Comprehensive assessment of alternative technologies for urban wastewater treatment - nature-based and nature-inspired

<jats:p>Three innovative technologies for treating urban wastewater, based on or inspired by nature, have been evaluated in the context of growing demands for the efficiency and sustainability of WWTPs. Constructed wetlands are characterized by very low energy consumption (0,28 – 11,56 kWh/p.e.·year) and simple operation and can provide ecosystem benefits and partial recovery of biogenic elements through plant biomass (2 – 4,9 g P/m²·year). The main limitations are the need for a significant area and lower flexibility at very low permissible output concentrations for N and P without an additional treatment stage. They are most suitable for agglomerations of up to 10 000 p.e., decentralized systems, and post-treatment. FCR-Organica offers compactness (up to 60 % smaller footprint), stable processes (12 – 18 kg/m³ biomass in the bioreactors), and high public acceptance (green integration into the urban environment), but requires more complex equipment and skilled operation. Energy consumption is 25,11 – 29,93 kWh/p.e.·year (for WWTP &lt; 10 000 p.e.) and 17,58 – 29,96 kWh/p.e.·year (for WWTP from 10 000 to 100 000 p.e.). AGS-Nereda provides process intensification (up to 75 % space savings), removal of C, N, and P in a single reactor without secondary clarifiers (ISV &lt; 50 mL/g), and energy consumption of 17,80 – 22,26 kWh/p.e.·year (for WWTPs from 10 000 to 100 000 p.e.) and 9,75 – 17,14 kWh/p.e.·year (for WWTPs &gt; 100 000 p.e.), but it is sensitive to operation mode, granules stability, and requires longer start-up period. All three technologies are applicable in Bulgaria when properly adapted to local characteristics and constraints.</jats:p>