Water Content Analysis of Sludge using NMR Relaxation Data and Independent Component Analysis Mika Liukkonen 1 Ekaterina Nikolskaya 2 Jukka Selin 2 Yrjö Hiltunen 2 1 Department of Environmental and Biological Sciences, University of Eastern Finland, Finland, mika.liukkonen@uef.fi Fiber Laboratory, South-Eastern Finland University of Applied Sciences, Finland, {ekaterina.nikolskaya,jukka.selin,yrjo.hiltunen}@xamk.fi Abstract In wastewater treatment, the dewatering of sludge is one of the most important steps, because it affects largely in both the process economics and the costs of sludge disposal. To optimize the dewatering processes, it would be beneficial to be aware of the different water types present in the sludge. In addition to free water, generally there are also mechanically, physically and chemically bound water within the sludge. All these water types behave differently when the sludge is dried, and they all require a different amount of energy when being removed. In this study, the Independent Component Analysis (ICA) method has been applied to an analysis of NMR (Nuclear Magnetic Resonance) relaxation data obtained from the measurement of wastewater sludge samples with a known moisture content. The results strongly suggest that the ICA method can be used for determining the amount of different water types within the wastewater sludge without a priori knowledge on their shares. Keywords: independent component analysis, water content, nuclear magnetic resonance, sludge, relaxation decay 1 Introduction Sludge is a semi-solid by-product remaining after wastewater treatment, industrial or refining processes. It is a separated solid suspended in a liquid, characteristically comprising large quantities of interstitial water between its solid particles (Global Water Community, 2015). This material can be dried to reduce its volume and to remove most of the moisture content of the solids within the sludge (Global Water Community, 2015). In wastewater treatment, the dewatering of sludge is one of the most important steps, because it affects largely both the process economics and the costs of sludge disposal. It is suggested by several authors that the moisture in activated sludge can be classified to the following four categories (Kopp & Dichtl, 2000; Vesilind 1994; Tsang & Vesiling, 1990; Vesilind & Hsu, 1997; Smith & Vesiling, 1995): x Free water: water which is not bound to the particles, including void water not affected by the capillary force. x Interstitial water: water bound by capillary forces inside crevices and interstitial spaces of flocs. x Surface water: water bound to the surface of solid particles by adhesive forces. x Bound intracellular water. This is a widely accepted classification and can be used as the reference in determining the main water types of sludge. Another classification of water types in sludge is to divide it in three groups, i.e. 1) free water, 2) mechanically bound water, and 3) physically or chemically bound water. The free water in sludge can be easily removed by mechanical means, whereas the bound water is held firmly within the floc, bound to the sludge or trapped between the sludge particles, and thus cannot be easily removed (Jin et al., 2004). The bound water can be further divided into chemically or physically bound water which is removable only by thermal drying, and mechanically bound water which is bound by weaker capillary forces (Colin & Gazbar, 1995). In summary, it has to be emphasized that determining the water types is not straightforward, and based on the literature it is difficult to reach an unambiguous interpretation on the distribution of water within activated sludge (Vaxelaire & Cézac, 2004). Furthermore, there seem to be no studies concentrating on the analysis of water types in sludge without a priori knowledge of the shares of different water types. Time domain nuclear magnetic resonance method (TD- NMR) is also becoming highly attractive for industrial applications due to relatively low price, mobility, easy operating, and simple sample preparation procedure. The most successful applications of TD- NMR confirmed by international standards are solid fat content determination in food and water (ISO 8292) and oil content in oilseeds (ISO 10565). They are based on the difference of NMR parameters of water and lipids and a low exchange degree between these two fractions. EUROSIM 2016 & SIMS 2016 317 DOI: 10.3384/ecp17142317 Proceedings of the 9th EUROSIM & the 57th SIMS September 12th-16th, 2016, Oulu, Finland