This study aimed to evaluate the impact of implementing routines of sludge and scum withdrawal in full-scale Upflow Anaerobic Sludge Blanket (UASB) reactors on the operational control and on the improvement of final effluent quality. The work was developed at Laboreaux STP (Population Equivalent = 70,000 inhabitants), located in the city of Itabira, in the state of Minas Gerais – Brazil. Two operating conditions were tested for hydrostatic scum removal, varying the pressure in the gas line and the height of the scum layer within the three phase separator. The effective removal of scum was only achieved in the three phase separators located near to the discharge line, indicating the necessity for improvements in the discharge system. Applying the concepts of minimum and maximum sludge mass in the UASB reactors at Laboreaux STP resulted in a dramatic improvement in the effluent quality of the reactors. In the periods when the reactor operated with quantities of biomass below the maximum established limit (10,000 kgST), the average concentrations of TSS, BOD and COD were below 109, 44 and 153 mg L−1, respectively.

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