This paper focuses the Piçarrão wastewater treatment plant (WWTP) located in Brazil; including its project, construction and operation, related to its first step, with working capacity until 2010 (208.785 inhabitants). The conception of the second step is also presented. This WWTP, based on the water quality of the receiving river, was designed to reach a secondary treatment level in the first step, and a tertiary treatment level in the second step. In the first step, preliminary treatment, UASB reactors, activated sludge with dissolved air flotation (DAF) and post-aeration were implanted. For the second step, denitrification, coagulation applying ferric chloride and UV disinfection should be included. In the second step, one of the UASB modules will be adapted to operate as an anoxic reactor for denitrification. The process/operation flow diagram resulted in a low complexity and relatively low cost treatment plant: USD$ 120.9 per inhabitant for implantation, and USD$ 219.05 per 1000m3 of treated wastewater. Average results for this first period of operation are: BOD5.20°C removal in the UASB reactors: 72.0%, global BOD5.20°C removal in the system: 91.4%; effluent turbidity: (11±5)NTU; total suspended solids in the effluent: (16±8)mg.L-1; fecal coliform removal ≥4 log and dewatered sludge production: 12.3 ton.d-1.

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