analyzed leachate data from 318 landfill sites primarily used for municipal solid waste disposal, focusing on their chemical and microbiological characteristics. The most prevalent and dominant components in landfill leachates are the chemical oxygen demand (COD, 3.7-75.9 × 103 mg/L) and NH4+ (0.03-0.81 × 104 mg/L), followed by salt species such as SO42- (0.03-5.25 × 103 mg/L), Cl- (3.2-7.8 × 103 mg/L), K+ (0.58-4.20 × 103 mg/L), Na+ (1.3-13.0 × 103 mg/L) and Ca2+ (2.35-230.23 × 103 mg/L), which exhibit significant fluctuations. Heavy metals and metalloids are widely distributed in most landfill leachates but at relatively low concentrations (<182.8 mg/L) compared to conventional parameters. Importantly, there is a distinct global variation in the occurrence of emerging environmental contaminants (ECs). Among these compounds, perfluorooctanoic acid (PFOA, 0.02-7.50 × 103 μg/L) of per- and poly-fluoroalkyl substances (PFAS), bisphenol A (BPA, 0.01-33.46 × 103 μg/L) belonged to endocrine-disrupting compounds (EDCs), together with di-ethyltoluamide (DEET, 1.0-1.0 × 103 μg/L) affiliated to pharmaceuticals and personal care products (PPCPs) are the most frequently detected in landfill leachates. Additionally, the microbial community compositions in most leachates are primarily dominated by Proteobacteria, Bacteroidota, Firmicutes, and Chloroflexi, and some of their abundances are correlated with the concentrations of NH4+, NO3-, Cl-, Na+ and Cr. Notably, the leading microbes driving advanced removal of inorganic nitrogen in the treatment systems are Candidatus Brocadia (anammox), denitrifying Thauera, nitrite-oxidizing bacteria Nitrospira, along with ammonia-oxidizing bacteria Nitrosomonas and Nitrosospira. The findings of this work provide a deeper insight into the leachate characteristics and the sustainable management of landfill leachates, especially presenting a snapshot of the global distribution of pollutants and also the microbiome.

Effects of micro-bubble aeration on the pollutant removal and energy-efficient process in a floc-granule sludge coexistence system

To investigate energy-saving approaches in wastewater treatment plants and decrease aeration energy consumption, this study successfully established a floc-granule coexistence system in a sequencing batch airlift reactor (SBAR) employing micro-bubble aeration. The analysis focused on granule formation and pollutant removal under various aeration intensities, and compared its performance with a traditional floc-based coarse-bubble aeration system. The results showed that granulation efficiency was positively associated with aeration intensity, which enhanced the secretion of extracellular polymeric substances (EPSs) and facilitated granule formation. The SBAR with the micro-aeration intensity of 30 mL·min-1 showed the best granulation performance (granulation efficiency 52.6%). In contrast to the floc-based system, the floc-granule coexistence system showed better treatment performance, and the best removal efficiencies of NH4+-N, TN, and TP were 100.0, 77.0, and 89.5%, respectively. The floc-granule coexistence system also enriched higher abundance of nutrients removal microbial species, such as Nitrosomonas (0.05-0.14%), Nitrospira (0.14-2.32%), Azoarcus (2.95-12.17%), Thauera (0.43-1.95%), and Paracoccus (0.76-2.89%). The energy-saving potential was evaluated, which indicated it is feasible for the micro-aeration floc-granule coexistence system to decrease the aeration consumption by 14.4% as well as improve the effluent.

Effect of transient organic load and aeration changes to pollutant removal and extracellular polymeric substances

Transient organic load shocks have an important influence on the removal of pollutants and the content and composition of extracellular polymeric substances (EPS). This study was based on a micro-pressure reactor (MPR) with the influent COD concentration as the variable, while different operating conditions were controlled by adjusting the aeration rate. The effect of single-cycle transient organic loading shocks on EPS and pollutant removal and the correlation between their changes were investigated. The results showed that COD removal was unaffected under the shock, and the effect of nitrogen and phosphorus removal decreased. As the incoming carbon source increased, the EPS content at shock increased, with the polysaccharide (PS) content being the most affected. As aeration increased, the effect of organic load shock on EPS and pollutant removal decreased. Under different aeration conditions, PS contributed to denitrification and anaerobic phosphorus release during transient organic load shocks, and protein (PN) contributed to aerobic phosphorus uptake. The reduction in PS and PN relative to the pre-shock caused by the shock resulted in the EPS exhibiting a favourable effect on COD removal and an inhibitory effect on the effectiveness of nitrogen and phosphorus removal.

Effect of temperature and storage methods on liquid digestate: Focusing on the stability, phytotoxicity, and microbial community

Identifying the stability and phytotoxicity of liquid digestate (LD) is necessary for safe agricultural utilization. Storage temperature, method, and time are critical factors that affect the stability and phytotoxicity of LD. This study therefore aimed to explore the dynamics of stability, phytotoxicity, and microbial community of LD in cattle farms under different storage conditions. The results showed that the contents of solids, organic matter, nitrogen, and phosphorous decreased during storage and exhibited temperature dependency. Conversely, the seed germination index increased, which was negatively correlated with dissolved organic carbon and ammonium nitrogen and positively correlated with certain bacteria (Thermovirga and Fastidiosipila). Open storage and/or higher temperature were found to contribute to the stabilization efficiency and phytotoxicity disappearance of LD. Open storage of LD at 30 °C for 60 days and 20 °C for 90 days was safe for its agricultural utilization, while hermetic storage of LD at 30 °C for 120 days and 20 °C for 150 days was safe. However, for storage at 10 °C for 180 days, additional post-treatment is required.

Comparative metagenomic analysis reveals rhizosphere microbial community composition and functions help protect grapevines against salt stress

Introduction

Soil salinization is a serious abiotic stress for grapevines. The rhizosphere microbiota of plants can help counter the negative effects caused by salt stress, but the distinction between rhizosphere microbes of salt-tolerant and salt-sensitive varieties remains unclear.

Methods

This study employed metagenomic sequencing to explore the rhizosphere microbial community of grapevine rootstocks 101-14 (salt tolerant) and 5BB (salt sensitive) with or without salt stress.

Results and Discussion

Compared to the control (treated with ddH₂O), salt stress induced greater changes in the rhizosphere microbiota of 101-14 than in that of 5BB. The relative abundances of more plant growth-promoting bacteria, including Planctomycetes, Bacteroidetes, Verrucomicrobia, Cyanobacteria, Gemmatimonadetes, Chloroflexi, and Firmicutes, were increased in 101-14 under salt stress, whereas only the relative abundances of four phyla (Actinobacteria, Gemmatimonadetes, Chloroflexi, and Cyanobacteria) were increased in 5BB under salt stress while those of three phyla (Acidobacteria, Verrucomicrobia, and Firmicutes) were depleted. The differentially enriched functions (KEGG level 2) in 101-14 were mainly associated with pathways related to cell motility; folding, sorting, and degradation functions; glycan biosynthesis and metabolism; xenobiotics biodegradation and metabolism; and metabolism of cofactors and vitamins, whereas only the translation function was differentially enriched in 5BB. Under salt stress, the rhizosphere microbiota functions of 101-14 and 5BB differed greatly, especially pathways related to metabolism. Further analysis revealed that pathways associated with sulfur and glutathione metabolism as well as bacterial chemotaxis were uniquely enriched in 101-14 under salt stress and therefore might play vital roles in the mitigation of salt stress on grapevines. In addition, the abundance of various sulfur cycle-related genes, including genes involved in assimilatory sulfate reduction (cysNC, cysQ, sat, and sir), sulfur reduction (fsr), SOX systems (soxB), sulfur oxidation (sqr), organic sulfur transformation (tpa, mdh, gdh, and betC), increased significantly in 101-14 after treatment with NaCl; these genes might mitigate the harmful effects of salt on grapevine. In short, the study findings indicate that both the composition and functions of the rhizosphere microbial community contribute to the enhanced tolerance of some grapevines to salt stress.

Mature landfill leachate treatment using granular sludge-based reactor (GSR) via nitritation/denitritation: Process startup and optimization

Mature landfill leachate wastewater (LLW) was characterized by high ammonia, refractory chemical oxygen demand (COD) and heavy metal contents, which limits the nitrogen removal in conventional activated sludge systems. Granular sludge is known to be more resistant to toxic compounds because of its dense structure and diverse microbial community. Here, granular sludge-based reactor (GSR) was applied with nitritation/denitritation (Nit/DNit) process for effective ammonia-rich mature LLW treatment at 20 °C. After a short startup period, the efficiencies of ammonia removal and total inorganic nitrogen removal stabilized at 99 % and 93 %, respectively, under a hydraulic retention time (HRT) of 6 h. High ammonia oxidation rate (~ 0.64 g N/g VSS/d) was achieved, with ~93 % ammonia conversing to nitrite before being reduced to nitrogen gas. Microbial analysis results revealed that Nitrosomonas (ammonia oxidizing bacteria) and Thauera (denitrifiers) were the dominant bacteria with key functional genes involved in the Nit/DNit. With an increase in the LLW loading, increased ammonia oxidation rates and biomass retention were also observed. This study demonstrated that granular sludge-based technology is feasible for mature LLW treatment.

Performances and enhanced mechanisms of nitrogen removal in a submerged membrane bioreactor coupled sponge iron system

Sponge iron is a potential material for nitrogen removal, but lack of a study about nitrogen removal in a membrane bioreactor (MBR) coupled with sponge iron. The performances and mechanisms of nitrogen removal of SI-MBR were investigated and compared it with that in GAC-MBR. The results showed that the average rate of organic matter removal in the SI-MBR was 92.74%, which was higher than that in the GAC-MBR (87.48%). And the average effluent NO₂^--N and NO₃^--N concentration in the SI-MBR (0.02 mg/L and 3.73 mg/L) was lower than that in the GAC-MBR (0.05 mg/L and 7.51 mg/L). Meanwhile, the highest nitrification rate and denitrification rate was respectively 3.544 ± 0.25 mg/(g VSS·h) and 6.643 ± 0.2 mg/(g VSS·h) in the SI-MBR, which was higher than that (3.094 ± 0.25 mg/(g VSS·h) and (6.376 ± 0.2 mg/(g VSS·h)) in the GAC-MBR. Additionally, the bacterial activities (e.g., DHA activity and respiratory activity) were obviously enhanced through the iron ion from sponge iron. The bacterial community in the SI-MBR system was more richness and diverse than that in the GAC-MBR. Ultimately, the mechanisms of enhanced biological nitrogen removal with sponge iron in MBR were analyzed. On the surface of sponge iron, the DIRB and FOB could use the iron ion from sponge iron as the electron transfer to improve the nitrogen and organic removal. With sponge iron, there is not only the nitrification bacteria and heterotrophic denitrifying microorganism enriched, but also the autotrophic denitrifying bacteria abounded obviously. The autotrophic denitrifying bacteria could use Fe(II) as an electron donor to achieve denitrification and enhance the nitrogen removal.

Modeling and assessment of the transfer effectiveness in integrated bioreactor with membrane separation

Integrating a reaction process with membrane separation allows for effective product removal, favorable shifting of the reaction equilibrium, overcoming eventual inhibitory or toxic effects of the products and has the advantage of being energy and space saving. It has found a range of applications in innovative biotechnologies, generating value-added products (exopolysaccharides, antioxidants, carboxylic acids) with high potential for separation/ concentration of thermosensitive bioactive compounds, preserving their biological activity and reducing the amount of solvents and the energy for solvent recovery. Evaluating the effectiveness of such integrated systems is based on fluid dynamics and mass transfer knowledge of flowing matter close to the membrane surface – shear deformation rates and shear stress at the membrane interface, mass transfer coefficients. A Computational Fluid Dynamics (CFD)-based approach for assessing the effectiveness of integrated stirred tank bioreactor with submerged membrane module is compiled. It is related to the hydrodynamic optimization of the selected reactor configuration in two-phase flow, as well as to the concentration profiles and analysis of the reactor conditions in terms of reaction kinetics and mass transfer.

Identification of key water parameters and microbiological compositions triggering intensive N2O emissions during landfill leachate treatment process

Landfill leachate treatment processes tend to emit more N₂O compared to domestic wastewater treatment. This discrepancy may be ascribed to leachate water characteristics such as high refractory COD, ammonium (NH₄⁺) content, and salinity. In this work, the leachate influent was varied to examine the N₂O emission scenarios. NH₄⁺-N, COD, and Cl^- concentrations ranged between 1000-2500, 1000-10,000, and 500-3000 mg L^-1, respectively. Simultaneously, we attempted to combine statistical analysis with high-throughput sequencing to understand the microbial mechanism with regards to N₂O emission. Results show that the strong N₂O emissions occur in the nitrifying tank due to the intensive aeration. The system receiving the lowest COD shows the maximum N₂O emission factor of 42.7% of the removed nitrogen. Both redundancy analysis and a structural equation model verify that insufficient degradable organics are the key water parameter triggering intensive N₂O emission within the designed influent limits. Furthermore, two essential but non-abundant functional bacteria, Flavobacterium (acting as a denitrifier) and Nitrosomonas (acting as a nitrifier), are identified as the core functional species that dramatically influence N₂O emissions. An increase in influent COD promotes the proliferation of Flavobacterium and inhibits Nitrosomonas, which in turn reduce N₂O release. Meanwhile, two keystone species of Castellaniella and Saprospiraceae unclassified are recognized. They may supply a suitable niche and integrity of the microbial community for N-cycle functional bacteria. These findings reveal the essential role of non-abundant species in microbial community, and expand the current understanding of microbial interactions underlying N₂O dynamics in leachate treatment systems.

Activated sludge microbial communities and hydrolytic potential in a full-scale SBR system treating landfill leachate

Landfill leachate, due to its recalcitrant nature and toxicity, poses a serious environmental threat, which requires the implementation of effective treatment processes. In this work, a full-scale treatment system consisting of two Sequencing Batch Reactors (SBRs) was used for the processing of landfill leachate of intermediate to mature age (BOD/COD ratio of 0.16). Biosystem operation resulted in BOD₅, COD and TKN removal efficiencies of 81%, 39% and 76%, respectively, whereas the low residual NO₃^--N concentration in the effluent (4.01 ± 0.10 mg/L) was indicative of the efficient denitrification process. Assessment of hydrolytic potential of activated sludge revealed high endocellular and extracellular lipase activities, which reached values up to 206 and 141 U/g protein respectively, possibly as the consequence of plastics degradation during maturation process. Implementation of Illumina sequencing indicated the predominance of Alphaproteobacteria, accompanied by members of Bacteroidetes, Betaproteobacteria and Chloroflexi. Paracoccus was the predominant genus identified, followed by representatives of the genera Bellilinea, Flavobacterium, Thauera and Truepera. Nitrosomonas was the major ammonia-oxidizing bacterium (AOB), while nitrite oxidation was mainly achieved by the uncultured nitrite-oxidizing bacterium (NOB) Candidatus Nitrotoga.

Co-occurrence of autotrophic and heterotrophic denitrification in electrolysis assisted constructed wetland packing with coconut fiber as solid carbon source

Aiming at the problems of lack of carbon sources for nitrogen removal and low phosphorus removal efficiency of constructed wetlands (CWs) in treating wastewater treatment plant (WWTP) effluent, an electrolysis assisted constructed wetland (E-CW) with coconut fiber as substrate and solid carbon sources was constructed. The synthetic secondary effluent was used as the influent of the E-CW with a wastewater treatment capacity of 140 L d^-1. The total nitrogen (TN) and the total phosphorus (TP) removal efficiency of the E-CW with coconut fiber treating WWTP effluent were 69.4% and 93.3%, respectively, which were 54.3% and 88.2% higher than those of CW with coconut fiber and no electrolysis. The removal efficiency of TN was 39.9% higher than that of E-CW with gravel. The current intensity had significant effect on nitrogen removal efficiency and the release of carbon sources from coconut fiber. When current intensity increased from 0.25 A to 1.00 A, the TN removal efficiency and nitrate removal rate increased by 21.1% and 0.21 mg L^-1 h^-1, respectively, and the volatile fatty acids (VFAs) released from coconut fiber increased by 57.7 mg L^-1. The 16S rRNA high-throughput sequencing results indicated that the main functional nitrogen-removing microbes were Hydrogenophaga, Thauera, Rhodanobacteraceae_norank, Xanthobacteraceae_norank, etc. Multiple paths including autotrophic denitrification with hydrogen and Fe²⁺ as electron donors and heterotrophic denitrification were achieved in the system. Meanwhile, the main functional lignocellulose degradation microbes were enriched in the system, including Cytophaga_xylanolytica_group, and Caldilineaceae. Because electrolysis created a favorable environment for them to release carbon sources from coconut fiber. This study provided a new perspective for advanced nutrients removal of WWTP effluent in CWs.

Genome-centric metagenomics provides new insights into the microbial community and metabolic potential of landfill leachate microbiota

Landfills are important sources of microorganisms associated with anaerobic digestion. However, the knowledge on microbiota along with their functional potential in this special habitat are still lacking. In this study, we recovered 1168 non-redundant metagenome-assembled genomes (MAGs) from nine landfill leachate samples collected from eight cities across China, spanning 42 phyla, 73 classes, 114 orders, 189 families, and 267 genera. Totally, 74.1% of 1168 MAGs could not be classified to any known species and 5.9% of these MAGs belonged to microbial dark matter phyla. Two putative novel classes were discovered from landfill leachate samples. The identification of thousands of novel carbohydrate-active enzymes showed similar richness level compared to the cow rumen microbiota. The methylotrophic methanogenic pathway was speculated to contribute significantly to methane production in the landfill leachate because of its co-occurrence with the acetoclastic and hydrogenotrophic methanogenic pathways. The genetic potential of dissimilatory nitrate reduction to ammonium (DNRA) was observed, implying DNRA may play a role in ammonium generation in landfill leachate. These findings implied that landfill leachate might be a valuable microbial resource repository and filled the previous understanding gaps for both methanogenesis and nitrogen cycling in landfill leachate microbiota. Our study provides a comprehensive genomic catalog and substantially provides unprecedented taxonomic and functional profiles of the landfill leachate microbiota.

Identification of key microorganisms in facultative stabilization ponds from dairy industries, using metagenomics

Wastewater stabilization ponds are a natural form of wastewater treatment. Their low operation and maintenance costs have made them popular, especially in developing countries. In these systems, effluents are retained for long periods of time, allowing the microbial communities present in the ponds to degrade the organic matter present, using both aerobic and anaerobic processes. Even though these systems are widespread in low income countries, there are no studies about the microorganisms present in them and how they operate. In this study, we analised the microbial communities of two serial full-scale stabilization ponds systems using whole genome shotgun sequencing. First, a taxonomic profiling of the reads was performed, to estimate the microbial diversity. Then, the reads of each system were assembled and binned, allowing the reconstruction of 110 microbial genomes. A functional analysis of the genomes allowed us to find how the main metabolic pathways are carried out, and we propose several organisms that would be key to this kind of environment, since they play an important role in these metabolic pathways. This study represents the first genome-centred approach to understand the metabolic processes in facultative ponds. A better understanding of these microbial communities and how they stabilize the effluents of dairy industries is necessary to improve them and to minimize the environmental impact of dairy industries wastewater.

Nitrogen Advanced Treatment of Urban Sewage by Denitrification Deep-Bed Filter: Removal Performance and Metabolic Pathway

This study aimed to explore the performance of denitrification deep-bed filter (DN-DBF) to treat municipal sewage for meeting a more stringent discharge standard of total nitrogen (TN) (10.0 mg L-1). A lab-scale DN-DBF was conducted to optimize operation parameters and reveal the microbiological mechanism for TN removal. The results showed that more than 12.7% TN removal was obtained by adding methanol compared with sodium acetate. The effluent TN concentration reached 6.0-7.0 mg L-1 with the optimal influent carbon and nitrogen ratio (C/N) and hydraulic retention time (HRT) (3:1 and 0.25 h). For the nitrogen removal mechanism, Blastocatellaceae_Subgroup_4 and norank_o_JG30-KF-CM45 were dominant denitrification floras with an abundance of 6-10%. Though large TN was removed at the top layer of DN-DBF, microbial richness and diversity at the middle layer were higher than both ends. However, the relative abundance of nitrite reductase enzymes (EC1.7.2.1) gradually increases as the depth increases; conversely, the relative abundance of nitrous oxide reductase gradually decreased.

Diversity of <i>Candidatus</i> Patescibacteria in Activated Sludge Revealed by a Size-‍Fractionation Approach

Uncultivated members of Candidatus Patescibacteria are commonly found in activated sludge treating sewage and are widely distributed in wastewater treatment plants in different regions and countries. However, the phylogenetic diversity of Ca. Patescibacteria is difficult to examine because of their low relative abundance in the environment. Since Ca. Patescibacteria members have small cell sizes, we herein collected small microorganisms from activated sludge using a filtration-based size-fractionation approach (i.e., 0.45–0.22‍ ‍μm and 0.22–0.1‍ ‍μm fractions). Fractionated samples were characterized using 16S rRNA gene amplicon and shotgun metagenomic sequence ana­lyses. The amplicon ana­lysis revealed that the relative abundance of Ca. Patescibacteria increased to 73.5% and 52.5% in the 0.45–0.22‍ ‍μm and 0.22–0.1‍ ‍μm fraction samples, respectively, from 5.8% in the unfractionated sample. The members recovered from the two size-fractionated samples included Ca. Saccharimonadia, Ca. Gracilibacteria, Ca. Paceibacteria, Ca. Microgenomatia, class-level uncultured lineage ABY1, Ca. Berkelbacteria, WS6 (Ca. Dojkabacteria), and WWE3, with Ca. Saccharimonadia being predominant in both fraction samples. The number of operational taxonomic units belonging to Ca. Patescibacteria was approximately 6-fold higher in the size-fractionated samples than in the unfractionated sample. The shotgun metagenomic ana­lysis of the 0.45–0.22‍ ‍μm fractioned sample enabled the reconstruction of 24 high-quality patescibacterial bins. The bins obtained were classified into diverse clades at the family and genus levels, some of which were rarely detected in previous activated sludge studies. Collectively, the present results suggest that the overall diversity of Ca. Patescibacteria inhabiting activated sludge is higher than previously expected.

Effects of sulfamethoxazole on aerobic sludge granulation process

AIMS

Our purpose was to clarify the effect of sulfamethoxazole (SMX) on the start-up period, particle formation, and treatment efficiency of an aerobic granular sludge system.

METHODS AND RESULTS

We compared an R1 granular sequencing batch reactor (GSBR) started with 5 μg L^-1 SMX and an R2 GSBR started without SMX, as a control, to investigate the impact of a trace amount of SMX (5 μg L^-1 ) on aerobic granular sludge (AGS) characteristics and the removal of conventional contaminants. AGS granulation in the R1 system was not inhibited by SMX, but the granule particle size was smaller than that in the R2 system. Both systems had good performance removing conventional pollutants. Extracellular polymeric substance secretion in the R1 system was lower than that in the R2 system. After stabilizing reactor operations, the SMX removal efficiency in the R1 system (~73.93%) was higher than that in the R2 system (~70.66%). The start-up modes also determined the differences in the microbial community structure of the AGS systems.

CONCLUSIONS

SMX-activated AGS performed better than AGS without SMX.

SIGNIFICANCE AND IMPACT OF STUDY

The study can help engineers determine start-up modes with varieties of antibiotics in AGS processes and provide references for the optimization of water treatment processes.

Culturing sludge fermentation liquid-driven partial denitrification in two-stage Anammox process to realize advanced nitrogen removal from mature landfill leachate

The two-stage partial nitrification (PN)-Anammox process, during long term treatment of high-ammonia nitrogen leachate, faces challenges such as the adaptation of nitrite oxidation bacteria (NOB) and failure of real-time control of pH. Resultant instabilities including NH₄⁺-N and NO₃^--N accumulation were overcome by culturing sludge fermentation liquid (SFL)-driven partial denitrification (PD) in situ in the Anammox process. Biodegradation of slowly biodegradable organics (SBO) in SFL created organics restriction condition, which limited the activity of denitrification bacteria and achieved its balance with Anammox bacteria. Produced NO₃^--N is reduced to NO₂^--N through PD, which further improved the removal of NH₄⁺-N through Anammox. NO₂^--N was utilized timely by Anammox bacteria, which avoid further reduction of NO₂^--N to N₂, and result in a high nitrate to nitrite transformation ratio (NTR) of 93.3%. Satisfactory nitrogen removal efficiency (NRE) and nitrogen removal rate (NRR) of 99.6% and 822.0 ± 9.0 g N/(m³∙d) were obtained, respectively. Key genera related to degradation of SBO, PD and Anammox were enriched. The value of narG/(nirK+nirS) increased from 0.05 on day 1-0.15 on day 250. Combining SFL-driven PD with two-stage Anammox process provided a novel insight for applying this process to realize advanced nitrogen removal in practical engineering.

Spatiotemporal and seasonal dynamics in the microbial communities of a landfill-leachate contaminated aquifer

The microbiome of an aquifer contaminated by landfill leachate and undergoing intrinsic remediation was characterised using 16S rRNA metabarcoding. The archaeal/bacterial V3-V4 hypervariable region of the 16S rRNA gene was sequenced using Illumina MiSeq, and multivariate statistics were applied to make inferences. Results indicate that the aquifer recharge and aquifer sediment samples harbour different microbial communities compared to the groundwater samples. While Proteobacteria dominated both the recharge and groundwater samples, Acidobacteria dominated the aquifer sediment. The most abundant genera detected from the contaminated aquifer were Polynucleobacter, Rhodoferax, Pedobacter, Brevundimonas, Pseudomonas, Undibacterium, Sulfurifustis, Janthinobacterium, Rhodanobacter, Methylobacter and Aquabacterium. The result also shows that the microbial communities of the groundwater varied spatially, seasonally and interannually, although the interannual variation was significant for only one of the wells. Variation partitioning analysis indicates that water chemistry and well distance are intercorrelated and they jointly accounted for most of the variation in microbial composition. This implies that the species composition and water chemistry characteristics have a similar spatial structuring, presumably caused by the landfill leachate plume. The study improves our understanding of the dynamics in subsurface microbial communities in space and time.

Enhanced pollutant removal from rural non-point source wastewater using a two-stage multi-soil-layering system with blended carbon sources: Insights into functional genes, microbial community structure and metabolic function

A two-stage multi-soil-layering system with blended carbon sources (MSL-BCS) was constructed at pilot scale for treatment of rural non-point source wastewater. Results showed the MSL-BCS system had effective removal efficiencies with 64% of TN and 60% of TP, respectively. The addition of BCS could result in higher (1.6-3.1 fold) denitrification gene abundances (nirS and nosZ) for enhancing denitrification. High-throughput sequencing approach revealed that the higher abundance (>50%) of Epsilonbacteraeotra (Genus: Sulfuricurvum, Family: Thiovulaceae, Class: Campylobacteria, Phylum: Epsilonbacteraeota) enriched in the surface of BCS, which suggested that Epsilonbacteraeotra are the keystone species in achieving nitrogen removal through enhancing denitrification at oligotrophic level. KEGG analysis indicated that BCS might release some signaling molecules for enhancing the energy metabolism process, as well as stimulate the enzyme activities of histidine kinase, glycogen phosphorylase and ATPase, and thereby the denitrification processes were strengthened in MSL-BCS system. Consequently, this study could provide some valuable information on the removal performance and mechanism of engineering MSL systems packed with BCS to govern the rural wastewater treatment.

Advances in Biological Nitrogen Removal of Landfill Leachate

With the development of economy and the improvement of people’s living standard, landfill leachate has been increasing year by year with the increase in municipal solid waste output. How to treat landfill leachate with high efficiency and low consumption has become a major problem, because of its high ammonia nitrogen and organic matter content, low carbon to nitrogen ratio and difficult degradation. In order to provide reference for future engineering application of landfill leachate treatment, this paper mainly reviews the biological treatment methods of landfill leachate, which focuses on the comparison of nitrogen removal processes combined with microorganisms, the biological nitrogen removal methods combined with ecology and the technology of direct application of microorganisms. In addition, the mechanism of biological nitrogen removal of landfill leachate and the factors affecting the microbial activity during the nitrogen removal process are also described. It is concluded that the treatment processes combined with microorganisms have higher nitrogen removal efficiency compared with the direct application of microorganisms. For example, the nitrogen removal efficiency of the combined process based on anaerobic ammonium oxidation (ANAMMOX) technology can reach more than 99%. Therefore, the treatment processes combined with microorganisms in the future engineering application of nitrogen removal in landfill leachate should be paid more attention to, and the efficiency of nitrogen removal should be improved from the aspects of microorganisms by considering factors affecting its activity.

Pilot-scale vermicomposting of sewage sludge mixed with mature vermicompost using earthworm reactor of frame composite structure

To improve the efficiency of sludge vermicomposting, a new cost-effective method is provided. It uses a new earthworm reactor with a frame composite structure for vermicomposting and reuses mature vermicompost to condition the sludge. Under the optimum conditions (proportion of earthworm droppings: 15%; thickness of sludge laying: 6 cm; moisture content of initial sludge mixture: 75%), the method of continuous operation described herein works well and presents three advantages compared with the traditional vermicomposting method: the short time required for vermicomposting (20.25 h); covering a small area (5 m2/t·d); and a low cost. In addition, the vermicompost obtained from sludge vermicomposting shows better stability and maturity (C/N: 14.96; GI: 86.42%; TOC: 188.5 mg/g; ash content: 516.2 mg/g). The investigation of the associated mechanisms, including 3D-EEM, TGA, SEM and microbial community analyses, revealed that the addition of mature vermicompost can speed up the progress of decomposition and humification of organic matter in sludge. The process of vermicomposting and adding mature vermicompost significantly modified the microbial community of sewage sludge, and the changes in microorganisms in vermicompost were related to the microorganisms in the earthworm gut.

The cotreatment of old landfill leachate and domestic sewage in rural areas by deep subsurface wastewater infiltration system (SWIS): Performance and bacterial community☆

In this work, two deep subsurface wastewater infiltration systems (SWISs) were constructed and fed with domestic sewage (control system, S1) and mixed wastewater consisting of old landfill leachate and domestic sewage (experimental system, S2). S1 and S2 exhibited favorable removal efficiencies, with TP (98.8%, 98.7%), COD (87.6%, 86.9%), NH₄⁺-N (99.8%, 99.9%) and TN (99.2%, 98.9%). Even when increasing the pollutant load in S2 by adding old landfill leachate, the almost complete removal performance could be maintained in terms of low effluent concentrations and even increased in terms of load removal capabilities, which included COD (19.4, 25.9 g∙m^-2·d^-1), NH₄⁺-N (8.2, 19.9 g∙m^-2·d^-1), TN (8.9, 20.6 g∙m^-2·d^-1). To investigate the transformation of dissolved organic matter along depth, Three-Dimensional Excitation Emission Matrix fluorescence spectroscopy combined with Fluorescence Regional Integration analysis was applied. The results showed that P_Ⅰ,n and P_Ⅱ,n (the proportions of biodegradable fractions) increased gradually from 6.59% to 21.8% at S2_20 to 10.8% and 27.7% at S2_110, but P_Ⅲ,n and P_Ⅴ,n (the proportions of refractory organics) declined from 23.1% to 27.8% at S2_20 to 21.1% and 16.4% at S2_110, respectively. In addition, high-throughput sequencing technology was employed to observe the bacterial community at different depths, and the predicted functional potential of the bacterial community was analyzed by PICRUSt. The results showed that the genera Flavobacterium, Pseudomonas, Vogesella, Acinetobacter and Aquabacterium might be responsible for refractory organic degradation and that their products might serve as the carbon source for denitrifiers to achieve simultaneous nitrate and refractory organic removal. PICRUSt further demonstrated that there was a mutual response between refractory organic degradation and denitrification. Overall, the combined treatment of domestic sewage and old leachate in rural areas by SWIS is a promising approach to achieve comprehensive treatment.

Different acetonitrile degraders and degrading genes between anaerobic ammonium oxidation and sequencing batch reactor as revealed by stable isotope probing and magnetic-nanoparticle mediated isolation

Microbial degraders play crucial roles in wastewater treatment processes, but their use is limited as most microbes are yet unculturable. Stable isotope probing (SIP) is a cultivation-independent technique identifying functional-yet-uncultivable microbes in ambient environment, but is unsatisfactory for substrates with low assimilation rate owing to the low isotope incorporation into DNA. In this study, we used acetonitrile as the target low-assimilation chemical in many wastewater treatment plants and attempted to identify the active acetonitrile degraders in the activated sludge, via DNA-SIP and magnetic-nanoparticle mediated isolation (MMI) which is another cultivation-independent approach without the requirement of substrate labeling. The two approaches identified different active acetonitrile degraders in a 3-day short-term anaerobic ammonium oxidation (ANAMMOX). MMI enriched significantly more acetonitrile-degraders than SIP, showing the advantages in identifying the active degraders for low-assimilation substrates. Sequencing batch reactor (SBR, 30-day degradation) helped in more incorporation of ¹⁵N-labeled acetonitrile into the active degraders, thus the same acetonitrile-degraders and acetonitrile-degrading genes were identified by SIP and MMI. Different acetonitrile degraders between ANAMMOX and SBR were attributed to the distinct hydrological conditions. Our study for the first time explored the succession of acetonitrile-degraders in wastewater and identified the active acetonitrile-degraders which could be further enriched for enhancing acetonitrile degradation performance. These findings provide new insights into the acetonitrile metabolic process in wastewater treatment plants and offer suggestive conclusions for selecting appropriate treatment strategy in wastewater management.

Improvement in nitrogen removal and changes in community structure in a sequencing batch reactor bioaugmented with P. stutzeri strain XL-2

The aim of this work was to study the bioaugmentation of P. stutzeri strain XL-2 in activated sludge to improve nitrogn removal from wastewater with the guide of growth kinetics. When 4250 mg/L COD and 80 mg/L NH₄⁺-N were applied, the TN removal efficiency in a bioaugmented sequencing batch reactor (SBR_XL) achieved 95%, while that in the control reactor (SBR_C) without strain XL-2 was only 84% (P < 0.05). The microbial community analysis demonstrated that strain XL-2 was successfully bioaugmented in SBR_XL, and increasing influent COD concentration promoted its abundance. Influent COD concentration played a dominant role in affecting community structure, while the bioaugmentation of strain XL-2 had much less impact on the community structure. Combined with principal coordinates analysis, redundancy analysis and FAPROTAX, the improvement of TN removal was mainly achieved by the bioaugmentation of strain XL-2, which played a major role in promoting aerobic denitrification.

Microbial community responses to agricultural biomass addition in aerated constructed wetlands treating low carbon wastewater

Using agricultural biomasses as solid carbon substrates in constructed wetlands (CWs) could be an effective way to achieve sustainable nitrogen removal for carbon-limited wastewater treatments. This study investigated the response of bacteria community in CWs to the addition of agricultural biomasses (wheat straw, walnut shell and apricot pit). Results indicated that the addition of different agricultural biomasses had distinct influence on bacterial communities in CWs. Both wheat straw and walnut shell increased the diversity of microbial communities and optimized the structure of microorganisms. The effect of apricot pit on the richness and evenness of microbial communities was not significant, but the composition of microorganisms was significantly affected at the phylum level, especially the relative abundance of phylum Saccharibacteria. Moreover, the addition of agricultural biomasses in CWs acclimatized more functional bacteria including nitrifier and denitrifier, which were proved to be positively correlated with the high-rate denitrification performance. The obtained results would be beneficial to understand the underlying microbial mechanism of nitrogen removal in CWs with agricultural biomass and provide some guidance on the practical application of CWs.

Long-Term Investigation into the Membrane Fouling Behavior in Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment Operated at Two Different Temperatures

In this study, the characteristics of activated sludge flocs were investigated and their effects on the evolution of membrane fouling were considered in the anaerobic membrane bioreactors (AnMBR), which were operated at 25 and 35 °C for municipal wastewater treatment. It was found that the membrane fouling rate of the AnMBR at 25 °C was more severe than that at 35 °C. The membrane fouling trends were not consistent with the change in the concentration of soluble microbial product (SMP). The larger amount of SMP in the AnMBR at 35 °C did not induce more severe membrane fouling than that in the AnMBR at 25 °C. However, the polysaccharide and protein concentration of extracellular polymeric substance (EPS) was higher in the AnMBR at 25 °C in comparison with that in the AnMBR at 35 °C, and the protein/polysaccharide ratio of the EPS in the AnMBR at 25 °C was higher in contrast to that in the AnMBR at 35 °C. Meanwhile, the fouling tendencies measured for the AnMBRs could be related to the characteristics of loosely bound EPS and tightly bound EPS. The analysis of the activated sludge flocs characteristics indicated that a smaller sludge particle size and more fine flocs were observed at the AnMBR with 25 °C. Therefore, the membrane fouling potential in the AnMBR could be explained by the characteristics of activated sludge flocs.

Nutrient removal performance and microbiome of an energy-efficient reciprocation MLE-MBR operated under hypoxic conditions

A critical challenge in the application of membrane bioreactors (MBR) for domestic wastewater treatment is its high energy consumption caused by continuous aeration for biofouling control. To reduce energy consumption and mitigate fouling in membranes, alternative configurations using dynamic shear-enhanced filtration by membrane reciprocation, rotation, and vibration to mechanically impose shear on membrane surfaces have been recently introduced. However, although these methods are effective at lowering energy usage, the nutrient removal efficiencies and microbial community compositions of these systems have not been well studied. In this study, a lab-scale no-aeration reciprocation membrane bioreactor was used to characterize the microbial composition, functional profile and nutrient removal of the reciprocation MBR system operated under hypoxic conditions. Microbial community analysis showed Proteobacteria (35%) and Saccharibacteria (27%) to be the most abundant phyla in the sludge and the biofilm samples, respectively. Nitrogen and phosphorus removal efficiencies were observed at 70% and 50% while the chemical oxygen demand concentration had about a 99% decrease in the effluent. Quantitative PCR of nutrient-removing genes revealed the presence of complete ammonia-oxidizing organisms (comammox) with a mean abundance of 1.88 × 10⁴ gene copies/g sludge, which explains the high ammonia removal despite a low abundance of canonical ammonia-oxidizing bacteria (AOB). Fluorescence in-situ hybridization showed a prevalence of nitrite-oxidizing bacteria (NOB) with clusters that are distant from other nutrient-removing communities, suggesting that their metabolism is not dependent on ammonia oxidizers. The reciprocation MBR configuration may be a suitable, more energy-efficient alternative to conventional air-scouring systems because of its biofouling mitigation and promising nutrient removal performed by the diverse microbial communities in its system.

Effects of pyrolysis temperature on soil-plant-microbe responses to Solidago canadensis L.-derived biochar in coastal saline-alkali soil

Because salinity of coastal soils is drastically increasing, the application of biochars to saline-alkali soil amendments has attracted considerable attention. Various Solidago-canadensis-L.-derived biochars prepared through pyrolysis from 400 to 600 °C were applied to coastal saline-alkali soil samples to optimise the biochar pyrolysis temperature and investigate its actual ecological responses. All biochars reduced the soil bulk density and exchangeable sodium stress and increased soil water-holding capacity, cation exchange capacity, and organic matter content. Principal-component-analysis results showed that pyrolysis temperature played an important role in the potential application of biochars to improve the coastal saline-alkali soil, mainly contributed to ameliorating exchangeable sodium stress and decreasing biochar-soluble toxic compounds. Furthermore, soil bulk density and organic matter, as well as carboxylic acids, phenolic acids and amines of biochar were major driving factors for bacterial community composition. Compared to low-temperature biochar (pyrolyzed below 550 °C), which showed higher toxicity for Brassica chinensis L. growth due to the higher content of carboxylic acids, phenols and amines, high-temperature biochar (pyrolyzed at or above 550 °C) possessed less amounts of these toxic functional groups, more beneficial soil bacteria and healthier for plant growth. Therefore, high-temperature biochar could be applied as an effective soil amendment to ameliorate the coastal saline-alkali soil with acceptable environmental risk.

Ecological and functional research into microbiomes for targeted phenolic removal in anoxic carbon-based fluidized bed reactor (CBFBR) treating coal pyrolysis wastewater (CPW)

Powdered activated carbon (PAC), lignite activated coke (LAC) and Fe-C carriers were applied to enhance CBFBRs to degrade targeted phenolics. In start-up stage, PAC and LAC equipped CBFBRs with higher environment adaptability and phenolic degradation capacity for phenol (>96%), p-cresol (>91%) and 3, 5-dimethylphenol (>84%) in comparison to Fe-C carrier. In recovery stage, the superior performance was also identified for CBFBRs in basis of PAC and LAC than Fe-C-based reactor. However, the Fe-C carrier assisted CBFBR with more stable degradation performance under impact loading. By comparing microbiomes, significantly enriched Brachymonas (54.80%-68.81%) in CBFBRs exerted primary role for phenolic degradation, and positively contributed to microbial network. Meanwhile, Geobacter in Fe-C-based reactor induced excellent impact resistance by enhancing interspecific electron transfer among microbes. Furthermore, the investigation on functional genes related to phenolic degradation revealed that anaerobic pathway accounted for demethylation procedure, while aerobic pathways dominated the phenolic ring-cleavage process.

Hybrid System Coupling Moving Bed Bioreactor with UV/O3 Oxidation and Membrane Separation Units for Treatment of Industrial Laundry Wastewater

This paper describes the investigations on the possibilities of treatment of wastewater generated in an industrial laundry with application of a combined biological-photooxidation- membrane system aimed at water recycle and reuse. The two treatment schemes were compared: 1) scheme A consisting of a treatment in a moving bed biological reactor (MBBR) followed by microfiltration (MF) and nanofiltration (NF), and 2) scheme B comprising MBBR followed by oxidation by photolysis enhanced with in situ generated O₃ (UV/O₃) after which MF and NF were applied. The removal efficiency in MBBR reached 95–97% for the biochemical oxygen demand; 90–93% for the chemical oxygen demand and 89–99% for an anionic and a nonionic surfactants. The application of UV/O₃ system allowed to decrease the content of the total organic carbon by 68% after 36 h of operation with a mineralization rate of 0.36 mg/L·h. Due to UV/O₃ pretreatment, a significant mitigation of membrane fouling in the case of both MF and NF processes was achieved. The MF permeate flux in the system B was over two times higher compared to that in the system A. Based on the obtained results it was concluded that the laundry wastewater pretreated in the MBBR-UV/O₃-MF-NF system could be recycled to any stage of the laundry process.

Evaluating influence of filling fraction of carriers packed in anaerobic side-stream reactors on membrane fouling and microbial community of the coupled membrane bioreactors

An anoxic/oxic membrane bioreactors (AO-MBR) and three identical anaerobic side-stream reactor coupled with anoxic/oxic membrane bioreactors (ASSR-MBR) were constructed and operated in parallel to investigate the appropriate filling fraction of carriers packed in ASSR, influences on pollutants removal, sludge reduction, membrane fouling and microbial community of ASSR-MBR. Inserting ASSR achieved efficient COD removal and nitrification, and packing carriers in ASSR obtained the highest sludge reduction efficiency of 50.5 % at filling fraction of 25 %. Compared to AO-MBR, inserting ASSR without carriers induced the release of viscous components in extracellular polymeric substances (EPS) and the formation of calcium carbonate-related bacteria on membrane surface, and thus deteriorated membrane fouling. Packing carriers with 25 % filling fraction promoted the hydrolysis of soluble microbial products and EPS, whilst reduced the viscoelasticity of sludge flocs. Higher filling fraction of 50 % increased the shear forces to the biofilm and biomarkers related to membrane fouling, and thus showed little improvement to alleviate membrane fouling. MiSeq sequencing revealed that although it enriched in the bulk sludge of conventional ASSR-MBR and the coupled reactor with filling fraction of 50 %, the floc-forming, hydrolytic and fermentative bacteria were more inclined to attach on the membrane surface and alleviate fouling process.

Mechanism of Membrane Fouling Control by HMBR: Effect of Microbial Community on EPS

A hybrid membrane bioreactor (HMBR) employing activated sludge and biofilm simultaneously is proved to represent a good performance on membrane fouling control compared to conventional membrane bioreactor (CMBR) by reducing extracellular polymeric substances (EPS), especially bound EPS (B-EPS). In order to better understand the mechanism of membrane fouling control by the HMBR in regard of microbial community composition, a pilot scale HMBR operated to treat domestic wastewater for six months, and a CMBR operated at the same time as control group. Results showed that HMBR can effectively control membrane fouling. When transmembrane pressure reached 0.1 MPa, the membrane module in the HMBR operated for about 26.7% longer than that in the CMBR. In the HMBR, the quantity of EPS was significantly lower than that in the CMBR. In this paper, soluble EPS was also found to have a close relationship with cake layer resistance. The species richness and diversity in the HMBR were higher than those in the CMBR, and a certain difference between the compositions of microbial communities in the two reactors was confirmed. Therefore, the difference in microbial community compositions may be the direct reason why EPS in the HMBR was lower than that in the CMBR.

Effects of extracellular polymeric substances and microbial community on the anti-scouribility of sewer sediment

Sewer sediment is the main source of overflow pollution, and the anti-scouribility of sewer sediment directly determines the amount of the discharged contaminants. In this study, sewer sediments of different depths were collected from combined and storm sewers in Shanghai, China. The anti-scouribility, represented by the shear stress of each layer of sewer sediment, was detected in situ. The microbial community and extracellular polymeric substances (EPS), including carbohydrates and proteins present in the sewer sediments were characterized. The results indicated that the distribution of the anti-scouribility of sewer sediment is regulated. There were positive correlations between the content of EPS, proteins, and carbohydrates, and the anti-scouribility of sediments (Pearson Corr. = 0.604, sig. = 0.219; Pearson Corr. = 0.623, sig. = 0.234; Pearson Corr. = 0.727, sig. = 0.359, respectively). Furthermore, the microbial community had a positive influence on anti-scouribility. In particular, the gram-positive bacterial phyla of Bacteroidetes and Firmicutes may be important and influential for the improvement of anti-scouribility of sediment owing to their production of cellulose.

New insights into pollutants removal, toxicity reduction and microbial profiles in a lab-scale IC-A/O-membrane reactor system for paper wastewater reclamation

In this study, an internal circulation-anoxic/aerobic (IC-A/O) process followed by ultrafiltration (UF) and reverse osmosis (RO) system was applied for paper wastewater reclamation. The IC-AO system presented a stable and efficient performance, achieving high removal of chemical oxygen demand (COD), total organic carbon (TOC) and total nitrogen (TN) with methane production rate of 132.8 mL/d. Acute toxicity to Daphnia magna (D. magna) was reduced significantly (83.2%) and the spearman's rank correlation analysis indicated that the toxicity of effluents from each reactor were positively correlated with COD and TOC. Hexadecanoic acid, octadecanoic acid and benzophenone were the main toxic contributors for biological effluent. Microbial community revealed that Anaerolinea was significantly related with organic pollutants. The UF-RO system further removed pollutants and toxicity with the final effluent COD, TOC, ammonium nitrogen (NH₄⁺-N) and TN of 32.6, 18.8, 0.3 and 9.2 mg/L, respectively, which proved that it was feasible for paper wastewater reuse. This study presented an efficient, practical and environmentally competitive system, and paved a foundation for the treatment and reuse of paper wastewater.

Low energy treatment of landfill leachate using simultaneous partial nitrification and partial denitrification with anaerobic ammonia oxidation

An up-flow anaerobic sludge blanket reactor (UASB), anoxic/oxic (A/O)-anaerobic ammonia oxidation reactor (ANAOR or anammox reactor), and anaerobic sequencing batch reactor (ASBR) were employed in the treatment of landfill leachate with partial nitrification-anammox and half-denitrification-anammox. The Chemical Oxygen Demand (COD) concentration, ammonium nitrogen (NH₄⁺-N) concentration, and total nitrogen (TN) concentration of the basal leachate was 2200-2500 mg/L, 1200-1300 mg/L, and 1300-1400 mg/L, respectively. After a 1:2 dilution using domestic sewage, the COD, NH₄⁺-N, and TN concentrations in the influent were 800-1000 mg/L, 400-430 mg/L, and 420-440 mg/L, respectively. After treatment, the final COD, NH₄⁺-N, and TN were decreased to 90-100 mg/L, 13-14 mg/L, and 35-38 mg/L, respectively. In the ASBR, organic carbon sources in sewage-diluted landfill leachate were introduced for the conversion of nitrate nitrogen (NO₃^--N) into nitrite nitrogen (NO₂^--N). This enabled the continued reaction of NO₂^--N with NH₄⁺-N from the newly introduced sewage-diluted landfill leachate via anammox. As a result, complete TN removal was achieved in the system. Microbial diversity analysis indicated that the relative abundance of ammonia-oxidizing bacteria (AOB) was four to five times greater than nitrite-oxidizing bacteria (NOB) in the A/O reactor, showing that partial nitrification was prevalent. The relative abundance of the anammox bacterium Candidatus Kuenenia gradually increased in each reactor, reaching a maximum of 1.17%-1.39%. Using this set-up, we achieved advanced, efficient, and economical, COD reduction and nitrogen removal. Taken together, the findings provide important insights into the optimal operation of landfill leachate treatments.

Improved performance of simultaneous nitrification and denitrification via nitrite in an oxygen-limited SBR by alternating the DO

In this study, the performance of simultaneous nitrification and denitrification via nitrite was investigated by alternating the dissolved oxygen (DO) concentration in a sequencing batch reactor with the DO-control area and the non-control area. In addition, bacterial communities and their metabolic functions were analyzed by high-throughput sequencing technology and phylogenetic investigation of the communities by reconstruction of unobserved states (PICRUSt). The removal efficiencies of NH₄⁺-N and total nitrogen via the nitrite pathway were 97.91 ± 2.04% and 72.28 ± 2.23%, respectively, by maintaining low DO levels (0.7 ± 0.1 mg/L) in the DO-control area. PICRUSt analysis showed that the metabolic potential of the bacterial community for amino acids, nucleotides, coenzymes and inorganic ions decreased, while the relative abundance of key enzymes involved in nitrification and denitrification, and the relative population of denitrifying bacteria increased when the DO decreased from 1.2 ± 0.2 mg/L to 0.7 ± 0.1 mg/L.

Nitrogen removal of anaerobically digested swine wastewater by pilot-scale tidal flow constructed wetland based on in-situ biological regeneration of zeolite

Dispersed swine wastewater has increasingly aggravated water pollution in China. Anaerobically digested dispersed swine wastewater was targeted and treated by a pilot-scale zoning tidal flow constructed wetland (TFCW) with a bottom wastewater saturation layer. The long-term application of in-situ biological regeneration of biozeolite, nitrogen removal performance, nitrogen removal pathways and microbial community of TFCW were investigated. Results showed that with the surface loads of 0.079, 0.022 and 0.024 kg/(m²·d), TFCW could decrease COD, NH₄N and TN by 84.75%, 74.13% and 67.13% respectively. Influent COD, NH₄N, TN and nitrates/nitrites produced by bioregeneration of NH₄N were mostly removed in zeolite layer and the remaining nitrates/nitrites could be further denitrified in bottom saturation layer. Theory of dynamic process of rapid-adsorption and bioregeneration for NH₄N removal was proposed. When this process reached dynamic equilibrium, the mass of adsorbed NH₄N onto zeolites remained relatively stable. When ambient temperature decreased to 16 °C, TFCW could still remove COD, NH₄N and TN by 73.79%, 72.99% and 70.71% with the surface loads of 0.103, 0.056 and 0.054 kg/(m²·d) respectively. Nitrification-denitrification which accounted for 80.32% of TN removal was the main nitrogen removal pathway. Dominant nitrifiers (Nitrosospira and Rhizomicrobium) and denitrifiers (Ottowia, Thauera and Rhodanobacteria) in biozeolite layer verified the existence of simultaneous nitrification and denitrification.

Dynamic membrane bioreactor (DMBR) for the treatment of landfill leachate; bioreactor's performance and metagenomic insights into microbial community evolution

The use of dynamic membranes as a low-cost alternative for conventional membrane for the treatment of landfill leachate (LFL) was investigated in this study. For this purpose a lab-scale, submerged pre-anoxic and post-aerobic bioreactor configuration was used with nylon mesh as dynamic membrane support. The study was conducted at ambient temperature and LFL was fed to the bioreactor in gradually increasing concentration mixed with tap water (from 20% to 100%). The results of this study demonstrated that lower mesh pore size of 52 μm achieved better results in terms of solid-liquid separation performance (turbidity <10 NTU) of the formed dynamic membrane layer as compared to 200 and 85 μm meshes while treating LFL. Consistently high NH₄⁺-N conversion efficiency of more than 98% was achieved under all nitrogen loading conditions, showing effectiveness of the formed dynamic membrane in retaining slow growing nitrifying species. Total nitrogen removal reached more than 90% however, the denitrification activity showed a fluctuating profile and found to be inhibited by elevated concentrations of free nitrous acid and NO₂^--N at low pH values inside the anoxic bioreactor. A detailed metagenomic analysis allowed a taxonomic investigation over time and revealed the potential biochemical pathways involved in NH₄⁺-N conversion. This study led to the identification of a dynamic system in which nitrite concentration is determined by the contribution of NH₄⁺ oxidizers (Nitrosomonas), and by a competition between nitrite oxidizers (Nitrospira and Nitrobacter) and reducers (Thauera).

Treatment of Landfill Leachate Using Activated Sludge Technology: A Review

Landfill leachate contains a large amount of organic matter and ammoniacal nitrogen. As such, it has become a complex and difficult issue within the water treatment industry. The activated sludge process has been found to be a good solution with low processing costs and is now therefore the core process for leachate treatment, especially for nitrogen removal. This paper describes the characteristics and treatment of leachate. Treatment of leachate using the activated sludge process includes the removal of organic matter, ammoniacal nitrogen, and total nitrogen (TN). The core method for the removal of organic matter involves anaerobic treatment supplemented with an aerobic process. Ammoniacal nitrogen is commonly removed using a conventional aerobic treatment, and advanced TN removal is achieved using endogenous denitrification or an anaerobic ammonium oxidation (ANAMMOX) process. Since biological processes are the most economical method for TN removal, a key issue is how to tap the full potential of the activated sludge process and improve TN removal from leachate. This complex issue has been identified as the focus of current scholars, as well as an important future direction for leachate research and development.

Microbial fuel cell and membrane bioreactor coupling system: recent trends

Membrane bioreactor (MBR) and microbial fuel cell (MFC) are new technologies based on microbial process. MBR takes separation process as the core to achieve the high efficient separation and enrichment the beneficiation of microbes during the biological treatment. MFC is a novel technology based on electrochemical process to realize the mutual conversion between biomass energy and electric energy, in order to solve the problems of serious membrane fouling and low efficiency of denitrification in membrane bioreactor, the low power generation efficiency, and unavailability of bioelectric energy of MFC. In recent years, MFC-MBR coupling system emerged. It can effectively mitigate the membrane fouling and reduce the excess sludge production. Simultaneously, the electricity can be used effectively. The new coupling system has good prospects for development. In this paper, we summarized the research progresses of the two kinds of coupling systems in recent years and analyzed the coupling structure and forms. Based on the above, the future development fields of the MFC-MBR coupling system were prospected.

Optimization aspects of the biological nitrogen removal process in a full-scale twin sequencing batch reactor (SBR) system in series treating landfill leachate

Despite the fact that biological nitrogen removal (BNR) process has been studied in detail in laboratory- and pilot-scale sequencing batch reactor (SBR) systems treating landfill leachate, a limited number of research works have been performed in full-scale SBR plants regarding nitrification and denitrification. In the current study, a full-scale twin SBR system in series of 700 m³ (350 m³ each) treating medium-age landfill leachate was evaluated in terms of its carbon and nitrogen removal efficiency in the absence and presence of external carbon source, i.e., glycerol from biodiesel production. Both biodegradable organic carbon and ammonia were highly oxidized [biochemical oxygen demand (BOD₅) and total Kjehldahl nitrogen (TKN) removal efficiencies above 90%], whereas chemical oxygen demand (COD) removal efficiency was slightly above 40%, which is within the range reported in the literature for pilot-scale SBRs. As the consequence of the high recalcitrant organic fraction of the landfill leachate, dissimilatory nitrate reduction was restricted in the absence of crude glycerol, although denitrification was improved by electron donor addition, resulting in TN removal efficiencies above 70%. Experimental data revealed that the second SBR negligibly contributed to BNR process, since carbon and ammonia oxidation completion was achieved in the first SBR. On the other hand, the low VSS/SS ratio, due to the lack of primary sedimentation, highly improved sludge settleability, resulting in sludge volume indices (SVI) below 30 mL g^-1.

Bioremediation of Landfill Leachate with Fungi: Autochthonous vs. Allochthonous Strains

Autochthonous fungi from contaminated wastewater are potential successful agents bioremediation thanks to their adaptation to pollutant toxicity and to competition with other microorganisms present in wastewater treatment plant. Biological treatment by means of selected fungal strains could be a potential tool to integrate the leachate depuration process, thanks to their fungal extracellular enzymes with non-selective catalytical activity. In the present work, the treatability of two real samples (a crude landfill leachate and the effluent coming from a traditional wastewater treatment plant) was investigated in decolorization experiments with fungal biomasses. Five autochthonous fungi, Penicillium brevicompactum MUT 793, Pseudallescheria boydii MUT 721, P. boydii MUT 1269, Phanerochaete sanguinea MUT 1284, and Flammulina velutipes MUT 1275, were selected in a previous miniaturized decolorization screening. Their effectiveness in terms of decolorization, enzymatic activity (laccases and peroxidases), biomass growth and ecotoxicity removal was compared with that of five allochthonous fungal strains, Pleurotus ostreatus MUT 2976, Porostereum spadiceum MUT 1585, Trametespubescens MUT 2400, Bjerkanderaadusta MUT 3060 and B. adusta MUT 2295, selected for their well known capability to degrade recalcitrant pollutants. Moreover, the effect of biomass immobilization on polyurethane foam (PUF) cube was assessed. The best decolorization (60%) was achieved by P. spadiceum MUT 1585, P. boydii MUT 721 and MUT 1269. In the first case, the DP was achieved gradually, suggesting a biodegradation process with the involvement of peroxidases. On the contrary, the two autochthonous fungi seem to bioremediate the effluent mainly by biosorption, with the abatement of the toxicity (up to 100%). The biomass immobilization enhanced enzymatic activity, but not the DP. Moreover, it limited the biomass growth for the fast growing fungi, MUT 721 and MUT 1269. In conclusion, robust and versatile strains coming from well-characterized collections of microorganisms can obtain excellent results comparing and even exceeding the bioremediation yields of strains already adapted to pollutants.