Real time monitoring of solids by a low-cost ultrasonic sensor : signal analysis and application in full-scale activated sludge systems and UASB reactors

• Ano de defesa: 2022
• Autor(a) principal: Rafael Pessoa Santos Brochado
• Orientador(a): Thiago de Alencar Neves
• Banca de defesa: Marcos Von Sperling, Thiago Bressani Ribeiro, Matheus Pimentel de Matos
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Minas Gerais
• Programa de Pós-Graduação: Programa de Pós-Graduação em Saneamento, Meio Ambiente e Recursos Hídricos
• Departamento: ENG - DEPARTAMENTO DE ENGENHARIA SANITÁRIA E AMBIENTAL
• País: Brasil
• Palavras-chave em Português: Anaerobic sludge; Aerobic sludge; Ultrasonic sensor; Solids real time monitoring; Signal attenuation; Sludge management
• Link de acesso: http://hdl.handle.net/1843/53106

One of the main aspects for the operational control of Sewage Treatment Plants (STPs) is related to sludge management. STPs with aerobic or anaerobic treatment requires proper control of solids in their reactors or settlers. The lack of a proper control can generate the solids washout, that deteriorates the quality of the treated effluent, thus polluting the water body. Real-time monitoring of solids by ultrasonic sensor (US sensor) is an alternative to manual measurement, which allows a faster response to the operator, less labor and lower energy consumption. US sensor is based on the pulse-echo technique, which estimates total suspended solid (TSS) content through ultrasonic attenuation. Laboratory scale tests showed that the type of solid, temperature and the presence of bubbles can interfere with the sensor reading. For temperature, the sensor itself can autocorrect its measurement, however, a model still needs to be consolidated for that. Full-scale tests were evaluated in a large-scale UASB (Upflow Anaerobic Sludge Blanket) reactor in Brazil, which failed to show correlation of total solids (TS) with ultrasonic attenuation. However, the sensor was located on the lateral region of the reactor. Its location is an important factor to be evaluated, since it was successfully tested in a demonstration-scale UASB reactor, being positioned at the center of the reactor. The sensor was also applied in two STPs in the Netherlands, in activated sludge systems. The sensor was positioned in a carousel unit and compared with a commercial optical sensor for TSS determination. In the first small-sized STP (STP Grou), the sensor showed measurements compatible with the gravimetric test of TSS for the period of one week. The measurements remained compatible during tests at STP Leeuwarden, a medium-sized STP for a period of 5 weeks. During that period the US sensor had a relative error of 1.14%, while the optical sensor 1.02% compared to the gravimetric test. After the third week, however, the US sensor showed an underestimation of TSS concentration, presenting values ​​of up to 0.08%, while the optical sensors and the gravimetric test maintained measurements close to 0.3%. This result probably indicates the need for monthly sensor calibration. One of the main problems encountered in full-scale application was the US sensor fouling. Mainly hairs were adhered to the reflection surface support causing the complete attenuation of the signal. For further tests, a cleaner design is recommended to avoid the adherence of solids on the support. Furthermore, the US sensor showed to me a promising technology for real time monitoring of solids in STPs. Further tests should be performed to improve the sensor development, so it can be a viable national commercial alternative for the sanitation companies.