Enhanced Biological Phosphorus Removal Activity Research Articles

Effects of enhanced biological phosphorus removal on rapid control of sludge bulking and fast formation of aerobic granular sludge

This study investigated the effects of enhanced biological phosphorus removal (EBPR) on rapid sludge bulking control and fast aerobic granular sludge (AGS) formation by adding 20 % of EBPR activated sludge to the bulking activated sludge (BAS) reactor. The results indicate that activating EBPR activity swiftly improved BAS settleability within 16 days, thus resolving sludge bulking issues. Subsequently, a settling time-based selection was employed, resulting in the BAS granulation within another 16 days. The rapid achievement of EBPR activity improved the BAS settleability and facilitated the formation of sludge aggregates, thereby expediting BAS granulation. Inhibition of filamentous bacteria and enrichment of slow-growing organisms contributed to both sludge bulking control and aerobic granulation. Furthermore, the increase in proteins/polysaccharides ratio facilitated the granulation process. Additionally, total nitrogen removal increased from 59.4 % to 71.7 % because of the mature AGS formation. This study provided an approach to simultaneously control sludge bulking and promote aerobic granulation.

Biological phosphorus removal and its microbial community in a modified full-scale activated sludge system under dry and wet weather dynamics

Enhanced biological phosphorus removal (EBPR) performance and microbial community dynamics during dry and wet-weather conditions of a full-scale treatment plant was evaluated by converting a section of activated sludge basins using low-cost operational modifications into an anoxic/anaerobic zone to promote EBPR. Two trains of the activated sludge system at the Des Moines, Iowa Metropolitan Wastewater Reclamation Facility were used for the study with one train modified for EBPR, and the other remained as nitrification-only for comparison.In addition to measuring the modification effectiveness for phosphorus removal, performance was compared during dry and wet weather conditions over the course of two summer seasons to improve understanding of wet and dry weather dynamics for EBPR. DNA sequencing and qPCR tests were conducted to develop an understanding of microbial population changes between control and modified basins and wet and dry weather conditions.Basin hydraulic retention times varied from 2.6 to 12.7 hours with an average of 8.9 hours. EBPR activity was successfully established in the modified basins with average phosphorus content of the return activated sludge 0.032 ± 0.002 compared to 0.016 ± 0.001 mg TP/mg TSS (95% confidence) in the control basins. Phosphorus removal was significantly decreased by prolonged wet weather conditions, particularly in year two of the study, however the modified basin maximum removal of 96% and average of 43.7 ± 5.3% remained significantly higher than the maximum of 46% and average 12.6 ± 2.4% removal in the control basins.DNA sequencing showed a significant increase in relative abundance of phyla Chloroflexi, Nitrospirae, and Verrucomicrobia in the modified basins, but no correlation to EBPR performance. qPCR indicated significant increase in relative quantity of Accumulibacter, but not for Actinetobacter-like phosphorus accumulating organisms (PAOs), which includes the PAO Tetrasphaera. Significant abundance of some Accumulibacter clades found within the modified basins was contrary to previous literature which focused on small-scale and batch studies. A higher than expected dominance of clade I and increased relative quantities of clades IIB and IIC during extended wet weather was observed which may have contributed to rapid recovery of phosphorus removal when dry weather resumed. The abundance of PAOs did not significantly correlate with changes in phosphorous removal performance, contrary to reports from previous small-scale and batch studies.

Living on the edge: Prospects for enhanced biological phosphorus removal at low sludge retention time under different temperature scenarios

The design of new wastewater treatment plants with the aim of capturing organic matter for energy recovery is a current focus of research. Operating with low sludge residence time (SRT) appears to be a key factor in maximizing organic matter recovery. In these new configurations, it is assumed that phosphorus is chemically removed in a tertiary step, but the integration of enhanced biological phosphorus removal (EBPR) into these short-SRT systems seems to be an alternative worth studying. A key point of this integration is to prevent the washout of polyphosphate accumulating organisms (PAO) despite the low SRT applied. However, the minimum SRT required to avoid PAO washout depends on temperature, due to its effects on reaction kinetics, gas transfer rates, biomass growth and decay rates. This work includes a wide range of short and long-term experiments to understand these interactions and shows which combinations of SRT and temperature are detrimental to PAO growth. For example, an EBPR system operating at 20 °C and SRT = 5 d showed good performance, but EBPR activity was lost at 10 °C. EBPR operated at SRT = 10 d had 86% P removal at 20 °C but decreased to 71% at 15 °C and progressively lost its activity at lower temperature. The temperature coefficient obtained for PAO show a low degree of temperature dependence (θ = 1.047 ± 0.014), and should be considered when designing short-SRT systems with EBPR.

Ensuring sustainability of conventional aerobic wastewater treatment system via bio-augmentation of aerobic bacterial consortium: An enhanced biological phosphorus removal approach

Enhanced biological phosphorus removal (EBPR) is an inevitable need of sustainable waste water treatment systems (WWTS). In this regard, this study aimed to investigate the potential of an aerobic continuously stirred tank reactor (CSTR), enriched with selected bacterial consortium, for enhanced phosphorus removal. The CSTR biomass was bioaugmented through addition of 12 distinct phosphorus accumulating and solubilizing strains. The medium and high strength synthetic waste water, having the phosphorus concentration in the range of 1.4–40 mg/L, was fed to the CSTR throughout this study. With respect to medium strength feed, total phosphorus (TP) removal efficiency reached up to 90% at an influent concentration of 20 mg/L, followed by a declining trend of removal efficiency as 62 and 30%, at the TP concentration of 30 and 40 mg/L, respectively. Contrary, the EBPR activity was observed to be inhibiting (lesser accumulation of phosphorus in biomass) at lower influent TP value of 10 mg/L, when the CSTR was operated with high strength waste water. Further, ammonical nitrogen and chemical oxygen demand removal performance of the system was observed to be independent of influent TP concentration. Detailed experimental investigations revealed that the inoculated bacterial consortium favored the transformation and storage of influent TP into intracellular storage of polyphosphate (poly-P). Overall, the results indicated that the sustainability of existing WWTS can be ensured through bioaugmentation of non-EBPR sludge to aerobically cultivated EBPR performing sludge.

Side-stream enhanced biological phosphorus removal (S2EBPR) process improves system performance - A full-scale comparative study

To address the common challenges in enhanced biological phosphorus removal (EBPR) related to stability and unfavorable influent carbon to phosphorus ratio, a side-stream EBPR (S2EBPR) process that involves a side-stream anaerobic biological sludge hydrolysis and fermentation reactor was proposed as an emerging alternative. In this study, a full-scale pilot testing was performed with side-by-side operation of a conventional anaerobic-anoxic-aerobic (A2O) process versus a S2EBPR process. A comparison of the performance, activity and microbial community between the two configurations was performed. The results demonstrated that, with the same influent wastewater characteristics, S2EBPR configuration showed improved P removal performance and stability than the conventional A2O configuration, especially when the mixers in the side-stream anaerobic reactor were operated intermittently. Mass balance analysis illustrated that both denitrification and EBPR were enhanced in S2EBPR configuration, where return activated sludge was diverted into the anaerobic zone to promote fermentation and enrichment of polyphosphate accumulating organisms (PAOs), and the influent was bypassed to the anoxic zone for enhancing denitrification. A relatively higher PAO activity and total PAO abundance were observed in S2EBPR than in A2O configuration, accompanied by a higher degree of dependence on glycolysis pathway than tricarboxylic acid cycle. No significant difference in the relative abundances of putative PAOs, including Ca. Accumulibacter and Tetrasphaera, were observed between the two configurations. However, higher microbial community diversity indices were observed in S2EBPR configuration than in conventional one. In addition, consistently lower relative abundance of known glycogen accumulating organisms (GAOs) was observed in S2EBPR system. Extended anaerobic retention time and conditions that generate continuous and more complex volatile fatty acids in the side-stream anaerobic reactor of S2EBPR process likely give more competitive advantage for PAOs over GAOs. PAOs exhibited sustained EBPR activity and delayed decay under extended anaerobic condition, likely due to their versatile metabolic pathways depending on the availability and utilization of multiple intracellular polymers. This study provided new insights into the effects of implementing side-stream EBPR configuration on microbial populations, EBPR activity profiles and resulted system performance.

Effect of Lactate on the Microbial Community and Process Performance of an EBPR System.

Candidatus Accumulibacter phosphatis is in general presented as the dominant organism responsible for the biological removal of phosphorus in activated sludge wastewater treatment plants. Lab-scale enhanced biological phosphorus removal (EBPR) studies, usually use acetate as carbon source. However, the complexity of the carbon sources present in wastewater could allow other potential poly-phosphate accumulating organism (PAOs), such as putative fermentative PAOs (e.g., Tetrasphaera), to proliferate in coexistence or competition with Ca. Accumulibacter. This research assessed the effects of lactate on microbial selection and process performance of an EBPR lab-scale study. The addition of lactate resulted in the coexistence of Ca. Accumulibacter and Tetrasphaera in a single EBPR reactor. An increase in anaerobic glycogen consumption from 1.17 to 2.96 C-mol/L and anaerobic PHV formation from 0.44 to 0.87 PHV/PHA C-mol/C-mol corresponded to the increase in the influent lactate concentration. The dominant metabolism shifted from a polyphosphate-accumulating metabolism (PAM) to a glycogen accumulating metabolism (GAM) without EBPR activity. However, despite the GAM, traditional glycogen accumulating organisms (GAOs; Candidatus Competibacter phosphatis and Defluvicoccus) were not detected. Instead, the 16s RNA amplicon analysis showed that the genera Tetrasphaera was the dominant organism, while a quantification based on FISH-biovolume indicated that Ca. Accumulibacter remained the dominant organism, indicating certain discrepancies between these microbial analytical methods. Despite the discrepancies between these microbial analytical methods, neither Ca. Accumulibacter nor Tetrasphaera performed biological phosphorus removal by utilizing lactate as carbon source.

Polyphosphate-accumulating organisms in full-scale tropical wastewater treatment plants use diverse carbon sources

Enhanced biological phosphorus removal (EBPR) is considered challenging in the tropics, based on a great number of laboratory-based studies showing that the polyphosphate-accumulating organism (PAO) Candidatus Accumulibacter does not compete well with glycogen accumulating organisms (GAOs) at temperatures above 25 °C. Yet limited information is available on the PAO community and the metabolic capabilities in full-scale EBPR systems operating at high temperature. We studied the composition of the key functional PAO communities in three full-scale wastewater treatment plants (WWTPs) with high in-situ EBPR activity in Singapore, their EBPR-associated carbon usage characteristics, and the relationship between carbon usage and community composition. Each plant had a signature community composed of diverse putative PAOs with multiple operational taxonomic units (OTUs) affiliated to Ca. Accumulibacter, Tetrasphaera spp., Dechloromonas and Ca. Obscuribacter. Despite the differences in community composition, ex-situ anaerobic phosphorus (P)-release tests with 24 organic compounds from five categories (including four sugars, three alcohols, three volatile fatty acids (VFAs), eight amino acids and six other carboxylic acids) showed that a wide range of organic compounds could potentially contribute to EBPR. VFAs induced the highest P release (12.0–18.2 mg P/g MLSS for acetate with a P release-to-carbon uptake (P:C) ratio of 0.35–0.66 mol P/mol C, 9.4–18.5 mg P/g MLSS for propionate with a P:C ratio of 0.38–0.60, and 9.5–17.3 mg P/g MLSS for n-butyrate), followed by some carboxylic acids (10.1–18.1 mg P/g MLSS for pyruvate, 4.5–11.7 mg P/g MLSS for lactate and 3.7–12.4 mg P/g MLSS for fumarate) and amino acids (3.66–7.33 mg P/g MLSS for glutamate with a P:C ratio of 0.16–0.43 mol P/mol C, and 4.01–7.37 mg P/g MLSS for aspartate with a P:C ratio of 0.17–0.48 mol P/mol C). P-release profiles (induced by different carbon sources) correlated closely with PAO community composition. High micro-diversity was observed within the Ca. Accumulibacter lineage, which represented the most abundant PAOs. The total population of Ca. Accumulibacter taxa was highly correlated with P-release induced by VFAs, highlighting the latter's importance in tropical EBPR systems. There was a strong link between the relative abundance of individual Ca. Accumulibacter OTUs and the extent of P release induced by distinct carbon sources (e.g., OTU 81 and amino acids, and OTU 246 and ethanol), suggesting niche differentiation among Ca. Accumulibacter taxa. A diverse PAO community and the ability to use numerous organic compounds are considered key factors for stable EBPR in full-scale plants at elevated temperatures.

Influence of varying COD and total phosphorus loading on EBPR performed in aerobic baffled reactor using dried powdered sludge

Previous research has indicated that enhanced biological phosphorus removal (EBPR) can be achieved under fully aerobic conditions. In this study, EBPR was performed for 384days using dried powdered sludge in an aerobic baffled reactor fed with medium strength (COD ∼400–500mg/L) and then high strength (COD ∼900–1000mg/L) synthetic wastewater. Total phosphorus (TP) concentration in the feed was varied between 1.4–40mg/L. The results showed that for medium strength influent, TP removal efficiency was over 90% up to 20mg/L of influent TP but decreased to 68% and 33% at 30 and 40mg/L of influent TP, respectively. For high strength influent, TP metabolism weakened and EBPR activity inhibited as biomass TP content was reduced. Experimental results also showed that TP release levels increased with biomass TP content and TP uptake occurred in the presence of carbon source. COD and NH4+-N removal efficiencies largely remained unaffected by different TP concentrations. TP removal efficiency was affected by its own concentration. Further investigations showed that TP was transformed to intracellular storage of polyphosphate (poly-P) with single stage aerobic process. The primarily reason for TP removal was the release of extracellular enzymes by microbes due to the addition of dried powdered sludge. Based on tracer studies, dead space in AeBR was found to range from 12.8 to 19.3%. The flow pattern in the AeBR was classified as an intermediate between plug and completely mixed flows. This study could provide an alternative for stable aerobic EBPR for medium strength wastewater.

Integrative microbial community analysis reveals full-scale enhanced biological phosphorus removal under tropical conditions

Management of phosphorus discharge from human waste is essential for the control of eutrophication in surface waters. Enhanced biological phosphorus removal (EBPR) is a sustainable, efficient way of removing phosphorus from waste water without employing chemical precipitation, but is assumed unachievable in tropical temperatures due to conditions that favour glycogen accumulating organisms (GAOs) over polyphosphate accumulating organisms (PAOs). Here, we show these assumptions are unfounded by studying comparative community dynamics in a full-scale plant following systematic perturbation of operational conditions, which modified community abundance, function and physicochemical state. A statistically significant increase in the relative abundance of the PAO Accumulibacter was associated with improved EBPR activity. GAO relative abundance also increased, challenging the assumption of competition. An Accumulibacter bin-genome was identified from a whole community metagenomic survey, and comparative analysis against extant Accumulibacter genomes suggests a close relationship to Type II. Analysis of the associated metatranscriptome data revealed that genes encoding proteins involved in the tricarboxylic acid cycle and glycolysis pathways were highly expressed, consistent with metabolic modelling results. Our findings show that tropical EBPR is indeed possible, highlight the translational potential of studying competition dynamics in full-scale waste water communities and carry implications for plant design in tropical regions.

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.

High-temperature EBPR process: The performance, analysis of PAOs and GAOs and the fine-scale population study of Candidatus “Accumulibacter phosphatis”

The applicability of the enhanced biological phosphorus removal (EBPR) process for the removal of phosphorus in warm climates is uncertain due to frequent reports of EBPR deterioration at temperature higher than 25 °C. Nevertheless, a recent report on a stable and efficient EBPR process at 28 °C has inspired the present study to examine the performance of EBPR at 24 °C–32 °C, as well as the PAOs and GAOs involved, in greater detail. Two sequencing batch reactors (SBRs) were operated for EBPR in parallel at different temperatures, i.e., SBR-1 at 28 °C and SBR-2 first at 24 °C and subsequently at 32 °C. Both SBRs exhibited high phosphorus removal efficiencies at all three temperatures and produced effluents with phosphorus concentrations less than 1.0 mg/L during the steady state of reactor operation. Real-time quantitative polymerase chain reaction (qPCR) revealed Accumulibacter-PAOs comprised 64% of the total bacterial population at 24 °C, 43% at 28 °C and 19% at 32 °C. Based on fluorescent in situ hybridisation (FISH), the abundance of Competibacter-GAOs at both 24 °C and 28 °C was rather low (<10%), while it accounted for 40% of the total bacterial population at 32 °C. However, the smaller Accumulibacter population and larger population of Competibacter at 32 °C did not deteriorate the phosphorus removal performance. A polyphosphate kinase 1 (ppk1)-based qPCR analysis on all studied EBPR processes detected only Accumulibacter clade IIF. The Accumulibacter population shown by 16S rRNA and ppk1 was not significantly different. This finding confirmed the existence of single clade IIF in the processes and the specificity of the clade IIF primer sets designed in this study. Habitat filtering related to temperature could have contributed to the presence of a unique clade. The clade IIF was hypothesised to be able to perform the EBPR activity at high temperatures. The clade's robustness most likely helps it to fit the high-temperature EBPR sludge best and allows it not only to outcompete other Accumulibacter clades but coexist with GAOs without compromising EBPR activity.

Long-term performance evaluation of EBPR process in tropical climate: start-up, process stability, and the effect of operational pH and influent C:P ratio

To date, little information is known about the operation of the enhanced biological phosphorus removal (EBPR) process in tropical climates. Along with the global concerns on nutrient pollution and the increasing array of local regulatory requirements, the applicability and compliance accountability of the EBPR process for sewage treatment in tropical climates is being evaluated. A sequencing batch reactor (SBR) inoculated with seed sludge from a conventional activated sludge (CAS) process was successfully acclimatized to EBPR conditions at 28 °C after 13 days' operation. Enrichment of Candidatus Accumulibacter phosphatis in the SBR was confirmed through fluorescence in situ hybridization (FISH). The effects of operational pH and influent C:P ratio on EBPR were then investigated. At pH 7 or pH 8, phosphorus removal rates of the EBPR processes were relatively higher when operated at C:P ratio of 3 than C:P ratio of 10, with 0.019-0.020 and 0.011-0.012 g-P/g-MLVSS•day respectively. One-year operation of the 28 °C EBPR process at C:P ratio of 3 and pH 8 demonstrated stable phosphorus removal rate of 0.020 ± 0.003 g-P/g-MLVSS•day, corresponding to effluent with phosphorus concentration <0.5 mg/L. This study provides the first evidence on good EBPR activity at relatively high temperature, indicating its applicability in a tropical climate.

Effects of glucose on the performance of enhanced biological phosphorus removal activated sludge enriched with acetate

The effects of glucose on enhanced biological phosphorus removal (EBPR) activated sludge enriched with acetate was investigated using sequencing batch reactors. A glucose/acetate mixture was serially added to the test reactor in ratios of 25/75%, 50/50%, and 75/25% and the EBPR activity was compared to the control reactor fed with 100% acetate. P removal increased at a statistically significant level to a near-complete in the test reactor when the mixture increased to 50/50%. However, EBPR deteriorated when the glucose/acetate mixture increased to 75/25% in the test reactor and when the control reactor abruptly switched to 100% glucose. These results, in contrast to the EBPR conventional wisdom, suggest that the addition of glucose at moderate levels in wastewaters does not impede and may enhance EBPR, and that glucose waste products should be explored as an economical sustainable alternative when COD enhancement of EBPR is needed.

Dynamics of microbial community structure of and enhanced biological phosphorus removal by aerobic granules cultivated on propionate or acetate.

Aerobic granules are dense microbial aggregates with the potential to replace floccular sludge for the treatment of wastewaters. In bubble-column sequencing batch reactors, distinct microbial populations dominated propionate- and acetate-cultivated aerobic granules after 50 days of reactor operation when only carbon removal was detected. Propionate granules were dominated by Zoogloea (40%), Acidovorax, and Thiothrix, whereas acetate granules were mainly dominated by Thiothrix (60%). Thereafter, an exponential increase in enhanced biological phosphorus removal (EBPR) activity was observed in the propionate granules, but a linear and erratic increase was detected in the acetate ones. Besides Accumulibacter and Competibacter, other bacterial populations found in both granules were associated with Chloroflexus and Acidovorax. The EBPR activity in the propionate granules was high and stable, whereas EBPR in the acetate granules was erratic throughout the study and suffered from a deterioration period that could be readily reversed by inducing hydrolysis of polyphosphate in presumably saturated Accumulibacter cells. Using a new ppk1 gene-based dual terminal-restriction fragment length polymorphism (T-RFLP) approach revealed that Accumulibacter diversity was highest in the floccular sludge inoculum but that when granules were formed, propionate readily favored the dominance of Accumulibacter type IIA. In contrast, acetate granules exhibited transient shifts between type I and type II before the granules were dominated by Accumulibacter type IIA. However, ppk1 gene sequences from acetate granules clustered separately from those of propionate granules. Our data indicate that the mere presence of Accumulibacter is not enough to have consistently high EBPR but that the type of Accumulibacter determines the robustness of the phosphate removal process.

The nature of the carbon source rules the competition between PAO and denitrifiers in systems for simultaneous biological nitrogen and phosphorus removal

The presence of nitrate in the theoretical anaerobic reactor of a municipal WWTP aiming at simultaneous C, N and P removal usually leads to Enhanced Biological Phosphorus Removal (EBPR) failure due to the competition between PAO and denitrifiers for organic substrate. This problem was studied in a continuous anaerobic–anoxic–aerobic (A 2/O) pilot plant (146 L) operating with good removal performance and a PAO-enriched sludge (72%). Nitrate presence in the initially anaerobic reactor was studied by switching the operation of the plant to an anoxic–aerobic configuration. When the influent COD composition was a mixture of different carbon sources (acetic acid, propionic acid and sucrose) the system was surprisingly able to maintain EBPR, even with internal recycle ratios up to ten times the influent flow rate and COD limiting conditions. However, the utilisation of sucrose as sole carbon source resulted in a fast EBPR failure. Batch tests with different nitrate concentrations (0–40 mg L −1) were performed in order to gain insight into the competition for the carbon source in terms of P-release or denitrification rates and P-release/C-uptake ratio. Surprisingly, no inhibitory or detrimental effect on EBPR performance due to nitrate was observed. A model based on ASM2d but considering two step nitrification and denitrification was developed and experimentally validated. Simulation studies showed that anaerobic VFA availability is critical to maintain EBPR activity.

Effect of pH reduction on polyphosphate- and glycogen-accumulating organisms in enhanced biological phosphorus removal processes

We investigated the effect of pH reduction on polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) in the enhanced biological phosphorus removal (EBPR) process. Three laboratory-scale EBPR reactors were used. Initially, the reactors were operated at pH 7.9±0.1 and 6.5±0.1, and after 27 days, the pH was lowered to 6.5±0.1 and 6.0±0.1, respectively. PAOs and GAOs were monitored using real-time quantitative polymerase chain reaction and/or fluorescent in situ hybridization. Phosphorus removal performance was also monitored. During the start-up period, high EBPR activity and increases in Candidatus 'Accumulibacter phosphatis' (Accumulibacter) and Candidatus 'Competibacter phosphatis' (Competibacter) were observed. In all runs, Accumulibacter and Competibacter were the dominant PAO and GAO, respectively. Accumulibacter began to decline 10-18 days after lowering the pH to 6.5±0.1. After lowering the pH to 6.0±0.1, the Accumulibacter population decreased immediately. Contrastingly, an obvious adverse effect of pH reduction on Competibacter was not observed. In all runs, EBPR activity began to deteriorate 6-12 days after Accumulibacter decline began. Thus, our results show that pH reduction had an immediate or delayed effect on Accumulibacter decline. Moreover, the time lag between the start of Accumulibacter decline and that of EBPR deterioration implies that EBPR deterioration by pH reduction went through unknown process.

Bacterial Community and “ Candidatus Accumulibacter” Population Dynamics in Laboratory-Scale Enhanced Biological Phosphorus Removal Reactors

"Candidatus Accumulibacter" and total bacterial community dynamics were studied in two lab-scale enhanced biological phosphorus removal (EBPR) reactors by using a community fingerprint technique, automated ribosomal intergenic spacer analysis (ARISA). We first evaluated the quantitative capability of ARISA compared to quantitative real-time PCR (qPCR). ARISA and qPCR provided comparable relative quantification of the two dominant "Ca. Accumulibacter" clades (IA and IIA) detected in our reactors. The quantification of total "Ca. Accumulibacter" 16S rRNA genes relative to that from the total bacterial community was highly correlated, with ARISA systematically underestimating "Ca. Accumulibacter" abundance, probably due to the different normalization techniques applied. During 6 months of normal (undisturbed) operation, the distribution of the two clades within the total "Ca. Accumulibacter" population was quite stable in one reactor while comparatively dynamic in the other reactor. However, the variance in the clade distribution did not appear to affect reactor performance. Instead, good EBPR activity was positively associated with the abundance of total "Ca. Accumulibacter." Therefore, we concluded that the different clades in the system provided functional redundancy. We disturbed the reactor operation by adding nitrate together with acetate feeding in the anaerobic phase to reach initial reactor concentrations of 10 mg/liter NO(3)-N for 35 days. The reactor performance deteriorated with a concomitant decrease in the total "Ca. Accumulibacter" population, suggesting that a population shift was the cause of performance upset after a long exposure to nitrate in the anaerobic phase.

Evidence and Long-Term Feasibility of Enhanced Biological Phosphorus Removal in Oxidation-Ditch Type of Aerated-Anoxic Activated Sludge Systems

This study investigated the potential of four full-scale oxidation ditches to accomplish enhanced biological phosphorus removal (EBPR). Despite the fact that none of the tested oxidation ditches were designed to perform EBPR, mixed liquors from all four ditches showed good specific phosphorus release and uptake rates, a typical characteristic of a typical EBPR biomass. The specific phosphorus release rates ranged from 0.042- to 0.254-mg P/mg VSS-d and the specific phosphorus uptake rates ranged from 0.023- to 0.125-mg P/mg VSS-d for the tested full-scale plants. The EBPR potential of one of the full-scale plants (Central Davis Sewer District) was further studied by changing the aeration patterns in the ditch. The mixed liquor in this full-scale plant exhibited good phosphorus release and uptake trends and dissolved phosphorus, as low as 1.26 mg/L, could be accomplished in the final effluent of this plant as a result of this optimization. The long-term feasibility of the EBPR in this full-scale was tested by running a bench-scale EBPR reactor, in which the anaerobic phase was replaced with aerated-anaerobic phase to simulate the mixed liquor environment that exists in Central Davis mixed liquor and, in general, in all oxidation-ditch-type activated sludge configurations. The bench-scale reactor showed consistent EBPR activity in the absence of an anaerobic environment and more than 85% phosphorus removal could be maintained in the reactor for more than 400 days. The intrafloc microanaerobic/anoxic zones, which may be present in the mixed liquor, did not seem to add to the EBPR efficiency under aerated-anaerobic conditions. Cloning and sequencing using Rhodocyclus specific forward primer RHC439 showed the abundance of organisms most closely falling in Rhodocyclaceae family but not related to CandidatusAccumulibacter phosphatis. Simultaneous 4′-6–Diamidino-2–phenylindole (DAPI) staining and fluorescent in situ hybridization (FISH) using RHC439 probe clearly demonstrated the participation of polyphosphate accumulating organism (PAOs) targeted by RHC439 (i.e., in Rhodocyclaceae family). Microautoradiography assisted FISH using RHC439 further confirmed the participation of PAOs in Rhodocyclaceae family.

Population dynamics in a sequencing batch reactor fed with glucose and operated for enhanced biological phosphorus removal

The study investigated the effect of glucose feeding as the sole carbon source on population dynamics in a sequencing batch reactor (SBR) operated for enhanced biological phosphorus removal (EBPR). The lab-scale SBR operation was started with a biomass taken from a WWTP plant performing EBPR and continued around two months. It exhibited a sequence of periods with different performance and biomass characteristics. The first period indicated predominant EBPR activity, involving phosphorus release in the anaerobic phase with PHA production as expected. Lactate generated from glucose fermentation was presumably converted to PHA by PAOs as an essential part of the EBPR activity. In the second period a major shift occurred in the population dynamics favoring the preferential growth and the predominance of GAOs which have the advantage of utilizing glucose directly and eventually the EBPR activity was deteriorated. The significant feature of the third period was the proliferation of filamentous microorganisms.

Changes in Polyhydroxy-Alkanoates (PHAs) during Enhanced Biological Phosphorus Removal with Dairy Industrial Wastewater

Using the industrial wastewater from a dairy plant, the performance of enhanced biological phosphorus removal (EBPR) with complex organic substances was evaluated. A laboratory-scale sequencing batch reactor (SBR) was operated and the organic loading rate in total chemical oxygen demand (tCOD) increased gradually from 200– 600 g-tCOD m−3 cycle−1 in three steps. As the organic loading increased, the food to microorganism ratio ( F/M ) increased from 0.16–0.27 (g-tCOD/g-MLVSS d). When it increased over 600 g-tCOD m−3 cycle−1 , the effluent phosphorus concentration fluctuated, showing an unstable EBPR activity. During the anaerobic condition, higher fraction of poly-3-hydroxyvalerate (PHV) was observed and the ratio of PHV to poly-3-hydroxybuyrate (PHB) production ( ΔPHV/ΔPHB ) ranged 1.2∼3.4 mM-C/mM-C . PHV was produced faster and used later than PHB. By applying fluorescent in situ hybridization (FISH) technique, the percentage of Rhodocyclus-related bacteria to the total cell counts was monitored as...