Biochar-mediated Anammox granular sludge: Formation/characteristics of pitaya type granular sludge and enhanced performance of Anammox process

Traditional Anammox granular sludge (AnGS) has disadvantages such as long formation time and low structural strength. Biochars have the potential for particle formation and structural stability of AnGS. Herein, different biochars (peach, coconut, jujube, and litchi biochars) were added to four expanded granular sludge bed (EGSB) reactors to investigate changes in sludge characteristics during Anammox start-up and stable Anammox granulation. Results showed that reactors with peach and coconut biochars achieved rapid start-up of Anammox, which were 15 days faster than that of the control reactor. Scanning electron microscopy (SEM) results showed the formation of the pitaya type AnGS with biochar as the crystal nucleus. Compared with the control, pitaya type AnGS particularly enriched the large-sized particle (1.0–3.0 mm), and had a higher specific Anammox activity (SAA) at the same particle size, along with an increase in mechanical strength (by ∼13%) and the relative abundance of functional bacteria (by 28–109%).