SLUDGE FREEZING AT A HIGH SPEED

We examined in this study the use of a “high-speed” freezing technique, with the assistance of liquid nitrogen freezing, to condition an activated sludge and an alum sludge. The freezing speed reached up to 200 µm/s (0.72 m/h), which is much faster than that adopted in most literature works on sludge freezing. After 3-min liquid nitrogen freezing the alum sludge could achieve finite improvement of dewaterability. Such an improvement is not noticeable for activated sludge. Curing has no effect on both sludges after liquid nitrogen freezing. However, curing does have profound influence on the slow-freezing activated sludge. The underlying mechanisms and the feasibility of using high-speed freezing to condition sludge are proposed and commented.