Sewage treatment in cities of the state of Minas Gerais, Brazil, that use the UASB reactor as the only biological treatment: A case study

Abstract

This article analyzed the performance of four Wastewater Treatment Plants (WWTP) in three cities in the state of Minas Gerais, Brazil, which use the UASB (Upflow Anaerobic Sludge Blanket) reactor as the only stage of biological treatment. When evaluating the characteristics of treated wastewater, it was verified that the WWTPs were not efficient enough to meet the disposal standards established by environmental agencies. Most of the sewage samples from Ipatinga municipality did not meet the minimum removal for BOD5 of 60 % and COD of 55 %, being 56 % and 46 % the average removals, respectively. These results suggest the need for improvements in the current biological treatment and/or the adoption of a polishing step. The raw sewage had high biodegradability (BOD5/COD>0.4) and the UASB reactors reduced this biodegradability (ranging from 0.2 to 0.43) by removing the content of easier degradation. A strong linear correlation (R2 = 0.85) was observed between COD and DBO5 data for the raw sewage from Timóteo municipality, making it possible to estimate the second parameter as a function of the first. When compared with wastewater characterized and used in fertigation studies, the treated sewage samples of the present study show potential for application in agricultural practices.