Assessing the life-cycle sustainability of algae and bacteria-based wastewater treatment systems: High-rate algae pond and sequencing batch reactor

High Rate Algae Ponds (HRAPs) are a promising technology for the treatment of municipal wastewater in locations with sufficient space and solar radiation. Algae-based processes do not require aeration, and thus have the potential to be less energy-intensive than activated sludge processes. We used a combination of LCA and LCCA analysis to evaluate the sustainability of HRAP systems, using data from the construction and operation of two demonstration-scale systems in Almería and Cádiz, Spain. As a reference for comparison, we used data from an activated sludge-based Sequencing Batch Reactor (SBR) treatment system in operation in Leppersdorf, Germany, which has comparable removal rates for a similar inflow. We focused solely on the actual wastewater treatment aspect of these technologies, excluding sludge treatment from this analysis. Based on our analysis, the current HRAP technology is more energy-efficient than activated sludge-based SBRs and requires only 22% of its electricity consumption. In addition, HRAP is more advantageous both economically (0.18 €/m³ versus 0.26 €/m³) and environmentally, with both lower global warming and eutrophication potentials (146.27 vs. 458.27 × 10⁻³ kg CO₂ equiv./m³; 126.14 vs. 158.01 × 10⁻⁶ kg PO₄ equiv./m³). However, the Net Environmental Benefit of SBR was slightly more favorable than of HRAP because of the higher removal rate for nutrients of SBR.