Magnesium carbonate precipitate strengthened aerobic granules

• Magnesium carbonate was precipitated inside aerobic granules.
• Treated granules have enhanced stability in 220 days test in continuous-flow reactors.
• Carbonate salt did not change much granule morphology or microbial communities.
• MgCO3 precipitation is a low cost and easy process for granule modification.

Aerobic granules were precipitated internally with magnesium carbonate to enhance their structural stability under shear. The strengthened granules were tested in continuous-flow reactors for 220 days at organic loadings of 6–39 kg/m3/day, hydraulic retention times of 0.44–19 h, and temperatures of 10 or 28 °C. The carbonate salt had markedly improved the granule strength without significant changes in granule morphology or microbial communities (with persistent strains Streptomyces sp., Rhizobium sp., Brevundimonas sp., and Nitratireductor sp.), or sacrifice in biological activity for organic degradation. MgCO3 precipitated granules could be used in continuous-flow reactor for wastewater treatment at low cost and with easy processing efforts.