Analysis of Means and Variances for Development of Ceramsite from Semi-dried Sewage Sludge and Clay

Abstract

The use of sewage sludge as additives in the manufacture of ceramic products has been attracting a growing interest from researchers in recent year. In this study, the preparation and characterization of sludge ceramsite manufactured from clay and semi-dried sewage sludge by an innovative composite modifier (ICM) were studied. Taguchi orthogonal experiment, with four variable factors, ratio of ICM to wet sewage sludge (WSS), ratio of clay to WSS, sintering temperature, duration time, and each at three levels, was used to optimize the experiment factors by the analysis of means and variances. Meanwhile, the characterizations (physical properties, microstructure properties and toxic metal leaching properties) of sludge ceramsite prepared under the optimum conditions were tested. The orthogonal experiments results showed that the most significant factor influencing the sludge ceramsite performance was the ratio of clay to WSS, and the mass ratio of clay to WSS to ICM = 1:1:0.05, coupled with sintering at 1180 for 5min, produced the highest quality sludge ceramsite. Property tests of sludge ceremsite showed that sludge ceremsite was light (with an apparent density of 518kg·m-3), waterproof (with a water absorption of 2.3%), hard (with a compressive strength of 9.8Mpa) and nontoxic (contents of toxic metal leaching test were found to be within the limits of China’s regulatory requirement). In addition, the results indicated that as a pretreatment, the addition of ICM, effectively decreased the pore size and improved the properties of the sintered ceramsite.