Beneficial Uses of Sludge from Water Purification Plants in Concrete Mix

Due to the constraints of landfill space and environmental concern, disposal of sludge from municipal water purification plants becomes environmentally challenging and costly in Taiwan. The objective of this study was to evaluate the feasibility of beneficial use of sludge from water purification plants in concrete for local construction applications. Chemical and physical characteristics (granulometry, moisture content, specific gravity, absorption capacity, and chemical compositions) of the sludge were first determined. The mean particle size of the dried sludge is smaller than 3.2 mu m and it can be classified as silt with high plasticity. Concrete specimens were then made of various amounts of the sludge and a solidification agent, and their properties were examined. Addition of sludge reduces the mechanical strength of the concrete; on the other hand, addition of the solidification agent increases the mechanical strength of the concrete to an acceptable range. The strength of the specimen was higher than the typically required strength of 210 kgf/cm(2). The concrete specimens could meet the compressive strength requirement with as low as 2% solidification agent and up to 30% sludge as a fine aggregate replacement. The results of the slump test indicate that the workability of most sludge/solidification agent/cement mixtures also falls into the acceptable range of 14-26 cm. The low toxicity characteristic leaching procedure (TCLP) leachate concentrations, good mechanical property, appropriate workability, and a lower disposal cost make the use of water purification plant sludge in concrete mix a viable alternative for beneficial use.