Desempenho energético e pegada de carbono de um sistema de esgotamento sanitário centralizado no nordeste brasileiro / Energy performance and carbon footprint of a centralized sewage system in northeastern Brazil

RESUMO O objetivo do trabalho foi avaliar a operação e manutenção de um sistema de esgotamento sanitário centralizado, composto de três subsistemas, que atende 367 mil habitantes no Nordeste do Brasil. A avaliação do ciclo de vida considerou um inventário amplo de operação e manutenção do sistema de esgotamento sanitário com as redes de coleta, estações de tratamento de esgoto, disposição do esgoto tratado no corpo hídrico e gestão do lodo. O arranjo tecnológico das estações de tratamento de esgoto avaliadas incluiu o reator do tipo upflow anaerobic sludge blanket, seguido de lagoa aerada e lagoa de polimento em um subsistema, e upflow anaerobic sludge blanket seguido de reator de lodo ativado por aeração prolongada em dois subsistemas. O desempenho energético utilizou o método de demanda de energia acumulada e a pegada de carbono empregou o método de potencial de aquecimento global de 100 anos do Painel Intergovernamental sobre Mudanças Climáticas. O sistema de esgotamento sanitário avaliado demandou 5,12 MJ·m−3 e emitiu 4,08 kg CO2eq·m−3. As maiores contribuições do sistema de esgotamento sanitário avaliado foram a eletricidade, com 62% da demanda energética, e as emissões diretas para o ar, com 94% da pegada de carbono, sendo as emissões dos reatores upflow anaerobic sludge blanket com 76% da pegada de carbono. A identificação dos aspectos e impactos ambientais do sistema de esgotamento sanitário avaliado apoia a inovação tecnológica e gerencial para otimizar o desempenho energético e mitigar as emissões de gases de efeito estufa.

ABSTRACT This aim of this work was to evaluate the operation and maintenance of a centralized wastewater treatment system, composed of three subsystems, which serves 367 thousand inhabitants in northeastern Brazil. The life cycle assessment considered a comprehensive inventory of the wastewater treatment system operation and maintenance with the collection networks, wastewater treatment plants, disposal of the treated wastewater in the water body and sludge management. The technological arrangement of the evaluated wastewater treatment plants included the Upflow Anaerobic Sludge Blanket reactor, followed by aerated and polishing ponds in one subsystem, and Upflow Anaerobic Sludge Blanket followed by extended aeration activated sludge in two subsystems. The energy performance used the cumulative energy demand method and the carbon footprint used the global warming potential method for 100 years of the Intergovernmental Panel on Climate Change. The evaluated wastewater treatment system presented 5.12 MJ·m−3 and 4.08 kg CO2eq·m−3. The largest contribution of the evaluated wastewater treatment system was the electricity use with 62% of the energy demand and direct emissions to the air with 94% of the carbon footprint, being direct emissions from Upflow Anaerobic Sludge Blanket reactors with 76% of the carbon footprint. The identification of environmental aspects and impacts of the evaluated wastewater treatment system supports technological and management innovations to optimize its energy performance and mitigate greenhouse gases emission.

Impact of treatment plant management on human health and ecological risks from wastewater irrigation in developing countries - case studies from Cochabamba, Bolivia.

Wastewater irrigation is a common practice in developing countries due to water scarcity and increasing demand for food production. However, there are health risks and ecological risks associated with this practice. Small-scale wastewater treatment plants (WWTPs) intend to decrease these risks but still face management challenges. This study assessed how the management status of five small-scale WWTPs in Cochabamba, Bolivia affects health risks associated with consumption of lettuce and ecological risks due to the accumulation of nutrients in the soil for lettuce and maize crops. Risk simulations for three wastewater irrigation scenarios were: raw wastewater, actual effluent and expected effluent. Results showed that weak O&M practices can increase risk outcomes to higher levels than irrigating with raw wastewater. Improving O&M to achieve optimal functioning of small-scale WWTPs can reduce human health risks and ecological risks up to 2 log10 DALY person-1 year-1 and to 2 log10 kg nitrogen ha-1 accumulated in soil, respectively.

Wastewater management in small towns - understanding the failure of small treatment plants in Bolivia.

Wastewater management in developing countries is a challenge, especially in small towns with rapid population growth. This study aims at assessing the performance and management of five treatment plants (TPs) in rural areas of Cochabamba, Bolivia. Pollutants' concentrations, wastewater flows, hydraulic and organic loads and hydraulic retention times were determined in three small treatment plants (2000-10,000 population equivalent [p.e.]; flow > 432 m3/d) and two very small treatment plants (<2000 p.e.; flow < 432 m3/d). The performance assessment was based on operational parameters, treatment efficiency and effluent quality. Management data were collected through semi-structured interviews with managers of local water associations. The results support that the poor performance of the TPs is due to lack of operational expertise and financial resources for adequate operation and maintenance (O&M). Additionally, effective treatment was affected by the type of technology used and whether the plant design included plans for O&M with available resources. This study contributes to a better understanding of actual operating conditions of wastewater TPs in small towns, thus providing needed information regarding technology selection, design, implementation and operation.