Utilization of Portland Cement and Municipal Solid Waste Incineration Fly Ash for Solidification/Stabilization of Sewage Sludge

A solidification/stabilization (S/S) process by using municipal solid waste incineration (MSWI) fly ash was applied to sewage sludge in order to find a safer way for the two wastes (sewage sludge and MSWI fly ash) disposal. The behaviour of pastes fabricated with various mass ratios of Portland cement/MSWI fly ash has been analysed in terms of mechanical strength, microstructure and leaching characteristics. The results showed that the unconfined compression strength (UCS) of solidified sludge decreased with the mixing amount of MSWI fly ash. However, with the addition of 5% MSWI fly ash represented 28 days UCS of 0.31 MPa, satisfying the landfill threshold of 0.3MPa. Scanning electron microscopy investigations revealed that a large amount of ettringite was present in solidified sludge, leading to a crystallizing network in the solidified products, and therefore, the enhancement of the strength. Environmental assessment of the final products in compliance leaching tests demonstrated that the concentration of heavy metals was below the detection limits.