Enhanced Biological Phosphorus Removal Process Research Articles

A flux-based stoichiometric model of enhanced biological phosphorus removal metabolism

Enhanced biological phosphorus removal (EBPR) in wastewater treatment involves metabolic cycling through the biopolymers polyphosphate (polyP), polyhydroxybutyrate (PHB), and glycogen. This cycling is induced through treatment systems that alternate between carbon-rich anaerobic and carbon-poor aerobic reactor basins. While the appearance and disappearance of these biopolymers has been documented, the intracellular pressures that regulate their synthesis and degradation are not well understood. Current models of the EBPR process have examined a limited number of metabolic pathways that are frequently lumped into an even smaller number of “reactions.” This work, on the other hand, uses a stoichiometric model that contains a complete set of the pathways involved in bacterial biomass synthesis and energy production to examine EBPR metabolism. Using the stoichiometric model we were able to analyze the role of EBPR metabolism within the larger context of total cellular metabolism, as well as predict the flux distribution of carbon and energy fluxes throughout the total reaction network. The model was able to predict the consumption of PHB, the degradation of polyP, the uptake of acetate and the release of Pi. It demonstrated the relationship between acetate uptake and Pi release, and the effect of pH on this relationship. The model also allowed analysis of growth metabolism with respect to EBPR.

A flux-based stoichiometric model of enhanced biological phosphorus removal metabolism

Enhanced biological phosphorus removal (EBPR) in wastewater treatment involves metabolic cycling through the biopolymers polyphosphate (polyP), polyhydroxybutyrate (PHB), and glycogen. This cycling is induced through treatment systems that alternate between carbon-rich anaerobic and carbon-poor aerobic reactor basins. While the appearance and disappearance of these biopolymers has been documented, the intracellular pressures that regulate their synthesis and degradation are not well understood. Current models of the EBPR process have examined a limited number of metabolic pathways that are frequently lumped into an even smaller number of “reactions.” This work, on the other hand, uses a stoichiometric model that contains a complete set of the pathways involved in bacterial biomass synthesis and energy production to examine EBPR metabolism. Using the stoichiometric model we were able to analyze the role of EBPR metabolism within the larger context of total cellular metabolism, as well as predict the flux distribution of carbon and energy fluxes throughout the total reaction network. The model was able to predict the consumption of PHB, the degradation of polyP, the uptake of acetate and the release of Pi. It demonstrated the relationship between acetate uptake and Pi release, and the effect of pH on this relationship. The model also allowed analysis of growth metabolism with respect to EBPR.

Waste activated sludge production of the enhanced biological phosphorus removal process

The effect of the enhanced biological phosphorus removal process (EBPR) on waste activated sludge (WAS) production and the type of phosphorus storage were investigated in two continuous‐flow activated‐sludge systems in a semitechnical scale. One of the plants was operated with the A/O® process, whereas the other plant was operated in a conventional, fully aerobic mode and served as a control. By monitoring the elementary composition of the activated‐sludge solids in plant II and by using phosphorus fractionations, it was found that nearly all of the enhanced phosphorus removal was due to storage as polyphosphate (poly‐P). The additional uptake of phosphorus resulted in an increase of the inorganic sludge mass, which was determined to be 3.05 g suspended solids (SS)/g P using the results of the measurements of the nonvolatile solid fraction. This value was confirmed experimentally by the measurement of the difference between the WAS production of plant I and plant II. Based on the specific WAS production, an additional dry solids production of 3.14 g SS/g P was calculated. No indications for a significant difference of the organic sludge production between both plants were found, although the organic WAS production was slightly higher in experimental periods with a relatively high phosphorus content of the activated‐sludge solids of plant II.

Enhanced biological phosphate removal: modelling and design in theory and practice

The need for Enhanced Biological Phosphorus Removal (EBPR) in wastewater treatment plants (WTP) is increasing so that the development of steady state design models for WTPs using nitrification, denitrification and EBPR becomes more and more important. In developing such a model, theoretical and practical aspects must be considered if the qualitative and quantitative statements regarding the influence of various wastewater conditions (e.g. substrate composition) and surrounding conditions (e.g. influence of nitrate, duration of the anaerobic contact time) affecting EBPR shall be described. The presented EBPR design model is verified using data from various WTPs (e.g. Berlin-Ruhleben) currently using EBPR practices. Sensitivity studies for the most important influencing parameters and surrounding conditions are done, using fictious plant data. Recommendations are given, based on these studies, for the optimization of the EBPR process. These recommendation illustrates the most effective means towards improving the surrounding conditions for EBPR (e.g. increase of amount of readily available organic substrate, decrease of sludge age) with regard to an increase of the biologically removed phosphorus concentration.

Operational factors affecting enhanced biological phosphorus removal at the waste water treatment plant in Helsingborg, Sweden

Enhanced biological phosphorus removal (EBPR) has since 1992 been run as a full-scale UCT-process in a part of the waste water treatment plant in Helsingborg. Between June 1993 and July 1994 an extended operational and microbiological investigation was conducted. It was shown that the major phosphorus removal mechanism was biological and that at the most 10% of the soluble phosphorus entering the biological reactor, was removed due to chemical reactions. The VFA-potential in pre-treated waste water has been found to be a key factor. At the waste water treatment plant in Helsingborg 1 mg phosphorus is removed for each 14 mg VFA-potential added. COD, soluble COD and BOD1 are correlated to the VFA-potential, which means that these measurements can be used as operational parameters. If enough VFA-potential is present, the concentration of soluble phosphorus will be lower than 0.3 mg/l in the effluent even at temperatures below 10°C. The mean concentration of soluble phosphorus in the effluent has been 0.29 mg/l during the period October 1993-July 1994. Effluent nitrogen concentration was during the evaluation period between 8–10 mg/l and it was found that PHA was one of the major carbon sources for denitrification. Compared with a pre-denitrification process in combination with simultaneous precipitation, both the filament index and the DSVI were lower in the EBPR process. Other operational factors that affect the process are oxygen and nitrate concentrations in flows to the anaerobic reactor and the degree of internal recirculation from the aerobic to the anoxic reactor.

Anaerobic substrate uptake by the enhanced biological phosphorus removal activated sludge treating real sewage

The enhanced biological phosphorus removal (EBPR) activated sludge process is a wastewater treatment process by which not only organic pollutants but also phosphorus are removed. In the EBPR process, it is known that organic matter in the influent is removed in the anaerobic phase of the sequencing anaerobic and aerobic conditions. Although the mechanism of the anaerobic substrate uptake is being revealed, the existing observations are based on the experiments with activated sludge acclimatized with synthetic sewage, or synthetic media. In this study, the anaerobic substrate uptake by EBPR activated sludge treating real sewage was examined. The sludge was obtained from a pilot plant of the University of British Columbia, Canada. And as the substrate, acetate, propionate, lactate, pyruvate, malate, succinate, and fermented sewage were examined. The results clearly showed that most part of the sink of carbon anaerobically taken up is explained by PHA (poly 3-hydroxyalkanoates), and that glycolysis is playing a significant role in the anaerobic uptake of acetate and propionate.

Release of phosphorus from ash produced by incinerating waste activated sludge from enhanced biological phosphorus removal

A technical problem involved in the phosphorus removal using the enhanced biological phosphorus removal (EBPR) process is disposal of the phosphorus rich waste sludge. There are possibilities that any phosphorus in the disposed sludge would release to water environment. If the release occurs, it will nullify the efforts made in wastewater treatment. This paper reports results of a preliminary study made to examine the fate of phosphorus in the ash is produced by incinerating waste sludge from a laboratory unit of the EBPR process. A large part of phosphorus in the ash released in a relatively short time. Most of the phosphorus released at a normal temperature was apparently polyphosphate. The release was very fast at a high temperature. The finding suggests that hot water elutriation could be used as a means of recovering phosphorus from the ash. It was also suggested that the release could be prevented by adding an appropriate amount of iron to the sludge to be incinerated. The released phosphorus was susceptible to precipitation by metals, especially iron.

Recovery of biological phosphorus removal after periods of low organic loading

Activated sludge plants for enhanced biological phosphorus removal (EBPR) are often disturbed by short periods of low organic loading. Depending on the exact nature of the disturbance this may result in a partial or complete depletion of the internal PHB stores. PHB and phosphate measurements in a pilot-scale EBPR process show that recovery from such disturbances is slow and temporarily results in high phosphate concentrations. The measurements strongly suggest that the main reason for this slow recovery is a dependency of P-uptake on a slowly rising level of PHB. In a number of batch experiments this dependency of P-uptake on PHB was clearly shown. Also, based on the results of these batch experiments, a more detailed analysis was made of the effect of organic loading and aeration time on EBPR recovery. It is concluded that to obtain EBPR recovery, the aeration time should be carefully adjusted to the organic loading, particularly if the organic loading is low.

Enhanced biological phosphate removal: modelling and design in theory and practice

The need for Enhanced Biological Phosphorus Removal (EBPR) in wastewater treatment plants (WTP) is increasing so that the development of steady state design models for WTPs using nitrification, denitrification and EBPR becomes more and more important. In developing such a model, theoretical and practical aspects must be considered if the qualitative and quantitative statements regarding the influence of various wastewater conditions (e.g. substrate composition) and surrounding conditions (e.g. influence of nitrate, duration of the anaerobic contact time) affecting EBPR shall be described. The presented EBPR design model is verified using data from various WTPs (e.g. Berlin-Ruhleben) currently using EBPR practices. Sensitivity studies for the most important influencing parameters and surrounding conditions are done, using fictious plant data. Recommendations are given, based on these studies, for the optimization of the EBPR process. These recommendations illustrate the most effective means towards improving the surrounding conditions for EBPR (e.g. increase of amount of readily available organic substrate, decrease of sludge age) with regard to an increase of the biologically removed phosphorus concentration.

Interactions between wastewater quality and phosphorus release in the anaerobic reactor of the EBPR process

Studies on enhanced biological phosphorus removal (EBPR) operation in activated sludge processes have been conducted on a pilot plant at the Sjölunda wastewater treatment plant in Malmö, Sweden, since 1986. The plant receives wastewater from a combined sewer system. The aim of this study was to investigate interactions between variations in the wastewater quality and the effect on the EBPR operation. The paper focuses on the overall role of the concentration of volatile fatty acids (VFA) in the influent wastewater on the EBPR process. Firstly, the relation between VFA, COD and phosphorus in the influent wastewater at the plant is examined. Secondly, the effect of pH on phosphate release under anaerobic conditions is investigated. Finally, the observed relation between phosphate release in the anaerobic zone in relation to the concentration of VFA in the influent wastewater is discussed. The pilot plant consists of two parallel, activated sludge systems with EBPR, one system with a solids retention time (SRT) of 4 days, operated without nitrification-denitrification and one system with a SRT of 21 days, operated with nitrification-denitrification. Results derived from daily, composite samples taken over 3 yr have formed the basis of a general description of the water quality and the performance of the process. In addition, intensive field studies and laboratory studies have been used as ways of investigating certain phenomena in more detail. The results of the pilot plant study showed that the concentration of total phosphorus on average was low in the effluent, below 0.5 mg P/l. Increased phosphorus concentrations were, however, observed on a number of occasions. High concentrations of phosphorus in the effluent were observed every year in July, which is the holiday period at industrial plants in Sweden. Other instances of increased phosphorus concentrations in the secondary effluent were recorded after prolonged periods of rain. Increasing flow rates due to rain lead to a dilution and a change in the composition of the COD in the influent wastewater. A laboratory study showed that the ratio of phosphorus release/HAc uptake depends on pH in the range of 6–8. At neutral pH a ratio of 0.35-0.4 mg P/mg COD was found. The results of an intensive field study on the pilot plant suggested a relationship of 0.5 mg P/mg COD. Hydrolysis and/or fermentation processes have to be taken into account when describing phosphorus release in the anaerobic reactor. However, it was clearly demonstrated that it is primarily the VFA in the influent wastewater that affect the release of phosphorus in the systems studied.

Upgrading a large wastewater treatment plant with the help of a large-scale pilot plant

A large scale pilot plant was designed and built and was run over several months in order to collect data and experiences for the final design of a 400.000 P.E. waste water treatment plant. The design and building of this pilot plant is explained with respect to the two objectives examination of plant performance and comparison of different treatment types. In two examples, concerning the influence of temperature and hydraulic balance on EBPR (Enhanced Biological Phosphorus Removal) process the results and their influence on the final design are described. Compared with a design according to the standard design rules in Germany (ATV-A131, 1991), the future large WWTP can meet the effluent requirements with 30% less volume. The costs for the pilot plant were less than 35% of the costs saved by the now possible reduction of tank volume.

Operational factors affecting enhanced biological phosphorus removal at the waste water treatment plant in Helsingborg, Sweden

Enhanced biological phosphorus removal (EBPR) has since 1992 been run as a full-scale UCT-process in a part of the waste water treatment plant in Helsingborg. Between June 1993 and July 1994 an extended operational and microbiological investigation was conducted. It was shown that the major phosphorus removal mechanism was biological and that at the most 10% of the soluble phosphorus entering the biological reactor, was removed due to chemical reactions. The VFA-potential in pre-treated waste water has been found to be a key factor. At the waste water treatment plant in Helsingborg I mg phosphorus is removed for each 14 mg VFA-potential added. COD, soluble COD and BOD1 are correlated to the VFApotential, which means that these measurements can be used as operational parameters. If enough VFApotential is present, the concentration of soluble phosphorus will be lower than 0.3 mg/l in the effluent even at temperatures below 10°C. The mean concentration of soluble phosphorus in the effluent has been 0.29 mg/l during the period October 1993–July 1994. Effluent nitrogen concentration was during the evaluation period between 8–10 mg/1 and it was found that PHA was one of the major carbon sources for denitrification. Compared with a pre-denitrification process in combination with simultaneous precipitation, both the filament index and the DSVI were lower in the EBPR process. Other operational factors that affect the process are oxygen and nitrate concentrations in flows to the anaerobic reactor and the degree of internal recirculation from the aerobic to the anoxic reactor.

Anaerobic substrate uptake b y the enhanced biological phosphorus removal activated sludge treating real sewage

The enhanced biological phosphorus removal (EBPR) activated sludge process is a wastewater treatment process by which not only organic pollutants but also phosphorus are removed. In the EBPR process, it is known that organic matter in the influent is removed in the anaerobic phase of the sequencing anaerobic and aerobic conditions. Although the mechanism of the anaerobic substrate uptake is being revealed, the existing observations are based on the experiments with activated sludge acclimatized with synthetic sewage, or synthetic media. In this study, the anaerobic substrate uptake by EBPR activated sludge treating real sewage was examined. The sludge was obtained from a pilot plant of the University of British Columbia, Canada. And as the substrate, acetate, propionate, lactate, pyruvate, malate, succinate, and fermented sewage were examined. The results clearly showed that most part of the sink of carbon anaerobically taken up is explained by PHA (poly 3-hydroxyalkanoates), and that glycolysis is playing a significant role in the anaerobic uptake of acetate and propionate.

Release of phosphorus from ash produced by incinerating waste activated sludge from enhanced biological phosphorus removal

A technical problem involved in the phosphorus removal using the enhanced biological phosphorus removal (EBPR) process is disposal of the phosphorus rich waste sludge. There are possibilities that any phosphorus in the disposed sludge would release to water environment. If the release occurs, it will nullify the efforts made in wastewater treatment. This paper reports results of a preliminary study made to examine the fate of phosphorus in the ash is produced by incinerating waste sludge from a laboratory unit of the EBPR process. A large part of phosphorus in the ash released in a relatively short time. Most of the phosphorus released at a normal temperature was apparently polyphosphate. The release was very fast at a high temperature. The finding suggests that hot water elutriation could be used as a means of recovering phosphorus from the ash. It was also suggested that the release could be prevented by adding an appropriate amount of iron to the sludge to be incinerated. The released phosphorus was susceptible to precipitation by metals, especially iron.

Upgrading a large wastewater treatment plant with the help of a large-scale pilot plant

A large scale pilot plant was designed and built and was run over several months in order to collect data and experiences for the final design of a 400.000 P.E. waste water treatment plant. The design and building of this pilot plant is explained with respect to the two objectives examination of plant performance and comparison of different treatment types. In two examples, concerning the influence of temperature and hydraulic balance on EBPR (Enhanced Biological Phosphorus Removal) process the results and their influence on the final design are described. Compared with a design according to the standard design rules in Germany (ATV-A131, 1991), the future large WWTP can meet the effluent requirements with 30% less volume. The costs for the pilot plant were less than 35% of the costs saved by the now possible reduction of tank volume.

Enhanced biological phosphate removal: modelling and design in theory and practice

The need for Enhanced Biological Phosphorus Removal (EBPR) in wastewater treatment plants (WTP) is increasing so that the development of steady state design models for WTPs using nitrification, denitrification and EBPR becomes more and more important. In developing such a model, theoretical and practical aspects must be considered if the qualitative and quantitative statements regarding the influence of various wastewater conditions (e.g. substrate composition) and surrounding conditions (e.g. influence of nitrate, duration of the anaerobic contact time) affecting EBPR shall be described. The presented EBPR design model is verified using data from various WTPs (e.g. Berlin-Ruhleben) currently using EBPR practices. Sensitivity studies for the most important influencing parameters and surrounding conditions are done, using fictious plant data. Recommendations are given, based on these studies, for the optimization of the EBPR process. These recommendations illustrate the most effective means towards improving the surrounding conditions for EBPR (e.g. increase of amount of readily available organic substrate, decrease of sludge age) with regard to an increase of the biologically removed phosphorus concentration.

Recovery of biological phosphorus removal after periods of low organic loading

Activated sludge plants for enhanced biological phosphorus removal (EBPR) are often disturbed by short periods of low organic loading. Depending on the exact nature of the disturbance this may result in a partial or complete depletion of the internal PHB stores. PHB and phosphate measurements in a pilot-scale EBPR process show that recovery from such disturbances is slow and temporarily results in high phosphate concentrations. The measurements strongly suggest that the main reason for this slow recovery is a dependency of P-uptake on a slowly rising level of PHB. In a number of batch experiments this dependency of P-uptake on PHB was clearly shown. Also, based on the results of these batch experiments, a more detailed analysis was made of the effect of organic loading and aeration time on EBPR recovery. It is concluded that to obtain EBPR recovery, the aeration time should be carefully adjusted to the organic loading, particularly if the organic loading is low.

Wastewater solids fermentation for volatile acid production and enhanced biological phosphorus removal

Fermentation of wastewater solids for volatile acid (VA) production was studied as part of a full‐scale demonstration of the Orange County Water and Sewer Authority (OWASA) process for enhanced biological phosphorus removal (EBPR). The VA yields in bench‐scale fermentation tests ranged between approximately 6% and 26% of feed volatile solids (VS) under a range of test conditions that included solids retention times (SRTs) between 2 and 6 days, fermenter solids concentrations between 0.43% and 2.6%, and temperatures between 14°C and 23°C. Higher VA yields were observed at higher SRTs, lower fermenter solids concentrations, and higher temperatures. Settleability tests indicated that gravity separation of fermented sludge may be limited to an underflow concentration of 3%. After blending a phosphorus‐rich waste activated sludge (WAS) with fermented primary solids, up to 42% of the WAS phosphorus was released within 5 hours. Two full‐scale demonstration fermentation designs were investigated during the study that included a 2‐month simultaneous testing period. Demonstration Fermenter No. 1 used rectangular dissolved air flotation thickeners that were retrofitted with submersible mixers, liquid‐solids separation zones, and covers for odor control. This unit proved difficult to operate and maintain because of the design of the unit and the demanding duty. During the 2‐month side‐by‐side test period, the VA yield averaged 0.05 mg/mg VS fed to the unit. The average VA composition of the fermenter product stream consisted of 41% acetic acid, 44% propionic acid, 9% butyric acid, and 5% valeric acid, Suspended solid, organic, and nutrient loads in the fermenter product stream averaged 3.1 mg solids/mg VA, 1.7 mg carbonaceous biochemical oxygen demand (CBOD5)/mg VA, 0.04 mg ammonia/mg VA, and 0.05 mg phosphorus/mg VA during the 8‐month testing period. The second fermenter used an existing sludge‐holding tank mixed intermittently with coarse bubble aeration and dewatering centrifuges for liquid‐solids separation. Demonstration Fermenter No. 2 proved to be quite reliable, although it provided less discretionary control over the fermentation process compared with Fermenter No. 1. During the side‐by‐side test, the VA yield averaged 0.05 mg/mg VS fed to the unit. The VA composition of the fermenter product stream averaged 38% acetic acid, 36% propionic acid, 16% butyric acid, and 10% valeric acid. During the 10‐month testing period, the solid, organic, and nutrient loads averaged 1.0 mg solids/mg VA, 2.4 mg CBOD5/mg VA, 0.15 mg ammonia/mg VA, and 0.11 mg phosphorus/mg VA in the fermenter product stream. Both demonstration fermenters produced an acceptable quality VA source for use in a 22 000 M3/day (6 mgd) full‐scale demonstration of the OWASA EBPR process. Performance of bench‐scale and full‐scale demonstration fermenters was highly variable (0.05 to 0.2 mg VA/mg VS feed). Commercial acetic acid was also used as the sole volatile acid source and as a supplement to the VA stream produced from the demonstration fermenters to stabilize EBPR performance.

Circulation of phosphorus in a system with biological p-removal and sludge digestion

Pilot plant studies of enhanced biological phosphorus removal (EBPR) based on an activated sludge process have been conducted at the Sjölunda plant since 1986. One of the main questions with respect to this process alternative is how the sludge treatment system is to be operated. In order to study the release of phosphorus from an EBPR sludge during anaerobic digestion, a study was performed with manually operated laboratory reactors. Fractionation procedures were used in order to characterize the sludge with respect to phosphorus. The influent wastewater quality determines the release and precipitation of phosphorus during anaerobic digestion. The potential for precipitation is in principle determined by the amount of metals in the influent wastewater which are removed with the wasted sludge. At the Sjölunda plant, a process scheme based on an EBPR process and anaerobic digestion requires that the circulation of phosphorus is prevented by means of addition of chemicals in order to acquire a phosphorus concentration of around 0.5 – 1 mg P/l in the secondary effluent.

Sleep and Alertness

<h3>Abstract</h3> Enhanced biological phosphorus removal (EBPR) is a globally important biotechnological process and relies on the massive accumulation of phosphate within special microorganisms. <i>Candidatus</i> Accumulibacter conform to classical physiology model for polyphosphate accumulating organisms and are widely believed to be the most important player for the process in full-scale EBPR systems. However, it was impossible till now to quantify the contribution of specific microbial clades to EBPR. In this study, we have developed a new tool to directly link the identity of microbial cells to the absolute quantification of intracellular poly-P and other polymers under <i>in situ</i> conditions, and applied it to eight full-scale EBPR plants. Besides <i>Ca</i>. Accumulibacter, members of the genus <i>Tetrasphaera</i> were found to be important microbes for P accumulation, and in six plants they were the most important. As these <i>Tetrasphaera</i> cells did not exhibit the classical phenotype of poly-P accumulating microbes, our entire understanding of the microbiology of the EBPR process has to be revised. Furthermore, our new single-cell approach can now also be applied to quantify storage polymer dynamics in individual populations <i>in situ</i> in other ecosystems and might become a valuable tool for many environmental microbiologists.