Methods for Quantifying Lime Incorporation into Dewatered Sludge. II: Field-Scale Application

Postlime stabilization of municipal sludge requires methods for assessing the degree of lime incorporation and stability of the final product, as well as for evaluating and monitoring the performance of individual components in the process. The goal of this research was to systematically apply selected measures of lime incorporation and stability at the District of Columbia Water and Sewer Authority’s Blue Plains advanced wastewater treatment plant (see the companion paper). The transfer of sludge by screw conveyance prior to the lime blender did not appear to make it more difficult to incorporate lime in a bench-scale mixer. However, in the full-scale system, it may impede mixing by rolling the sludge into large plugs, and thus creating a discontinuous supply of sludge to the blender. Screw conveyance of limed sludge downstream from the blender appears to subject the limed sludge to additional mixing, resulting in improved lime incorporation and stabilization. The impact of lime purity $(\mathrm{CaO}\%)$ appeared to be minimal within the range tested; however, increasing the lime particle diameter did significantly lengthen the mixing time required for stabilization. In addition, overdosing of lime was shown to be ineffective for compensating for poor lime incorporation.