Solidification and Stabilization of Sewage Sludge and MSWI Bottom Ash for Beneficial Use as Construction Materials

Abstract

This paper investigates the feasibility of converting municipal sewage sludge and municipal solid waste incineration (MSWI) bottom ash to a construction material for the dikes of a sludge-only containment. The sewage sludge and MSWI bottom ash were solidified and stabilized by various binders including portland cement, lime, gypsum, and a combination of some of these binders. The solidified/stabilized products, referred to as solidified sludge, would possess higher strength and lower leachability of toxicity, and thus may be beneficially used as the dike construction material. To assess the feasibility of the beneficial use, a series of laboratory tests including strength test, leaching test, wetting-drying test, and biodegradation test was performed to determine the most suitable binder, the optimum mixing ratio, and both short-term and long-term properties of the solidified sludge. It was found that the use of combined cement and gypsum as a binder was most effective in increasing strength of the solidified sludge and decreasing leaching potential. Wetting-drying cycles reduced both short-term and long-term strengths of the solidified sludge. After four cycles (over eight months), the unconfined compression strength (UCS) was decreased by 78% while the cohesion intercept was decreased by 71% and the friction angle by 17%. Biodegradation also reduced the UCS of the solidified sludge, and after the 12-month test, the reduction in UCS was approximately 73%. The findings of the laboratory tests indicated that both short-term and long-term properties of the solidified sludge should be considered in the design and construction of the containment dikes.