The significance of denitrifying polyphosphate accumulating organisms in biological nutrient removal activated sludge systems

2002 ◽  
Vol 46 (1-2) ◽  
pp. 129-138 ◽  
Author(s):  
Z.-R. Hu ◽  
M.C. Wentzel ◽  
G.A. Ekama
Keyword(s):  
Experimental Data ◽  
Activated Sludge ◽  
Nutrient Removal ◽  
P Uptake ◽  
Biological Nutrient Removal ◽  
Advantages And Disadvantages ◽  
Polyphosphate Accumulating Organisms ◽  
Very High ◽  
Total P ◽  
Activated Sludge Systems

In this paper the advantages and disadvantages of denitrifying PAOs (polyphosphat accumulating organisms) in conventional BNRAS (biological nutrient removal activated sludge) and external nitrification BNRAS (ENBNRAS) systems are evaluated, with experimental data exhibiting a range of anoxic P uptake from low (<10%) to very high (>60%). The results indicate that the specific denitrification rate of the PAOs on internally stored PHB COD is about 1/5th of that of the “ordinary” heterotrophic organisms on SBCOD, and the PAOs contribute little (maximum 20%) to the denitrification in BNRAS systems even when the anoxic P uptake is high (60% of the total P uptake). Considering the unpredictable nature of anoxic P uptake and the reduction in BEPR it causes compared with aerobic P uptake BEPR, it is concluded that anoxic P uptake does not add a significant advantage to the BNR system.

Difficulties and developments in biological nutrient removal technology and modelling

1999 ◽  
Vol 39 (6) ◽  
pp. 1-11 ◽  
Author(s):  
George A. Ekama ◽  
Mark C. Wentzel
Keyword(s):  
Activated Sludge ◽  
Nutrient Removal ◽  
P Uptake ◽  
Biological Nutrient Removal ◽  
Filamentous Bulking ◽  
Recent Developments ◽  
Removal Technology ◽  
Hydrolysis Of ◽  
Activated Sludge Systems ◽  
P Removal

Filamentous bulking and the long sludge age required for nitrification are two important factors that limit the wastewater treatment capacity of biological nutrient removal (BNR) activated sludge systems. A growing body of observations from full-scale plants indicate support for the hypothesis that a significant stimulus for filamentous bulking in BNR systems in alternating anoxic-aerobic conditions with the presence of oxidized nitrogen at the transition from anoxic to aerobic. In the DEPHANOX system, nitrification takes place externally allowing sludge age and filamentous bulking to be reduced and increases treatment capacity. Anoxic P uptake is exploited in this system but it appears that this form of biological excess P removal (BEPR) is significantly reduced compared with aerobic P uptake in conventional BNR systems. Developments in the understanding of the BEPR processes of (i) phosphate accumulating organism (PAO) denitrification and anoxic P uptake, (ii) fermentation of influent readily biodegradable (RB)COD and (iii) anaerobic hydrolysis of slowly biodegradable (SB)COD are evaluated in relation to the IAWQ Activated Sludge Model (ASM) No.2. Recent developments in BEPR research do not yet allow a significant improvement to be made to ASM No. 2 that will increase its predictive power and reliability and therefore it remains essentially as a framework to guide further research.

External nitrification in biological nutrient removal activated sludge systems

2001 ◽  
Vol 43 (1) ◽  
pp. 251-260 ◽  
Author(s):  
Z.-R. Hu ◽  
M. C. Wentzel ◽  
G. A. Ekama
Keyword(s):  
Activated Sludge ◽  
Nutrient Removal ◽  
Mass Fraction ◽  
Large Scale ◽  
Oxygen Demand ◽  
P Uptake ◽  
Biological Nutrient Removal ◽  
Fixed Media ◽  
Media System ◽  
Polyphosphate Accumulating Organisms

A biological nutrient removal (BNR) activated sludge (AS) scheme incorporating external nitrification in a fixed media system is evaluated. A laboratory scale investigation of the scheme indicates that it holds considerable potential for BNRAS system intensification through major reduction in sludge age and oxygen demand and significant improvement in sludge settleability. Because the BNRAS system is not required to nitrify, its anoxic mass fraction can be considerably enlarged at the expense of the aerobic mass fraction creating conditions that (i) allow it to achieve high N removals with domestic wastewaters with high TKN/COD ratios and (ii) promote anoxic P uptake polyphosphate accumulating organisms (PAO) to develop in the system. From this, and earlier investigations with conventional BNR systems, it appears that anoxic P uptake biological excess P removal (BEPR) is only about two thirds of aerobic P uptake BEPR. Inclusion of anoxic P uptake PAOs in, and exclusion of nitrifiers from, the BNRAS system are not essential for the scheme. However, conditions that promote aerobic P uptake to maximize BEPR, are also conducive to nitrifier growth, which, if supported in the BNRAS system, would require virtual complete nitrification in the fixed media system to avoid nitrate interference with BEPR. Before the scheme can be implemented at large scale, an engineering and economic evaluation is required to quantify its potential benefits and savings.

A comparison of biological nutrient removal in intermittent cyclic and continuous activated sludge systems

1994 ◽  
Vol 11 (1-4) ◽  
pp. 149-159 ◽  
Author(s):  
Kin-man Ho ◽  
Paul F. Greenfield ◽  
Linda L. Blackall ◽  
Peter R.F. Bell ◽  
Andre Krol
Keyword(s):  
Activated Sludge ◽  
Nutrient Removal ◽  
Biological Nutrient Removal ◽  
Activated Sludge Systems

Sludge production and oxygen demand in nutrient removal activated sludge systems

1996 ◽  
Vol 34 (5-6) ◽  
pp. 43-50 ◽  
Author(s):  
P. S. Barker ◽  
P. L. Dold
Keyword(s):  
Oxygen Consumption ◽  
Activated Sludge ◽  
Nutrient Removal ◽  
Suspended Solids ◽  
Model Simulation ◽  
Oxygen Demand ◽  
Biological Nutrient Removal ◽  
Solids Concentration ◽  
Volatile Solids ◽  
Activated Sludge Systems

Results of model simulations indicate that without the assumption of COD loss, predictions of oxygen consumption and volatile suspended solids production are significantly over-estimated for biological excess phosphorus removal (BEPR) activated sludge systems (and to a lesser extent anoxic-aerobic systems). These systems apparently consume less oxygen and produce less volatile solids than aerobic systems for the same amount of COD removal. A general model for biological nutrient removal systems has recently been presented by Barker and Dold. Three mechanisms for COD loss are suggested, based on results of COD balances for different types of activated sludge system. Model simulation results with and without the assumption of COD loss are discussed, as well as the influence of influent COD composition on predictions of volatile suspended solids concentration/production and oxygen consumption.

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