Alkalinity control in sludge propels the conversion of concrete slurry waste into micro- and nano-sized biogenic CaCO 3 .

The utilization of Bacillus sp. for the production of bio-CaCO 3 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 CaCO 3 . 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 CaCO 3 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 CO 2 and facilitate storage. Thus, the alkaline regulation of metabolism between microbe and CSW provides a novel way of sludge to initiate MICP.