Weak electric field strengthens the β-oxidation degradation of fatty acids by activated sludge to produce micro-nano CaCO3

Although a significant portion of calcium-rich concrete waste slurry water is unusable, converting this calcium into micro-nano CaCO3 enhances the performance of concrete materials. In this study, an electric field facilitated microbial β-oxidation, supplying sufficient carbonate for microbially induced carbonate precipitation (MICP) to produce valuable micro-nano CaCO3. Experimental results show that in the 0.5V·cm-1, the accumulated concentration of carbonate changed most significantly, increasing by 10.24 times to 1400mg·L-1. Correspondingly, the maximum increase in SCOD bio-degradation rate was 2.57mg·L-1·h-1，consequently leading to a maximum 1.32 times increase in the yield of micro-nano CaCO3. Furthermore, the DC field had a positive effect on bacterial EPS secretion, with increased excretion of proteins and polysaccharides, which was beneficial for the adsorption and uptake of organics. Then the electric field increased the abundance of Proteobacteria in sludge by a maximum of 8.17%, which also led to an improvement in the organic matter degradation ability of sludge. Finally, the NAD+, NADH, and FAD coenzymes involved in fatty acid degradation increased by 1.82, 1.87, and 1.25 times, respectively. And the number of FadL and FadD gene related to FAs metabolism were increased remarkably, which accelerated the uptake and acylation of FAs and relieved the inhibition of β-oxidation. In short, this work provides a novel strategy for MICP utilization in calcium-rich wastewater.