A belt filter apparatus for treating material to separate solid and liquid components comprises an endless belt structure adapted to circulate around a path incorporating guide roller structures around which the belt structure passes. The endless belt structure comprises an elongate belt portion of water permeable material, and has two opposed longitudinal edges. A zipper releasably connects the two longitudinal edges together to form a tubular structure with a flexible sidewall. The circulating path includes an assembly zone where the longitudinal edges are brought together and connected by the zipper to form the tubular structure, and a disassembly zone at which the zipper is released to separate the longitudinal edges and open the tubular structure. Means are provided for compressing a portion of the tubular structure to express liquid from the material contained in the tubular structure. The liquid discharges from the tubular structure through the water permeable belt portion.