“Multivariate analysis and steady-state modelling of nutrient mechanisms in activated
sludge treatment of pulp and paper wastewater”
Lucy COTTER
M.Sc. Student
Introduction
Modelling of activated sludge treatment processes has been investigated in some detail for
municipal wastewater treatment, primarily using the Activated Sludge Models (ASM) first
developed by the International Water Association (IWA, Henze et al. 1987). ASM1 is still the
“state of the art” in many studies (Gernaey et al. 2004). These models have been modified for pulp
and paper industrial wastewater (Bolmstedt, 2000).
Modelling of nutrient mechanisms within the framework of the ASM models has been attempted at
various degrees of complexity (Lindblom, 2003, NCASI AST model, Barker & Dold, 1997).
Nutrient mechanisms specific to nutrient-deficient industrial wastewater, such as that seen in the
pulp and paper industry, have been the subject of research in recent years (NCASI TB 826, 2001,
Slade et al. 2004, Paprican Report PSR 560, 2006).
Nutrient control strategies are varied, from the “accepted” ratio of nutrient dosing to influent BOD
load, to the more complex nutrient on-line measurement with feed-back change minimisation
control (Hynninen & Viljakainen, 1994).
While the biochemical mechanisms of nutrient transformation during wastewater treatment are well
documented, there remain several uncertainties such as the minimum nutrient requirements for
stable AST operation (NCASI TB 826), and the interaction between nutrient control and the control
of other growth pressures (dissolved oxygen, pH, temperature, F/M ratio, BOD, toxicity &
hydraulic retention time), which are critical if mill data are to be used for nutrient control. A
thorough understanding of the nutrient transformation mechanisms and effective nutrient control
strategies could permit stable AST operation for high BOD removal and simultaneous nutrient
minimisation or optimisation. This is becoming increasingly important as the regulatory authorities
in the US and Canada are introducing new and/or more stringent limits for nutrient
mass/concentration levels, particularly in site-specific effluent discharge permits (Clean Water Act,
US Water Quality Trading schemes, Great Lakes Water Quality Agreement of 1987, NCASI TB
826, 2001, Pulp and Paper Effluent Regulations, Environment Canada 2004).
The advantages of nutrient optimisation include reduced operating costs for nutrient addition, and
reduced capital spending, should it be required to achieve low nutrient discharge levels, in terms of
savings on new plant items such as those required for chemical precipitation of phosphorus for
example. A less tangible and important cost savings would be due to improved AST control and
lower potential for out-of-compliance events such as filamentous bulking due to nutrient
deficiencies.
This research project comprises the execution and analysis of a survey exploring the design and
operation of North American activated sludge treatment (AST) plants with respect to nutrient use,
measurement and control, the development of a steady-state mechanistic model of the operation of
an activated sludge treatment plant at an integrated newsprint mill, and a multivariate analysis
(MVA) of the mill data in order to derive models which are suitable for nutrient control guidance.
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Overall Objectives
The objective of this project is to develop a systematic methodology for the modelling of AST's
suitable for improved nutrient control, which can account for effluent characteristics, AST system
design, and AST system operation including its impact on nutrient residuals.
Modelling will include use of the ASM models via the GPS-X software program, site data collection,
model calibration and validation, and MVA analysis to extract specific information relative to nutrient
control.
Potential Benefits
The results of the model and MVA will be used to optimise the operation of an operating AST in
terms of minimum nutrient use, measurement and control. The potential benefits to the mill include:
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increased understanding and control of the AST process,
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a working model of the AST process, and possibly,
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reduced nutrient usage, which would translate to an operational financial savings.
The overall methodology will be generalized for publication in the literature, so that other mills can
consider its implementation.
Methodology
 Literature review of key technical areas related to this project: AST design and operation, AST
modelling, nutrient modelling, nutrient control, MVA analysis…
 Detailed AST survey: A survey of AST's in Canada will be conducted under the auspices of
PAPTAC, and the targeted response is in the order of 40 plants. The survey results will be
analysed to find correlations between plant design, operation and nutrient use, measurement
and control
 Understand mill objectives with respect to nutrient optimization.
 Steady state modelling of AST plant at an integrated newsprint mill, using GPS-X software
 Model calibration and validation using mill operating data
 Incorporation of data into an empirical model developed using MVA, suitable for nutrient
control guidance
 Proposal and evaluation of nutrient control strategy
References
[1]
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J. Bolmstedt, "Dynamic modelling of an activated sludge process at a pulp and paper mill." Masters.
Thesis, Lund, Sweden: Lund Institute of Technology, 2000.
D. Buckley, "Selected pulp and paper industry experience with the control of nutrients in
biologically treated effluents," National Council for Air and Stream Improvement, Inc (NCASI),
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