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.

Hydrogen sulphide (H₂S) represents one of the main odorant gases emitted from wastewater treatment plants (WWTP) and a mathematical model can be a fast and low cost tool to estimate its emission. In this work H₂S emission rates in a WWTP, composed of an up-flow anaerobic sludge blanket (UASB) reactor and an aerobic biofilter (BF), are estimated using four mathematical models available in the literature (AP-42, GPC, TOXCHEM+ and WATER8). The results show that the GPC model leads to the best agreement with the experimental data, except for the biofilter due to its lack of capability to include biodegradation as a H₂S removal process. On the other hand, the AP-42 and WATER8 models showed a slightly better ability to predict H₂S removal in the biofilter than the TOXCHEM+ model, as all models underestimate the H₂S concentration decay.