All of this is added together (or taken away for the credit) and is used to calculate
the aeration system requirements and normally includes a peaking factor to allow for
peaks in load of up to 40%. This all creates inefficiencies in the activated sludge
plant design.
There are four areas where advanced activated sludge plant control can create
efficiencies in operation:
• The first, and most obvious, is to limit the biomass oxygen demand by limiting
the physical quantity of biomass required to successfully treat the wastewater.
• The second is to control the oxygen required to treat the nitrogenous load to just
more than is needed (to allow for a small safety factor) by using feedback
ammonia control, feed forward ammonia control or potentially a combination
of both.
• To control and stabilise the flows (and load) coming through the works and,
where possible, eliminate the peaking factor as much as possible.
• Maximise the denitrification credit by increasing the size of the anoxic zone by
utilising the concept of swing zones, thereby allowing a greater size anoxic zone
when the temperature allows.
There are numerous ways to control the activated sludge plant and its many
variants to maximise the treatment objectives. These include using many more
sensors than the basic methods including:
• Respirometry that will look at the bacterial health and calculate the specific
oxygen utilisation rate
• Sludge Volume Index that will look at speed of the settleability of the sewage
sludge and waste sludge, based upon the capacity of the final settlement tanks to
hold the mass of sludge
• Nitrous oxide sensors that will look at the performance of the denitrification
process, the stress levels of the bacterial population and control the efficiency of
the wastewater treatment process
Practically, there are many types of secondary treatment processes, and the aim of
the process needs to be understood thoroughly. Is it a case of removing all pollutants
within the biological treatment stage? Or is it using the process for resource
recovery? This is an area that the industry is heading towards, potentially setting
things up for a tertiary stage where products are removed. This is all going to affect
the monitoring and control strategy of the secondary (and potentially tertiary)
treatment process.
3.2.3 Measuring and Controlling Sludge and Resource Recovery
Processes
It is when the wastewater treatment works is a sludge treatment centre that the real
value of wastewater comes into force, and this is an area of the business that should
resemble “the factory approach” much more than is currently the case. There are,
Monitoring and Controlling a Smarter Wastewater Treatment System: A UK. . .
133
the aeration system requirements and normally includes a peaking factor to allow for
peaks in load of up to 40%. This all creates inefficiencies in the activated sludge
plant design.
There are four areas where advanced activated sludge plant control can create
efficiencies in operation:
• The first, and most obvious, is to limit the biomass oxygen demand by limiting
the physical quantity of biomass required to successfully treat the wastewater.
• The second is to control the oxygen required to treat the nitrogenous load to just
more than is needed (to allow for a small safety factor) by using feedback
ammonia control, feed forward ammonia control or potentially a combination
of both.
• To control and stabilise the flows (and load) coming through the works and,
where possible, eliminate the peaking factor as much as possible.
• Maximise the denitrification credit by increasing the size of the anoxic zone by
utilising the concept of swing zones, thereby allowing a greater size anoxic zone
when the temperature allows.
There are numerous ways to control the activated sludge plant and its many
variants to maximise the treatment objectives. These include using many more
sensors than the basic methods including:
• Respirometry that will look at the bacterial health and calculate the specific
oxygen utilisation rate
• Sludge Volume Index that will look at speed of the settleability of the sewage
sludge and waste sludge, based upon the capacity of the final settlement tanks to
hold the mass of sludge
• Nitrous oxide sensors that will look at the performance of the denitrification
process, the stress levels of the bacterial population and control the efficiency of
the wastewater treatment process
Practically, there are many types of secondary treatment processes, and the aim of
the process needs to be understood thoroughly. Is it a case of removing all pollutants
within the biological treatment stage? Or is it using the process for resource
recovery? This is an area that the industry is heading towards, potentially setting
things up for a tertiary stage where products are removed. This is all going to affect
the monitoring and control strategy of the secondary (and potentially tertiary)
treatment process.
3.2.3 Measuring and Controlling Sludge and Resource Recovery
Processes
It is when the wastewater treatment works is a sludge treatment centre that the real
value of wastewater comes into force, and this is an area of the business that should
resemble “the factory approach” much more than is currently the case. There are,
Monitoring and Controlling a Smarter Wastewater Treatment System: A UK. . .
133