Biosolids and microorganisms synergistically enhance aggregate stability and organic carbon sequestration of bauxite residue

Weak aggregate stability and low organic carbon content in bauxite residue restrict ecological rehabilitation. To eliminate these restrictions, a 1‐year column experiment was conducted to investigate the effects of introducing biosolids (BS), biosolids plus microorganisms (BSM) into bauxite residue on the aggregate stability, changes of organic carbon content, and growth of ryegrass (Lolium perenne L.) in bauxite residue. Compared with control group (CK), BS and BSM treatments increased dry‐sieve size distributions of bauxite residue aggregates in 2‐1 and 1‐0.25 mm, mean weight diameter (MWD), particle sizes of aggregates, complex Al oxide, and free Fe oxide in bauxite residue. The average particle sizes in bauxite residue following CK, BS, and BSM treatments after the harvest of plants were obtained to be ~121, ~201, and ~272 nm, respectively. In addition, BS and BSM treatments also increased aggregate‐associated humic substances and carbon content in bauxite residue. The carbon contents in bauxite residue following CK, BS, and BSM treatments after the harvest of plants reached ~18.8%, ~42.9%, and ~67.7%, respectively. The plant height, fresh weight, and dry weight of ryegrass following BSM treatment reached the maximum, which were 27.2 cm, 2.83 g, and 0.28 g, respectively. Results demonstrated that aggregate stability and carbon sequestration of bauxite residue were enhanced following amendment application, and the combined application of biosolids and microorganisms is superior than single BS. This implies that BSM treatment has a potential for plant establishment in bauxite residue disposal areas.