Abstract
Life cycle assessment (LCA) has been used to evaluate environmental impacts of products or processes including wastewater treatment. Uncertainty has not received adequate attention in LCA studies. Uncertainty inherited in LCA steps such as the life cycle inventory (LCI) or the life cycle impact assessment (LCIA) method use is unavoidable, but it affects LCA outcomes and associated decision-making. The objective of this paper was to show the impact of uncertainty from LCI and LCIA method on LCA outcomes by using a case study base approach on wastewater sludge treatment processes. A qualitative analysis included setting criteria about what data to be included in LCI, characterization of data, differentiating between major and minor contributors in LCI modeling, evaluation of data quality indicators, setting achievable alternative scenarios, and selecting proper LCIA method were used, in addition to quantitative analysis included assigning most appropriate values for data gaps and proper distribution, and conducting probabilistic analysis to evaluate overall uncertainty. This research used a full-scale wastewater treatment plant in Missouri, USA for case study in which multiple hearth incineration (MHI) is the existing process, while fluid bed incineration (FBI) and anaerobic digestion (AD) were proposed as the alternatives. Using ReCipe method, the study revealed that variation in LCA results of MHI is 63.4% for a single end-point score of 57.9 mPt. On the two alternative processes, it is 54.6% probable that FBI would have more environmental impact than AD. The case study showed that the proposed steps were able to address issues of data uncertainty. Due to differences in characterization, normalization, and weighting factors, different LCIA methods may point out different conclusions and need to be addressed in evaluation.
Highlights
Life cycle assessment (LCA) has been used to evaluate environmental impacts of products or processes
life cycle inventory (LCI) parameters are defined as distributed values: the values of each parameter vary in its respective range due to uncertainty
At 2.5% limit, fluid bed incineration (FBI) process minus anaerobic digestion (AD) process shows -3.34E-09, indicating FBI process could be taken as a process of lower damage on ecosystems when comparing to AD process, when the confidence level is decreased to lower end
Summary
Life cycle assessment (LCA) has been used to evaluate environmental impacts of products or processes. LCA can assess the potential environmental impacts from all stages of a product or a process life cycle. Many efforts were made to incorporate uncertainty analysis in LCA studies, it is still uncommon practice (Lioyd and Ries, 2007). The impact of uncertainty on outcomes of LCA were not considered in many studies, including a number of comparative evaluations of different wastewater sludge management and treatment processes (such as Lederer and Rechberger, 2010; Hong et al, 2009; Pasqualino et al, 2009; Akwo, 2008; Tarantini et al, 2007; Svanstrom et al, 2005; and Suh and Rousseaux, 2002). Neglecting the impact of uncertainty in LCA studies may results in reducing confidence on LCA outcomes. Niero et al (2014) showed that it is difficult to draw a robust conclusion between some wastewater treatment techniques if uncertainty analysis was not adequately addressed
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