Using a UASB reactor for thickening and digestion of discharged sludge from submerged aerated biofilters

Results from one year of experimental monitoring the wastewater treatment plant of UFES (Federal University of Espírito Santo) treating a residential urban area of city of Vitoria ES, Brazil, have shown a good performance by a UASB reactor as a part of domestic sewage treatment and also performing aerobic sludge thickening and digestion. The total solids concentration around 6% was obtained in main sludge blanket at bottom of reactor despite a high daily aerobic sludge load discharged from four aerobic submerged biofilters containing 0.4% TS and 80% of VS/TS. Similar values were found in another experimental period when the reactor was fed only with raw domestic sewage. The average removal efficiency of organic matter and suspended solids observed for domestic sewage treatment are around 63% of SS and 64% COD. These results were obtained in the UASB reactor working with or without aerobic sludge recycling, with constant or variable load and hydraulic detention time (HDT) less than 6 hours. A proposed mass balance allows a theoretical assessment of aerobic sludge digestion and accumulation into UASB reactor.