Sources of anammox granular sludge and their sustainability in treating low-strength wastewater

Anaerobic ammonium oxidation (anammox) has been widely applied in the treatment of high-strength nitrogen wastewaters. However, few engineering practices were reported to treat low-strength nitrogen wastewaters. In this study, three types of anammox granular sludge (GS) were separately collected from the expanded granular sludge bed (EGSB) reactors treating nitrogen wastewaters at high (H-), moderate (M-) and low (L-) nitrogen loading rates (NLRs), and employed for the treatment of low-strength nitrogen wastewater in sequencing batch advanced nitrogen removal (ANR) systems. The ANR system with M-GS (namely M-ANR system) was most useful. At the initial biomass concentration of 2.43 g-VSS·L−1, cycle length of 8 h and influent total nitrogen (TN) concentration of less than 15 mg·L−1, the performance data were as follows: effluent TN of less than 1 mg·L−1, TN removal efficiency of more than 92.8%, the nitrogen removal rate (NRR) of 0.039 kg-N·m−3·d−1. The efficient performance lasted as long as 46 cycles, indicating the sustainability of the M-ANR system. The advanced microscopic analysis and metagenomic analysis were applied to reveal the successful but non-permanent treatment by the M-ANR system. The long-time lag between biomass decay and sludge activity decay provided a window period for the good performance of M-ANR system. However, the weak support of oligotrophic habitat for anaerobic ammonium oxidizing bacteria community was doomed to the degradation of anammox GS, resulting in gradual loss of their activities. A periodic addition of fresh M-GS or a periodic rejuvenation cultivation in the eutrophic habitat is necessary to achieve a permanent performance. [Display omitted] •Three types of anammox sludge were evaluated for advanced nitrogen removal.•The sludge in moderate nitrogen loading rate reactor was most useful and sustainable.•The mechanism was revealed for the successful while non-permanent treatment.•Two strategies were proposed to achieve a successful and permanent performance.