Study On The Drying Characteristics Of Thin-layer Foamed Sludge In High-thermal And Microwave Conditions

Sludge contains large amounts of heavy metals, pathogens and organic contaminants. If handled and disposed improperly it w ould cause secondary pollution probably, endangering the ecological security and human health. As the dehydrated sludge of municipal wastewater treatment plants is highly viscous and sticky, moisture in the dehydrated sludge is difficult to remove further. Sl udge drying technology is one of the most challenging technical tasks in the field of wastewater handling. Sludge drying technology can remove the moisture of dewatered sludge, reducing its volume and weight dramatically, though making it easy to transport, landfill and incinerate. It has important significance to study on the drying characteristics of sludge under new drying technologies, which contribute to develop high-efficiency, rapid and low energy consumption technologies and save the cost of sludge drying.In this study, the foam-mat drying and the foam-mat assisted microwave drying were employed for drying dehydrated sludge. Meanwhile, the characteristics and influencing factors of foam-mat drying under high temperature conditions and microwave drying were focused, which in order to provide a new fast-speed drying method for sludge dewatering.After adding Calcium oxide in dewatered sludge, it became alkaline environment. This could destroy the cell walls of microorganisms, so th at abundant intracellular biological surfactant was dissolved into sludge, making the surface tension of the sludge decreased. The foamed sludge could be formed with appropriate mechanical whipping. When stirring speed was(62±5) r/min, stirring time was 2 0 minutes, and the sludge density was 0.78g/m L, the foaming drying under high temperature conditions had the best result. The shorter drying time of foamed sludge resulted from the more water from bound type transform into free type, the lower internal res istance to moisture and heat transfer of the foamed sludge, and the larger surfer area exposed to drying air.The microwave drying experiments were carried out by inverter microwave oven. The effects of radiation time, microwave power and the thickness of sludge on foamed sludge drying process was studied. Drying characteristics of 2 mm, 4 mm and 8 mm thin-layer foamed sludge have similar features under different output power conditions. The foaming pretreatment and microwave radiation made capillary water, adsorbed water and bound water transforming into free water and the constant speed drying stage accounting for a larger proportion. The experimental data were simulated by the data processing software Origin 8. The result showed that the Page model have the largest values of R2, the minimum ?2 and residual sum of squares. That is to say Page model has a better prediction for the microwave drying characteristics of sludge than others. In the process of the foamed sludge under high-temperature drying, Logistic model best fitting the results.