Solar-enhanced low-temperature biological wastewater treatment

Biological wastewater treatment (BWT) is critical to safeguard the aqueous environment. However, enzyme activities in microbial metabolism are inhibited by low temperatures, making BWT implementation in cold environments challenging. Here we propose a strategy to endow BWT facilities with low-temperature operation resilience by integrating photothermal technology with BWT using photothermal carriers (PTCs). Specifically, α-Fe2O3@polyaniline was coated onto a high-conductivity SiC ceramic matrix on a PTC, forming functional partitions for bacterial colonization. The upper layers of the PTCs have an interlaced porous structure and photothermal functions, which provided stable energy conversion and light shielding. The heat conducted downward formed a mesophilic, lightless zone in the lower PTC layers, resulting in high thermal conduction and bioaffinity. Consequently, anammox bacteria, a key biome for sustainable BWT, can be enriched in these PTCs, as evidenced by a 21.4% increase in abundance and a 2.2-fold increase in biomass. With the use of PTCs in a BWT facility under 0.6 kW m−2 illumination, the nitrogen removal performance at low temperature (15 °C) was 5.8 times higher than the case without the use of PTCs. Overall, this work shows how solar energy can be used to enhance the resilience of BWT to low temperatures, improving the applicability of BWT in cold regions.