Sludge blanket control is crucial to any wastewater treatment process. Accurate monitoring of this part can benefit process efficiency and cost savings.
In the primary and secondary sedimentation stages, sewage flows through large tanks called clarifiers or settlement tanks. In the primary tank, they are used to settle sludge by allowing grease and oils to rise to the surface, where they are skimmed off. A rotating bridge moves around the tank slowly to scrape off unwanted particles from the top of the water.
The heavier sludge suspended in the wastewater will stratify to the bottom of the settlement tank. The point where this stratification occurs is referred to as the “sludge blanket.” In secondary clarifiers/tanks, microorganisms digest the organic matter in the wastewater, creating the sludge floc, which will settle at the bottom of the tank.
Sludge level measurement measures the distance between the sludge blanket and the water level at the top of the tank. Once the sludge has reached the required density, the accompanying controller will switch on the pumps and pump it into digestors, preparing it for the secondary treatment stage. Many control factors ensure a well-performing system in the secondary stage, but the sludge blanket level is essential.
Once the sludge has been utilised to its potential in the primary and secondary stages, it becomes waste sludge. It undergoes further treatment, often via anaerobic digestion, thickening, and dewatering, so it can then be used in composting and land application as a fertiliser.
Why measure sludge blanket level?
Monitoring the sludge blanket level has advantages and benefits, including capital-saving costs and reduced carbon footprints.
Effective sludge level measurement can help municipal and industrial treatment plants generate electricity. Many large sewage treatment works burn the gas in digestors to drive electricity turbines. More gas produced results in more electricity generated. One of the most important gas volume determinants is the sludge’s quality and density delivered to the digestors.
Operators can ensure that sludge extraction pumps are used efficiently. Excess or poorly settled sludge does not wash out into wastewater effluent paths. This can prevent costly overspills and regulation breaches.
Further sludge handling processes, such as thickeners and dewatering equipment, perform better when fed with a higher sludge concentration. The diluted and lower-concentration sludge will require increased dosing, digestor heating, and pumping costs.
On top of plant and operation savings, it also enables operating companies to save on the labour costs of manual sampling. This means that a wealth of feedback is instantly available, allowing for overall greater system control for plant managers and wastewater engineers worldwide.
Thames Water implement Pulsar solution
Thames Water is one institution that has implemented Pulsar Measurement’s solution as part of an improvement project. It was introduced at one of its primary sewage treatment works in Berkshire, UK. The project included installing eight Pulsar Sludge Finder 2 continuous sludge interface monitoring systems to help with compliance and operational improvements.
Pulsar Measurement’s eight Sludge Finder 2 systems were installed onto the eight final settlement tanks at Reading sewage treatment works. This was in combination with Pulsar Measurement’s local radio system option. It communicated with matched receivers to the local MCC over 50 metres. This signal was then further connected via the site’s PLC and to the main SCADA overview.
The systems continuously monitor the sludge blanket within the Thames Water final settlement tanks. The system sounds an alarm when an unwanted discharge occurs in the adjacent foundry brook. It has improved return-activated sludge retention, a key factor when adhering to compliance and process requirements.
Pulsar Measurement’s Sludge Finder 2 sludge interface monitor offers a versatile, accurate and reliable solution to the problem of continuously and accurately measuring interface levels in primary, secondary or final settlement tanks and Sequencing Batch Reactor (SBR) systems.
Operating ultrasonically through liquid, Sludge Finder 2 uses echo processing algorithms to identify the sludge interface level by digital echo processing techniques.
Sludge Finder 2 also benefits from a self-cleaning underwater acoustic sensor, which removes any algae buildup. It results in continuous, reliable sludge level measurement. That results in a reduced need for sludge pumping and dosing optimisation. Staff can concentrate on other tasks.
Thames Water has been impressed by the monitoring system and its benefits to its improvement project at Reading STW.
How can an effective sludge blanket level measurement be achieved?
The Pulsar Measurement Sludge Finder 2 provides reliable and continuous sludge blanket-level measurement. The Viper transducer operates ultrasonically through the wastewater by measuring the distance between the sludge blanket surface.
The Viper transducer has a built-in external wiper blade. This keeps the transducer face clean and debris-free, eliminating the need for costly downtime and maintenance of a submersible sensor.
Traditionally, manual sludge blanket level measurement techniques required engineers and operators to be exposed to wastewater and sludge for an extended time. These techniques were labour-intensive and time-consuming. They also presented health and safety issues with personnel exposed to hazardous substances.
Automating this process with non-contacting sludge level measurement eliminates these issues. It allows staff to see real-time sludge blanket echo graphs on screen without going near the media.
Pulsar Measurement’s sludge blanket level system can help municipal or industrial treatment plants ensure their treatment process runs efficiently. It allows them to generate their own electricity and ensures that excess sludge is not pumped into local water sources. The Sludge Finder 2 and Viper transducer are designed to ensure compliance with health, safety, and environmental regulations.
For more information, visit https://pulsarmeasurement.com/
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