Análise e gerenciamento de impactos ambientais no tratamento de esgoto doméstico mediante avaliação de ciclo de vida

Abstract

This research has investigated the use of Life Cycle Assessment (LCA) in the analysis and management of environmental impact (EI) of domestic sewage treatment systems (DSTS). At first, life cycle inventories (LCI) of the operational phase of DSTS applicable to Brazilian conditions were structured as follows: i) facultative lagoon (FL); ii) anaerobic lagoon (AL) + FL; iii) AL + FL + maturation lagoon; iv) upflow anaerobic sludge blanket (UASB) + constructed wetlands system (CWS); v) UASB + PBF (percolator biological filters); and vi) UASB + conventional activated sludge. The major differences in proportion among the DSTS relate to sludge production and atmospheric emissions with, for instance, the emission of methane having been 22 times higher in the UASB + CWS system, compared to the system composed of FL. These results indicate the need to contemplate the production and destination of the operation byproducts within the scope of the LCA to a more faithful visualization of the DSTS. By means of the LCA of the UASB + CWS and UASB + PBF systems under two different routes of destination of biogas and sludge, it was observed that, in general, the UASB + PBF model performed better results in the most sophisticated route (boiler + biofertilizer) rather than in the flare + landfill route, due to a higher sludge production. However, the EI potential related to quicklime demonstrated the need to investigate sanitizer processes alternative to lime, confirming the hypothesis that the management of byproducts is crucial to improve of environmental sustainability of DSTS. From the case study of a large sewage treatment plant (STP), it was found that the use of biogas generated at the station for cogeneration (energy and heat) decreases the potential of EI at the station. Also, the feasibility of the STP exceeding energy use for sludge drying was verified, with the possibility to speculate that this scenario might have had better results if the sludge had been used as biofertilizer, once there is expectation that the thermal exposure can result in sludge sanitizing. From the performed studies it was possible to validate the LCI methodological model proposed to the operation phase and to the alternative routes for management of byproducts generated by DSTS. It was also found that the LCA can effectively contribute to the discussion about the parameters required by legislation, given the confirmation of the need for management of byproducts generated for the improvement of the environmental performance of these units.