Laboratory method of microbial induced solidification/stabilization for municipal solid waste incineration fly ash

Area of Science:

• Environmental Engineering
• Geotechnical Engineering
• Microbiology

Background:

• Municipal solid waste incineration (MSWI) fly ash poses environmental risks due to heavy metal leaching.
• Existing stabilization methods often require external additives.
• MSWI fly ash contains significant endogenous calcium, a key component for carbonate precipitation.

Purpose of the Study:

• To investigate the efficacy of microbial induced carbonate precipitation (MICP) for stabilizing MSWI fly ash.
• To utilize the inherent calcium in fly ash for calcite precipitation, avoiding external calcium sources.
• To assess the impact of MICP on heavy metal leachability and the mechanical properties of MSWI fly ash.

Main Methods:

• Utilized MSWI fly ash with high endogenous CaO content (44.5%).
• Employed a bacterial solution with an optical density (OD600) of approximately 1.0.
• Mixed fly ash and bacterial solution at a 1 kg:0.3 L ratio, curing at 20°C and ≥95% humidity for 7 days.
• Verified carbonate precipitation using SEM-EDS and quantified via acid-dissolving.

Main Results:

• Significantly reduced heavy metal leachability (Zn, Cr, Pb) to meet landfill site pollution control standards.
• Increased unconfined compressive strength by approximately 40%.
• Confirmed calcite precipitation through SEM-EDS and acid-dissolving methods.

Conclusions:

• MICP is an efficient and effective method for stabilizing MSWI fly ash.
• The technique successfully immobilizes heavy metals through carbonate formation.
• This approach offers a sustainable solution for managing MSWI fly ash, enabling reuse or safe disposal.