Enhanced biological phosphorus removal in a sequencing batch reactor using propionate as the sole carbon source

Performance of short-cut denitrifying phosphorus removal and microbial community structure in the A2SBR process

ABSTRACTAcclimatization of short-cut denitrifying polyphosphate accumulating organisms (SDPAOs), metabolic mechanism, and operating parameters were analyzed to investigate the performance of the anaerobic/anoxic sequencing batch reactor (A2SBR) process. The high-throughput sequencing technology was employed to explore the microbial community structures of activated sludge systems. The experimental results illustrated that SDPAOs were successfully enriched with three-phase inoculation for 36 days. The removal rates of TP and NO2--N were 93.22% and 91.36%, respectively, under the optimal parameters of a pH of 7.5, an SRT of 26 days, a temperature of 24 ℃ and a COD of 200.00 mg·L-1 using acetate as the carbon source. In the anaerobic stage, 82.20% external carbon source was converted into 88.78 mg·g-1 PHB, and the removal rate of NO2--N in the anoxic stage was characterized by ΔNO2--N/ΔPHB, anoxic ΔP/ΔPHBeffective was 0.289, which was higher than anaerobic ΔP/ΔCODeffective of 0.203. Ignavibacterium and Povalibacter with significant phosphorus removal ability were the dominant bacterial genera. The nitrogen and phosphorus removal could be realized simultaneously in an anaerobic/anoxic sequencing batch reactor. Therefore, this study provided an important understanding of the removal of nitrogen and phosphorus from low-carbon nitrogen wastewater.

Evaluation of various carbon sources on ammonium assimilation and denitrifying phosphorus removal in a modified anaerobic-anoxic-oxic process from low-strength wastewater

A pilot-scale continuous-flow modified anaerobic-anoxic-oxic (MAAO) process examined the impact of external carbon sources (acetate, glucose, acetate/propionate) on ammonium assimilation, denitrifying phosphorus removal (DPR), and microbial community. Acetate exhibited superior efficacy in promoting the combined process of ammonia assimilation and DPR, enhancing both to 50.0 % and 60.0 %, respectively. Proteobacteria and Bacteroidota facilitated ammonium assimilation, while denitrifying phosphorus-accumulating organisms (DPAOs) played a key role in nitrogen (N) and phosphorus (P) removal. Denitrifying glycogen-accumulating organisms (DGAOs) aided N removal in the anoxic zone, ensuring stable N and P removal and recovery. Acetate/propionate significantly enhanced DPR (77.7 %) and endogenous denitrification (37.9 %). Glucose favored heterotrophic denitrification (29.6 %) but had minimal impact on ammonium assimilation. These findings provide valuable insights for wastewater treatment plants (WWTPs) seeking efficient N and P removal and recovery from low-strength wastewater.

Carbon, nitrogen, and phosphorus metabolic relationships and reaction mechanisms in SBBR processes in the plateau habitat

In this study, two laboratory-scale SBBR reactors were established in a plateau habitat. Using high flux sequencing, the SBBR process was compared by natural sediment and autotrophic sludge to characterize the functional modules and functional genes of carbon, nitrogen, and phosphorus metabolism under different working conditions and to analyze the reaction mechanism. The results showed that all the functional modules of carbon metabolism and nitrogen metabolism were found in the SBBR process, except for methane metabolism, which occurred at 25 °C in tank 2, the functional modules related to methane metabolism are enhanced at all working conditions. Except for methane metabolism, all functional genes in tank 2 are inhibited by different working conditions, whereas tank 1 shows a slight enhancement. The different working conditions in nitrogen metabolism demonstrate inhibition of functional modules and functional genes in both tanks. Oxidative phosphorylation was missing five functional modules, except for M00153, where only two genes, K00424 and K22501, are missing, all of the required genes are missing in the other four functional modules. Overall the different conditions demonstrated some inhibition in both reaction tanks of the SBBR process. It is preferable to use self-cultivated sludge for membrane acclimation when operating the SBBR process in a plateau habitat. The findings of this study can be used to further research microbial carbon, nitrogen, and phosphorus metabolism mechanisms in SBBR processes in plateau habitats.

The impact of pH on the anaerobic and aerobic metabolism of Tetrasphaera-enriched polyphosphate accumulating organisms

Members of the genus Tetrasphaera are putative polyphosphate accumulating organisms (PAOs) that have been found in greater abundance than Accumulibacter in many full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants worldwide. Nevertheless, previous studies on the effect of environmental conditions, such as pH, on the performance of EBPR have focused mainly on the response of Accumulibacter to pH changes. This study examines the impact of pH on a Tetrasphaera PAO enriched culture, over a pH range from 6.0 to 8.0 under both anaerobic and aerobic conditions, to assess its impact on the stoichiometry and kinetics of Tetrasphaera metabolism. It was discovered that the rates of phosphorus (P) uptake and P release increased with an increase of pH within the tested range, while PHA production, glycogen consumption and substrate uptake rate were less sensitive to pH changes. The results suggest that Tetrasphaera PAOs display kinetic advantages at high pH levels, which is consistent with what has been observed previously for Accumulibacter PAOs. The results of this study show that pH has a substantial impact on the P release and uptake kinetics of PAOs, where the P release rate was >3 times higher and the P uptake rate was >2 times higher at pH 8.0 vs pH 6.0, respectively. Process operational strategies promoting both Tetrasphaera and Accumulibacter activity at high pH do not conflict with each other, but lead to a potentially synergistic impact that can benefit EBPR performance.

Glycerol conversion by aerobic granular sludge

Glycerol is abundantly present in wastewater from industries such as biodiesel production facilities. Glycerol is also a potential carbon source for microbes that are involved in wastewater nutrient removal processes. The conversion of glycerol in biological phosphorus removal of aerobic granular sludge processes has not been explored to date. The current study describes glycerol utilization by aerobic granular sludge and enhanced biological phosphorus removal (EBPR). Robust granules with good phosphorus removal capabilities were formed in an aerobic granular sludge sequencing batch reactor fed with glycerol. The interaction between the fermentative conversion of glycerol and product uptake by polyphosphate accumulating organisms (PAO) was studied using stoichiometric and microbial community analysis. Metagenomic, metaproteomic and microscopic analysis identified a community dominated by Actinobacteria (Tessaracoccus and Micropruina) and a typical PAO known as Ca. Accumulibacter. Glycerol uptake facilitator (glpF) and glycerol kinase (glpK), two proteins involved in the transport of glycerol into the cellular metabolism, were only observed in the genome of the Actinobacteria. The anaerobic conversion appeared to be a combination of a substrate fermentation and product uptake-type reaction. Initially, glycerol fermentation led mainly to the production of 1,3-propanediol (1,3-PDO) which was not taken up under anaerobic conditions. Despite the aerobic conversion of 1,3-PDO stable granulation was observed. Over time, 1,3-PDO production decreased and complete anaerobic COD uptake was observed. The results demonstrate that glycerol-containing wastewater can effectively be treated by the aerobic granular sludge process and that fermentative and polyphosphate accumulating organisms can form a food chain in glycerol-based EBPR processes.

Enhanced Bio-P removal: Past, present, and future - A comprehensive review

Excess amounts of phosphorus (P) and nitrogen (N) from anthropogenic activities such as population growth, municipal and industrial wastewater discharges, agriculture fertilization and storm water runoffs, have affected surface water chemistry, resulting in episodes of eutrophication. Enhanced biological phosphorus removal (EBPR) based treatment processes are an economical and environmentally friendly solution to address the present environmental impacts caused by excess P present in municipal discharges. EBPR practices have been researched and operated for more than five decades worldwide, with promising results in decreasing orthophosphate to acceptable levels. The advent of molecular tools targeting bacterial genomic deoxyribonucleic acid (DNA) has also helped us reveal the identity of potential polyphosphate-accumulating organisms (PAO) and denitrifying PAO (DPAO) responsible for the success of EBPR. Integration of process engineering and environmental microbiology has provided much-needed confidence to the wastewater community for the successful implementation of EBPR practices around the globe. Despite these successes, the process of EBPR continues to evolve in terms of its microbiology and application in light of other biological processes such as anaerobic ammonia oxidation and on-site carbon capture. This review provides an overview of the history of EBPR, discusses different operational parameters critical for the successful operation of EBPR systems, reviews current knowledge of EBPR microbiology, the influence of PAO/DPAO on the disintegration of microbial communities, stoichiometry, EBPR clades, current practices, and upcoming potential innovations.

Research advances of the phosphorus-accumulating organisms of Candidatus Accumulibacter, Dechloromonas and Tetrasphaera: Metabolic mechanisms, applications and influencing factors

Phosphorus-accumulating organisms (PAOs), which harbor metabolic mechanisms for phosphorus removal, are widely applied in wastewater treatment. Recently, novel PAOs and phosphorus removal metabolic pathways have been identified and studied. Specifically, Dechloromonas and Tetrasphaera can remove phosphorus via the denitrifying phosphorus removal and fermentation phosphorus removal pathways, respectively. As the main PAOs in biological phosphorus removal systems, the conventional PAO Candidatus Accumulibacter and the novel PAOs Dechloromonas and Tetrasphaera are thoroughly discussed in this paper, with a specific focus on their phosphorus removal metabolic mechanisms, process applications, community abundance and influencing factors. Dechloromonas can achieve simultaneous nitrogen and phosphorus removal in an anoxic environment through the denitrifying phosphorus removal metabolic pathway, which can further reduce carbon source requirements and aeration energy consumption. The metabolic pathways of Tetrasphaera are diverse, with phosphorus removal occurring in conjunction with macromolecular organics degradation through anaerobic fermentation. A collaborative oxic phosphorus removal pathway between Tetrasphaera and Ca. Accumulibacter, or a collaborative anoxic denitrifying phosphorus removal pathway between Tetrasphaera and Dechloromonas are future development directions for biological phosphorus removal technologies, which can further reduce carbon source and energy consumption while achieving enhanced phosphorus removal.

The phylogeny, ecology and ecophysiology of the glycogen accumulating organism (GAO) Defluviicoccus in wastewater treatment plants

This comprehensive review looks critically what is known about members of the genus Defluviicoccus, an example of a glycogen accumulating organism (GAO), in wastewater treatment plants, but found also in other habitats. It considers the operating conditions thought to affect its performance in activated sludge plants designed to remove phosphorus microbiologically, including the still controversial view that it competes with the polyphosphate accumulating bacterium Ca. Accumulibacter for readily biodegradable substrates in the anaerobic zone receiving the influent raw sewage. It looks at its present phylogeny and what is known about it's physiology and biochemistry under the highly selective conditions of these plants, where the biomass is recycled continuously through alternative anaerobic (feed); aerobic (famine) conditions encountered there. The impact of whole genome sequence data, which have revealed considerable intra- and interclade genotypic diversity, on our understanding of its in situ behaviour is also addressed. Particular attention is paid to the problems in much of the literature data based on clone library and next generation DNA sequencing data, where Defluviicoccus identification is restricted to genus level only. Equally problematic, in many publications no attempt has been made to distinguish between Defluviicoccus and the other known GAO, especially Ca. Competibacter, which, as shown here, has a very different ecophysiology. The impact this has had and continues to have on our understanding of members of this genus is discussed, as is the present controversy over its taxonomy. It also suggests where research should be directed to answer some of the important research questions raised in this review.

Simultaneous biological removal of nitrogen and phosphorus from secondary effluent of wastewater treatment plants by advanced treatment: A review

With the advancement of water ecological protection and water control standard, it is the general trend to upgrade the wastewater treatment plants (WWTPs). The simultaneous removal of nitrogen and phosphorus is the key to improve the water quality of secondary effluent of WWTPs to prevent the eutrophication. Therefore, it is urgent to develop the applicable technologies for simultaneous biological removal of nitrogen and phosphorus from secondary effluent. In this review, the composition of secondary effluent from municipal WWTPs were briefly introduced firstly, then the three main treatment processes for simultaneous nitrogen and phosphorus removal, i.e., the enhanced denitrifying phosphorus removal filter, the pyrite-based autotrophic denitrification and the microalgae biological treatment system were summarized, their performances and mechanisms were analyzed. The influencing factors and microbial community structure were discussed. The advanced removal of nitrogen and phosphorus by different technologies were also compared and summarized in terms of performance, operational characteristics, disadvantage and cost. Finally, the challenges and future prospects of simultaneous removal of nitrogen and phosphorus technologies for secondary effluent were proposed. This review will deepen to understand the principles and applications of the advanced removal of nitrogen and phosphorus and provide some valuable information for upgrading the treatment process of WWTPs.

Nitrite and nitrate inhibition thresholds for a glutamate-fed bio-P sludge

Enhanced biological phosphorus removal (EBPR) is an efficient and sustainable technology to remove phosphorus from wastewater. A widely known cause of EBPR deterioration in wastewater treatment plants (WWTPs) is the presence of nitrate/nitrite or oxygen in the anaerobic reactor. Moreover, most existing studies on the effect of either permanent aerobic conditions or inhibition of EBPR by nitrate or free nitrous acid (FNA) have been conducted with a "Candidatus Accumulibacter" or Tetrasphaera-enriched sludge, which are the two major reported groups of polyphosphate accumulating organisms (PAO) with key roles in full-scale EBPR WWTPs. This work reports the denitrification capabilities of a bio-P microbial community developed using glutamate as the sole source of carbon and nitrogen. This bio-P sludge exhibited a high denitrifying PAO (DPAO) activity, in fact, 56% of the phosphorus was uptaken under anoxic conditions. Furthermore, this mixed culture was able to use nitrite and nitrate as electron acceptor for P-uptake, being 1.8 μg HNO₂-N·L^-1 the maximum FNA concentration at which P-uptake can occur. Net P-removal was observed under permanent aerobic conditions. However, this microbial culture was more sensitive to FNA and permanent aerobic conditions compared to "Ca. Accumulibacter"-enriched sludge.

Coconut shell ash enhances short-chain fatty acids production from anaerobic algae fermentation

This study proposed a novel method to enhance short-chain fatty acids (SCFAs) production from anaerobic algae fermentation by using coconut shell ash. The maximum SCFAs production was 683.0 mg COD/g VS at the ash dosage of 1.2 g/g TS, which was about 1.4-folds that of the control, and the enhancement of acetate production was the main path for the promotion of SCFAs. Coconut shell ash increased the pH and alkalinity of digestate, thereby reducing the use of alkaline reagents and being more resistant to acidic environments. Coconut shell ash promoted the processes of solubilization, hydrolysis and acetogenesis, and enriched hydrolytic microorganisms (e.g., Candidatus Microthrix) and acidifying microorganisms with acetate as substrate (e.g., Caldilinea and Proteiniphilum). Anaerobic fermentation residue with ash containing inorganic elements has the potential to be used as fertilizer, making this waste-control-waste strategy with more economic and environmental benefits for potential practical applications.

Effects of antibiotics on enhanced biological phosphorus removal and its mechanisms

Many kinds of antibiotics are continuously discharged into wastewater and typically cause a great decrease in sewage treatment performance, whereas mechanisms of differences in the impacts of commonly used antibiotics on phosphate removal are still elusive. Thus, an enhanced biological phosphorus removal (EBPR) system, as an effective method of phosphate removal, was developed, and its performance in the treatment of artificial wastewater containing antibiotics at short- (8 h) and long-term (15 days) exposure was investigated. The results show that phosphorus removal was consistently inhibited by the addition of antibiotics with a significant difference (P < 0.05). To interpret the phenomena, mechanistic equations were developed, and the results indicate that for short-term tests, the difference was mainly caused by the suppression of polyhydroxyalkanoate (PHA) degradation and the activity of polyphosphate kinase (PPK), resulting in the different inhibition of the soluble orthophosphorus (SOP) uptake process. For long-term tests, the difference in SOP uptake was principally caused by the inhibition of PHA degradation and the activity of PPK, whereas the difference in SOP release resulted from the inhibition of activities of exopolyphosphatase (PPX) and adenylate kinase (ADK). Moreover, micro-mechanisms of such inhibition were identified from molecular docking and electrostatic potential.

A review of biochemical diversity and metabolic modeling of EBPR process under specific environmental conditions and carbon source availability

Enhanced biological phosphorus removal (EBPR) is one of the most promising technologies as an economical and environmentally sustainable technique for removal of phosphorus from wastewater (WW). However, with high capacity of EBPR, insufficient P-removal is a major yet common issue of many full-scale wastewater treatment plants (WWTP), due to misinterpreted environmental and microbial disturbance. By developing a rather extensive understanding on biochemical pathways and metabolic models governing the anaerobic and aerobic/anoxic processes; the optimal operational conditions, environmental changes and microbial population interaction are efficiently predicted. Therefore, this paper critically reviews the current knowledge on biochemical pathways and metabolic models of phosphorus accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) as the most abundant microbial populations in EBPR process with an insight on the effect of available carbon source types in WW on phosphorus removal performance. Moreover, this paper critically assesses the gaps and potential future research in metabolic modeling area. With all the developments on EBPR process in the past few decades, there is still lack of knowledge in this critical sector. This paper hopes to touch on this problem by gathering the existing knowledge and to provide farther insights on the future work onto chemical transformations and metabolic strategies in different conditions to benefit the quantitative model as well as WWTP designs.

Comparison of nitrite accumulation performance and microbial community structure in endogenous partial denitrification process with acetate and glucose served as carbon source

Although the combination of endogenous partial denitrification (EPD) and Anammox (EPD-AMX) were developed for deep-level nitrogen removal, the effects of different carbon source were not clear. In this study, the EPD performance was investigated comparatively with acetate (EPD_A) and glucose (EPD_G). Results revealed that through regulating chemical oxygen demand to phosphate ratio, Candidatus_Competibacter was highly enriched in EPD_A (54.2%) and EPD_G (51.3%), resulting high intracellular carbon storage efficiencies (90.2% and 85.3%, respectively). More stable nitrite accumulation was observed in EPD_G than EPD_A. But, higher specific nitrite generated rate (r_NO2, 8.25 > 7.04 mgN·gVSS^-1·h^-1) and nitrate-to-nitrite transformation rate (NTR, 87.9% > 85.2%) were achieved in EPD_A than those in EPD_G. The functional bacterium was also shifted to Defluviicoccus in both EPD_A (30.6%) and EPD_G (25.8%). Moreover, with whether acetate or glucose, the EPD-AMX processes could achieve the same level of total nitrogen removal efficiencies (88.7% and 91.3%, respectively) via anammox mainly (87.8% and 89.4%, respectively).

Revealing the Metabolic Flexibility of "Candidatus Accumulibacter phosphatis" through Redox Cofactor Analysis and Metabolic Network Modeling

Environmental fluctuations in the availability of nutrients lead to intricate metabolic strategies. "Candidatus Accumulibacter phosphatis," a polyphosphate-accumulating organism (PAO) responsible for enhanced biological phosphorus removal (EBPR) from wastewater treatment systems, is prevalent in aerobic/anaerobic environments. While the overall metabolic traits of these bacteria are well described, the nonavailability of isolates has led to controversial conclusions on the metabolic pathways used. In this study, we experimentally determined the redox cofactor preferences of different oxidoreductases in the central carbon metabolism of a highly enriched "Ca Accumulibacter phosphatis" culture. Remarkably, we observed that the acetoacetyl coenzyme A reductase engaged in polyhydroxyalkanoate (PHA) synthesis is NADH preferring instead of showing the generally assumed NADPH dependency. This allows rethinking of the ecological role of PHA accumulation as a fermentation product under anaerobic conditions and not just a stress response. Based on previously published metaomics data and the results of enzymatic assays, a reduced central carbon metabolic network was constructed and used for simulating different metabolic operating modes. In particular, scenarios with different acetate-to-glycogen consumption ratios were simulated, which demonstrated optima using different combinations of glycolysis, glyoxylate shunt, or branches of the tricarboxylic acid (TCA) cycle. Thus, optimal metabolic flux strategies will depend on the environment (acetate uptake) and on intracellular storage compound availability (polyphosphate/glycogen). This NADH-related metabolic flexibility is enabled by the NADH-driven PHA synthesis. It allows for maintaining metabolic activity under various environmental substrate conditions, with high carbon conservation and lower energetic costs than for NADPH-dependent PHA synthesis. Such (flexible) metabolic redox coupling can explain the competitiveness of PAOs under oxygen-fluctuating environments.IMPORTANCE Here, we demonstrate how microbial storage metabolism can adjust to a wide range of environmental conditions. Such flexibility generates a selective advantage under fluctuating environmental conditions. It can also explain the different observations reported in PAO literature, including the capacity of "Ca Accumulibacter phosphatis" to act like glycogen-accumulating organisms (GAOs). These observations stem from slightly different experimental conditions, and controversy arises only when one assumes that metabolism can operate only in a single mode. Furthermore, we also show how the study of metabolic strategies is possible when combining omics data with functional cofactor assays and modeling. Genomic information can only provide the potential of a microorganism. The environmental context and other complementary approaches are still needed to study and predict the functional expression of such metabolic potential.

Effect of endogenous metabolisms on survival and activities of denitrifying phosphorus removal sludge under various starvation conditions

Denitrifying phosphorus removal sludge are usually faced with various famine environments in wastewater treatment plants (WWTPs). Endogenous metabolisms under aerobic, anoxic, and anaerobic starved conditions were characterized to investigate their impact on survival and activities of denitrifying polyphosphate accumulating organisms (DPAOs). DPAOs utilized intracellular polymers to survive and presented diverse consumed priorities of PHA types under various starvations. The biomass decay rate was approximately 2.7 and 1.7 times lower for aerobic condition than for anoxic and anaerobic conditions owing to the maximum maintenance energy requirement for aerobic condition (68.6 mmol/C-molVSS ATP). During short-term starvations, significant activity decay for anaerobic starved sludge was attributed to its distinctive endogenous metabolisms. For long-term starvations, the higher amounts and preponderant type of PHA (PHB) reserve favored to the greater DPAO activities for anoxic starved sludge. The results show that anoxic condition may be an implementable strategy for maintaining denitrifying phosphorus removal performance in WWTPs.

The impact of temperature on the metabolism of volatile fatty acids by polyphosphate accumulating organisms (PAOs)

This study investigated the effects of different carbon sources on enriched Accumulibacter PAO cultures at high temperature (30 °C) and compared the carbon transformation with low temperature (20 °C) cases reported in literature, revealing several key metabolic differences. While PAOs seemed to prefer propionate anaerobically as compared to other VFAs at high temperature, high aerobic glycogen replenishment was realized with propionate as the anaerobic carbon source, a trait not previously observed at low temperatures. Therefore, it was found that propionate is not correlated with high P removal by Accumulibacter PAO at high temperatures. A combined substrate of acetate, propionate and perhaps butyrate seemed to be a better carbon source combination, since the total VFA uptake rate increased by up to 46%, and this increased the aerobic P-removal efficiency by up to 38.4% and reduced the glycogen recovery by more than 63% compared to the use of only propionate as substrate. This study improves our understanding of how to stimulate successful EBPR operation in warm climates by augmenting the P removal performance of PAOs.

Versatile Process for the Preparation of Nanocomposite Sorbents: Phosphorus and Arsenic Removal

Nanomaterials are being increasingly utilized for environmental remediation. The use of these materials, however, is greatly hindered due to challenges in material handling and deployment. Here we present a novel nanocomposite synthesis method based on the direct growth of nanoparticles on and within solid support materials, referred to as Crescoating. In this work, iron and copper nanoparticles have been grown on polyurethane support materials using this process and applied as sorbents for dissolved phosphorus and arsenic in water, respectively. These nanocomposite sorbents exhibit rapid sorption with saturation occurring in less than 5 min. The loading capacity is 104.8 mg PO₄^3- g^-1 and 254.4 mg As(III) g^-1 for the iron and copper nanocomposite sorbents respectively, which is up to four times higher than commercially available alternatives. In addition, phosphorus can be recovered from the iron nanocomposite sorbent. This coating by growth process produces nanocomposites that do not emit particles and has the capability to be scaled and applied to other nanoparticles for diverse pollutant sorption applications.

A novel metabolic-ASM model for full-scale biological nutrient removal systems

This study demonstrates that META-ASM, a new integrated metabolic activated sludge model, provides an overall platform to describe the activity of the key organisms and processes relevant to biological nutrient removal (BNR) systems with a robust single-set of default parameters. This model overcomes various shortcomings of existing enhanced biological phosphorous removal (EBPR) models studied over the last twenty years. The model has been tested against 34 data sets from enriched lab polyphosphate accumulating organism (PAO)-glycogen accumulating organism (GAO) cultures and experiments with full-scale sludge from five water resource recovery facilities (WRRFs) with two different process configurations: three stage Phoredox (A2/O) and adapted Biodenitro™ combined with a return sludge sidestream hydrolysis tank (RSS). Special attention is given to the operational conditions affecting the competition between PAOs and GAOs, capability of PAOs and GAOs to denitrify, metabolic shifts as a function of storage polymer concentrations, as well as the role of these polymers in endogenous processes and fermentation. The overall good correlations obtained between the predicted versus measured EBPR profiles from different data sets support that this new model, which is based on in-depth understanding of EBPR, reduces calibration efforts. On the other hand, the performance comparison between META-ASM and literature models demonstrates that existing literature models require extensive parameter changes and have limited predictive power, especially in the prediction of long-term EBPR performance. The development of such a model able to describe in detail the microbial and chemical transformations of BNR systems with minimal adjustment to parameters suggests that the META-ASM model is a powerful tool to predict and mitigate EBPR upsets, optimise EBPR performance and to evaluate new process designs.

Effects of carbon source on the formation, stability, bioactivity and biodiversity of the aerobic granule sludge

Three aerobic granular sludge systems were operated as sequencing batch reactors (SBR) with acetate, ethanol and glucose as carbon source. The SBR cycle was 6 h, with an anaerobic phase followed by an aerobic phase. The acetate granules (>1.5 mm) had the greatest microbial diversity and better results in terms of removal efficiency for carbon and nutrients (TN ≈ 72% and TP ≈ 42%) and also in the resistance tests. However, partial disintegration was observed. On the other hand, when ethanol was the substrate, the granules were stable, good nitrogen removal was achieved (TN ≈ 53%), but phosphorus removal was not favored (TP ≈ 31%). Glucose presented the lowest efficiency values for nitrogen (TN ≈ 44%) and phosphorous removal (TP ≈ 21%), and the granules formed (<1 mm) had the lowest microbial diversity. Therefore, the carbon source had a high impact on the characteristics of the granules.

Overall effect of carbon production and nutrient release in sludge holding tank on mainstream biological nutrient removal efficiency

The potential of hydrolysis/fermentation of activated sludge in sludge holding tank (SHT) to produce additional carbon for the biological nutrient removal (BNR) process was investigated. The study was conducted in anaerobic batch tests using the BNR sludge (from a full-scale Westside process) and the mixture of BNR sludge with conventional non-BNR activated sludge (to have higher biodegradable particulate chemical oxygen demand (bpCOD) in sludge). The BioWin 4.1 was used to simulate the anaerobic batch test of the BNR sludge. Also, the overall effect of FCOD production and nutrient release on BNR efficiency of the Westside process was estimated. The experimental results showed that the phosphorous uptake of sludge increased during hydrolysis/ fermentation condition up to the point when poly-P was completely utilized; afterwards, it decreased significantly. The BioWin simulation could not predict the loss of aerobic phosphorous uptake after poly-P was depleted. The results showed that in the case of activated sludge with relatively higher bpCOD (originating from plants with short sludge retention time or without primary sedimentation), beneficial effect of SHT on BNR performance is feasible. In order to increase the potential of SHT to enhance BNR efficiency, a relatively low retention time and high sludge load is recommended.

Changes in microbial communities during volatile fatty acid production from cyanobacterial biomass harvested from a cyanobacterial bloom in a river

Volatile fatty acid (VFA) production, utilization of soluble organic compounds, and associated microbial consortia were investigated after different pretreatments (untreated, alkaline, and thermal-alkaline) using cyanobacterial biomass as a substrate. Compared to the untreated control, soluble carbohydrate concentrations were almost the same after alkaline and thermal-alkaline pretreatments, but soluble protein concentration was 1.58 times higher after alkaline pretreatment and 1.81 times higher after thermal-alkaline pretreatment. However, the highest degree of acidification was obtained after alkaline pretreatment (55.36 ± 3.00%). Microbial communities in the untreated control differed only slightly from those after thermal-alkaline pretreatment, but were clearly distinct from those after alkaline pretreatment. After alkaline pretreatment, protein-utilizing bacteria became relatively predominant. These results revealed the relationships between efficiency of VFA production and the shift in microbial community.

Municipal wastewater biological nutrient removal driven by the fermentation liquid of dairy wastewater

Carbon substrate is required by biological nutrient removal (BNR) microorganism, but it is usually insufficient in the influent of many municipal wastewater treatment plants. In this study the use of ethanol-enriched fermentation liquid, which was derived from dairy wastewater, as the preferred carbon substrate of BNR was reported. First, the application of dairy wastewater and food processing wastewater and their fermentation liquid as the carbon substrate of BNR was compared in the short-term tests. The fermented wastewater showed higher BNR performance than the unfermented one, and the fermentation liquid of dairy wastewater (FL-DW), which was obtained under pH 8 and fermentation time of 6 day, exhibited the highest phosphorus (95.5%) and total nitrogen (97.6%) removal efficiencies due to its high ethanol content (57.9%). Then, the long-term performance of FL-DW acting as the carbon substrate of BNR was compared with that of acetate and ethanol, and the FL-DW showed the greatest phosphorus and total nitrogen removal. Further investigation showed that the use of FL-DW caused the highest polyhydroxyalkanoates (PHAs) synthesis in BNR microbial cells, and more PHAs were used for phosphorus uptake and denitrification rather than glycogen synthesis and microbial growth. The FL-DW can be used as a preferred carbon substrate for BNR microbes.

ABBREVIATIONS

AB: aerobic end sludge active biomass; BNR: biological nutrient removal; DW: dairy wastewater; FL-DW: fermentation liquid of dairy wastewater; FPW: food processing wastewater; FL-FPW: fermentation liquid of food processing wastewater; PHAs: polyhydroxyalkanoates; PHB: poly-3-hydroxybutyrate; PHV: poly-3-hydroxyvalerate; PH2MV: poly-3-hydroxy-2- methylvalerate; PAOs: phosphorus accumulating organisms; SBR: sequencing batch reactor; SOP: soluble ortho-phosphorus; TN: total nitrogen; TSS: total suspended solids; VSS: volatile suspended solids; VFAs: volatile fatty acids; WWTPs: wastewater treatment plants.

Volatile fatty acid recovery by anaerobic fermentation from blue-green algae: Effect of pretreatment

The aims of this study were to quantify how pretreatment affects production of volatile fatty acids (VFAs) from cyanobacterial biomass and production of subsequent microbial lipid by an oleaginous microorganism that uses the VFAs as carbon sources. The highest biomass solubilization was obtained using thermal-alkaline (th-alkaline) pretreatment (33.1%), followed by alkaline pretreatment (29.1%), and thermal pretreatment (7.2%), but the highest VFA yield was obtained using alkaline pretreatment (0.54±0.02g/gVS), followed by the untreated condition (0.47±0.03g/gVS), and th-alkaline pretreatment (0.44±0.02g/gVS). Although VFA yield was higher using alkaline pretreatment condition than in the untreated condition, the difference was not great. However, lipid productivity by Cryptococcus curvatus after the alkaline pretreatment condition was 2.0-fold higher than that under the untreated condition. This study confirmed the feasibility of using biologically produced VFAs from cyanobacterial biomass for microbial lipid production by the oleaginous microorganism.

Cooperation between Candidatus Competibacter and Candidatus Accumulibacter clade I, in denitrification and phosphate removal processes

Although simultaneous P-removal and nitrate reduction has been observed in laboratory studies as well as full-scale plants, there are contradictory reports on the ability of PAO I to efficiently use nitrate as electron acceptor. Such discrepancy could be due to other microbial groups performing partial denitrification from nitrate to nitrite. The denitrification capacities of two different cultures, a highly enriched PAO I and a PAO I-GAO cultures were assessed through batch activity tests conducted before and after acclimatization to nitrate. Negligible anoxic phosphate uptake coupled with a reduction of nitrate was observed in the highly enriched PAO I culture. On the opposite, the PAO I-GAO culture showed a higher anoxic phosphate uptake activity. Both cultures exhibited good anoxic phosphate uptake activity with nitrite (8.7 ± 0.3 and 9.6 ± 1.8 mgPO₄-P/gVSS.h in the PAO I and PAO I-GAO cultures, respectively). These findings suggest that other microbial populations, such as GAOs, were responsible to reduce nitrate to nitrite in this EBPR system, and that PAO I used the nitrite generated for anoxic phosphate uptake. Moreover, the simultaneous denitrification and phosphate removal process using nitrite as electron acceptor may be a more sustainable process as can: i) reduce the carbon consumption, ii) reduce oxygen demand of WWTP, and iii) due to a lower growth yield contribute to a lower sludge production.

Multi-cycle operation of enhanced biological phosphorus removal (EBPR) with different carbon sources under high temperature

Many studies reported that it is challenging to apply enhanced biological phosphorus removal (EBPR) process at high temperature. Glycogen accumulating organisms (GAOs) could easily gain their dominance over poly-phosphate accumulating organisms (PAOs) when the operating temperature was in the range of 25 °C-30 °C. However, a few successful EBPR processes operated at high temperature have been reported recently. This study aimed to have an in-depth understanding on the impact of feeding strategy and carbon source types on EBPR performance in tropical climate. P-removal performance of two EBPR systems was monitored through tracking effluent quality and cyclic studies. The results confirmed that EBPR was successfully obtained and maintained at high temperature with a multi-cycle strategy. More stable performance was observed with acetate as the sole carbon source compared to propionate. Stoichiometric ratios of phosphorus and carbon transformation during both anaerobic and aerobic phases were higher at high temperature than low temperature (20±1 °C) except anaerobic PHA/C ratios within most of the sub-cycles. Furthermore, the fractions of PHA and glycogen in biomass were lower compared with one-cycle pulse feed operation. The microbial community structure was more stable in acetate-fed sequencing batch reactor (C2-SBR) than that in propionate-fed reactor (C3-SBR). Accumulibacter Clade IIC was found to be highly abundant in both reactors.

Effects of different ratios of glucose to acetate on phosphorus removal and microbial community of enhanced biological phosphorus removal (EBPR) system

In this study, the effects of different ratios of glucose to acetate on enhanced biological phosphorus removal (EBPR) were investigated with regard to the changes of intercellular polyhydroxyalkanoates (PHAs) and glycogen, as well as microbial community. The experiments were carried out in five sequencing batch reactors (SBRs) fed with glucose and/or acetate as carbon sources at the ratios of 0:100 %, 25:75 %, 50:50 %, 75:25 %, and 100:0 %. The experimental results showed that a highest phosphorus removal efficiency of 96.3 % was obtained with a mixture of glucose and acetate at the ratio of 50:50 %, which should be attributed to more glycogen and polyhydroxyvalerate (PHV) transformation in this reactor during the anaerobic condition. PCR-denaturing gradient gel electrophoresis (DGGE) analysis of sludge samples taken from different anaerobic/aerobic (A/O) SBRs revealed that microbial community structures were distinctively different with a low similarity between each other.

Enhanced primary sludge sonication by heat insulation to reclaim carbon source for biological phosphorous removal

Ultrasound pretreatment is a potent step to disintegrate primary sludge (PS). The supernatant of sonicated PS is recycled as an alternative carbon source for biological phosphorus removal. In this study, we investigated the role of temperature on PS disintegration during sonication. We found that a temperature of 60°C yielded a dissolution rate of about 2% soluble chemical oxygen demand (SCOD) as compared to 7% SCOD using sonication at the specific energy (SE) of 7359kJ/kg TS. Using the SE of 6000kJ/kg TS with heat insulation during sonication, the SCOD dissolution rate of PS was similar to the result at the SE of 7051kJ/kg TS without heat insulation. Upon treatment with sonication, the PS released low concentrations of Cu and Zn into the supernatant. The phosphorus-accumulating organisms (PAOs) used the supernatant of sonicated PS as the carbon source. Supplementation with the diluted sonicated PS supernatant (SCOD≈1000mg/L) in anaerobic phase resulted in the release of phosphorus (36mg/L) and the production of polyhydroxyalkanoates (PHAs) (0.36g PHA/g SS). Compared with sodium acetate, higher polyhydroxyvalerate (PHV) faction in the polyhydroxyalkanoates (PHAs) was observed in the biomass when incubated with sonicated PS as the carbon source. This work provides a simple pathway to conserve energy and to enhance efficiencies of ultrasonic pretreatment and the recovery of carbon source from the sludge for improving the phosphorus removal in the ENR system.

Denitrification of nitrate and nitrite by 'Candidatus Accumulibacter phosphatis' clade IC

Phosphate accumulating organisms (PAO) are assumed to use nitrate as external electron acceptor, allowing an efficient integration of simultaneous nitrogen and phosphate removal with minimal organic carbon (COD) requirements. However, contradicting findings appear in literature regarding the denitrification capacities of PAO due to the lack of clade specific highly enriched PAO cultures. Whereas some studies suggest that only PAO clade I may be capable of using nitrate as external electron acceptor for anoxic P-uptake, other studies indicate that PAO clade II may be responsible for anoxic P-removal. In the present study, a highly enriched PAO clade IC culture (>99% according to FISH) was cultivated in an SBR operated under Anaerobic/Oxic conditions and subsequently exposed to Anaerobic/Anoxic/Oxic conditions using nitrate as electron acceptor. Before and after acclimatization to the presence of nitrate, the aerobic and anoxic (nitrate and nitrite) activities of the PAO I culture were assessed through the execution of batch tests using either acetate or propionate as electron donor. In the presence of nitrate, significant P-uptake by PAO I was not observed before or after acclimatization. Using nitrite as electron acceptor, limited nitrite removal rates were observed before acclimatization with lower rates in the acetate fed reactor without P-uptake and slightly higher in the propionate fed reactor with a marginal anoxic P-uptake. Only after acclimatization to nitrate, simultaneous P and nitrite removal was observed. This study suggests that PAO clade IC is not capable of using nitrate as external electron acceptor for anoxic P-removal. The elucidation of the metabolic capacities for individual PAO clades helps in better understanding and optimization of the relation between microbial ecology and process performance in enhanced biological phosphate removal processes.

What could the entire cornstover contribute to the enhancement of waste activated sludge acidification? Performance assessment and microbial community analysis

BACKGROUND

Volatile fatty acids (VFAs) production from waste activated sludge (WAS) digestion is constrained by unbalanced nutrient composition (low carbon-to-nitrogen ratio). Characteristics conditioning by extra carbon sources, normally in the mixture of raw solid, has been reported to be an efficient approach to enhance WAS acidification. However, little attention has been paid to the contributions of other adjustment forms. Moreover, the corresponding ecological estimation has not been investigated yet.

RESULTS

In this study, the feasibility of corn stover (CS) conditioning with three adjustment forms [pretreated straw (S), hydrolysate (H) and hydrolysate + straw (HS)] in improving VFAs production from WAS was demonstrated. It was observed that the highest VFAs yield was achieved in H co-digesting test (574 mg COD/g VSS), while it was only 392 mg COD/g VSS for WAS digesting alone. VFAs composition was strongly adjustment form-dependent, as more acetic (HAc) and propionic (HPr) acids were generated in CS_HS and S, respectively. High-throughput sequencing analysis illustrated that acid (especially HAc)-producing characteristic genera (Bacteroides, Proteiniclasticum and Fluviicola) and HPr-producing characteristic genera (Mangroviflexus and Paludibacter) were detected by CS_HS and S conditioning, respectively.

CONCLUSIONS

Corn stover conditioning greatly upgraded the WAS acidification performance, especially for the CS_H adjustment form, and the VFAs yield gained was considerably larger than that previously reported. CS adjustment forms played an important role in structuring the innate microbial community in WAS. Canonical correlation analysis illustrated that characteristic genera, with better hydrolysis and acidification abilities, could be enriched by the feedstocks with certain content of cellulose, hemicellulose or their saccharification hydrolysates. Moreover, ecological estimation revealed that, as far as the entire CS (including S and H) per acre was concerned, the capacity of WAS treatment would reach that produced in a one million mts capacity wastewater treatment plants (WWTPs) per day. These findings may have crucial implications for the operation of WWTPs.

Assessment of crude glycerol for Enhanced Biological Phosphorus Removal: Stability and role of long chain fatty acids

Enhanced Biological Phosphorus Removal (EBPR) of urban wastewaters is usually limited by the available carbon source required by Polyphosphate Accumulating Organisms (PAO). External carbon sources as volatile fatty acids (VFA) or other pure organic compounds have been tested at lab scale demonstrating its ability to enhance PAO activity, but the application of this strategy at full-scale WWTPs is not cost-effective. The utilization of industrial by-products with some of these organic compounds provides lower cost, but it has the possible drawback of having inhibitory or toxic compounds to PAO. This study is focused on the utilization of crude glycerol, the industrial by-product generated in the biodiesel production, as a possible carbon source to enhance EBPR in carbon-limited urban wastewaters. Crude glycerol has non-negligible content of other organic compounds as methanol, salts, VFA and long chain fatty acids (LCFA). VFA and methanol have been demonstrated to enhance PAO activity, but there is no previous study about the effect of LCFA on PAO. This work presents the operation of an EBPR SBR system using crude glycerol as sole carbon source, studying also its long-term stability. The effect of LCFA is evaluated at short and long-term operation, demonstrating for the first time EBPR activity with LCFA as sole carbon source and its long-term failure due to the increased hydrophobicity of the sludge.

Influence of temperature on volatile fatty acid production and microbial community structure during anaerobic fermentation of microalgae

The objectives of this study were to investigate the effect of operating temperature on volatile fatty acids (VFAs) production from microalgal biomass, and to clarify the relationships between VFAs accumulation at different temperatures and the corresponding bacterial communities. The VFA yields were 0.10±0.017, 0.12±0.008, and 0.34±0.009 g/g VS at 35, 45, and 55 °C, respectively. The proportion of acetic acid decreased from 85.6% to 65.8% as operating temperature increased, whereas that of propionic acid increased from near 0% to 15.5% and that of iso-valeric acid remained relatively stable (10.2-11.2%). Bacterial communities at different operating temperatures consisted mostly of the phyla Proteobacteria, Bacteroidetes, and Firmicutes, which can degrade organic compounds effectively. Bacillus sp. was more predominant at 55 °C than at mesophilic temperatures, suggesting that this microorganism contributed significantly to the higher hydrolysis rate and VFA yield at this operating temperature.

Intracellular Accumulation of Glycine in Polyphosphate-Accumulating Organisms in Activated Sludge, a Novel Storage Mechanism under Dynamic Anaerobic-Aerobic Conditions

Dynamic anaerobic-aerobic feast-famine conditions are applied to wastewater treatment plants to select polyphosphate-accumulating organisms to carry out enhanced biological phosphorus removal. Acetate is a well-known substrate to stimulate this process, and here we show that different amino acids also are suitable substrates, with glycine as the most promising. (13)C-labeled glycine and nuclear magnetic resonance (NMR) were applied to investigate uptake and potential storage products when activated sludge was fed with glycine under anaerobic conditions. Glycine was consumed by the biomass, and the majority was stored intracellularly as free glycine and fermentation products. Subsequently, in the aerobic phase without addition of external substrate, the stored glycine was consumed. The uptake of glycine and oxidation of intracellular metabolites took place along with a release and uptake of orthophosphate, respectively. Fluorescence in situ hybridization combined with microautoradiography using (3)H-labeled glycine revealed uncultured actinobacterial Tetrasphaera as a dominant glycine consumer. Experiments with Tetrasphaera elongata as representative of uncultured Tetrasphaera showed that under anaerobic conditions it was able to take up labeled glycine and accumulate this and other labeled metabolites to an intracellular concentration of approximately 4 mM. All components were consumed under subsequent aerobic conditions. Intracellular accumulation of amino acids seems to be a novel storage strategy for polyphosphate-accumulating bacteria under dynamic anaerobic-aerobic feast-famine conditions.

Treatment of agro based industrial wastewater in sequencing batch reactor: performance evaluation and growth kinetics of aerobic biomass

A sequencing batch reactor (SBR) with a working volume of 8 L and an exchange ratio of 25% was used to enrich biomass for the treatment of the anaerobically treated low pH palm oil mill effluent (POME). The influent concentration was stepwise increased from 5000 ± 500 mg COD/L to 11,500 ± 500 mg COD/L. The performance of the reactor was monitored at different organic loading rates (OLRs). It was found that approximately 90% of the COD content of the POME wastewater was successfully removed regardless of the OLR applied to the SBR. Cycle studies of the SBR show that the oxygen uptake by the biomass while there is no COD reduction may be due to the oxidation of the storage product by the biomass. Further, the growth kinetic parameters of the biomass were determined in batch experiments using respirometer. The maximum specific growth rate (μmax) was estimated to be 1.143 day(-1) while the half saturation constant (Ks) with respect to COD was determined to be 0.429 g COD/L. The decay coefficient (bD) and biomass yield (Y) were found to be 0.131 day(-1) and 0.272 mg biomass/mg COD consumed, respectively.

The impact of aeration on the competition between polyphosphate accumulating organisms and glycogen accumulating organisms

In wastewater treatment plants (WWTPs), aeration is the major energetic cost, thus its minimisation will improve the cost-effectiveness of the process. This study shows that both the dissolved oxygen (DO) concentration and aerobic hydraulic retention time (HRT) affect the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). At low DO levels, Accumulibacter PAOs were shown to have an advantage over Competibacter GAOs, as PAOs had a higher oxygen affinity and thus largely maintained their aerobic activity at low DO levels, while GAO activity decreased. Bioreactor operation at low DO levels was found to increase the PAO fraction of the sludge. Furthermore, an increase in aerobic HRT (at a DO level of 2 mg O2/L), promoted the proliferation of GAOs over PAOs, decreasing the EBPR efficiency. Overall, this study shows that low aeration can be beneficial for EBPR performance through selecting for PAOs over GAOs, which should be incorporated into WWTP models in order to minimise energetic costs and improve WWTP sustainability.

Effects of Cd(II) on wastewater biological nitrogen and phosphorus removal

Short-term and long-term effects of Cd(II) on wastewater biological nitrogen and phosphorus removal were investigated with respect to microorganism abundances, enzyme activities, and polyhydroxyalkanoates (PHAs) and glycogen transformations. Though no obvious effects on wastewater biological nutrient removal were observed after short-term exposure, the long-term exposure of 10 mg L(-)(1) Cd(II) inhibited nitrification and phosphorus uptake. Compared with the absence of Cd(II), the presence of 10 mg L(-1) of Cd(II) decreased total nitrogen and phosphorus removal efficiencies from 97% and 98% to 88% and 18%, respectively. Mechanism studies revealed that Cd(II) affected the transformations of intracellular PHAs and glycogen, and the activities of oxidoreductase and polyphosphate kinase, resulted in the decrease of nitrite oxidizing bacteria and polyphosphate accumulating organisms abundance, which might be the major reason for the negative effects of long-term exposure to 10 mg L(-1) Cd(II) on biological nitrogen and phosphorus removal.

The effect of substrate competition on the metabolism of polyphosphate accumulating organisms (PAOs)

The type of carbon source present in the wastewater is one factor that affects the competition between polyphosphate accumulating organisms (PAO) and glycogen accumulating organisms (GAO) and therefore, the efficiency of the enhanced biological phosphorus removal (EBPR) process. This study investigated the impact of the carbon source composition on the anaerobic and aerobic kinetics of PAOs and the EBPR performance of an 85% PAO enrichment. When both acetate (HAc) and propionate (HPr) were present, propionate was depleted more quickly, with a constant uptake rate of 0.18 ± 0.02 C-mol/(C-mol biomass·h), while the acetate uptake rate decreased with an increase in propionate concentration, due to the substrate competition between acetate and propionate. The metabolic model for PAOs was modified to incorporate the anaerobic substrate competition effect. The aerobic rates for phosphorus (P) uptake, glycogen production and polyhydroxyalkanoates (PHA) degradation were within the same range for all tests, indicating that these rates are essentially independent of the acetate and propionate concentration, simplifying the calibration procedure for metabolic models. The metabolic model applied to describe the anaerobic and aerobic activity agreed well with the experimental data of HAc, HPr, P, PHA and biomass growth. The low glycogen consumption observed suggest that some reducing equivalents were generated anaerobically through the TCA cycle. The results of this work suggest that the propionate uptake kinetics by PAOs can provide them an advantage over GAOs in EBPR systems, even when the propionate fraction of the influent is relatively low.

Impact of butyrate on microbial selection in enhanced biological phosphorus removal systems

Microbial selection in an enhanced biological phosphorus removal system was investigated in a laboratory-scale sequencing batch reactor fed exclusively with butyrate as a carbon source. As reported in the few previous studies, butyrate uptake was slow and phosphorus (P) release occurred during the entire anaerobic period. Polyphosphate-accumulating organism (PAO), i.e. Candidatus Accumulibacter phosphatis (named as Accumulibacter), glycogen-accumulating organisms (GAOs), i.e. Candidatus Competibacter phosphatis (named as Competibacter) and Defluviicoccus-related, tetrad-forming alphaproteobacteria (named as Defluviicoccus) were identified using fluorescence in situ hybridization analysis. The results show that Accumulibacter and Defluviicoccus were selected in the butyrate-fed reactor, whereas Competibacter was not selected. P removal was efficient at the beginning of the experiment with an increasing percentage relative abundance (% RA) of PAOs. The % RA of Accumulibacter and Defluviicoccus increased from 13% to 50% and 8% to 16%, respectively, and the % RA of Competibacter decreased from 8% to 2% during the experiment. After 6 weeks, P removal deteriorated with the poor correlation between the percentage of P removal and % RA of GAOs.

Multilevel correlations in the biological phosphorus removal process: From bacterial enrichment to conductivity-based metabolic batch tests and polyphosphatase assays

Enhanced biological phosphorus removal (EBPR) from wastewater relies on the preferential selection of active polyphosphate-accumulating organisms (PAO) in the underlying bacterial community continuum. Efficient management of the bacterial resource requires understanding of population dynamics as well as availability of bioanalytical methods for rapid and regular assessment of relative abundances of active PAOs and their glycogen-accumulating competitors (GAO). A systems approach was adopted here toward the investigation of multilevel correlations from the EBPR bioprocess to the bacterial community, metabolic, and enzymatic levels. Two anaerobic-aerobic sequencing-batch reactors were operated to enrich activated sludge in PAOs and GAOs affiliating with "Candidati Accumulibacter and Competibacter phosphates", respectively. Bacterial selection was optimized by dynamic control of the organic loading rate and the anaerobic contact time. The distinct core bacteriomes mainly comprised populations related to the classes Betaproteobacteria, Cytophagia, and Chloroflexi in the PAO enrichment and of Gammaproteobacteria, Alphaproteobacteria, Acidobacteria, and Sphingobacteria in the GAO enrichment. An anaerobic metabolic batch test based on electrical conductivity evolution and a polyphosphatase enzymatic assay were developed for rapid and low-cost assessment of the active PAO fraction and dephosphatation potential of activated sludge. Linear correlations were obtained between the PAO fraction, biomass specific rate of conductivity increase under anaerobic conditions, and polyphosphate-hydrolyzing activity of PAO/GAO mixtures. The correlations between PAO/GAO ratios, metabolic activities, and conductivity profiles were confirmed by simulations with a mathematical model developed in the aqueous geochemistry software PHREEQC.

Biosynthesis of poly(hydroxybutyrate-hydroxyvalerate) from the acclimated activated sludge and microbial characterization in this process

This study investigated the effects of substrate composition (acetate and propionate) on synthesis of various mix of poly(hydroxybutyrate-hydroxyvalerate) (P(HB/HV)) from activated sludge, which was acclimated using a single carbon (acetate) and mixed carbons (acetate and propionate). Results of batch P(HB/HV) production tests indicated that the yield and synthesis rate of P(HB/HV) decreased as the proportion of propionate in the substrate increased. However, mixed-carbon-acclimated sludge with acetate and propionate exhibited better P(HB/HV) production performance than with acetate-acclimated sludge in terms of substrate utilization, yield of P(HB/HV) and HV fraction in P(HB/HV). The desired hydroxyvalerate (HV) fraction (0-74%) of the P(HB/HV) could be obtained based on the substrate composition and sludge acclimation. Furthermore, PCR-DGGE analysis indicated that specific species dominated the activated sludge used for P(HB/HV) production. Acidobacteria and Burkholderiales were the dominant bacterial populations and played an important role in HV synthesis.

Optimized aeration strategies for nitrogen and phosphorus removal with aerobic granular sludge

Biological wastewater treatment by aerobic granular sludge biofilms offers the possibility to combine carbon (COD), nitrogen (N) and phosphorus (P) removal in a single reactor. Since denitrification can be affected by suboptimal dissolved oxygen concentrations (DO) and limited availability of COD, different aeration strategies and COD loads were tested to improve N- and P-removal in granular sludge systems. Aeration strategies promoting alternating nitrification and denitrification (AND) were studied to improve reactor efficiencies in comparison with more classical simultaneous nitrification-denitrification (SND) strategies. With nutrient loading rates of 1.6 gCOD L(-1) d(-1), 0.2 gN L(-1) d(-1), and 0.08 gP L(-1) d(-1), and SND aeration strategies, N-removal was limited to 62.3 ± 3.4%. Higher COD loads markedly improved N-removal showing that denitrification was limited by COD. AND strategies were more efficient than SND strategies. Alternating high and low DO phases during the aeration phase increased N-removal to 71.2 ± 5.6% with a COD loading rate of 1.6 gCOD L(-1) d(-1). Periods of low DO were presumably favorable to denitrifying P-removal saving COD necessary for heterotrophic N-removal. Intermittent aeration with anoxic periods without mixing between the aeration pulses was even more favorable to N-removal, resulting in 78.3 ± 2.9% N-removal with the lowest COD loading rate tested. P-removal was under all tested conditions between 88 and 98%, and was negatively correlated with the concentration of nitrite and nitrate in the effluent (r = -0.74, p < 0.01). With low COD loading rates, important emissions of undesired N2O gas were observed and a total of 7-9% of N left the reactor as N2O. However, N2O emissions significantly decreased with higher COD loads under AND conditions.

Role of carbon substrates in facilitating energy reduction and resource recovery in a traditional activated sludge process: investigation from a biokinetics modeling perspective

Three activated sludge processes (ASPs) were modeled and driven by dissolved complex organics (F-ASP), propionic acid (P-ASP), and acetic acid (A-ASP), and various parameters were subsequently estimated. The energy depletion for carbon removal was 0.146, 0.120, and 0.119 kWh/m(3) of treated wastewater for F-ASP, P-ASP, and A-ASP, respectively, suggesting that acetic acid can forward energy conservation. The ratio of substrate storage to oxidation in F-ASP, P-ASP, and A-ASP was 0, 0.25, and 0.52, respectively, further demonstrating that substrate eliminations from P-ASP and A-ASP were both dominated by substrate storage for polymer production, not by total oxidation; thus, they exhibited lower energy-consuming levels than F-ASP. Quantification of bioenergy production and nutrient acquisition from the excess sludge of the three ASPs were conducted subsequently, and A-ASP was found to facilitate phosphorus capture.

Microbial contributions to phosphorus cycling in eutrophic lakes and wastewater

Phosphorus is a key element controlling the productivity of freshwater ecosystems, and microbes drive most of its relevant biogeochemistry. Eutrophic lakes are generally dominated by cyanobacteria that compete fiercely with algae and heterotrophs for the element. In wastewater treatment, engineers select for specialized bacteria capable of sequestering phosphorus from the water, to protect surface waters from further loading. The intracellular storage molecule polyphosphate plays an important role in both systems, allowing key taxa to control phosphorus availability. The importance of dissolved organic phosphorus in eutrophic lakes and mineralization mechanisms is still underappreciated and understudied. The need for functional redundancy through biological diversity in wastewater treatment plants is also clear. In both systems, a holistic ecosystems biology approach is needed to understand the molecular mechanisms controlling phosphorus metabolism and the ecological interactions and factors controlling ecosystem-level process rates.