Using marimo as a nature-derived microalgal-bacterial granular consortium for municipal wastewater treatment

The photo-driven biological wastewater treatment processes based on the microalgae-bacteria symbioses or bio-granules have gained accelerated interest under the era of carbon neutrality. Marimo is a natural microalgal-bacterial granular consortium found in lake ecosystems, similar to microalgal-bacterial granular sludge (MBGS) cultivated in laboratory. However, the potential of marimo for wastewater treatment has not been explored. To imitate nature, this study first evaluated the feasibility of marimo for wastewater treatment as compared with MBGS under outdoor conditions for proof-of-concept. The results showed that marimo differ-entiated from MBGS in both of the morphology and physical structure. Particularly, the bio-granule of marimo had a homogeneous and compact structure, while MBGS had a layered and relatively loose structure on the contrary. Additionally, marimo and MBGS had different microbial community structure, which mainly contained Chlorophyta (Aegagropila) and Cyanobacteria (Leptolyngbya and Pantanalinema), respectively. However, consid-erable organics and nutrients could be removed over the day-night cycles by both marimo and MBGS. When marimo adapted to the wastewater, the gap of removal efficiencies between these two processes gradually narrowed. Additionally, the potential functions of marimo and MBGS also became similar gradually. In general, the morphology, performance and function of marimo gradually turned similar to MBGS, implying their ho-mologous relationship. This study is expected to provide inspirations for developing nature-derived marimo as a novel wastewater treatment technology.