Rapid reactivation of long-term frozen preservation anammox granular sludge by biochar: Performance, mechanism and artificial neural network optimization

Abstract

Anaerobic ammonia oxidation (Anammox) is an efficient nitrogen removal technology for wastewater, and has been successfully applied in practical wastewater treatment. The preservation and rapid reactivation of anammox bacteria (AnAOB) play an important role in the anammox application. Biochar has been widely used in the water treatment industry due to its stable structure, economic and environmental protection characteristics. Hence, this study used biochar to accelerate anammox granular sludge (AnGS) performance recovery after 60 d preservation under low-temperature frozen (−20 °C). The time of AnGS recovery in the group with biochar addition was shortened by 15 d than the natural recovery group. Meanwhile, biochar addition improved the shock loading resistance of the anammox system. EPS secretion, and the types and quantities of functional groups in EPS increased under biochar stimulation, especially tighter PN. The functional groups in biochar can act as electron shuttles during anammox process, accelerating the electron transfer rate. Biochar addition enhanced the relative abundance of AnAOB, especially Candidatus Brocadia. PICRUSt analysis indicated that biochar promoted key gene related to anammox process and accelerated the recovery of frozen sludge. In addition, the changes in effluent nitrogen removal efficiency were successfully predicted by artificial neural network modeling with R = 0.9895 and MSE = 0.0048. This result may provide a new technological idea for the rapid recovery of AnGS under long time frozen conditions.