Granular activated carbon promoting re-granulation of anammox-hydroxyapatite granules for stable nitrogen removal at low phosphate concentration

• Published in: The Science of the total environment Vol. 805; p. 150359
• Main Authors: Liang, Lei, Luo, Jinghuan, Xiao, Xiangmin, Wang, Jianwei, Hong, Meng, Deng, Chao, Li, Yu-You, Liu, Jianyong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.01.2022
• Subjects: activated carbon; anaerobic ammonium oxidation; Anammox; crystallization; environment; Granular activated carbon; Granulation; Hydroxyapatite; inoculum; microbial communities; nitrogen; phosphorus; sludge; Sludge disintegration; total nitrogen; total suspended solids; water content; Anammox; Granular activated carbon; Hydroxyapatite; Granulation; Sludge disintegration
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.150359

Anaerobic ammonium oxidation (anammox) coupled with hydroxyapatite (HAP) crystallization not only achieves simultaneous nitrogen removal and phosphorus recovery, but also cultivates excellent anammox granules. However, a floatation and wash-out of anammox-HAP granules was occurred at low phosphate concentrations. In this study, a reactor inoculated with mature anammox-HAP granules and fed with low phosphate (5 mg P/L) was added with granular activated carbon (GAC) to maintain sludge granulation and nitrogen-removing stability. At influent total nitrogen >800 mg/L and nitrogen loading rate ~ 9.8 kg/m3/d, a satisfactory nitrogen removal of around 88% was maintained during 140 days of operation. Insufficient phosphate supplement resulted in a sludge bulking, with suspended solid and sludge density decreased whereas sludge water content and expansion ratio increased due to HAP loss. Nevertheless, the sludge re-granulation was found at the later stage as the proportion of granules in 2.8– 3.35 mm went up to 37.4% after large granules disintegrated into small pieces at the initial stage. The settling velocity was finally ranging from 129.8 to 182.2 m/h. In addition, Candidatus Brocadia was increased from 2.1% to 20.1% and dominated in the microbial community. These findings suggest GAC was able to promote re-granulation of anammox-HAP granules at low phosphate concentration, which avoids sludge flotation and widens their application as an inoculum. [Display omitted] •Stable nitrogen removal at low PO43− concentration was achieved with GAC addition.•Granules disintegration occurred after PO43− reduction.•Sludge re-granulation was promoted by GAC.•Candidatus Brocadia was increased from 2.1% to 20.1% and dominated the community.