EVALUATION OF UASB EFFLUENT POLISHING ALTERNATIVES FOR MUNICIPAL APPLICATIONS

For the City of Curitiba, Brazil and surrounding areas, a proposed sewage infrastructure project (ParanaSAN) will incorporate the construction of new collection system components, expansion and upgrade of 5 existing treatment facilities, as well as the construction of 18 new treatment plants. One of the key features of the adopted wastewater treatment scheme is the incorporation of anaerobic processes in the liquid treatment train for municipal wastewaters. SANEPAR (the project's implementing agency) has developed in-house Upflow Anaerobic Sludge Blanket Reactor (UASB or RALF, the corresponding acronym in Portuguese) technology that has been widely used throughout the state. All of the new treatment facilities will incorporate this low-cost and simple technology as a first step. The UASB's, that can remove close to 60 to 75% of the influent BOD5 load on an average basis, will have to be followed by a polishing step to further remove organic matter. Under the ParanaSAN project, a technical-economical evaluation of viable polishing options was conducted for treatment facilities ranging in capacity from 0,44 to 1,05 m3/s (10 to 24 mgd). Polishing processes considered included unaerated lagoons, trickling filters, biological aerated filters, and dissolved air flotation. This paper discusses the general methodology and presents the results of this evaluation.