In China

the sludge production is gradually increasing recently

while most of disposal processes require a reduction in the water content of sludge to a certain extent. Low-temperature drying with heat pumps is an economical and efficient sludge drying technology

which is also free from geographical restrictions. Owing to the unclear characteristics of sludge drying at low temperature

influences of temperature and particle size on sludge drying rate were studied by controlling these two variables separately in constant temperature and humidity chamber. And visualized relationships among drying rate and two factors were obtained by applying curve fitting method. Moreover

moisture release characteristics of iron-calcium-carbon-based conditioning sludge in low-temperature drying and traditional drying cases were comparatively explored by using a self-designed vertical sludge drying system. The results indicated that even at 60-80℃

drying rate still significantly accelerated with temperature increasing. A decreasing quadratic fitting polynomial satisfied the relation between drying time reduction and temperature increment. An incremental cubic fitting polynomial is awfully appropriate for the connection between drying time and sludge particle mass in the cases of various kinds of sludge. It is remarkable that iron-calciumcarbon-based conditioner can dramatically improve the sludge drying performance

because CaO and rice husk can increase the porosity and thermal conductivity of sludge

and the latter has a more obvious effect on low-temperature drying in the early stage.