Blending organic material with municipal solid waste incinerator bottom ash to promote in-situ carbonation in road base

Abstract

The use of municipal solid waste incinerator bottom ash for road-base construction is an accepted practice in Europe and Asia, and of growing interest in the US. It is common practice to cure bottom ash by stockpiling it for several weeks before using it in this application. The curing process exposes the bottom ash to atmospheric carbon dioxide, which promotes carbonation, lowering its pH (making it less alkaline), and making many heavy metals less soluble. While this process makes bottom ash a more environmentally acceptable material, it takes time and requires additional handling. This article investigates a concept to facilitate carbonation of bottom ash in its compacted state, potentially eliminating the stockpile curing process. It is demonstrated here that blending a small amount of organic material with bottom ash will accelerate carbonation and lower pH in compacted samples by providing a carbon source for bacteria to produce carbon dioxide. Different quantities of biosolids (1%, 2%, 3%, and 5% by mass) were added to compacted bottom ash samples to examine the effect of organic materials on carbonation, and results were compared with a compacted control bottom ash sample. The pH of the control bottom ash sample decreased from 12.07 to 9.78 after 63 days, while the pH of the sample containing 5% biosolids decreased from 11.70 to 9.74 in only 7 days and to 8.18 after 63 days. Physical testing was conducted to examine suitability for beneficial use. The results indicate that bottom ash containing less than 3% biosolids met minimum bearing strength requirements for road base.

Physical and Chemical Properties, Pretreatment, and Recycling of Municipal Solid Waste Incineration Fly Ash and Bottom Ash for Highway Engineering: A Literature Review

“…Because the base is between the surface layer and the subgrade, it will not directly contact with water and soil, so it reduces the risk of heavy metal pollution and is regarded as an ideal recycling method of fly ash and bottom ash [43,186,187]. Considering the environmental safety and structural characteristics, fly ash and bottom ash must be pretreated before they are used as base materials [188].…”

“…When the bottom ash is mixed with sand or soil, the strength of the mixture can also be improved [182,191,194]. Bottom ash has been widely used as a subgrade filler, and the strength, stability, and durability are good [186]. If it is washed before it is used as subgrade filling material, the chloride and other soluble substances can be reduced, so as to reduce the impact on the surrounding environment [195].…”

Valorization of MSWI Bottom Ash as a Function of Particle Size Distribution, Using Steam Washing

“…(iii) washing with water [15][16][17]; (iv) natural carbonation, or aging [18]. Washing with water-based solutions (largely adopted in the Netherlands), in combination with physical separation as a function of the particle size, is very effective in removing water-soluble salts and reducing the concentration of heavy metals and organic matter [15][16][17][19][20][21].…”