Impact of membrane solid-liquid separation on design of biological nutrient removal activated sludge systems

2005 ◽  
Vol 89 (6) ◽  
pp. 630-646 ◽  
Author(s):  
M. Ramphao ◽  
M. C. Wentzel ◽  
R. Merritt ◽  
G. A. Ekama ◽  
T. Young ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Nutrient Removal ◽  
Biological Nutrient Removal ◽  
Liquid Separation ◽  
Solid Liquid ◽  
Solid Liquid Separation ◽  
Activated Sludge Systems

scholarly journals Design and performance of BNR activated sludge systems with flat sheet membranes for solid-liquid separation

2007 ◽  
Vol 56 (6) ◽  
pp. 105-113 ◽  
Author(s):  
G.J.G. du Toit ◽  
M.C. Ramphao ◽  
V. Parco ◽  
M.C. Wentzel ◽  
G.A. Ekama
Keyword(s):  
Activated Sludge ◽  
P Uptake ◽  
Biological Nutrient Removal ◽  
Design Parameters ◽  
System Response ◽  
Conventional System ◽  
Liquid Separation ◽  
Solid Liquid ◽  
Solid Liquid Separation ◽  
Activated Sludge Systems

The use of immersed membranes for solid-liquid separation in biological nutrient removal activated sludge (BNRAS) systems was investigated at lab scale. Two laboratory-scale BNR activated sludge systems were run in parallel, one a MBR system and the other a conventional system with secondary settling tanks. Both systems were in 3 reactor anaerobic, anoxic, aerobic UCT configurations. The systems were set up to have, as far as possible, identical design parameters such as reactor mass fractions, recycles and sludge age. Differences were the influent flow and total reactor volumes, and the higher reactor concentrations in the MBR system. The performances of the two systems were extensively monitored and compared to identify and quantify the influence of the membranes on system response. The MBR UCT system exhibited COD, FSA, TKN, TP and TSS removals that were consistently equivalent or superior to the conventional system. Better P removal in the MBR was attributed to lower observed P uptake in the anoxic zone. High nitrate loads to the anoxic reactor appeared to be the determining factor in stimulating P uptake. The MBR UCT system had a greater sludge production than the conventional system. This was partly attributable to the retention of all solids in the MBR reactor. For steady state design this increase is accommodated by increasing the influent unbiodegradable particulate COD fraction. Additionally an attempt was made to determine the Alpha values in the oxygen transfer rate. This paper briefly summarises and compares the results from both systems, and the conclusions that can be drawn from these results.

A comparison of BNR activated sludge systems with membrane and settling tank solid–liquid separation

2006 ◽  
Vol 53 (12) ◽  
pp. 295-303 ◽  
Author(s):  
M.C. Ramphao ◽  
M.C. Wentzel ◽  
G.A. Ekama ◽  
W.V. Alexander
Keyword(s):  
Activated Sludge ◽  
Design Approach ◽  
Biological Nutrient Removal ◽  
Liquid Separation ◽  
Primary Sludge ◽  
Mass Fractions ◽  
The Cost ◽  
Solid Liquid ◽  
Solid Liquid Separation ◽  
Raw Wastewater

Installing membranes for solid–liquid separation into biological nutrient removal (BNR) activated sludge (AS) systems makes a profound difference not only to the design of the membrane bio-reactor (MBR) BNR system itself, but also to the design approach for the whole wastewater treatment plant (WWTP). In multi-zone BNR systems with membranes in the aerobic reactor and fixed volumes for the anaerobic, anoxic and aerobic zones (i.e. fixed volume fractions), the mass fractions can be controlled (within a range) with the inter-reactor recycle ratios. This zone mass fraction flexibility is a significant advantage of MBR BNR systems over BNR systems with secondary settling tanks (SSTs), because it allows changing the mass fractions to optimise biological N and P removal in conformity with influent wastewater characteristics and the effluent N and P concentrations required. For PWWF/ADWF ratios (fq) in the upper range (fq∼2.0), aerobic mass fractions in the lower range (fmaer<0.60) and high (usually raw) wastewater strengths, the indicated mode of operation of MBR BNR systems is as extended aeration WWTPs (no primary settling and long sludge age). However, the volume reduction compared with equivalent BNR systems with SSTs will not be large (40–60%), but the cost of the membranes can be offset against sludge thickening and stabilisation costs. Moving from a flow unbalanced raw wastewater system to a flow balanced (fq=1) low (usually settled) wastewater strength system can double the ADWF capacity of the biological reactor, but the design approach of the WWTP changes away from extended aeration to include primary sludge stabilisation. The cost of primary sludge treatment then has to be offset against the savings of the increased WWTP capacity.

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.

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

Upgrading performance of an activated sludge process through addition of talqueous powder

1996 ◽  
Vol 34 (5-6) ◽  
pp. 75-83 ◽  
Author(s):  
J. Cantet ◽  
E. Paul ◽  
F. Clauss
Keyword(s):  
Activated Sludge ◽  
Control Unit ◽  
Physical Structure ◽  
Experimental Models ◽  
Volume Index ◽  
Liquid Separation ◽  
Floc Structure ◽  
Rapid Effect ◽  
Solid Liquid ◽  
Solid Liquid Separation

This study is intended to induce better performance of existing activated sludge wastewater plants without modifying the physical structure of the plant. The process consists in injecting a specific mineral powder into the aeration stage with two precise purposes: firstly to improve floc structure and thus facilitate solid/liquid separation in the clarifier, and secondly to reduce nitrogenous pollution. By means of two experimental models the indisputable and rapid effect of talc/chlorite blend on the solid/liquid separation was established (with a sludge volume index improvement by a factor of 2 to 3 within a few days) compared with a control unit. The increase in nitrification capacity of the system is also clearly shown with nitrification yields being increased by 30%. These results lead us to believe that it is possible to use this process of enhanced nitrification for running a plant reliably without dysfunctioning. Problems linked to hydraulic or biological excess loading can be solved this way. Moreover, the addition of talqueous powder improves sludge dewaterability.

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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