Role of bio-chemical scale interactions in the Co-landfill of municipal solid waste and bottom ash.

Co-landfill of municipal solid waste (MSW) and bottom ash (BA) has accelerated the scaling of the leachate collection systems (LCS). The matrix of biofilm formation and mineral deposition makes the scaling process in LCS more complicated. However, the fate of metals released from BA and the role of microorganisms in the leachate, which determine the chemical and biological scaling, are not well understood; the scale adsorption ability is little discussed. We analyzed the microorganism response and scale properties under various simulated landfill conditions with different MSW to BA ratios. The adsorption ability of the scales was evaluated through ultrasonic treatment. Scale characterization revealed that Ca²⁺ plays different roles with co-landfilled BA. Under BA-only landfilling conditions, Ca²⁺ was precipitated as CaCO₃, with a strong adsorption ability. The co-landfilling of BA and MSW resulted in the formation of a thicker scale compared to BA landfilling alone. Interestingly, the hydrophilic surface of the biofilm enhanced the descaling efficiency, achieving up to 85%. Microbial composition analysis at the genus level revealed that the co-landfilling with BA significantly influenced the microbial community. Particularly, BA enhanced the biofilm formation ability of the microorganisms. Additionally, the scales adhering to polyvinyl chloride (PVC) pipes developed a distinct microenvironment different from the leachate, with a noticeable increase in anaerobic bacteria. These findings offer new insights into scale control and pipeline failure caused by aging and corrosion.