Biological Excess Phosphorus Removal Research Articles

The influence of dissolved oxygen on partial nitritation/anammox performance and microbial community of the 200,000 m3/d activated sludge process at the Changi water reclamation plant (2011 to 2016).

Mainstream partial nitritation/anammox (PN/A), coupled with excess biological phosphorus removal, in a 200,000 m3/d step-feed activated sludge process (Train 2) in the Changi Water Reclamation Plant (WRP), Singapore, has been studied and reported. This paper presents an overview of process performance and the microbial community during the period from 2011 to 2016. The site data showed that, along with the reduction of dissolved oxygen (DO) from 1.7 to 1.0 mg O2/L in the aeration zones, the concentrations of ammonium and nitrate of the final effluent increased, while nitrite decreased, resulting in an increase of 2.4 mg N/L of total inorganic nitrogen. Autotrophic nitrogen removal was higher than heterotrophic biological nitrogen removal under higher DO concentration conditions, but decreased under low DO operating condition. These macro-scale changes were caused by shifts of the nitrogen-converting microbial community. The ammonia oxidizing bacteria (AOB) population abundance was reduced by 30 times, while the nitrite oxidizing bacteria (NOB) population abundance and specific activity increased significantly with a shift of dominant genus from Nitrobacter to Nitrospira. The ratio of AOB and NOB specific activities were reduced from 12.8 to 1.6, and the ex situ nitrite accumulation ratio reduced from 76% to 29%. Changes in the microbial community and overall process performance illustrated that, compared to the excellent NOB suppression under high DO conditions, NOB were more active after the DO concentration reduction despite still being partly suppressed. This case study demonstrated, for the first time, the influence of DO reduction on the nitrogen conversion microbial community and PN/A process performance for a suspended growth system. Its relevance to biofilm and hybrid PN/A processes is also discussed.

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

Biological nutrient removal (BNR) activated sludge (AS) systems produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When this sludge is thickened to 3–6% total suspended solids (TSS) and digested (aerobic or anaerobic), a high proportion of N and P are released to the bulk liquid resulting in high concentrations of ammonia/nitrate and orthophosphate up to several hundred mg/ℓ (without denitrification or P precipitation). This research investigates P removal by P precipitation in anoxic-aerobic digestion of P-rich BNR system WAS. The experimental setup for this work was a lab-scale membrane UCT BNR system fed real settled sewage with added acetate, orthophosphate, and cations Mg and K to increase biological excess P removal. This WAS was fed to batch aerobic digesters at various TSS concentrations, and to two 20-day retention time continuous anoxic-aerobic digesters (AnAerDig) with aeration cycles of 3-h air on and 3-h air off, one fed concentrated WAS (20 g TSS/ℓ ) and the other fed diluted WAS (3 g TSS/ℓ). Nitrogen removal has been discussed in the previous paper. This paper focuses on the P removal by P precipitation observed in the batch tests and continuous systems. The rate of polyphosphate release (bGP) during batch aerobic digestion at low TSS without P precipitation was found to be 2.5 times faster than the endogenous respiration rate (bG) of phosphorus accumulating organics (PAO), i.e. bGP = 0.1/d. This rate was then applied to the high-TSS aerobic batch tests and continuous anoxic-aerobic digesters to estimate the P precipitation at various TSS concentrations, with and without additional Mg or Ca dosing. Newberyite (MgHPO4·3H2O) and amorphous tricalcium phosphate (ACP or TCP, Ca3(PO4)2·xH2O) are found to be the most common phosphate precipitates.Keywords: biological excess phosphorus removal, waste activated sludge, anoxic-aerobic digestion, phosphaterelease, mineral precipitation

Precipitation of iron-hydroxy-phosphate of added ferric iron from domestic wastewater by an alternating aerobic–anoxic process

Abstract Removal of phosphorus from a municipal wastewater by simultaneous precipitation of iron-hydroxy-phosphate (IHP) was investigated. The addition of Fe 3+ was performed to supplement biological excess phosphorus removal by a completely mixed alternating aerobic–anoxic (AAA) activated sludge process. The cycles of 3-h anoxic time and 3-h aerobic digestion were set to controlling a single-sludge nitrification–denitrification. In this study, attempt has been made to analyse the effects of initial dissolved Fe/P molar ratio and pH on IHP precipitation. The AAA treatment process to remove soluble reactive and total phosphorus from domestic wastewater had a moderate efficiency. The empirical formula of IHP that differs from different pH ranges was verified. Two types of Fe 4 (OH) 9 PO 4 and Fe 5 (OH) 6 (PO 4 ) 3 precipitate may occur in different conditions of the AAA process. The efficiency of phosphorus removal from domestic wastewater by an AAA process was verified to contribute to a working methodology for the application of technologies in the field of domestic wastewater treatment.

The effects of modification for contact stabilization activated sludge on EBPR

Excessive phosphorus can cause eutrophication in water bodies and needs to be reduced in most wastewaters before being discharged into receiving waters. The excess biological phosphorus removal (EBPR) process has been shown to be an economical and environmentally compatible method for reducing phosphorus from wastewaters. Despite the complexity of EBPR mechanisms, appropriately designed and operated treatment plants can easily achieve phosphorus (P) removal as long as EBPR-available organic substrates such as short chain volatile fatty acids (VFAs) and an aerobic–anaerobic (respectively) reactor configuration are provided. Some factors and operating conditions, adversely affect the performance of EBPR plants.Available design and research information for the EBPR process were directly related to organic strength, solids and phosphorus content in wastewater. The success of excess biological phosphorus removal (EBPR) process is largely dependent on the characteristics of organic carbon present in wastewater. The COD and BOD5 content of wastewater will also determine whether a phosphorus removal EBPR system is required. For this paper, the performance of EBPR was investigated using modified contact stabilization activated sludge pilot plant. The study involved the construction of pilot plant which was setup in Quhafa WasteWater Treatment Plant (WWTP), Al Fayoum, Egypt. Results showed average removal efficiencies of COD, BOD5 and TP are 91%, 92% and 85% respectively.

Nutrient removal, microbial community and sludge settlement in anaerobic/aerobic sequencing batch reactors without enhanced biological phosphorus removal

Nutrient removal, microbial community and sludge settlement were examined in two 3-litre laboratory-scale anaerobic/aerobic sequencing batch reactors (SBRs). One SBR was operated at 10 degrees C and the other SBR at 20 degrees C. Different from conventional enhanced biological phosphorus removal, most of the soluble sodium acetate was removed in the aerobic phase and no organic carbon uptake or biological phosphorus release occurred in the anaerobic phase. In this type of anaerobic/aerobic SBR, the phosphorus removal and sludge settlement seemed to be unstable, and the dominant microorganism was Zoogloea sp. Although no excess biological phosphorus removal occurred, extracellular phosphorus precipitation contributed a significant proportion to total phosphorus removed. Sludge volume index decreased with increasing phosphorus contents in the biomass under all conditions. The functions of extracellular polymeric substances in sludge settlement and phosphorus removal depended on the environmental conditions applied.

A general kinetic model for biological nutrient removal activated sludge systems: Model evaluation

Hu et al. (2007) presented a general kinetic model for biological nutrient removal (BNR) activated sludge (AS) systems in general, but for external nitrification (EN) BNRAS (ENBNRAS) systems in particular. In this article, this model is evaluated against a large number of experimental data sets. In this evaluation, the model is first used to simulate a wide variety of conventional internal nitrification (IN) BNRAS systems to evaluate its predictions and also evaluate the model parameters suggested by Hu et al. (2007), and to calibrate those constants for which values are not available in the literature. Simulation results indicate that the model, with appropriately calibrated parameters, is capable of predicting COD removal, nitrification and denitrification and two types of biological excess phosphorus removal (BEPR), namely aerobic and anoxic/aerobic P uptake BEPR. The model is then used to simulate the ENBNRAS systems to evaluate its capacity of simulating the behaviour of this system. Simulation results show that the model is capable of simulating the behaviour of the ENBNRAS systems, including COD, nitrification, denitrification and BEPR, particularly anoxic P uptake BEPR, with the values of kinetic and stoichiometric parameters obtained in modelling conventional BNRAS systems, except for micro(NIT), K(MP), eta(PAO) and eta(H) which required calibration.

Agricultural use of municipal wastewater sludges: phosphorus availability of biological excess phosphorus removal sludges

Reuse of sewage sludges as phosphorus fertiliser requires the estimation of the plant availabilities of phosphorus (P) from different sludges. This study investigates the effect of lime stabilisation on the phosphorus availability from biological phosphorus removal sludges. In the first part of the study, pot experiments were carried out to assess the fertilising effect of a dewatered biological phosphorus removal sludge. Availability of P was determined in terms of plant-uptake. In the second part of the study, incubation tests were carried out to observe the change in the available P with time when the waste activated sludge (WAS) from an enhanced biological phosphorus removal (EBPR) process is mixed with the same soil. In this part, the plant available P was measured in terms of Olsen extractable P. A P-deficient, alkaline soil was used in the experiments and Lollium Perenne was selected as the testing plant. The results of the pot experiments revealed that lime-stabilisation of the sludge considerably decreased or retarded the availability of P in the sludge. In the incubation tests, the availability of phosphorus in the lime stabilised and nonstabilised sludge amended soil samples was close to each other. In general, P-availability was increased due to the sludge application except for the lime-stabilised dewatered sludge.

Comparison of aerobic and anoxic phosphorus uptake in ndbepr systems (uct and enbnras)

Two Nitrification-Denitrification Biological Excess Phosphorus Removal (NDBEPR) systems have been operated for 8.5 months in order to compare their Biological Excess Phosphorus Removal (BEPR) performance. One of these systems, i.e. the University of Cape Town (UCT) system, exhibits mainly aerobic P uptake while the External Nitrification Biological Nutrient Removal Activated Sludge (ENBNRAS) system is characterised by high anoxic P uptake. It was observed that when operating with predominantly aerobic P uptake, the UCT system released more P than the ENBNRAS system, even though it had a lower anaerobic mass fraction. However, when the influent TKN/COD was high, i.e. > 0.1, anoxic P uptake also occurred in the UCT system and P release dropped to lower levels than in the ENBNRAS. Accordingly, P uptake of the UCT system was 5 mg P/l influent higher than that of the ENBNRAS system, when it was predominantly aerobic, but 9 mg P/l influent lower when anoxic P uptake occurred. As a result, the UCT system achieved superior P removal when aerobic P uptake was predominant (23% higher), but when high influent TKN/COD promoted anoxic P uptake the P removal of the UCT system was poorer than that of the ENBNRAS system. This study clearly showed that anoxic P uptake is not beneficial to NDBEPR systems.

Combined denitrification and excess biological phosphorus removal in discontinuous operated biofilm systems

The sorption-denitrification-P-removal (S-DN-P) process combines biological excess P-removal (BEPR) and denitrification using immobilized biomass. The accumulation of denitrifying polyP organisms is achieved by sequencing anaerobic/anoxic conditions. The immobilized biomass is in alternating contact with primary treated wastewater (anaerobic sorption-phase) and nitrified wastewater (denitrification phase). In the sorption phase, P-release takes place and readily biodegradable organic substrate, e.g. volatile fatty acid, is taken up and stored by polyP accumulating organisms (PAO). In addition to this, other organic matter is physically/chemically adsorbed in the biofilm structures. In the denitrification phase, the biomass denitrifies the stored and adsorbed organic substrate and, at the same time, P-uptake and polyP formation occurs. This paper presents results of investigations at laboratory and half-technical scale. At laboratory scale different types of carriers were tested regarding their suitability for the S-DN-P-process. In half-technical scale a biofilter and a moving bed reactor (MBR) were tested. In the biofilter a stable removal of nitrate and phosphate was achieved. However, it was not possible to achieve similar results in the MBR process. Especially the release and uptake of phosphate showed no clear tendency although the uptake of acetate was good. Reasons for this could be the accumulation of glycogen accumulating organisms which impair the metabolism of PAO.

Selection of Denitrifying Phosphorus Accumulating Organisms in Activated Sludge

Although anoxic phosphorus uptake has been demonstrated, the conditions that stimulate or inhibit the anoxic uptake are not fully understood. In this study, the possibility of achieving biological excess phosphorus removal in sequencing batch reactors using nitrate as an electron acceptor without including an aerobic phase has been confirmed. The use of an anaerobic/anoxic/aerobic sequencing batch reactor allows anoxic phosphorus uptake to be achieved, in spite of the low fraction of denitrifying phosphorus accumulating organisms present in the inoculum. Biomass characterisation was carried out to determine the denitrifying fraction of the phosphorus accumulating organisms in sequencing batch reactors operating at different operational conditions. With anaerobic/anoxic/aerobic cycle, it was demonstrated that the disadvantage of denitrifying phosphorus accumulating organisms due to the lower substrate utilisation efficiency in anoxic conditions relative to aerobic conditions, is not so effective to cause the “strictly aerobic” phosphorus accumulating organisms to dominate in the system.

Selection of Denitrifying Phosphorus Accumulating Organisms in Activated Sludge

Although anoxic phosphorus uptake has been demonstrated, the conditions that stimulate or inhibit the anoxic uptake are not fully understood. In this study, the possibility of achieving biological excess phosphorus removal in sequencing batch reactors using nitrate as an electron acceptor without including an aerobic phase has been confirmed. The use of an anaerobic/anoxic/aerobic sequencing batch reactor allows anoxic phosphorus uptake to be achieved, in spite of the low fraction of denitrifying phosphorus accumulating organisms present in the inoculum. Biomass characterisation was carried out to determine the denitrifying fraction of the phosphorus accumulating organisms in sequencing batch reactors operating at different operational conditions. With an anaerobic/anoxic/aerobic cycle, it was demonstrated that the disadvantage of denitrifying phosphorus accumulating organisms due to the lower substrate utilisation efficiency in anoxic conditions relative to aerobic conditions, is not so effective to cause the "strictly aerobic" phosphorus accumulating organisms to dominate in the system.

Evaluation of the Potential Effects of Equalization on the Performance of Biological Phosphorus Removal Systems

Experimental data confirming that the phosphorus removal efficiency in biological excess phosphorus removal (BEPR) systems temporarily decreases when the amount of volatile fatty acids (VFAs) added in the anaerobic phase is suddenly increased are presented. This decrease in efficiency results from the fact that acetate uptake is a rapid process and that the phosphate concentration at the end of the anaerobic phase increases rapidly. Because of the nonlinear dependence of the phosphate uptake rate on the poly-beta-hydroxyalkanoate (PHA) content of phosphate-accumulating organisms (PAOs), the increase in PAO PHA content associated with VFA uptake is not able to cause a proportional increase in the rate of phosphate uptake. This causes a temporary imbalance between phosphate release and uptake, leading to lower phosphate removal efficiency. The VFA loading to full-scale BEPR systems is not constant throughout the day, and temporary imbalances such as the ones imposed in the batch tests can occur in full-scale systems. The effect of diurnal variations in loading was demonstrated through simulation of the behavior of an A/OTM system receiving a time-variable influent. Equalization is proposed as a method to diminish the potential for imbalances between phosphate release and uptake by avoiding sudden increases of VFA loading to the plant. Significant improvements in the effluent quality from the simulated system were achieved using equalization. The improvements were greater when the influent contained VFAs than when the VFAs were formed by fermentation in the anaerobic zone. The simulations suggested that it may be possible to decrease the amount of phosphorus discharged by a factor as high as 4 through use of concentration equalization. When both flow and concentration equalization were used, the total amount of phosphorus discharged was decreased by a factor of 8. Equalization can be used, in concert with other strategies for preservation of the PHA content of PAOs under periods of low loadings, to minimize the magnitude of Monday phosphate peaks.

Expert control of DO in the aerobic reactor of an activated sludge process

An expert control structure is proposed for the control of dissolved oxygen (DO) in a Nitrification Denitrification Biological Excess Phosphorus Removal (NDBEPR) plant to account for the several processes that are influenced by the DO concentration in the aerator. In the scheme a supervisory fuzzy controller determines the set point of an inner DO control loop where an Adaptive Robust Generic Model Control (ARGMC) controller is used. The fuzzy supervisory control has a hierarchical structure. Off-line measurements of biological parameters of influent and effluent streams can be used to periodically update the set points of the fuzzy controllers. The complete control scheme has been designed for an actual plant and tested by a simulation programme based on the n. 2 IAWQ model for the biological reactors and on separate models of the clarification and thickening phases for the settler. Simulation and experimental results show that good operation conditions can be obtained.

Effects of pH on the rates of aerobic metabolism of phosphate-accumulating and glycogen-accumulating organisms.

The effect of pH on the aerobic metabolism of phosphorus-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) was studied using aerobic batch experiments performed at pH 6.5, 7.0, and 7.5. For PAOs, the rates of phosphate uptake, polyhydroxy-alkanoates consumption, and biomass growth observed at pH 6.5 were 42, 70, and 53%, respectively, of the rates observed at pH 7.0. In contrast, the rates for GAOs were relatively independent of pH for the range tested. The results suggest that the stability of biological excess phosphorus removal (BEPR) is strongly dependent on the pH in the aerobic zone. If the pH is low, growth of PAOs will be inhibited whereas the growth of GAOs will be only mildly affected. This may lead to the proliferation of GAOs in BEPR systems, resulting in reduced phosphorus removal.

PH as a key factor in the competition between glycogen-accumulating organisms and phosphorus-accumulating organisms.

The effects of pH on the anaerobic metabolism of glycogen-accumulating organisms (GAOs) and phosphorus-accumulating organisms (PAOs) were compared using models for the kinetics of acetate uptake. The comparison revealed that GAOs take up acetate faster than PAOs when the pH of the anaerobic zone is less than 7.25, but that PAOs remove acetate faster than GAOs at pHs greater than 7.5. It was also found that the growth efficiencies of the two organisms are similar. Furthermore, the amount of polyhydroxy-alkanoates available after replenishment of the polymers used during acetate uptake under anaerobic conditions is similar for the two organisms, making GAOs highly competitive in nutrient removal systems. The effects of pH on the competition between the two organisms were demonstrated during the operation of a laboratory-scale sequencing batch reactor. When the overall pH of the system was low, poor phosphate removal was observed. When the pH of the system was allowed to increase to a maximum of 7.5, phosphate removal improved, but was still incomplete. Total removal was only achieved when the pH of the system was never allowed to drop lower than 7.25. After the minimum pH in the system was increased, total removal of phosphate was achieved in 14 days. The results showed that pH control is a promising strategy for minimizing the accumulation of GAOs and increasing the reliability of biological excess phosphorus removal systems.

Contribution of Pseudomonas spp. to phosphorus uptake in the anoxic zone of an anaerobic-anoxic-aerobic continuous activated sludge system

A continuously operated laboratory-scale (32 L) nitrification denitrification biological excess phosphorus removal (NDBEPR) activated sludge system (modeled on the 3-stage Phoredox configuration) was maintained for 140 d. The transition from a non-biological excess phosphorus removal (BEPR) sludge to one exhibiting a strong BEPR mechanism was monitored. Mixed liquor seed inoculum was obtained from a full-scale single aerobic activated sludge installation and subjected to conditions conducive to BEPR, i.e. increasing influent acetate (HAc) concentrations. At a sludge age of 10 d with 100% HAc feed, the system was capable of removing a maximum of ca. 40 mgPO4-P/L from the bulk liquid; P/VSS of ca. 0.27 (mgP/mgVSS); and VSS/TSS of 0.53 (mgVSS/mgTSS) in the aerobic zone was attained. Although typical BEPR phosphorus transformation patterns were routinely observed, i.e. anaerobic phosphate release and aerobic phosphate uptake, phosphate uptake in the anoxic zone was also recorded indicating the presence of denitrifying phosphorus accumulating organisms (DPAOs) in the sludge community. The microbial community was screened (using both isolation and direct methods of analysis) for the presence of Pseudomonas spp. as this genus is known to perform both polyphosphate accumulation and denitrification processes. Isolation of anoxic mixed liquor bacteria on solid media and identification using the APl 20NE system resulted in the total dominance of the Pseudomonads (> 50%). However, direct fluorescent in situ hybridizations (FISH) revealed that Pseudomonas spp. only constituted ca. 3% of the total bacterial community indicating that other bacterial genera are contributing to simultaneous polyphosphate accumulation and denitrification processes in the anoxic zones of NDBEPR systems.

Evolution of the Southpest Wastewater Treatment Plant

The treated effluent of the Southpest Wastewater Treatment Plant is discharged into a small, low-flow branch of the Danube susceptible to eutrophication. The first, high-load activated sludge system with a hydraulic retention time of 2.5 hrs in the aerated basins, was installed here in 1966. The paper presents the evolution of the technology by illustrating the effects of the different changes carried out since 1991. Reconfiguration of the existing activated sludge basins connected originally in parallel into an arrangement of tanks in series increased the settleability of the sludge as well as the efficiency of COD removal significantly. Introduction of an anaerobic zone preceding the aerated basins facilitated biological excess phosphorus removal with a consequent release in the thickener and digester. Introducing lime addition into the recycled sludge processing wastes significantly improved the performance of the system. However, since there had been no provision built for eliminating the nitrate content of the recycled sludge, efficiency of phosphorus removal proved to be dependent on the eventually occurring nitrification. In order to achieve both an effective nitrogen and phosphorus removal the current technology established in 1999 applies a nitrification and a denitrification filter following the activated sludge unit and uses precipitation for phosphorus removal.

PETRO concept: fortunate process similarities for both biological excess phosphorus (BEPR) and micro-algae removal in pond-based BNR system

PETRO concept: fortunate process similarities for both biological excess phosphorus (BEPR) and micro-algae removal in pond-based BNR system

Evaluation of the Capacity of Phosphorus‐Accumulating Organisms To Use Nitrate and Oxygen as Final Electron Acceptors: A Theoretical Study on Population Dynamics

Ability of phosphorus‐accumulating organisms (PAGs) capable of using both nitrate and oxygen as temlinal electron acceptors to compete successfully in biological excess phosphorus removal (BEPR) systems was assessed relative to purely aerobic PAGs. The anoxic‐aerobic population has a significant competitive disadvantage when competing with PAGs that can only use oxygen because of a lower thermodynamic efficiency of anoxic growth compared to aerobic growth. This causes less efficient use of stored poly‐β‐hydroxy‐butyrate under anoxic conditions, leading to the washout of the anoxic‐aerobic population from the system. This analysis provides a potential explanation of why growth of denitrifying PAGs (DPAGs) has not been observed in some BEPR systems. This work also suggests that introduction of even a small aerobic zones in a BEPR system will strongly affect accumulation of DPAGs. In addition, a hypothetical model to describe acetate uptake under anoxic conditions was developed, and simulations performed with it produced results that agree with experimental observations published in the literature.

Denitrification kinetics in biological N and P removal activated sludge systems treating municipal wastewaters

The denitrification kinetics at 12, 20 and 30°C in nitrification denitrification biological excess phosphorus removal (NDBEPR) systems were delineated in batch tests on sludge harvested from laboratory scale M/UCT systems. In some investigations, it was found that the P release and uptake were confined exclusively (>95%) to the anaerobic and aerobic reactors respectively and the observed P removal conformed to the BEPR model of Wentzel et al. In these investigations, due to an absence of anoxic P uptake (substantiated by PHB measurements), it could be inferred that the phosphate accumulating organisms (PAOs) did not significantly contribute to the denitrification. The ordinary heterotrophic organism (OHO) and PAO groups were separated with the aid of the BEPR model of Wentzel et al. Ascribing the denitrification to the OHO group performing this process, the specific rates of denitrification associated with the utilization of slowly biodegradable COD (SBCOD) in the primary (K′2) and secondary (K′3) anoxic reactors were calculated and compared with the rates in ND systems (K2 and K3). In other investigations it was found that P release and uptake were not confined exclusively to the anaerobic and aerobic reactors respectively and the observed P removal was only about 60% of that expected from the BEPR model of Wentzel et al. In these investigations significant P uptake under anoxic conditions was observed so the PAOs may have been involved with the denitrification. However, the denitrification rates were calculated as before by attributing it exclusively to the OHOs. Widely varying K'2 rates were observed at 20°C, ranging from 0.071 to 0.335 mgNO3-N/(mgAHVSS.d). The variation in K' rate is mainly due to widely varying OHO active fraction estimates for NDBEPR systems.