Keywords: dehydrated sewage sludge, direct melting, heavy metals, fly ash, deposited particles, zinc, metal phosphate, diffusion, deposition mechanisms, thermophoresis, gravity, sewage sludge furnace, environmental pollution
Investigation of a direct melting dehydrated sewage sludge pilot plant
A direct melting dehydrated sewage sludge furnace was tested to obtain the basic operating parameters. Observation of particles (fly ash and deposited particulates) inside the pilot plant was performed to determine the particle properties. The results showed that dehydrated sewage sludge could be directly melted at a temperature of 1400?C with stable combustion. With regard to the fly ash, the majority of the particle size distribution was observed to be in the range 0.1?1 ?m, and amongst heavy metals, the highest concentration in the ash was for zinc. For the deposited particle fraction, most were observed to be in the size range 2?20 ?m and the main inherent chemical compound was associated with metal phosphate. Moreover, at different temperatures inside each chamber, the compositions and chemical compounds were found to change. To estimate the amount of deposited particles, the deposition flux was calculated by various deposition mechanisms, and it was found that diffusion was the dominant deposition mechanism, followed by thermophoresis and gravity, respectively.