Contribuição para o aprimoramento de reator UASB aplicado ao tratamento de esgoto sanitário : inoculação e controle da manta de lodo

Abstract

The present research aimed at assessing the suitability of anaerobic granular sludge obtained from the treatment of industrial effluent as inoculum of a UASB reactor treating sewage, and developing and testing an ultrasonic device for monitoring and controlling the sludge blanket. In the first stage of the research, a demo-scale UASB reactor (V=14 m3 ) was inoculated with anaerobic granular sludge and subsequently monitored for 154 days for the evolution of physical and microbiological characteristics and activity of the sludge, as well as regarding the performance of the reactor in the removal of COD, BOD and TSS. In the second stage of the research, an ultrasonic device for monitoring and controlling the sludge blanket in UASB reactors was tested for 254 days. The operation of the ultrasonic sensor is based on the attenuation of ultrasonic waves by the solid particles in suspension present in the reactor. The device was installed inside the three-phase separator of the reactor, in order to allow the determination of the concentration of solids in the upper part of the digestion compartment of the UASB reactor. The results of the different biomass characterization analyzes showed that the sludge inoculated in the reactor underwent a granule disintegration process, accompanied by loss of solids and effluent quality, reaching flocculent sludge characteristics (particles smaller than 0.3 mm) from the 70th operating day. This finding led to the division of stage 1 of the research into two phases for evaluating the performance of the UASB reactor: day 1 to 70 (operation with granular inoculum), and day 71 to 154 (operation with flocculent sludge). The results indicated low removal efficiencies of total COD during phase 1, 39 %, against 73%, during phase 2 of stage 1. As the removal efficiencies of filtered COD were similar during phases 1 and 2, it is believed that the low efficiencies observed during phase 1 were due to the presence of particulate organic material in the effluent, resulted from the breakdown of the granules. The results of the second stage of the research showed that the ultrasonic device was able to measure, with great precision, the concentration of total solids in the desired reading range (0 to 0.5%), as validated by the gravimetric method (R2 = 0.970 ). It was also observed the progression of the relative error in the measurements as the concentration of total solids approached the detection limit of the device (1%). The general results of the research indicated that the granular inoculum did not improve the performance of the UASB reactor and that the tested ultrasonic device proved to be a promising alternative for the control of solids in the digestion compartment of UASB reactors.