Heavy Metal Removal from Sewage Sludge Ash with Physical Separation

Abstract

This study focused on a low-cost, energy-saving air classification method to reduce the concentrations of heavy metals, particularly arsenic (As) and cadmium (Cd), which hinder the use of sewage sludge ash as fertilizer. Elemental analysis of ash samples obtained from domestic fluidized bed incineration plants revealed that heavy metals are selectively concentrated in the smaller particle size range. Applying an air classifier utilizing the Coanda effect to these samples allowed the particles to be classified into three categories: fine particles, medium particles, and coarse particles. The results showed that, particularly in the ash containing high concentrations of As and Cd, heavy metals were concentrated in the fine particles, while the heavy metal concentrations in the medium and coarse particles were successfully reduced to half of the regulatory limit for fertilizer use. These findings confirm that fine particle separation using an air classifier is an effective, sustainable method for reducing heavy metal concentrations from sewage sludge ash.