Alkalinity control in sludge propels the conversion of concrete slurry waste into micro- and nano-sized biogenic...

The utilization of Bacillus sp. for the production of bio-CaCO₃ in concrete crack repair and strength enhancement has attracted considerable attention. However, microbial-induced calcium carbonate precipitation (MICP) has yet to be explored as a precedent with activated sludge. Here calcium sourced from concrete slurry waste (CSW) and carbon from sludge microbial β-oxidation under alkaline were used to generate micro/nano CaCO₃. The results indicate that the main crystalline form of the generated precipitated particles is calcite, with a particle size ranging from 0.7 to 10 μm. Minimal heavy metals were found in the supernatant following settling. And at the optimum pH of 8.5-9, carbon capture reached 743 mg L^-1, and CaCO₃ production reached 1,191 mg L^-1, and dominant phylum were Proteobacteria and Bacteroidota, with Thauera being a prevalent genus adept in β-oxidation. Mass balance analysis showed that alkali promotes microbial β-oxidation of organisms to produce CO₂ and facilitate storage. Thus, the alkaline regulation of metabolism between microbe and CSW provides a novel way of sludge to initiate MICP.