Deep treatment is a common approach to enhance pollutant removal for biological wastewater treatment technologies (BWTTs), and life cycle assessment (LCA) holds substantial advantages to support process optimization. However, there lacks of LCA-based benchmarks that cover human-nature nexuses and stakeholder involvement, which limits the guidance and eco-design of BWTTs. This study proposed a decision-support system (DSS) by linking LCA with Water Quality Model and Conjoint Analysis. Three major findings were identified based on a demonstrative case (constructed wetland bioaugmented by dosing different microbial inocula): (1) Increasing bacterial intensities would achieve net environmental improvement, but it might not apply to all cases; (2) Making full use of natural self-purification capacity could partly replace the functions of BWTTs; (3) Stakeholders would concern aquatic environmental improvement when receiving river that had limited environmental capacity. Overall, the DSS provided a data-driven platform for screening options before determinations were made to constrain wastewater treatment sustainability.

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Determination of appropriate effluent quality limits (EQL) for wastewater treatment plants in China is a complicated process involving multiple factors that need joint consideration. Based on advantages of compiling the energy and material flows as well as the emissions into air, water and soil, life cycle assessment (LCA) presents a standardized approach for evaluation of EQL alternatives. However, challenges arise when incorporating more factors is indispensable, especially for the elements concerning downstream receiving water body, official watershed planning and stakeholder's participation. To this end, an integrated LCA-based decision-support platform named HIT.WATER scheme is proposed, linking the currently available LCA system with Water Quality Model (WQM), Plackett–Burman (PB) design and Conjoint Analysis (CA). A demonstrative case study was conducted to illustrate the processing procedures. Results obtained in the current study show that the officially defined river functions and the downstream cross-section distances resulted in more significant effects on the assessment outcome than other factors such as self-purification coefficients and weighting factors. Nevertheless, the comparisons among EQL alternatives were carried out and the differences were observed, which were dynamic, varying with the changed conditions of either natural factors (e.g. downstream distances) or human factors (e.g. officially defined river functions). Quantitatively presenting the dynamic comparisons to indicate the differences among the alternatives was a principal function of the HIT.WATER scheme. In particular, the approach allows the environmental impacts of EQL examined from various perspectives, which is conducive to the preclusion of “one-size-fits-all” determination with sustainability consideration. Stakeholder's participation was achieved through a transparent decision-making process, and their selection and judgment criterion could be explicitly presented using quantitative metrics. We conclude that the HIT.WATER scheme can be applied to broader scales where the evaluation of paradigm shifts (technological advancement or effluent standard changes) in sewage systems is necessary.

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This present study aims to analyze the differences in results of different site-directional life cycle assessment
(LCA) methods applied in the field of wastewater treatment. Site-generic methods were employed and
compared with China-specific methods on a full-scale wastewater treatment case. A set of Chinese
normalized factors were developed and employed to compare with world normalization factors. No
substantial discrepancies in results were obtained from the two different sets of normalization factors. In
the phase of life cycle impact assessment, the e-Balance showed substantial discrepancies in results,
compared with the CML method that is widely applied in LCA. The discrepancies were mainly attributed
to the cause that in e-Balance more emphasis is on regional water pollution potential (that is: chemical
oxygen demand (COD) as an independent impact category). Moreover, discrepancies in the results were
also investigated by applying different site-directional weighting methods. Besides the specific locations
where the weighting methods were designed for, this study showed that employing different
environmental indicators in impact categories was another important factor that resulted in differences
in the LCA results of the different weighting methods.@en