The Characterization of Water in Peat

Abstract

The functionality and ultimate use of peat are intimately bound up with the way in which absorbed water behaves in the host matrix. Control of the amount of absorbed water, the dynamics of water loss in drying, and the gain of water in rewatering are important determinants in its commercial exploitation. We examined the nature and behavior of water in a range of different Irish peat samples by exploiting the combined capabilities of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and proton nuclear magnetic resonance (NMR). Up to four different forms of water were detected in heavily hydrated peat: absorbed or tightly bound water, which is non‐freezable and behaves like a glass at low temperatures; two forms of loosely bound water; and bulk water. Increasing temperature across the subambient regime revealed the sequential onset of mobility of the different forms of water. The transitions are well‐defined in terms of both water concentration and the temperature at which motion sets in. Unlike hydrated polymers, NMR estimates of the maximum amounts of bound water at low temperatures depend on overall water content, reflecting the extent to which the peat matrix can restructure and swell when hydrated. The TGA, which maps out the loss of water under controlled conditions of temperature and atmosphere, offers additional evidence on the mechanism of dehydration, indicating that drying on a small scale under laboratory conditions is not grossly impeded by internal barriers. The gratifying consistency between the data from the three experimental techniques used, along with pertinent data in the literature, give additional insights into the role of water in peat.

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils~!2009-07-26~!2009-12-04~!2010-06-15~!

“…Furthermore, the extractability of organic pollutants was found to be affected by the hydration time of soils indicating physical and physicochemical changes of SOM upon swelling [2]. Although it is known that SOM swelling includes volumetric expansion [1], water redistribution and reopening of small-sized pores [6] as well as SOM reorganisation [7,8] a mechanistic model describing the *Address correspondence to this author at the Department of Environmental and Soil Chemistry, Institute of Environmental Sciences, Universität, Koblenz-Landau, Fortstr. 7, 76829 Landau, Germany; Tel: +49(6341) 280-571; Fax: +49(6341) 280-576; E-mail: schaumann@uni-landau.de fundamental processes of SOM swelling is not available until now.…”

“…Peats are the product of accumulation and humification of plant material in certain special wet habitats [7,9], and are commercially used as fuel and horticulture medium [7].…”

“…The Q values for different materials after water sorption ranged between 1.3 and 1.6 for peat, 2.0 for cellulose and 1.6 for chitin. [1] Unlike synthetic polymers, McBrierty et al [7,8] reported that the peat matrix re-organises during swelling, thereby permitting access to a greater number of water molecules to the hydrophilic sites. Furthermore, up to four different types of water in hydrated peat samples were identified using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and proton nuclear magnetic resonance (NMR) relaxometry.…”

“…They differentiated between tightly bound or non-freezable water, up to two types of loosely bound or freezable water and freezable bulk water. Non-freezable water is predominantly hydration water and/or water that interacts chemically with hydrophilic moieties in the matrix showing glassy behaviour with a transition temperature around -123°C to -83°C [7]. The character of loosely bound water deviates less dramatically from that of normal water.…”

Wood production, wood technology, and biotechnological impacts

“…Physical and chemical properties of peat (lightweight long-lasting material, water holding capacity, porosity and aeration properties, mineral leaching, nutrient retention, pH range, etc.) well satisfy needs for plant growth when combined in commercial peat formulations with suitable fertilisers (McBriertry et al 1996, Macz et al 2001, Clemmensen 2004, Agner & Schenk 2005. form in plant substrates.…”