Biochar accelerates the start-up of the anammox process: Phenomenon and potential mechanisms

Biochar was applied to accelerate the establishment of the anaerobic ammonium oxidation (anammox) reactor without temperature control (10 to 37 °C). 5 g/L coconut and apricot charcoal were added in R1 and R2. As a result, it took 121, 85 and 90 days for the start-up of R0, R1 and R2. The anammox pathway related functional gene (hzsB) in the bottom region of R0, R1 and R2 were 4.86 × 1011, 1.31 × 1012 and 5.85 × 1011 copies/g after 215-day operation which was significantly greater than that in the seeding sludge (2.56 × 107 copies/g). Candidatus Kuenenia and C. Brocadia were enriched in all reactors and the maximum nitrogen removal rate of R0, R1 and R1 were 1.29, 1.41 and 1.48 kgN/(m3·d), respectively. Biochar promoted the electron transfer capacity, resulting in the increase of functional gene responsible for the anammox pathway. The anammox microbes were enriched and specific anammox activity and nitrogen removal efficiency were improved eventually. The findings in our study could provide an alternative to establish the anammox process rapidly without temperature control.