Artificial dewatering of peat. Part 2. The structure of Finnish peat and its influence on water retention

The water binding properties of peat were studied with six peat samples from two peat production areas in Finland. The samples represented the two main types of Finnish peat, Sphagnum and Carex. The degree of humification varied. The most important physical and chemical properties and the water binding properties of the samples were measured and compared. Several different methods of analysing peat were evaluated during the course of the study. The water retention capacities measured for the samples varied strongly with the dewatering procedure. For example, despite the large water retention capacity measured for the ErS peat in metric suction experiments, it was dried more effectively than the other ErS peats by pressing. A direct connection between water retention capacity and the physical and chemical properties was thus difficult to establish. Pressing without the addition of a flocculant was the most effective dewatering method for low-humified peats with large mean particle size and low carbon content. The effect of pressing on Sphagnum peat samples could be predicted from the infrared spectra. Medium and highly humified peats were more effectively dried by water suction suggesting that the methods may complement each other. If a flocculant is not used, water suction drying would seem to give slightly higher dry peat contents than pressing. Thermal drying experiments involving low-temperature thermo gravimetry revealed that the direct water binding forces in the samples did not differ appreciably in the range 10 - 50 % dry peat per weight. However, pressing reduced the water binding forces, showing that differences in water binding properties are mainly attributable to structural factors, such as particle size distribution and porosity. On the whole, Carex peaks were more easily dewatered than Sphagnum peats. Peat sampling is a very important part of the research work. The sensitivity and difficulty of peat sampling became particularly obvious to us during the work. The sample sources generated in this project have been utilised in other projects, and also the results from the physical and chemical characterisation of the samples.