Bottom-up approach in the assessment of environmental impacts and costs of an innovative anammox-based process for nitrogen removal

Abstract

In recent decades, the wastewater treatment sector has undergone a shift to adapt to increasing discharge limits. In addressing the evaluation of innovative technologies, it is necessary to determine the scale at which reliable and representative values of environmental impacts and costs can be obtained, ensuring that the system under assessment follows the direction of eco-efficiency. This study has evaluated the environmental and economic indicators of an autotrophic nitrogen removal technology (ELAN^®) from laboratory conception (1.5 L) to full scale (2 units of 115 m³) using the Life Cycle Assessment (LCA) methodology. Indirect emissions related to electricity consumption are the main contributor in all impact categories except eutrophication. Electricity consumption referred to the functional unit (1 m³ of treated wastewater) decreases as the scale increases. The rationale behind this can be explained, among other reasons, by the low energy efficiency of small-scale equipment (pumps and aerators). Accordingly, a value of approximately 25 kg CO_2eq per m³ of treated water is determined for laboratory scale, compared to only 5 kg CO_2eq per m³ at full-scale. When it comes to assessing the reliability of data, a pilot scale system of 0.2 m³ allowed to perform a trustworthy estimation of environmental indicators, which were validated at full-scale. In terms of operational costs, the scale of approximately 1 m³ provided a more accurate estimate of the costs associated with energy consumption.

Keywords: Eco-efficiency; Economic evaluation; Life cycle assessment (LCA); Partial nitritation-anammox; Scale-up analysis; Sustainable wastewater treatment.