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 pore filling has garnered attention. However, microbial-induced calcium carbonate precipitation (MICP) has yet to be explored as a precedent with activated sludge. Calcium sourced from concrete slurry waste (CSW) and carbon from sludge microbial β-oxidation under alkaline were successfully used to generate micro-/nano-CaCO3. The sphere precipitate was identified as the calcite crystal of 0.7–10 μm, the minimal heavy metals were found in the supernatant, and the trace metals could be removed by sludge discharge. At the optimum pH of 8.5–9, carbon capture reached 743 mg L−1, and CaCO3 production reached 1,191 mg L−1. Alkali promotes proteins as a carbon source, and a decrease in their relative content indicates that they are β-oxidized to produce CO2 and facilitate storage. Here, the dominant phyla were Proteobacteria and Bacteroidota, with Thauera being a prevalent genus adept in β-oxidation. Thus, the alkaline regulation of metabolism between microbe and CSW provides a novel way for sludge to generate bio-CaCO3 and initiate MICP.