Understanding the Mechanics of Desiccation Cracking of Alum Sludge: Experimental Results and Model Verification

摘要

Sludge drying beds are commonly used for the dewatering of alum sludge. It has been well known that sludge that cracks well on drying beds dewater better. Unfortunately, the mechanics of desiccation cracking of alum sludge has not been well understood, drmeci et al. (2004) developed a mathematical model that can describe the mechanics of desiccation cracking of alum sludge on sand drying beds. The goal of this study is to test the validity of the model using controlled laboratory-scale experiments. The results indicate that the desiccation-cracking model shows good agreement with experimental data, and can be used to predict the critical water concentration at which the first crack is expected to occur for a particular sludge. In addition, the model can be used to manipulate the p (coefficient of shrinkage), d (tensile strength at fracture) and E (Young's modulus) parameters by chemical addition, and generate a sludge that cracks better and dries faster, and lowers the operational costs for treatment plants.