The mechanism of improving the dehydration and viscosity of municipal activated sludge (MAS) with calcined magnesia

To deal with the problems of water content and high viscosity in municipal activated sludge, which lead to a restriction in resource utilisation, we used calcined magnesia to treat the sludge. As shown in the X-ray diffraction analysis, compared with untreated municipal activated sludge, the mineral composition, including kaolin [Al 2Si 2O 5(OH) 4] and chloritoid [(Fe, Mg)Al 2Si 2O 5(OH) 2], in the municipal sludge treated with calcined magnesia dramatically changed. Because its intramolecular water disappears and a portion of the water content is evaporated during the reaction between the calcined magnesia and water, the dehydration rate of the municipal waste activated sludge increased, the drying time was shortened to 5.30 min and the dried coat thickness increases at least 3-fold. Using a scanning electron microscope, we determined that using calcined magnesia to treat municipal activated sludge leads to a coagulation of fine particles and an increase in rough particles, along with a reduction in soil particles of less than 0.01 mm by up to 69%. Using calcined magnesia to treat the municipal activated sludge can improve its dehydration properties and lower the viscosity and cost in a simple operation. Additionally, it provides magnesium to plants for thermophilic fermentation, creating favourable conditions for aerobic composting.