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In the project it was determined that temperature and bubbles can greatly affect the ultrasonic signal. Temperature can be predicted by the ultrasonic sensor, by calculating the velocity time, thus, it can be applied in regions with a large amplitude of temperature. The bubbles effect can vary according to the flow rate. Low flow is recommended for the frequency of 200 kHz, and the sensor’s position should be horizontal to avoid the accumulation of bubbles in the transducer surface. Depending on the type of solids, the attenuation of the ultrasonic signal also showed different behaviors. The ultrasonic sensor was also compared to an optic commercial sensor in a full-scale activated sludge system in RWZI Grou (small WWTP) and RWZI Leeuwarden (Medium WWTP) and showed similar measurement of suspended solids, however, a cleaning routine of the sensors must be implemented in both cases. After 3 weeks the measurements in RWZI Leeuwarden showed an underestimation of the TSS compared to the gravimetric test and optic sensor. Probably regular calibration is necessary in a period of no more than 3 weeks. The measurement of the blanket level was not possible at the frequency of 200 kHz by the ultrasonic sensor, since the sludge did not reflect the ultrasonic waves back to the transducer, only the bubbles did it. It is recommended for further research testing higher frequency to evaluate the reflection of the sludge. Moreover, it was developed a functional routine for the signal treatment, capable of detecting the distance from the transducer to a material with good reflection properties, such as the glass surface used in the sensor.
The application of sensors in water technology is a crucial step to provide broader, more efficient and circular systems. Among the different technologies used in this field, ultrasound-based systems are widely used, basically to generate energy peaks for cell lysis and particle separation. In this work, we propose the adaptation of an ultrasound system to monitor the concentration of solid particles in wastewater treatment plants settlers as well as to indicate sludge level (real time). A similar sensor was developed and tested in another project which operated successfully at solids concentration up to 1% in UASB reactors. Such measurements are nowadays obtained via time-consuming physical (solids) analysis, which can compromise the efficiency of the settlers and the quality of the effluent. The present project proposes an improved version of the sensor, which will combine solids concentration monitoring and sludge level detection. The defined targets have the intention to make a sensor with a much broader range of applications, been suitable not only for UASB reactors but also to settler and aerobic tanks.
The project is a cooperation between the Water Technology lectoraat of NHL Stenden University of Applied Sciences, two SME’s - YNOVIO B.V. and Lamp-ion B.V. - and the INCT group (Brazil). If proven feasible, the concept can generate a big business market to the involved Dutch partners as well as favor the automation of WWTP in the Netherlands, Brazil and around the world.