Abstract: A belt pressure filter comprises a gravity dewatering zone for dewatering a sludge as a function of the gravity and a forced dewatering zone for a forced dewatering of the sludge by means of external pressure. An endless filter belt travels from the gravity dewatering zone to the forced dewatering zone. The coagulated sludge is supplied onto the filter belt by means of the gravity dewatering zone. Information representing the level of the sludge deposited on the belt is obtained as an information concerning the dewatering ability of the coagulated sludge supplied onto the filter belt. The traveling speed of the filter belt is calculated and controlled on the basis of the above described level information which represents the layer thickness and hence also the solids concentration. The optimum amount of a dosage of a coagulating agent is determined based on the traveling speed of the filter belt as calculated.

Abstract: A filter press adapted to travel a filter cloth. Sludge is fed under pressure from mouthpieces into between double filter cloths put between a set of filter plates arranged side by side. The sludge is separated into filter cake and filtrate. The former remains between the double filter cloths and the latter passes through the filter cloth and is discharged from the side of the filter plates. The filter cake falls off the filter cloth when the filter plates are spread out to strain it.