On the Determination of Water Content in Biomass Processing

Processing of lignocellulosic materials to fuels such as methane and bioethanol may involve several processing steps including pretreatment, saccharification, fermentation, and anaerobic digestion. The amounts of substrate used in these processes are usually based on dry matter content, and the processes themselves typically lead to a change in dry matter content. Thus, it is of great importance to be able to measure dry matter accurately. Dry matter content is commonly determined by measuring loss of water during oven drying. We have used Karl Fischer (KF) titration to measure the water content in a wide range of biomass fractions and have compared these data to results obtained by oven drying. This revealed considerable differences for all tested materials. For lignocellulosic materials, oven drying tends to overestimate dry matter content for untreated material. On the other hand, oven drying generally underestimates dry matter content in pretreated materials due to loss of organic volatiles. These differences have major consequences for the calculation of mass balances and yields in bioprocessing. The KF method gives more accurate water determination than oven drying due to the unique selectivity of the analysis. The method is suitable for the analysis of lignocellulosic biomasses and is particularly useful for determination of water content in pretreated materials, where oven drying usually underestimates the dry matter content due to loss of volatiles.