Alkalinity control in sludge propels the conversion of concrete slurry waste into micro- and nano-sized biogenic CaCO3

Abstract

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. HIGHLIGHTS Utilizing concrete slurry waste as a calcium source and sludge β-oxidation as a carbon source can successfully produce bio-CaCO3.; pH 8.5–9 is the optimal alkaline control for Thauera to be the dominant genus undergoing β-oxidation to produce CO2.; Bio-CaCO3 is a 0.7–10 μm calcite particle, which is an excellent material for repairing concrete.; There is no risk of heavy metal leakage during operation.;

Keywords

• calcite
• concrete slurry waste
• micp
• micro- and nano-sized biogenic caco3
• thauera