Influence of biochar derived from sugarcane bagasse at different carbonization temperatures on anammox granular formation

Biochar derived from sugarcane bagasse, carbonized at temperatures of 300, 550, and 800 °C, exhibit different characteristics, such as pH, functional groups, specific surface area, and released nutrients. These three types of biochar were separately added into the enriched anammox cultures, influencing granular formation and nitrogen removal. The addition of biochar300 proved to be the most effective in stimulating anammox granular formation. On day 141 of operation, granular size >1.40 mm could be observed in all 3 biochar-amended reactors. The volatile suspended solids of these granules increased 3.2-fold, 1.2-fold, and 1.8-fold respectively compared to the reactor control without biochar addition. Furthermore, both short-term and long-term investigations of biochar addition demonstrated that biochar300 consistently promoted anammox activity surpassing additions of biochar550 and biochar800, especially during the start-up period. Based on various biochar300 dosing experiment, the higher doses may indicate higher electron exchange capacity. However, doses at levels ≥20 g L−1 negatively impacted the performance of the anammox system. The addition of biochar550 and 800 led to crystal accumulation and precipitation within granules. The crystals were identified as calcite, carbonate hydroxyapatite, and hydroxyapatite by using the XRD technique. Moreover, microbial community after the long-term biochar addition was analyzed by using next-generation sequencing technique.