METHOD FOR DEHYDRATING EXCESS SLUDGE AND METHOD FOR ESTIMATING DEHYDRATION PROPERTIES OF EXCESS SLUDGE

PROBLEM TO BE SOLVED: To provide a method for dehydrating excess sludge, capable of performing the extremely good and stable dehydration of excess sludge by estimating the necessary addition amount of a chemical agent and the water content of a dehydrated cake from the properties of excess sludge, and a method for estimating dehydration properties of excess sludge. SOLUTION: A floating substance (SS), a net organic component (NVSS), an amount of mucilage (MUS), chemical injection-free centrifugal water content (W0), an SS colloid equivalent value (SSCE), a supernatant liquid colloid equivalent value (FLCE1) and a supernatant liquid colloid equivalent value (FLCE2) after the addition of an inorganic flocculant are measured with respect to excess sludge generated by the activated sludge treatment of wastewater and the inorganic flocculant of which the addition ratio is 0.9-1.1 times by weight of an addition ratio estimated from formula [1]; addition ratio (wt.%/SS) of inorganic flocculant=0.560SS-O.373NVSS-68.533SSCE-152.57FLCE1+9.271 and a polymer of which the addition ratio is 0.9-1.1 times by weight of an addition ratio estimated from formula [2]; addition ratio (wt.%/SS) of polymer=-0.192SS-13.283FLCE2-0.093W0+9.673 are added to excess sludge to dehydrate the excess sludge. In the method for estimating the dehydration properties of the excess sludge, the addition ratio of the inorganic flocculant, the addition ratio of the polymer and the water content of the dehydrated cake are estimated on the formulae [1], [2] and formula [3]; water content (wt.%) of dehydrated cake=-1.860SS-0.049 NVSS+0.475W0+0.15MUS+36.546.