Sludge-sludge interaction in the enhanced biological phosphorus removal process.

Metabolisms related to enhanced biological phosphorus removal (EBPR) were found to be affected when two activated sludges with different EBPR activities were mixed together. In the present study, two laboratory scale EBPR processes were operated in parallel, one of them with higher and another with lower EBPR activities. The activated sludges from the two reactors were mixed together at different mixing ratios. The supernatant was made the same for all mixing ratios, anaerobic-aerobic batch experiments were performed, and acetate uptake rate and phosphate release rate under anaerobic conditions and phosphate uptake rate under aerobic condition were determined. The metabolic rates measured were expected to be linear to the mixing ratios, as the supernatant was the same for all mixing ratios, whereas the metabolic rates were either promoted or inhibited by mixing of sludges. As an indicator for the sludge mixing effect on the metabolic rates, mixing effect intensity (MEI) was introduced. Chemical substances that are produced by microorganisms in activated sludge are proposed to be one of the possible causes of the sludge mixing effect.     

Low temperature effects on phosphorus release and uptake by microorganisms in ebpr plants

A continuous flow pilot plant with a mixed population of activated sludge was used to investigate the influence of temperatures between 5°C and 20°C on the efficiency of enhanced biological phosphorus removal (EBPR) and on the phosphorus release and uptake mechanisms. Bacterial strains, isolated at different temperatures, were tested for their ability to store polyphosphate. At temperatures of between 15°C and 20°C the uptake of phosphate in the aerobic reactor was correlated directly with the quantity of phosphate released in the anaerobic zone. Mainly aerobic microorganisms were isolated. In batch tests they showed comparatively high polyphosphate storing capacities. There was no indication that Acinetobacter sp. played a dominant role in the processes of EBPR. A drop in temperature to 10°C and then to 5°C had no significant influence on the efficiency of EBPR. In spite of a clearly reduced release of phosphate in the anaerobic zone, the bacterial uptake of phosphate reached unchanged high levels. Because of reduced nitrification at low temperatures, making the anoxic zone into an additional anaerobic zone, facultative anaerobic microorganisms accumulated in the microbial population. They showed the best abilities to store polyphosphate under these conditions, whereas aerobic bacteria lost their polyphosphate storing capacities.     

Influence of ORP variation, carbon source and nitrate concentration on denitrifying phosphorus removal by DPB sludge from dephanox process.

The effect of added carbon source and nitrate concentration on the denitrifying phosphorus removal by denitrifying phosphorus removal bacteria sludge was systematically studied using batch experiments, at the same time the variation of ORP was investigated. Results showed that the denitrifying and phosphorus uptake rate in the anoxic phase increased with the high initial anaerobic carbon source addition. However, once the initial COD concentration reached a certain level, which was in excess of the PHB saturation of Poly-p bacteria, residual COD carried over to the anoxic phase inhibited the subsequent denitrifying phosphorus uptake. This was equal to supplementing the external carbon source to the anoxic phase, furthermore the higher the external carbon source concentration the more powerful the inhibition caused. High nitrate concentration in the anoxic phase increased the initial denitrifying phosphorus rate. Oncethe nitrate was exhausted, phosphate uptake changed to phosphate release. Moreover, the time of this turning point occurred later with the higher nitrate addition. On the other hand, through on-line monitoring the variation of the ORP with different initial COD concentration, it was found that ORP could be used as a control parameter for phosphorus release, but it is impossible to utilize ORP for controlling the dinitrification and anoxic phosphorus uptake operations.     

On-line titrimetric monitoring of anaerobic-anoxic EBPR processes.

Denitrifying phosphorus accumulating organisms (DPAO) are able to remove nitrogen and phosphorus simultaneously. The use of DPAO in EBPR systems results in a substantial saving on aeration cost and a lower sludge production when compared to anaerobic-aerobic EBPR systems. This process is usually studied in sequencing batch reactors (SBR) and monitored with off-line measurements. However, off-line monitoring implies low frequency data sampling and delay between sampling and obtainment of the results. For this reason, an online measurement such as titrimetry is strongly recommended to improve the daily management of the lab-scale SBR. This paper shows different applications of titrimetric measurements for on-line monitoring of DPAO lab-scale SBR cycles. The results demonstrate that titrimetry is a suitable tool for detecting the end of phosphorus release and carbon substrate depletion point in the anaerobic phase. Moreover, this paper proposes the indirect measurement of nitrate/nitrite uptake rate with titrimetric measurements, which allows the on-line estimation of its concentration during the anoxic phase. Therefore, titrimetry is an on-line measurement with a high potential to implement new control strategies in DPAO lab-scale SBR systems.     

Biochemistry of enhanced biological phosphorus removal and anaerobic COD stabilization.

Improved design strategies at BNR plants should include cost reductions so that the consumers and water authorities will be more willing to build EBPR plants instead of conventional activated sludge plants. Through efficient design, actual savings in construction and operation costs can be realized. For this reason, anaerobic stabilization of COD needs to be seriously considered during design for direct energy savings at the plants. The existence of anaerobic stabilization has been demonstrated through experimental work. Evaluation of operational data from existing plants has also indicated the definite presence of anaerobic stabilization at plants that include anaerobic zones for EBPR as part of their operation. By exploring the biochemical reactions taking place in EBPR process, particularly the involvement of the storage mechanisms for PHA, poly-P and glycogen storage, the potential mechanisms of the anaerobic stabilization of COD in EBPR systems was explored. The resultant balances pointed out the importance of glycogen metabolism in terms of conserving carbon and providing a sink for the reducing equivalents produced under aerobic conditions. This mechanism is different from those observed in anoxic-aerobic and conventional aerobic activated sludge systems, and appears to be at least partially responsible for the observed anaerobic stabilization of COD.     

Hydrolysis and fermentation of activated sludge to enhance biological phosphorus removal.

The conventional mainstream enhanced biological phosphorus removal (EBPR) process depends on the quality of the raw incoming wastewater. An alternative sidestream EBPR process is presented, where the substrates for storage by the polyphosphate accumulating organisms (PAOs) instead come from hydrolysis of the return activated sludge. This process is studied in full-scale at two treatment plants and quantified by means of phosphorus release rates and readily biodegradable COD (RBCOD) accumulation rates. It was seen that not only was a significant amount of RBCOD stored by PAOs but an approximately equal amount was accumulated in the sidestream hydrolysis tank and made available for the subsequent nitrogen removal process. The phosphorus release of the sludge with and without addition of different substrates was furthermore studied in laboratory scale. The study showed that the process is promising and in a number of cases will have significant advantages compared with the conventional mainstream 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.     

Improving the start-up of an EBPR system using OUR to control the aerobic phase length: a simulation study.

The enhanced biological phosphorus removal (EBPR) process is based on enriching the sludge with polyphosphate accumulating organisms (PAO) which are scarce in conventional non-EBPR wastewater treatment plant sludge. Hence, the start-up of EBPR systems (i.e. enriching the sludge with PAO) can be very slow and complex. A simulation study of a possible improvement of the start-up of an EBPR system in a sequencing batch reactor is presented in this work. The improvement is based on reducing the length of the aerobic phase so that it coincides with the depletion of orthophosphate from the medium. This improvement, though verified by simulation to be very successful, requires a good on-line orthophosphate sensor. To avoid this technical limitation, a link between oxygen uptake rate (OUR) measurements and orthophosphate presence is proposed. This link allows the control of the aerobic phase length with OUR as a measured variable and, consequently, a considerable improvement with respect to the conventional fixed aerobic phase length operation. An improvement of 95% in the ratio of PAO to heterotrophs and an increase of 30% in the final amount of PAO in sludge is achieved with this control strategy. The kinetic mod for simulations was a modification of the Activated Sludge Model 2d.     

Experimental and model-based evaluation of the role of denitrifying polyphosphate accumulating organisms at two large scale WWTPs in northern Poland.

The capabilities of denitrifying Polyphosphate Accumulating Organisms (DPAOs) in two large-scale plants in northern Poland performing enhanced biological phosphorus removal (EBPR) were evaluated in this study. A series of batch tests with the process biomass aimed at the measurements of phosphate release (with artificial substrate and real wastewater) and subsequent phosphate uptake under anoxic/aerobic conditions. The process kinetics were predicted using ASM2d implemented in the GPS-X ver. 4.0.2 simulation package. The results from one experimental series (summer) were used for the model calibration, whereas the results from another series (spring) were used for the model validation. The model parameters were also accurately confirmed by predictions of the accompanying field measurements in the full-scale bioreactors. The experimental and simulation results revealed that a relatively small fraction of PAO could denitrify (eta(NO3,PAO) = 0.32). The denitrification rates associated with the anoxic storage of PP and the anoxic growth of PAO only constituted 16.0-21.0% of the denitrification rates associated with the anoxic activity of "ordinary" heterotrophs.     

The large PAO cells in full-scale EBPR biomass samples are not yeast spores but possibly novel members of the beta-Proteobacteria.

Large, homogenous clusters of coccobacilli were found to be abundant in the biomasses from a conventional plant at Rosebud, Victoria, Australia. The identity and the in situ physiology of these dominant microorganisms were investigated in this study. These large clustered cells were revealed to be neither Gram positive nor Gram negative bacteria and contain polyP granules. Cells with similar features were also observed in some enhanced biological phosphate removal (EBPR) systems and reported as yeast spores and Rhodocyclus-related polyphosphate accumulating organisms (PAOs). In this study, fluorescent in situ hybridization (FISH) probing showed these cells were prokaryotic and members of the beta-Proteobacteria. However, these large clustered cells did not respond to the PAO mix FISH probes. The in situ physiology of these large cells was studied with FISH in combination with microautoradiography (MAR) in order to understand their substrate assimilation abilities under different conditions as well as their phosphate uptake ability. These cells were able to take up acetate, glutamate and aspartate, but not glucose under both aerobic and anaerobic conditions. Nile Blue A staining in combination with MAR showed that cells incubated under anaerobic conditions contained polyhydroxyalkanoates (PHA) granules. In addition, MAR showed aerobic 33Pi assimilation with all these substrates, consistent with them supporting an EBPR capacity in these large cells. As well as raising doubts about a role for yeasts in EBPR, this study suggests that much still needs to be learned about the identity and level of biodiversity of the PAO in EBPR systems, and emphasizes the benefits of using techniques like FISH/MAR and PHA staining/MAR to resolve the in situ physiology of the populations of interest there.     

Specific SBR population behaviour as revealed by comparative dynamic simulation analysis of three full-scale municipal SBR wastewater treatment plants.

Three full-scale municipal sequential batch reactor (SBR) wastewater treatment plants (WWTPs) were investigated by dynamic simulation studies using ASM1. All three WWTPs showed similar kinetic and stoichiometric conditions in the SBR population behaviour after calibration of the models. The simulation results detected only a discrepancy to the ammonia online data during and shortly after shock loading under anoxic and anaerobic conditions that so far could not be adjusted by the ASM1 model. However, these differences did not severely affect the quality of the simulations nor the effluent flows. Additionally, in all cases a dynamic alpha factor curve occurred during the aeration phases that was verified by further oxygen transfer measurements. This might reveal new aspects for the process control, design and simulation of SBR WWTPs. A short lag phase was detected in many cases at the beginning of the first aeration phase.     

Relationship between the electric conductivity and phosphorus concentration variations in an enhanced biological nutrient removal process.

Phosphorus release and uptake in a sequencing batch reactor were monitored by the simple online measurements of electric conductivity (EC) and oxidation-reduction potential (ORP), and the result was verified by the measurement of phosphate concentration changes. The influence of nitrate ion presence on the phosphorus removal was evaluated by a jar test operated in the cyclic anaerobic (anoxic)-aerobic condition. The relationships of EC, ORP and metal species with phosphorus concentrations were investigated. Under strict anaerobic conditions, EC showed positive correlation with phosphorus concentrations, but it became negligible under anoxic conditions with nitrate present. Strong inverse correlation was found between ORP values and phosphorus concentration. The increase and decrease of magnesium and potassium ions took place in accordance with phosphorus release and uptake, and the relationship between the metal species and phosphorus changes was clearer in the anaerobic condition than anoxic condition.     

Analysis of phosphorus removal and anaerobic selector performance in a full-scale activated sludge process in Singapore.

This paper analyses the performance of the anaerobic selector (A/O process) in a full-scale activated sludge process receiving mostly industrial sewage discharge (> 60%) in Singapore. In addition to the sludge settleability, enhanced biological phosphorus removal (EBPR) was studied. The sludge volume index (SVI) reduced from 200 to 80 ml g(-1) and foaming was suppressed significantly, indicating the effectiveness of the anaerobic selector in improving sludge settleability. The phosphorus removal efficiency was 66%, and 7.5 mg HAc-COD was consumed per mg PO4(3-) -P removed. In the anaerobic compartment, 31% of the SCOD and 73% of the acetic acid in the settled sewage were removed with PO4(3-) -P release of 14.1 mg PO4(3-)-P l(-1). The linear correlation between PO4(3-) -P release in the anaerobic compartment and PO4(3-) -P uptake in the aerobic compartment indicates that there is about 0.8 mg PO4(3-) -P release in the anaerobic compartment per mg PO34(3-) -P uptake in the aerobic compartment. The fates of volatile fatty acids (VFAs) and its short chain acids (SCAs) in the process were studied and discussed.     

Effect of chlorination bulking control on water quality and phosphate release/uptake in an anaerobic-oxic activated sludge system.

This study evaluates the effect of chlorination bulking control on water quality and phosphate release/uptake in an anaerobic-oxic activated sludge system. A series of batch experiments with different specific NaOCl mass dose were conducted to determine the sludge settling properties, supernatant water quality and phosphate metabolism behavior of filamentous bulking sludge. The harvested sludge was from a continuous-flow anaerobic-oxic (A/O) activated sludge pilot-plant, i.e., enhanced biological phosphorus removal (EBPR) system, operated with 15 days of sludge retention time. The filamentous bacteria in the A/O pilot plant were identified to be Thiothrix according to Eikelboom's classification techniques, which was in accordance with the high influent sulfate concentration of this study (50 mg/L sulfate). Increasing NaOCI concentration, as revealed by experimental results, obviously decreased the sludge settling properties (SVI values and zone settling velocities) and meanwhile significantly reduced supernatant water quality (COD, SS, TP) mainly due to higher suspended solids caused by floc disruption. Moreover, the nine-hour batch experiments indicated that high NaOCI dosage (40 mg/gMLSS) completely deteriorated phosphate metabolism of EBPR sludge. Such a high dosage of chlorination further confirmed overdosing through disappearance of intracellular PHB and death of protozoa by microscopic investigation. Still, phosphate release/uptake behavior of EBPR sludge properly functions at low NaOCl dosage (5 mg/g MLSS). Besides, phosphate metabolism worsens rapidly before the SVI value reaches its lowest level. These findings imply that determining NaOCI requirement with merely SVI values can readily result in chlorination overdosing. Proper NaOCI dosage requires a delicately balanced consideration between sludge settling improvement, water quality demand and phosphate metabolism. Batch test of phosphate release/uptake is apparently a prerequisite to conclude an appropriate NaOCl dosage for bulking control.     

Evaluation of the origin of nitrate influencing the Klju? groundwater source, Serbia

This paper describes the use of the dual isotope method involving δ(15)N and δ(18)O measurements of dissolved nitrates to assess the origin and fate of groundwater nitrate at the Klju? groundwater source, Serbia. A sampling campaign was conducted in September 2007 during flow conditions obtaining groundwater from observation wells and river water fed by a shallow aquifer hosted in alluvial (sandy-gravel) sediments. Nitrate isotope ratios ranged from +5.3 to +16.9‰ and δ(18)O(NO(3)) values varied from -2.3 to +5.0‰. Two major contamination sources were identified with isotopic compositions characteristic for nitrate derived from nitrification of soil organic nitrogen (+5.3 to +7.8‰ for δ(15)N) resulting in nitrate concentrations of 33.6 and 78.8 mg/L and nitrate derived from animal wastes or human sewage, e.g. via septic systems, yielding δ(15)N values of +9.9 to +11.9‰ and elevated nitrate concentrations of 31.2-245.8 mg/L. The occurrence of nitrification and denitrification was also revealed based on concentration and isotope data for dissolved nitrate.     

Development and optimisation of VFA driven DEAMOX process for treatment of strong nitrogenous anaerobic effluents.

The recently proposed DEAMOX (DEnitrifying AMmonium OXidation) process combines the anammox reaction with autotrophic denitrifying conditions using sulphide as an electron donor for the production of nitrite from nitrate within an anaerobic biofilm. This paper firstly presents a feasibility study of the DEAMOX process using synthetic (ammonia + nitrate) wastewater where sulphide is replaced by volatile fatty acids (VFA) as a more widespread electron donor for partial denitrification. Under the influent N-NH+4/N-NO3(-) and COD/N-NO3(-) ratios of 1 and 2.3, respectively, the typical efficiencies of ammonia removal were around 40% (no matter whether a VFA mixture or only acetate were used) for nitrogen loading rates (NLR) up to 1236 mg N/l/d. This parameter increased to 80% by increasing the influent COD/N-NO3(-) ratio to 3.48 and decreasing the influent N-NH4 +/N-NO3(-) ratio to 0.29. As a result, the total nitrogen removal increased to 95%. The proposed process was further tested with typical strong nitrogenous effluent such as reject water (total N, 530-566 mg N/l; total COD, 1530-1780 mg/l) after thermophilic sludge anaerobic digestion. For this, the raw wastewater was split and partially ( approximately 50%) fed to a nitrifying reactor (to generate nitrate) and the remaining part ( approximately 50%) was directed to the DEAMOX reactor where this stream was mixed with the nitrified effluent. Stable process performance up to NLR of 1,243 mg N/l/d in the DEAMOX reactor was achieved resulting in 40, 100, and 66% removal of ammonia, NOx(-), and total nitrogen, respectively.     

The distribution and movement of polyphosphate and associated cations in sludges from ndebpr plants in different configurations at pilot scale

A gradual change in the mode and location of intracellular storage of polyphosphate was observed during a long-term pilot-scale evaluation of operating efficiency of a number of EBPR process configurations used for model calibration. The location of intracellular polyphosphate, (defined by the extraction procedure), was seen to change from a long chain form to a lower molecular weight or short chain form under the influence of nitrate return to the anaerobic zone, which was related to a number of factors including influent character (TKN/COD, influent RBCOD) and process configuration, however during trials with high TKN/COD (⩾0.13) the storage of polyphosphate was observed to exist predominately in the short chain form. The behaviour of EBPR biomass in a sequencing batch reactor demonstrated mobilisation and storage of polyphosphate from only the low MW form.     

Effect of thermal alkaline pretreatment on the anaerobic digestion of wasted activated sludge

The effect of alkaline pretreatment of waste-activated sludge, using two models to study the sequential hydrolysis rates of suspended (Sanders' surface model) and dissolved (Goel's saturation model) solids, on the mesophilic and thermophilic anaerobic digestion rate is evaluated. The pretreatment, which reduces the size of the solids, increases the reaction rate by increasing the surface area and the specific surface hydrolysis constant (K(SBK)); at thermophilic conditions from 0.45 x 10(-3) kg m(-2) d(-1) for the fresh sludge to 0.74 x 10(-3) kg m(-2) d(-1) for the pretreated sludge and at mesophilic conditions these values are 0.28 x 10(-3) kg m(-2) d(-1) and 0.47 x 10(-3) kg m(-2) d(-1) confirming the usefulness of a pretreatment for solids reduction. But for soluble solids, the thermoalkaline pretreatment decreases the reaction rates by inducing a competitive inhibition on the thermophilic anaerobic digestion rate while in the mesophilic range, a non-competitive inhibition is observed. A mathematical simulation of the consecutive reactions, suspended solids to dissolved solids and to methane in staged anaerobic thermophilic-mesophilic digestion, shows that with 4% suspended solids concentration it is better not to use a thermoalkaline pretreatment because overall solids reduction and total methane production are not as good as without pretreatment.     

Fine-scale differences between Accumulibacter-like bacteria in enhanced biological phosphorus removal activated sludge.

A lab-scale sequencing batch reactor (SBR) and six full-scale wastewater treatment plants (WWTPs) performing enhanced biological phosphorus removal (EBPR) were surveyed. The abundance of Accumulibacter-related organisms in the full-scale plants was investigated using fluorescent in situ hybridization. Accumulibacter-related organisms were present in all of the full-scale EBPR plants, at levels ranging from 9% to 24% of total cells. The high percentage of Accumulibacter-related organisms seemed to be associated with configurations which minimize the nitrate recycling to the anaerobic zone and low influent BOD:TP ratios. PCR-based clone libraries were constructed from the community 16S rRNA gene plus the internally transcribed spacer region amplified from the SBR and five of the full-scale WWTPs. Comparative sequence analysis was carried out using Accumulibacter-related clones, providing higher phylogenetic resolution and revealing finer-scale clustering of the sequences retrieved from the SBR and full-scale EBPR     

城市污水脱氮除磷SBR在线控制系统研究

SBR采用进水—厌氧—好氧—缺氧—好氧—沉淀—出水的运行方式处理城市污水。反应器装备有DO、ORP和pH等在线检测传感器。DO、ORP和pH变化的一些特征点可以用来判断和控制SBR中污水脱氮除磷过程的各个步骤。这包括:厌氧时,ORP和pH的转折点对应磷的释放;一次好氧时,DO、ORP的氨肘和pH的氨谷对应硝化结束;缺氧时,ORP的硝酸盐膝和pH的硝酸盐峰对应反硝化结束;二次好氧时,DO、ORP碳肘对应剩余碳的氧化结束,pH的转折点对应聚磷结束。控制系统能进行全自动运行来完成污水的脱氮除磷。