Biological Phosphorus Removal Systems Research Articles

Assessment of three different approaches for integrating phosphorus recovery from sewage sludge and derived products in existing wastewater treatment plants

Three different technological solutions, namely acidogenic fermentation and chemical extraction (alkaline or acidic), followed by precipitation with 1 % Ca(OH)2, were investigated in the view of integrating phosphorus recovery into existing wastewater treatment plants. Experiments were conducted at the lab-scale using (i) sludge taken from biologically and chemically promoted phosphorus removal activated sludge processes and (ii) ashes obtained from sludge muffle incineration. Results highlighted the benefits of enhanced biological phosphorus removal (EBPR) systems rather than chemically promoted phosphorus removal in not only phosphorus extraction (up to 40 % with EBPR) and recovery directly from secondary sludge (P precipitation between 66 and 92 %), but after sludge incineration as well (P extraction up to 96 % and precipitation above 96 %). Acidogenic fermentation ensured the highest phosphorus release from EBPR sludge (equal to a concentration in solution of 122 mg/L P-PO43−), while the derived ashes had a lower level of metal contamination (particularly Fe and Al content < 2 %). The phosphorus-rich product obtained by means of the recovery process showed relevant metal contamination (Cu, Zn, and Ni) under some operating conditions, suggesting the need for further treatments.

Phosphorus Release Dynamics from Ashes during a Soil Incubation Study: Effect of Feedstock Characteristics and Combustion Conditions

Recovering phosphorus (P) through combustion from waste streams, like wastewater sludge and animal manure, offers a promising solution. This research explores the P release patterns in different ashes derived from secondary raw materials, using a long-term soil incubation lasting 160 days. The study evaluated the P release dynamics in five types of ashes from enhanced biological phosphorus removal (EBPR) systems and pig slurry burned at different temperatures. According to the results, a primary effect was observed on P bioavailability during the initial incubation period. All tested ashes release more than 50% of the total P applied between days 5 and 10. Ashes from EBPR exhibited higher P release than those from pig manure, indicating ash origin as a key factor in P release. Additionally, combustion temperature was crucial, with higher temperatures resulting in increased P release rates. Furthermore, the Pearson correlation revealed a strong relationship between the characteristics of the ashes and the amount of P release. Overall, these findings suggest that ashes could be a valuable P-source for agriculture avoiding the process of wet chemical P extraction, thus reducing both economic and environmental costs.

Metabolic shifts in glycogen-accumulating organisms: Exploring carbon and phosphorus dynamics under two distinct phosphorus limitation modes

Glycogen-accumulating organisms (GAOs) are recognized as competitors of phosphorus-accumulating organisms (PAOs) in enhanced biological phosphorus removal (EBPR) systems. However, different types of GAOs exhibit unique metabolic traits in different environments. To characterize the metabolic activity of GAOs, two distinct modes were constructed. Long-term operation with the mode of anaerobic post-drainage demonstrated the successful establishment of a rapid and enduring GAOs system dominated by Candidatus Contendobacter community. Acetate was completely consumed within 60 min of the anaerobic phase. Concurrently, glycogen levels decreased by 0.062 g Glycogen/g SS, while intracellular carbon storage of poly-hydroxybutyrate (PHB) and poly-hydroxyvalerate (PHV) increased by 0.027 g PHB/g SS and 0.007 g PHV/g SS, respectively. Various concentrations of phosphorus loads illustrated the resistance of the system to high phosphorus loads, while maintaining glycogen accumulating metabolism (GAM). Under complete phosphorus limitation, no correlation between glycogen and acetate was observed during the initial 140 d. The addition of 1 mg/L phosphate to the influent preserved the typical GAM characteristics. Moreover, the pathway involved in glycogen conversion to trehalose may be pivotal in enhancing anaerobic glycogen degradation. The complete tricarboxylic acid cycle ensured efficient energy production, thereby sustaining the foundational metabolism. Notably, sucC and mdh were critical regulators of energy flux. This study provides a distinctive metabolic profile of a robust and resilient GAOs model with Ca. Contendobacter.

Two new clades recovered at high temperatures provide novel phylogenetic and genomic insights into Candidatus Accumulibacter.

Candidatus Accumulibacter, a key genus of polyphosphate-accumulating organisms, plays key roles in lab- and full-scale enhanced biological phosphorus removal (EBPR) systems. A total of 10 high-quality Ca. Accumulibacter genomes were recovered from EBPR systems operated at high temperatures, providing significantly updated phylogenetic and genomic insights into the Ca. Accumulibacter lineage. Among these genomes, clade IIF members SCELSE-3, SCELSE-4, and SCELSE-6 represent the to-date known genomes encoding a complete denitrification pathway, suggesting that Ca. Accumulibacter alone could achieve complete denitrification. Clade IIC members SSA1, SCUT-1, SCELCE-2, and SCELSE-8 lack the entire set of denitrifying genes, representing to-date known non-denitrifying Ca. Accumulibacter. A pan-genomic analysis with other Ca. Accumulibacter members suggested that all Ca. Accumulibacter likely has the potential to use dicarboxylic amino acids. Ca. Accumulibacter aalborgensis AALB and Ca. Accumulibacter affinis BAT3C720 seemed to be the only two members capable of using glucose for EBPR. A heat shock protein Hsp20 encoding gene was found exclusively in genomes recovered at high temperatures, which was absent in clades IA, IC, IG, IIA, IIB, IID, IIG, and II-I members. High transcription of this gene in clade IIC members SCUT-2 and SCUT-3 suggested its role in surviving high temperatures for Ca. Accumulibacter. Ambiguous clade identity was observed for newly recovered genomes (SCELSE-9 and SCELSE-10). Five machine learning models were developed using orthogroups as input features. Prediction results suggested that they belong to a new clade (IIK). The phylogeny of Ca. Accumulibacter was re-evaluated based on the laterally derived polyphosphokinase 2 gene, showing improved resolution in differentiating different clades.

Minimizing biological sludge generation in a sidestream enhanced biological phosphorus removal (S2EBPR) system: full-scale evaluation and modeling insights

Minimizing biological sludge generation in a sidestream enhanced biological phosphorus removal (S2EBPR) system: full-scale evaluation and modeling insights

Revisiting the role of Acinetobacter spp. in side-stream enhanced biological phosphorus removal (S2EBPR) systems

We piloted the incorporation of side-stream enhanced biological phosphorus removal (S2EBPR) with A/B stage short-cut nitrogen removal processes to enable simultaneous carbon-energy-efficient nutrients removal. This unique configuration and system conditions exerted selective force on microbial populations distinct from those in conventional EBPR. Interestingly, effective P removal was achieved with the predominance of Acinetobacter (21.5 ± 0.1 %) with nearly negligible level of known conical PAOs (Ca. Accumulibacter and Tetrasphaera were 0.04 ± 0.10 % and 0.47 ± 0.32 %, respectively). Using a combination of techniques, such as fluorescence in situ hybridization (FISH) coupled with single cell Raman spectroscopy (SCRS), the metabolic tracing of Acinetobacter-like cells exerted PAO-like phenotypic profiling. In addition, comparative metagenomics analysis of the closely related Acinetobacter spp. revealed the EBPR relevant metabolic pathways. Further oligotyping analysis of 16s rRNA V4 region revealed sub-clusters (microdiversity) of the Acinetobacter and revealed that the sub-group (oligo type 1, identical (100 % alignment identity) hits from Acinetobacter_midas_s_49494, and Acinetobacter_midas_s_55652) correlated with EBPR activities parameters, provided strong evidence that the identified Acinetobacter most likely contributed to the overall P removal in our A/B-shortcut N-S2EBPR system. To the best of our knowledge, this is the first study to confirm the in situ EBPR activity of Acinetobacter using combined genomics and SCRS Raman techniques. Further research is needed to identify the specific taxon, and phenotype of the Acinetobacter that are responsible for the P-removal.

Optimizing sludge retention time for sustainable photo-enhanced biological phosphorus removal systems: Insights into nutrient fate, microbial community, and bacterial phototolerance

Photo-enhanced Biological Phosphorus Removal (PEBPR) systems, promising wastewater treatment technology, offer efficient phosphorus removal without external oxygen. However, comprehending the impact of sludge retention time (SRT) on the system is crucial for successful implementation. This study investigated the SRT effect on nutrient fate, microbial community, and bacterial phototolerance in PEBPR systems. PEBPR systems exhibited good bacterial phototolerance at SRT of 10, 15, and 20 d, with optimal phosphorus-accumulation metabolism observed at SRT of 10 and 15d. However, at SRT of 5d, increased light sensitivity and glycogen-accumulating organisms (GAOs) growth resulted in poor P removal (71.9%). Accumulibacter-IIC were the dominant P accumulating organisms (PAOs) at SRT of 10, 15, and 20 d. Accumulibacter-I, IIC and IIF were the major PAOs at SRT of 5 d. The decrease in SRT promoted the microalgal population diversity, and Dictyosphaerium and Chlorella were the major microalgal species in this study. Flow cytometry results revealed high light intensity triggered intracellular Fe2+ efflux, limiting translation activity and metabolism. Moreover, PAOs had lower phototolerance than GAOs due to Poly-P bound intracellular Mg2+ affecting enzyme activity. This study provides an in-depth understanding of PEBPR systems operation strategy toward environmentally sustainable wastewater treatment.

Simultaneous decarbonization and phosphorus removal by Tetrasphaera elongata with glucose as carbon source under aerobic conditions

Previous researches have recognized the vital role of Tetrasphaera elongata in enhanced biological phosphorus removal systems, but the underlying mechanisms remain under-investigated. To address this issue, this study investigated the metabolic characteristics of Tetrasphaera elongata when utilizing glucose as the sole carbon source. Results showed under aerobic conditions, Tetrasphaera elongata exhibited a glucose uptake rate of 136.6 mg/(L·h) and a corresponding phosphorus removal rate of 8.6 mg P/(L·h). Upregulations of genes associated with the glycolytic pathway and oxidative phosphorylation were observed. Noteworthily, the genes encoding the two-component sensor histidine kinase and response regulator transcription factor exhibited a remarkable 28.3 and 27.4-fold increase compared with the group without glucose. Since these genes play a pivotal role in phosphate-specific transport systems, collectively, these findings shed light on a potential mechanism for simultaneous decarbonization and phosphorus removal by Tetrasphaera elongata under aerobic conditions, providing fresh insights into phosphorus removal from wastewaters.

Enhanced biological phosphorus removal systems adapting to seawater intrusion: Impacts of varying carbon source on metabolic adaptation in Candidatus Accumulibacter phosphatis

In enhanced biological phosphorus removal (EBPR) systems, seawater intrusion may introduce uncertainty into the metabolism of Polyphosphate Accumulating Organisms (PAOs), especially when volatile fatty acid (VFA) profiles derived from fermentation liquids serves as the carbon source. This study investigated the impacts of varying sea salt salinity levels on the metabolism of Accumulibacter with different VFA as carbon sources. As sea salt salinity increased from 0.5 % to 3.5 %, catabolism (phosphorus release, glycogen and PHA biodegradation) was inhibited to a much lower degree compared to anabolism (phosphorus uptake, glycogen and PHA synthesis). Under seawater conditions, the intracellular free Mg2+ was partially excreted, leading to a subsequent reduction in glycogen metabolism and PHA synthesis. The decrease in PHA synthesis resulted in the diminished aerobic metabolic activity and polyphosphatase (PPX) enzyme activity, collectively causing decreased phosphorus uptake. Moreover, additional energy consumption was used to alleviate osmotic stress, which limited the energy used for esterase activity, translation activity, and phosphorus and glycogen metabolism, resulting in a decrease in growth activity. When using butyrate as a carbon source, Accumulibacter exhibited the highest metabolic activity (49.8 %), making it more adaptable to seawater conditions. The clade IIF was the dominant Accumulibacter in seawater conditions and could synthesize more PHA with butyrate, isobutyrate and valerate as a carbon source, respectively, stabilizing aerobic metabolism. Therefore, fermentation liquid containing high concentrations of butyrate and the activated sludge dominated by clade IIF have the potential to enhance the stabilization of EBPR systems in wastewater treatment plants infiltrated by seawater.

Responses of antibiotic resistance genes in the enhanced biological phosphorus removal system under various antibiotics: Mechanisms and implications

The effects of antibiotics on the proliferation of antibiotic resistant genes (ARGs) in WWTPs have drawn great attention in recent years. The effects of antibiotics on ARGs in the enhanced biological phosphorus removal (EBPR) system and its mechanisms, however, are still not well understood. In this study, EBPR systems were constructed using activated sludge to investigate the effects of ten commonly detected antibiotics in the environment on the proliferation of ARGs and the mechanisms involved. The results showed that the total abundance of ARGs increased to varying degrees with the addition of different antibiotics (0.05 mmol/L), and the top 30 ARGs increased by 271.1 % to 370.0 %. Mobile genetic elements (MGEs), functional modules, and the bacteria community were consistently related to the changes in ARGs. Refractory antibiotics, in particular, have a stronger promoting effect on transduction in the EBPR system. The insertion sequence common region (ISCR) and transposon (Tnp) were identified as crucial factors in the proliferation of ARGs. Moreover, the risk of polyphosphate accumulating organisms (PAOs) carrying ARGs in the presence of antibiotics should not be ignored. Our findings emphasize the potential efficacy of employing strategies that target the reduction of MGEs, regulation of cellular communication, and management of microbial communities to effectively mitigate the risks associated with ARGs.

Effect of different enrichment methods on the independent biological phosphorus removal performance after nitrogen removal using immobilized fillers

In order to find a biological phosphorus removal enrichment method with high performance and low energy consumption, two enrichment methods were used in this study, namely gradient carbon source addition (S1) and fixed carbon source addition (S2). The two enrichment methods were applied to the enrichment of phosphorus removing bacteria in an independent biological phosphorus removal system based on nitrogen removal by immobilized fillers. The phosphorus removal performance, stoichiometry and microbial structure were compared for the two enrichment methods. It was found that PO43--P remained 0.15–0.2 mg/L at the end of enrichment in S1, while PO43--P increased from 0.27 to 0.38 mg/L at the end of enrichment in S2. Stoichiometric analysis showed that S1 used more PHAs (1.47 molC/L) for phosphorus absorption, while S2 used nearly half of the PHAs (0.87 molC/L) for glycogen synthesis. Moreover, the absorbed phosphorus content in S2 was significantly less than S1 (5.67 < 8.65 mg/L). As a result, denitrifying phosphorus-removing bacteria predominated S1, while phosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) both played a role in S2. Dechloromonas, the dominant denitrifying PAO in both S1 and S2 increased from 0.26 % to 3.34 % and 1.04 %, respectively, while Defluviicoccus, a typical GAO, changed from 0.24 % to 0.2 % and 2.01 %, respectively. As a result, gradient carbon source enrichment demonstrated a better phosphorus removal effect and dominant bacteria, whereas the fixed carbon source enrichment increased the abundance of GAOs while negatively impacting the phosphorus removal effect.

Microbiome assembly mechanism and functional potential in enhanced biological phosphorus removal system enriched with Tetrasphaera-related polyphosphate accumulating organisms

Tetrasphaera-related polyphosphate accumulating organisms (PAOs) are the key functional guilds for enhanced biological phosphorus removal (EBPR) systems. Their biomass enrichment can be enhanced by the nitrification inhibitor allylthiourea (ATU). However, the underlying assembly mechanism and the functional potential of the EBPR microbiome regulated by ATU are unclear. This study investigates the effect of ATU on microbiome assembly and functional potential by closely following the microbiota dynamics in an EBPR system enriched with Tetrasphaera-related PAOs for 288-days before, during and after ATU addition. The results showed that ATU addition increased microbiota structural similarity and compositional convergence, and enhanced determinism in the assembly of EBPR microbiome. During exposure to ATU, Tetrasphaera-related PAOs were governed by homogeneous selection and the dominant species revealed by 16S rRNA gene-based phylogenetic analysis shifted from clade III to clade I. Meanwhile, ATU supply promoted significant enrichment of functional genes involved in phosphate transport (pit) and polyphosphate synthesis and degradation (ppk1 and ppk2), whereas both Nitrosomonas and ammonia monooxygenase-encoding genes (amoA/B/C) assignable to this group of nitrifying bacteria decreased. Moreover, ATU addition relieved the significant abundance correlation between filamentous bacteria Ca. Promineofilum and denitrifying Brevundimonas (FDR-adjusted P < 0.01), damaging their potential synergic or cooperative interactions, thus weakening their competitiveness against Tetrasphaera-related PAOs. Notably, ATU withdrawn created opportunistic conditions for the unexpected explosive growth and predominance of Thiothrix filaments, leading to a serious bulking event. Our study provides new insights into the microbial ecology of Tetrasphaera-related PAOs in EBPR system, which could guide the establishment of an efficient microbiota for EBPR.

Aerobic granular sludge formation and stability in enhanced biological phosphorus removal system under antibiotics pressure: Performance, granulation mechanism, and microbial successions

Wastewater containing antibiotics can pose a significant threat to biological wastewater treatment processes. This study investigated the establishment and stable operation of enhanced biological phosphorus removal (EBPR) by aerobic granular sludge (AGS) under mixed stress conditions induced by tetracycline (TC), sulfamethoxazole (SMX), ofloxacin (OFL), and roxithromycin (ROX). The results show that the AGS system was efficient in removing TP (98.0%), COD (96.1%), and NH4+-N (99.6%). The average removal efficiencies of the four antibiotics were 79.17% (TC), 70.86% (SMX), 25.73% (OFL), and 88.93% (ROX), respectively. The microorganisms in the AGS system secreted more polysaccharides, which contributed to the reactor's tolerance to antibiotics and facilitated granulation by enhancing the production of protein, particularly loosely bound protein. Illumina MiSeq sequencing revealed that putative phosphate accumulating organisms (PAOs)-related genera (Pseudomonas and Flavobacterium) were enormously beneficial to the mature AGS for TP removal. Based on the analysis of extracellular polymeric substances, extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and microbial community, a three-stage granulation mechanism was proposed including adaption to the stress environment, formation of early aggregates and maturation of PAOs enriched microbial granules. Overall, the study demonstrated the stability of EBPR-AGS under mixed antibiotics pressure, providing insight into the granulation mechanism and the potential use of AGS for wastewater treatment containing antibiotics.

Phosphate Starvation Responses in Plants and Microbe Mediated Phosphorus Recycling in Soil: A Review

Phosphorus (P) is an essential macronutrient, crucial for intensification of agricultural production. Although P is a vital nutrient for all life forms but in natural ecosystem it is least available owing to its high reactive nature. Plants have developed diverse adaptive strategies to improve Pi acquisition and utilization under inadequate condition. They undergo numerous modifications at morphological, physiological, and biochemical level to maintain P homeostasis under deplete conditions of P. In last decades, notable development has been made in utilizing microbes for regulating P supply in soil solution. In this review, we focused on the understanding of P uptake from soil, mobilization within plants, phosphate starvation responses and efficacy of microorganisms in facilitating external P to plants. Moreover, other metabolism in microorganism viz. phosphate accumulation is an important trait of microbes to maintain labile P in soil solution. Application of phosphate accumulating microbes is well known in enhanced biological phosphorus removal (EBPR) system and heavy metal remediation. This review also discussed the phosphate accumulation mechanism in microbes and their importance in regulating P supply in soil. Current knowledge and further exploration of mechanism involved by P accumulating microbes may offer better insight of the regulatory events controlling P homeostasis. It will be beneficial for developing more efficient sustainable technologies to augment P use efficiency in soil for better plant growth promotion and nutrient starvation alleviation.

A comprehensive study of biological phosphorus removal systems from economic and environmental perspectives based on the optimization approach

Different biological phosphorus removal systems (BPRSs) are evaluated from economic and environmental perspectives by employing the Taguchi optimization approach for the first time. The BPRSs were simulated and compared in terms of total phosphorus removal efficiency (TP RE) using GPS-X software. Step Bio-P, the most efficient system, was selected for the subsequent environmental and cost analysis. At the optimum condition, the Step Bio-P with a 96.98% TP RE stood at the first rank, followed by the Johannesburg (83.17%)> University of Cape Town (UCT) (79.63%)> anaerobic/anoxic/oxic (A 2 O) (79.31%)> anoxic/oxic (AO) (78.89%)> Bardenpho (70.48%). Marine and freshwater ecotoxicity (59.57%) and freshwater eutrophication (11.84%) received the highest environmental impacts. Construction (77.66%) and amortization (7.3%) caused the maximum cost contributions. The sensitivity analysis revealed that chemical oxygen demand (COD) (17.48%) and TP (9.98%) imposed the maximum effects on the environmental categories. These results can be used as a guideline for wastewater reclamation. • Step Bio-P showed the highest TP removal efficiency (96.98%) • The Taguchi optimization confirmed the role of initial TP on the RE (30.08%) • Marine and freshwater ecotoxicity (59.57%) showed the highest environmental impacts. • Construction possessed the maximum cost contributions (77.66%). • The sensitivity analysis showed the effect of COD and TP on the environmental impacts.

The Occurrence and Role of Tetrasphaera in Enhanced Biological Phosphorus Removal Systems

The application of enhanced biological phosphorus removal (EBPR) in wastewater treatment plants (WWTPs) has commonly been utilized worldwide. However, the optimum efficiency has not been realized over the past decades, prompting many studies and publications. The limitations, especially comprehension of the abundance and actual potential of polyphosphate-accumulating organisms (PAOs), are not fully understood. Recently identified putative PAOs, Tetrasphaera, present a vast metabolic versatility compared to Candidatus Accumulibacter. The characterisation of Tetrasphaera unique abilities to utilize various carbon substrates, volatile fatty acids production and consistent high abundance, presents potential boosts towards the process efficiency improvement. This paper provides the existing knowledge on the physiology, morphology and genetic description of PAOs with a special attention to the current state of research on Tetrasphaera and its potential. In addition, process conditions and their influence on the microbial activities in EBPR systems are discussed.

Response of performance, sludge characteristics, and microbial communities of biological phosphorus removal system to salinity

The effects of salinity on highly enriched polyphosphate- or glycogen-accumulating organisms (PAOs or GAOs) have been revealed, which is meaningful but idealized. In this study, three salinity levels (0.5%, 1.0%, and 0.75%) were sequentially adopted in a PAOs and GAOs coexisted biological phosphorus removal (BPR) reactor within 150 days. Compared to a slight decrease of phosphorus removal efficiency (PRE) under 0.5% salinity (from 96.09% to 73.68%), doubled salinity (1.0%) resulted in a lengthy recovery period and a sharp PRE decline (13.89%), and the PRE was merely kept at 27.39% even through salinity was decreased to 0.75% hereafter. Salinity was also found to stimulate more extracellular protein secretion, resulting in sludge volume index reduction (<32.87 mL/g) and particle size enlargement (222.78 μm on average). Hyphomicrobium (0.96%–1.76%) and unclassified_f_Rhodobacteraceae (4.72%–13.33%) could resist certain salinity and conduct BPR, but better salt-tolerant Candidatus_Competibacter eventually became the predominant genus (>40%).

An effective titanium salt dosing strategy for phosphorus removal from wastewater: Synergistic enhancement of chemical and biological treatment

Titanium salt coagulant, as a new type of water treatment agent, has been widely studied, but most researches do not consider its effect on the biological treatment. In this study, different doses of TiCl4 were added to the biological phosphorus removal (BPR) system to investigate the impact of TiCl4 on BPR. The results showed that the addition of TiCl4 not only significantly reduced the phosphorus concentration in effluent (below 0.5 mg/L), but also kept it stable. Moreover, the sedimentation performance of activated sludge was improved, which was superior to the control group. According to the results of flow cytometry (FCM), a small amount of TiCl4 significantly improved the bioactivities, but excessive dosage caused inhibition. When the dosage of TiCl4 below 20 mg/L, polyphosphate accumulating metabolism (PAM) was strengthened. In addition, the richness of microbial community and the relative abundance of Candidatus Accumulibacter clades also increased. However, when the dosage reached 60 mg/L, the relative abundance of Candidatus Competibacter increased and the BPR system was deteriorated. This study suggests that the addition of appropriate concentration of TiCl4 can realize the synergistic enhancement of biological and chemical phosphorus removal in sewage treatment.

Effect of granular matrix on functional flora in EBPR system

Enhanced biological phosphorus removal (EBPR) is a very mature phosphorus removal technology, but there is still a problem of unstable treatment effect in the operation of actual wastewater treatment plants, so the study on the effect of phosphorus removal performance still needs to be further studied. Because there are a lot of granular matrix in municipal wastewater, it occupies an important proportion in the total Chemical Oxygen Demand (COD) of municipal wastewater, and the fluctuation of granular matrix concentration is also related to the instability of phosphorus removal effect. Therefore, it is of practical guiding significance to further explore the influence of granular matrix on the functional bacteria community of phosphorus removal in the enhanced biological phosphorus removal system. The acetic acid was used as a carbon source to enrich and cultivate phosphorus accumulating bacteria. After the enrichment and the system was stable, soluble starch was added into the water to study the effects of granular matrix on phosphorus removal performance and functional bacteria community in EBPR system. The results showed that acetic acid was beneficial to the proliferation of phosphorus-accumulating bacteria in the enrichment stage, and the phosphate removal rate of the system could reach more than 99%. After the system is stabilized, granular matrix with different concentrations is added to the system in three stages, and the phosphate removal rate of the system gradually decreases. With the increasing of granular matrix concentration in the influent, the phosphorus removal performance of sludge decreased gradually, the maximum phosphorus release rate and maximum phosphorus uptake rate of sludge decreased, and the acetic acid utilization rate ΔP/ΔHAc value also decreased. Fluorescence in situ hybridization was used to measure the changes of functional bacteria in activated sludge under different conditions. With the increase of the concentration of soluble starch, the proportion of PAOs gradually decreased, and the proportion of GAOs gradually increased. Granular matrix exists in the internal of floc sludge and cannot be utilized by PAOs, which results in inhibition of the growth of PAOs and weakened activity. This indicates that the higher concentration of granular matrix will lead to a decrease in the proportion of PAOs in EBPR system, and then lead to a decrease in the phosphorus removal activity of activated sludge, and ultimately reduce the phosphorus removal effect of EBPR system.

Exploration of the metabolic flexibility of glycogen accumulating organisms through metatranscriptome analysis and metabolic characterization

Glycogen accumulating organisms (GAOs) are closely related to the deterioration of enhanced biological phosphorus removal systems. However, the metabolic mechanisms that drive GAOs remain unclear. Here, the two-thirds supernatant of a reactor were decanted following the anaerobic period to enrich GAOs. Long-term monitoring demonstrated that the system was stable and exhibited typical characteristics of GAOs metabolism. Acetate was completely consumed after 60 min of the anaerobic phase. The level of glycogen decreased from 0.20 to 0.14 g/gSS during the anaerobic phase, whereas the level of glycogen significantly increased to 0.21g/gSS at the end of the aerobic period. Moreover, there was almost no phosphate release and absorption in the complete periods, thus confirming the successful construction of a GAOs enrichment system. Microbial community analysis demonstrated that Ca. Contendobacter was among the core functional genera and showed the highest activity among all of the communities. Furthermore, our study is the first to identify the involvement of the ethyl-malonyl-CoA pathway in the synthesis of polyhydroxyvalerate via croR, ccr, ecm, mcd, mch and mcl genes. The Embden-Meyerhof-Parnas (EMP) pathway was preferentially used via glgP. Furthermore, the glyoxylate cycle was the main source of ATP under anaerobic conditions, whereas the tricarboxylic acid cycle provided ATP under aerobic conditions. aceA and mdh appeared to be major modulators of the glyoxylate pathway for controlling energy flow. Collectively, our findings not only revealed the crucial metabolic mechanisms in a GAOs enrichment system but also provided insights into the potential application of Ca. Contendobacter for wastewater treatment.