A 120 m3 UASB reactor for domestic wastewater treatment was designed and built, based upon results obtained through the operation of a 106 L pilot unit. This system was operated for four years for demonstration and technology development purposes. The results obtained in the first year of operation were already previously presented.
After this period, some modifications were carried out aiming at design and operation and maintenance and facilities improvement. This was followed by a continuous 2-year operating period. In this work are presented some of the results obtained in this second phase of operation, with hydraulic retention times ranging from 5 to 15 h, resulting in an effluent with 50 to 150 mg COD.L−1 and 40 to 85 mg BOD.L−1. Some criteria are presented, together with the experience acquired in the development of this technology from the pilot reactor phase. During this period, several lectures and discussions about the system were held in relation to its use, operation and efficiency, leading to considerations about the advantages and convenience of this choice, by establishing a comparison between it and other wastewater treatment processes.