Sustainability assessment of sludge and biogas management in wastewater treatment plants using the LCA technique

Abstract Upflow anaerobic sludge blanket reactors (UASBs) used in sewage treatment generate two useful byproducts: sludge and biogas. This study evaluated the sustainability of four different scenarios for the treatment and final destination of biological sludge and biogas in a medium-sized wastewater treatment plant (WWTP) in South Brazil. At this plant, the sludge is sanitized by Prolonged Alkaline Stabilization and applied to agriculture (base scenario). Scenario 1 is about biogas use to dry sludge, which is taken to be used in agriculture. In Scenarios 2 and 3 the heat of the sludge burning is used for drying and sanitation. Finally, in Scenario 3 the ashes are destined to landfills. An environmental impact assessment was performed through life-cycle assessment using the ReCiPe 2016 evaluation method. Social life-cycle assessment indicators, adapted and developed for WWTPs, were used for social assessment. Economic assessment was performed through the analysis of life-cycle costs. The dashboard of sustainability (DoS) method was used for global assessment of sustainability. For overall sustainability assessment, Scenario 1 had the highest score (678 points) (best scenario) in the DoS. The environmental dimension was what facilitated this scenario. For this dimension, the following indicators presented the highest points when compared to the other scenarios: soil acidification, ozone formation, terrestrial ecosystem. The base scenario had the lowest score (worst case scenario) (375 points).

摘要 污水处理领域常用的上流式厌氧污泥床反应器（Upflow anaerobic sludge blanket reactors, UASBs）可产生两类高利用价值的副产物：污泥与沼气。本研究针对巴西南部一座中型污水处理厂（wastewater treatment plant, WWTP）的生物污泥及沼气的处理与最终处置方案，评估了四种不同场景的可持续性表现。
该厂当前采用长期碱性稳定化（Prolonged Alkaline Stabilization）工艺对污泥进行无害化处理，并将其农用，此为基准场景。场景1为利用沼气干化污泥后用于农业生产；场景2与场景3均借助污泥焚烧产生的热量完成污泥干化与无害化处理；其中场景3额外将焚烧所得灰分送至填埋场进行最终处置。
本研究采用ReCiPe 2016评估方法开展生命周期评价，以此完成环境影响评估；采用针对污水处理厂适配开发的社会生命周期评价指标开展社会维度评估；通过生命周期成本分析完成经济评估；并运用可持续性仪表盘（dashboard of sustainability, DoS）方法开展全局可持续性综合评价。
经可持续性仪表盘综合评估，场景1得分最高（678分），为最优场景，其环境维度表现最为突出。该维度下，土壤酸化、臭氧生成、陆地生态系统相关指标得分均显著高于其余场景。基准场景得分最低（375分），为最差场景。