angle of the unit to speed up or slow down the process enables control of the
thickening and dewatering stages in drum thickening and centrifugation, allowing
for thinner or thicker product which is then transferred to the digestion stage.
If consistency is achieved, then it spreads throughout the entire process, achieving
the ultimate aim. However, in reality, consistency is not usually achieved throughout
the whole process, and the challenge is to bring balance from imbalance. This is
where the measurement and control systems come into play.
3.3 Holistic Control: Model-Based and Multivariate Process
Control
The WTW as a whole can be controlled manually by analysing and responding to
the data produced by the instrumentation, but this is a labour-intensive process
which requires continuous adjustments. On the larger scale treatment works, there
is normally some sort of automation within the process to realise process-based
efficiencies over standard manual operation. This can be as simple as a single
instrument-based control loop, or as complicated as a multivariate process control
system.
Within the past 5–8 years, the principles of individual process control on the
activated sludge plant have been gathered into integrated advanced process control
systems in the UK by two commercial organizations and one or two of the water
utilities. The water companies themselves have tried to do this with PID loop
controls and, in some cases with cascade loop control systems, some of which
have had some success in Europe.
Hach Lange developed the Water Treatment Optimization system (WTOS),
which is very much an advanced process control system based upon instrumentation.
The WTOS system utilized Hach Lange instrumentation and a process model based
upon the ASM1 activated sludge model [21].
One of the first full-scale installations controlled with the WTOS system was a
250,000 population equivalent four-stage Bardenpho plant with methanol addition
in the second anoxic zone. The system and controller that was developed for this
treatment plant looked to monitor and automate the whole process, including the
nitrification and methanol dosing. This first installation conducted a trial over a
10-week period and managed to achieve a 20% reduction in the amount of aeration,
control of the amount of ammonia that was discharged, and a 50% reduction in the
amount of methanol that was consumed.
Since its first implementation in 2008, this technology has developed even further
with other control modules including a nitrification module (which includes sludge
age control) specifically designed for the activated sludge plant, as well as modules
that are designed for other plant processes.
The second approach to advanced process control has again been based on
model-based controllers but is less reliant on instrumentation and more reliant on
Monitoring and Controlling a Smarter Wastewater Treatment System: A UK. . .
135
thickening and dewatering stages in drum thickening and centrifugation, allowing
for thinner or thicker product which is then transferred to the digestion stage.
If consistency is achieved, then it spreads throughout the entire process, achieving
the ultimate aim. However, in reality, consistency is not usually achieved throughout
the whole process, and the challenge is to bring balance from imbalance. This is
where the measurement and control systems come into play.
3.3 Holistic Control: Model-Based and Multivariate Process
Control
The WTW as a whole can be controlled manually by analysing and responding to
the data produced by the instrumentation, but this is a labour-intensive process
which requires continuous adjustments. On the larger scale treatment works, there
is normally some sort of automation within the process to realise process-based
efficiencies over standard manual operation. This can be as simple as a single
instrument-based control loop, or as complicated as a multivariate process control
system.
Within the past 5–8 years, the principles of individual process control on the
activated sludge plant have been gathered into integrated advanced process control
systems in the UK by two commercial organizations and one or two of the water
utilities. The water companies themselves have tried to do this with PID loop
controls and, in some cases with cascade loop control systems, some of which
have had some success in Europe.
Hach Lange developed the Water Treatment Optimization system (WTOS),
which is very much an advanced process control system based upon instrumentation.
The WTOS system utilized Hach Lange instrumentation and a process model based
upon the ASM1 activated sludge model [21].
One of the first full-scale installations controlled with the WTOS system was a
250,000 population equivalent four-stage Bardenpho plant with methanol addition
in the second anoxic zone. The system and controller that was developed for this
treatment plant looked to monitor and automate the whole process, including the
nitrification and methanol dosing. This first installation conducted a trial over a
10-week period and managed to achieve a 20% reduction in the amount of aeration,
control of the amount of ammonia that was discharged, and a 50% reduction in the
amount of methanol that was consumed.
Since its first implementation in 2008, this technology has developed even further
with other control modules including a nitrification module (which includes sludge
age control) specifically designed for the activated sludge plant, as well as modules
that are designed for other plant processes.
The second approach to advanced process control has again been based on
model-based controllers but is less reliant on instrumentation and more reliant on
Monitoring and Controlling a Smarter Wastewater Treatment System: A UK. . .
135