be done to make efficiency savings and very few “resources” that can be recovered
from biological filter treatment streams.
With the development of tighter standards, and certainly on large facilities,
activated sludge plants are much more common as a biological treatment stage
along with numerous variants that are designed for nutrient control (Biological
Nutrient Removal plants and Enhanced Biological Phosphorus Removal Plants).
The overall measurement and control aim is to maintain the biological mass at the
right levels to achieve the desired treatment goals.
Activated sludge plants tend to be very energy heavy as, the tighter the consent,
the more intensive the treatment process is. This is especially true of aeration control.
This is also applicable to managing the biological balance within the plant, through
the control and return of the bacterial mass, and waste of biological solids.
The simplest of these control systems is direct control of the air within the
activated sludge plant, by using the measurement of dissolved oxygen and ramping
blowers up and down in line with the demand for air. This is not a very common
technique in practice, as the variation in oxygen being measured will cause constant
ramping of the blower system. Instead, a much more common approach in a simple
aeration control system is to pressurise an aeration header and maintain the pressure
using blower ramping and dissolved oxygen measurement to control the position of
modulating valves. How these valves are controlled is where the efficiencies in
aeration control lie, including feedback control in-line with measured concentrations
of target parameters, or feed forward control using Activated Sludge Models.
Controlling the whole balance of the system, including the sludge solids, is actually
the way to manage the efficiency of the whole activated sludge system for maximum
benefit. Moving to the resource factory approach, this can be tailored depending
upon the treatment outcomes. Figure 4 shows a conventional activated sludge plant
system including its control systems.
At the most basic, the dissolved oxygen concentration is used to adjust the
aeration lane valves (open or closed). The level of the dissolved oxygen measured
in the lane creates the pressure to drop in the aeration manifold when the valve is
opened, and this pressure drop starts the aeration blowers to maintain a set point
pressure. In the slightly more advanced systems, there is a feedback loop from the
ammonia concentration which sets a dynamic oxygen set point which the plant
attempts to maintain.
Of course, on top of this is the control of the actual biomass within the activated
sludge system. The importance of this is reflected in the oxygen required to treat the
load to the biological process.
Oxygen requirements in an activated sludge plant can be split into four main
areas:
• Oxygen required to treat the carbonaceous load (BOD)
• Oxygen required to treat the nitrogenous load (ammonia)
• Oxygen required by the biomass to breathe
• A credit caused by the conversion of nitrate to nitrogen gas in the anoxic zone
Monitoring and Controlling a Smarter Wastewater Treatment System: A UK. . .
131
from biological filter treatment streams.
With the development of tighter standards, and certainly on large facilities,
activated sludge plants are much more common as a biological treatment stage
along with numerous variants that are designed for nutrient control (Biological
Nutrient Removal plants and Enhanced Biological Phosphorus Removal Plants).
The overall measurement and control aim is to maintain the biological mass at the
right levels to achieve the desired treatment goals.
Activated sludge plants tend to be very energy heavy as, the tighter the consent,
the more intensive the treatment process is. This is especially true of aeration control.
This is also applicable to managing the biological balance within the plant, through
the control and return of the bacterial mass, and waste of biological solids.
The simplest of these control systems is direct control of the air within the
activated sludge plant, by using the measurement of dissolved oxygen and ramping
blowers up and down in line with the demand for air. This is not a very common
technique in practice, as the variation in oxygen being measured will cause constant
ramping of the blower system. Instead, a much more common approach in a simple
aeration control system is to pressurise an aeration header and maintain the pressure
using blower ramping and dissolved oxygen measurement to control the position of
modulating valves. How these valves are controlled is where the efficiencies in
aeration control lie, including feedback control in-line with measured concentrations
of target parameters, or feed forward control using Activated Sludge Models.
Controlling the whole balance of the system, including the sludge solids, is actually
the way to manage the efficiency of the whole activated sludge system for maximum
benefit. Moving to the resource factory approach, this can be tailored depending
upon the treatment outcomes. Figure 4 shows a conventional activated sludge plant
system including its control systems.
At the most basic, the dissolved oxygen concentration is used to adjust the
aeration lane valves (open or closed). The level of the dissolved oxygen measured
in the lane creates the pressure to drop in the aeration manifold when the valve is
opened, and this pressure drop starts the aeration blowers to maintain a set point
pressure. In the slightly more advanced systems, there is a feedback loop from the
ammonia concentration which sets a dynamic oxygen set point which the plant
attempts to maintain.
Of course, on top of this is the control of the actual biomass within the activated
sludge system. The importance of this is reflected in the oxygen required to treat the
load to the biological process.
Oxygen requirements in an activated sludge plant can be split into four main
areas:
• Oxygen required to treat the carbonaceous load (BOD)
• Oxygen required to treat the nitrogenous load (ammonia)
• Oxygen required by the biomass to breathe
• A credit caused by the conversion of nitrate to nitrogen gas in the anoxic zone
Monitoring and Controlling a Smarter Wastewater Treatment System: A UK. . .
131